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6: Week 6: Pests, Predators, and Parasitoids, Pt. II - Biology

6: Week 6: Pests, Predators, and Parasitoids, Pt. II - Biology


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6: Week 6: Pests, Predators, and Parasitoids, Pt. II

Impact of avian and arthropod predation on lepidopteran caterpillar densities and plant productivity in an ephemeral agroecosystem

*Cerruti R. R. Hooks, Department of Plant and Environmental Protection Sciences, University of Hawaii at Manoa, 3050 Maile Way, Gilmore 310, Honolulu, HI 96822, U.S.A. E-mail: [email protected] Search for more papers by this author

Department of Plant and Environmental Protection Sciences, University of Hawaii at Manoa, Honolulu and

Department of Entomology, University of California, Riverside, U.S.A.

Department of Plant and Environmental Protection Sciences, University of Hawaii at Manoa, Honolulu and

*Cerruti R. R. Hooks, Department of Plant and Environmental Protection Sciences, University of Hawaii at Manoa, 3050 Maile Way, Gilmore 310, Honolulu, HI 96822, U.S.A. E-mail: [email protected] Search for more papers by this author

Department of Plant and Environmental Protection Sciences, University of Hawaii at Manoa, Honolulu and

Department of Entomology, University of California, Riverside, U.S.A.


Introduction

Plants have two different resistance mechanisms against herbivorous insects, namely direct and indirect resistance. Direct resistance affects herbivores through physical (e.g. thorns) or chemical (e.g. toxins or digestibility reducers) plant traits. Indirect resistance influences the effectiveness of natural enemies of herbivores through, for example, the emission of volatile herbivore-induced secondary plant metabolites that attract the natural enemies ( Karban & Baldwin, 1997 Dicke & Baldwin, 2010 ). Secondary plant metabolites that mediate direct resistance, however, may affect not only herbivores. They can also negatively influence natural enemies of herbivores, either directly through feeding on the herbivore that contains the secondary metabolites, or indirectly through reduced host or prey quality ( Francis et al., 2001a Harvey, 2005 Ode, 2006 ). This may result in a conflict between direct and indirect plant resistance ( Sznajder & Harvey, 2003 Gols & Harvey, 2009 ). With some exceptions (see Sznajder & Harvey, 2003 Gols & Harvey, 2009 and references therein), direct and indirect resistance strategies are mostly studied independently, disregarding the potential evolutionary conflict between them.

To study effects of secondary plant metabolites on natural enemies of herbivores, we focus on glucosinolates. Glucosinolates are a group of secondary metabolites that are characteristic for the plant family Brassicaceae and that show considerable variation in concentrations between and within species of this family ( Gols et al., 2008 van Dam et al., 2009 ). When herbivores damage plant tissues, glucosinolates become exposed to myrosinases, enzymes that are spatially separated from glucosinolates in intact plant tissues. Myrosinases degrade glucosinolates to compounds such as (iso)thiocyanates and nitriles, depending among others on the side chain of the glucosinolate. These hydrolysis products are toxic to a wide variety of insects ( Bones & Rossiter, 2006 Halkier & Gershenzon, 2006 ). Glucosinolates and their breakdown products have negative effects on generalist insect herbivores, for example by deterring feeding or decreasing survival ( Halkier & Gershenzon, 2006 Hopkins et al., 2009 ). Specialist herbivores of brassicaceous plants, in contrast, have evolved special adaptations to detoxify glucosinolates ( Ratzka et al., 2002 Wittstock et al., 2004 ), and use these compounds as feeding or oviposition stimulants ( van Loon et al., 1992 Miles et al., 2005 ). Glucosinolates also affect organisms on higher trophic levels. Several specialist natural enemies of herbivores are attracted by volatile breakdown products of glucosinolates ( Bradburne & Mithen, 2000 Blande et al., 2007 Mumm et al., 2008 ). Glucosinolates from the host plant may, however, also negatively affect natural enemies that feed on glucosinolate-containing herbivores ( Francis et al., 2001b Vanhaelen et al., 2002 Sznajder & Harvey, 2003 ). Some specialist herbivores sequester glucosinolates from the host plant and use these as a defence against their natural enemies ( Müller et al., 2001 Bridges et al., 2002 Müller & Brakefield, 2003 ). Sequestration of glucosinolates by the herbivore Brevicoryne brassicae L. (Hemiptera: Aphididae), for example, has been shown to decrease the performance of generalist predators such as ladybirds ( Francis et al., 2001b Kazana et al., 2007 Pratt, 2008 ).

The objectives of this study were (i) to test herbivore-mediated effects of glucosinolates on the performance of two generalist predators, the marmalade hoverfly (Episyrphus balteatus de Geer Diptera: Syrphidae) and the common green lacewing (Chrysoperla carnea Stephens Neuroptera: Chrysopidae) and (ii) to test whether intraspecific plant variation affects predator performance. The predators were fed either B. brassicae or Myzus persicae Sulzer (Homoptera: Aphididae) reared on four white cabbage (Brassica oleracea L. convar. capitata var. alba) cultivars that have previously been shown to differ in their glucosinolate profiles and resistance to herbivores ( Broekgaarden et al., 2008 Poelman et al., 2008 Kabouw et al., 2010 ). Brevicoryne brassicae and M. persicae differ in the concentration of glucosinolates, as well as in the presence of toxic hydrolysis products of these glucosinolates. Brevicoryne brassicae sequesters glucosinolates from the phloem of its host plant and contains aphid-produced myrosinases ( Jones et al., 2001 Francis et al., 2002 ). Upon tissue damage by carnivores, the sequestered glucosinolates in B. brassicae come into contact with aphid myrosinases, causing the formation of toxic breakdown products ( Bridges et al., 2002 Kazana et al., 2007 ). Myzus persicae does not sequester glucosinolates, but excretes them in the honeydew, and does not contain myrosinases that could break down the glucosinolates that are present in the gut into toxic breakdown products ( Francis et al., 2001b ). Aphid predators will therefore encounter high concentrations of toxic glucosinolate breakdown products when feeding on B. brassicae, but not when feeding on M. persicae. We hypothesised that, based on the difference in concentrations of glucosinolates and their breakdown products, the performance of C. carnea and E. balteatus will be lower when fed B. brassicae than when fed M. persicae. Furthermore, we expect that variation in glucosinolate composition among the host-plant cultivars would affect the glucosinolate composition of the aphids feeding on these cultivars, as well as the possible formation of breakdown products (which depends on the side chain identity, see above), and thereby the performance of the natural enemies feeding on these aphids.

Effects of sequestration of glucosinolates by B. brassicae on aphid predators (mainly lady bird beetles and hoverflies) have been tested before (see, for example, Francis et al., 2001b Kazana et al., 2007 Pratt, 2008 ). Previous studies often (i) only reported the glucosinolate concentrations in the host plant, and not in the prey insect itself, or (ii) linked glucosinolate concentrations in total leaf material to glucosinolate concentrations in the aphid, whereas aphids do not chew leaf tissue, but feed on phloem sap exclusively. Our study presents novel data because we have analysed glucosinolate concentrations as well as profiles in the phloem sap and the aphids feeding on this phloem sap. This resulted in a detailed comparative analysis of the effects of glucosinolate sequestration of a specialist aphid on two of its main predator species, of which one, the green lacewing, has not yet been the subject of testing effects of glucosinolates on its performance. We discuss the effects of intraspecific plant variation in glucosinolate composition on aphid–predator interactions in the context of a possible conflict between direct and indirect plant resistance.


Figure Captions

Fig. 148 . Female German cockroach, Blattella germanica, with attached oötheca shortly before it was dropped.

Fig. 149 . Developmental periods for 4 species of cockroaches at a constant temperature of 82 °F (28 °C) and relative humidity of 70% (shorter bar in each pair) and at ordinary room conditions. Reduction in size of bar for the oriental cockroach indicates a possible 2-year cycle for some individuals. (From Gould and Deay, 1940.).

Fig. 150 . Characteristic resting position of a German cockroach in a narrow crevice. (From P. B. Cornwell [1968], The Cockroach, courtesy Hutchinson Publishing Group, Ltd.).

Fig. 151 . Oöthecae of the brownbanded cockroach, Supella longipalpa, as they are characteristically deposited in clusters on vertical surfaces.

Fig. 152 . American cockroach, Periplaneta americana (nymph).

Fig. 153 . Median longitudinal section of a German cockroach that had been left on a deposit of stained boric add until "knockdown." The dark intestinal contents show the point reached by the boric acid within the intestinal tract.

Fig. 154 . Truck-mounted, gasoline-powered centrifugal blower for applying insecticide dust into the sewer system. Fig. 155 . Pictorial key to common domestic flies in the United States. (From Scott and Littig, 1962.) Fig. 156 . Morphological characters of the generalized fly (top) and numbered wing veins (bottom) used for identification of species. (From Dodge, 1954.).

Fig. 157 . Head and thorax of the male (left) and female house fly, showing difference in width of space between eyes. (Photo by Stennett S. Heaton, courtesy Shell Chemical Company.).

Fig. 158 . House fly, Musca domestica. Eggs, larva, newly developed pupa, and older pupa. (Each division of the scale below represents one-sixteenth in., or about 1.5 min.).

Fig. 159 . Face fly, Musca autumnalis. (Drawing by Ruth DeNicola.) Fig. 160. Domestic flies (females). A, house fly, Musca domestica, B, stable fly, Stomoxys calcitrans C. false stable fly, Muscina stabulans D, little house fly, Fannia canicularis. (From B. Greenberg [1971], Flies and Disease, courtesy Princeton University Press.).

Fig. 161. Black garbage fly, Ophyra leucostoma (female). (From B. Greenberg [1971], Flies and Disease, courtesy Princeton University Press.).

Fig. 162. Little house fly, Fannia canicularis. Left to right: adult female pupa dorsal (left) and ventral views of larva. (Photo by Stennett S. Reaton, courtesy Shell Chemical Company.).

Fig. 163. Eggs of little house fly, Fannia canicularis (left) and coastal fly, Fannia femoralis. (Photo by Stennett S. Heaton, courtesy Shell Chemical Company.).

Fig. 164. Coastal fly, Fannia femoralis. Top left, adult female top right, pupa bottom, dorsal, lateral, and ventral views of larva. (Photo by Stennett S. Heaton, courtesy Shell Chemical Company.).

Fig. 165 . Cluster fly, Pollenia rudis. (Drawing by Ruth DeNicola.).

Fig. 167 . Blow flies (females). A, Calliphora vicina B, Phaenicia sericata C, Phormia regina D, Protophormia terraenovae. (From B. Greenberg [1971], Flies and Disease, courtesy Princeton University Press.).

Fig. 168 . A flesh fly, Sarcophaga haemorrhoidalis (female). (From B. Greenberg [1971], Flies and Disease, courtesy Princeton University Press.).

Fig. 169 . Vinegar fly, Drosophila melanogaster (female). (From B. Greenberg [1971], Flies and Disease, courtesy Princeton University Press.).

Fig. 170 . House-infesting ants. A, Argentine ant, Iridomyrmex humilis, B, Iridemyrmex pruinosus C, longspined harvester ant, Veromessor andrei, D, jetblack harvester ant, Veromessor pergandei E, western bigheaded ant, Pheidole hyatti, F, California acrobat ant, Crematogaster californica. (Courtesy R. R. Snelling.).

Fig. 171 . Argentine ant, Iridomyrmex humilis (worker).

Fig. 172 . Longspined harvester ant, Veromessor andrei.

Fig. 173 . California acrobat ant, Crematogaster californica.

Fig. 174 . House-infesting ants. A, Pharaoh ant, Monomorium pharaonis D, little black ant, Monomorium minimum, C, thief ant, Solenopsis molesta D, pavement ant, Tetramorium caespitum E, velvety tree ant, Liometopum occidentale F, pyramid ant, Dorymyrmex pyramicus. (Courtesy R. R. Snelling.).

Fig. 175 . A, bicolored pyramid ant, Dorymyrmex bicolor D, odorous house ant, Tapinoma sessile C, crazy ant, Paratrechina longicornis, D, small honey ant, Prenolepis imparis E, Lasius niger F, Lasius pallitarsis. (Courtesy R. R. Snelling.).

Fig. 176 . Winged females of the odorous house ant, Tapinoma sessile.


Methods

Experimental Overview

We used a landscape-level experiment with manipulative and observational components to measure effects of forest fragmentation on intraspecific hostplant quality and caterpillar mortality due to parasitoids. Over the summers of 2017 and 2018, we collected caterpillars and leaves from temperate deciduous forest patches in Connecticut (U.S.A.) varying in size by two orders of magnitude. We compared leaf water content from plants grown in either small and heavily fragmented forests or large, continuous forests. Caterpillars were reared in laboratory environments to study their growth efficiency (performance in response to hostplant quality) on leaves collected from small and large forest patches. Additionally, laboratory-rearing also allowed us to quantify relative parasitism rates of caterpillars collected in forest patches of varying size.

Study Sites

Our study sites spanned a 3,500 km 2 area in central and eastern Connecticut, U.S.A., in which the landscape is composed of patches of Northeastern Coastal Forest (Olson et al., 2001) surrounded by a matrix of suburban and agricultural land (Figure 1). We took advantage of existing forest patches ranging in area from 2.93 to 1,013 ha (Table 1). Forest patches were selected in blocks, with each block containing 2𠄳 fragments of contrasting area so that each small forest fragment (㱐 ha) was paired with a large forest fragment (𾈀 ha) and sometimes an additional medium forest fragment (50� ha). The inclusion of fragments of contrasting area within each block ensured that fragment sizes were spatially interspersed to avoid issues with spatial autocorrelation in the statistical analyses. Forest boundaries varied and included two-lane roads, major highways, powerline clearings, and residential areas. Many of the sites in the small area class are bordered by major edges such as roads, multi-lane highways, power-line clearings, residential development, or industrial or commercial facilities. Within each forest patch, we restricted our collecting to upland areas that were similar in forest composition, comprising primarily mature Quercus alba (white oak), Quercus rubra (red oak), Acer rubrum (red maple), Acer saccharum (sugar maple), Carya spp. (hickories), and Betula lenta (black birch). Common woody understory species were Hamamelis virginiana (witch hazel), Kalmia latifolia (mountain laurel), Ostrya virginiana (American hophornbeam) and Carpinus caroliniana (American hornbeam). Plant communities were relatively homogeneous across sites. We did not collect data near patch edges, although both the small and large sites typically harbored more exotic plant species at the edge.

Figure 1. Map of Connecticut with forest fragments in green, county boundaries in black, and inset showing the position of Connecticut within the United States. Superimposed on the map of Connecticut are our 25 study sites spanning a 3,500 km 2 area in east-central Connecticut. Experimental blocks are represented by different colors, and fragment area is indicated by shape. Large fragments are 𾈁 ha, medium sites are 51� ha, and small sites are 㱐 ha. See Table 1 for further site and block information.

Table 1. Forest sites used varied in size by two orders of magnitude.

Plants

We studied growth performance and parasitism of caterpillars collected from A. rubrum and H. virginiana because these plant species were common in all forest sites and consistently harbored both dietary specialist and generalist caterpillars.

Caterpillars

Caterpillars of various larval stages were collected from A. rubrum and H. virginiana branches and saplings at 28 forest sites over the same 6-week period in June and early July of 2017 and 2018. In total, 882 caterpillars were collected, representing 49 species. We beat branches with a wooden dowel to shake caterpillars from branches onto a 1 m 2 canvas sheet (Wagner, 2005). All caterpillars ϡ cm in length were collected and individually placed into 33 ml plastic vials with a leaf from the host plant on which they were found. Caterpillars were collected with equal sampling effort in each patch as part of a concurrent study investigating the strength of bird and ant predation in forest patches of varying size. The community composition of caterpillar species was similar across patches of varying size as the host plants used harbor a typical and consistent community of dietary specialist caterpillars that feed exclusively on either A. rubrum or H. virginiana, respectively, and dietary generalist caterpillars that feed on many of the hardwood species found in these forests. For caterpillar species with ϥ individuals collected, 94% (16/17) of dietary generalist species and 100% (9/9) of dietary specialist species were found in both large and small patches.

To characterize the diet breadth of caterpillar species, we identified every caterpillar to the species level so that we could compile host plant records for each caterpillar species using our own data and published sources (Wagner et al., 2002, 2011 Wagner, 2005). Based on these hostplant records, we calculated pairwise phylogenetic distances between woody hosts of each caterpillar species using a large phylogeny of seed plants (Smith and Brown, 2018). The mean of these pairwise phylogenetic distances was then used as a quantitative measure of diet breadth for each caterpillar species (Figure 2). Based on this quantitative measure of diet breadth, the caterpillar community studied here appears to fit discretely into two groups (specialist or generalist). Caterpillars that entirely or predominantly consume plants from one taxonomic family were considered dietary specialists, whereas caterpillars that commonly consume plants from ϡ plant family were considered dietary generalists (Figure 2). Therefore, we evaluate all analyses using the discrete diet breadth descriptors, “specialist” and “generalist” to make analyses and interpretation more straightforward. Small sample sizes of caterpillar species precluded comparative analyses at the caterpillar species level.

Figure 2. A comparison of each caterpillar species' continuous measure of diet breadth (mean phylogenetic distance among hostplant species) and categorically defined specialist and generalist subsets of the caterpillar community. Horizontal bars represent the median, box edges represent the 1st and 3rd interquartile range, whisker tips represent the minimum and maximum, and points are outliers. Outliers represent caterpillar species with small sample sizes.

Experimental Methods

Herbivore Performance Assay of Hostplant Quality

To test the hypothesis that forest fragmentation may alter the intraspecific quality of host plants as food for caterpillars, we reared all field-collected caterpillars from both years under controlled conditions in a laboratory setting. We measured variation in food quality for each hostplant species as the variation in growth efficiency of these lab-reared caterpillars. Upon laboratory arrival, each caterpillar was placed individually in a 160 ml plastic cup with a lid and starved for 24 h prior to initial weighing to avoid weighing gut contents and to account for disparities in larval instar among caterpillars at the time of collection. After starvation, each caterpillar was weighed to the nearest 1 mg and was randomly assigned a diet treatment group of either leaves from small (㱐 ha) or large (𾈀 ha) forests. Each caterpillar in the assay received leaves only from its randomly assigned treatment group and from the hostplant species on which it was collected. Each day, each caterpillar in the assay received new leaves from a batch of field-collected leaves (see below). Leaves used in the assay were stored for no more than 5 days. Five days of sealed storage at 4ଌ had no effect on leaf water content for either hostplant species (linear regression, Pstorage.duration > 0.05, data not shown).

As a proxy for total food consumed, the fecal pellets of each caterpillar in the assay were collected daily and dried to constant mass at the end of the assay. Caterpillars completed the assay after pupating. Subsequently, pupae were sacrificed by overnight storage at �ଌ, and then dried to constant mass. Many caterpillars brought to the laboratory for rearing either died from unknown causes (N = 468), pupated shortly after collection (N = 25), were parasitized (N = 71), or had incomplete data (N = 31) and were excluded from the assay. While none of the caterpillars that died from unknown causes had parasitoids emerge, it is possible that some of these individuals were parasitized. We did not dissect cadavers to confirm the cause of death. The proportion of caterpillars that died from unknown causes was similar among treatment groups (χ 2 = 0.01, df = 1, P = 0.91). Similarly, whether caterpillars were collected from large or small forest fragments had little influence on unknown mortality (χ 2 = 1.71, df = 1, P = 0.19).

Leaf Water Content

To test the hypothesis that forest fragmentation alters phenotypic variation in plant traits, we compared the water content of leaves of A. rubrum and H. virginiana collected from 21 forest sites ranging in size from 3 to 1,013 ha in the summer of 2018. Leaf water content is a reliable measure of food quality for folivores of temperate trees, as it often correlates positively with herbivore growth rate, leaf nitrogen, and overall palatability (Mattson and Scriber, 1987). Leaves were transported to the laboratory in sealed plastic bags kept in a cooler with ice. In the laboratory, leaves were stored in sealed plastic bags containing a damp paper towel and refrigerated at 4ଌ. Upon laboratory arrival, 10� randomly selected leaves from each host plant at each site were weighed to the nearest 1 mg. Leaves were then dried at 40ଌ for 1 week, or until stable dry masses were reached. Leaf water content was calculated as the ratio of water mass to fresh mass. Although leaves used for water content measurements were haphazardly selected, we intentionally avoided leaves that were not representative of the leaves that would be fed to caterpillars. That is, leaves with necrotic edges, browning, extreme size, or other anomalies were not used in either the leaf water content study or the performance assay.

Parasitoid Emergence

Throughout the performance assay, all caterpillars that had parasitoids emerge were removed from the assay and recorded. In 2018, we supplemented these data by separately rearing 189 caterpillars that were field-collected from 26 sites within the same fragmentation network used in the performance assay. Only caterpillars from A. rubrum and H. virginiana were collected. These supplemental caterpillars were individually reared in 160 ml plastic cups in similar laboratory conditions as the performance assay.

Data Analysis

All analyses were performed in R, version 3.5.1 (R Core Team., 2018).

Growth efficiency, quantified as pupal dry mass per unit dry fecal mass, was used as a measure of hostplant quality from the herbivores' perspective. Growth efficiency was quantified as the slope of the relationship between Log10 (dry pupal mass) and Log10 (dry fecal mass) (Singer, 2001). Growth efficiency is the amount of growth per unit plant material consumed, with fecal mass as a proxy for the amount of plant material consumed. Variation in this slope indicates variation in caterpillar growth efficiency and interactions between covariates (e.g., leaf origin and caterpillar diet breadth) and the relationship between dry fecal mass on dry pupal mass measure the covariates' effect on growth efficiency. We used a linear mixed-effects model (Bates et al., 2015) to analyze variation in Log10 (dry pupal mass) across individual caterpillars as a function of Log10 (dry fecal mass), leaf origin (small or large forest patches), the year the caterpillar was reared (2017 or 2018), hostplant species, and caterpillar diet breadth. To quantify how caterpillar growth efficiency varies between dietary generalists and specialists, we included a two-way interaction between diet breadth and Log10 (dry fecal mass). To determine whether this efficiency is modified by factors such as leaf origin and year, we also included each of these factors in a three-way interaction with diet breadth and Log10 (dry fecal mass). We allowed the intercept and effect of caterpillar species to vary among individuals as normally-distributed random effects (random intercept and slope model) to account for the variation among species in both Log10 (dry pupal mass) and growth efficiency. In preliminary analyses, the initial mass of the caterpillars was added as covariate. However, this term did not modify growth efficiency in any iteration of the model and was subsequently dropped from further analyses. The caterpillars in this experiment were fed leaves from small or large forest patches from multiple blocks. As a result, we cannot separate the variance associated with block from the error variance.

To quantify the effect of forest fragmentation on leaf water content we used a generalized linear mixed-effects model with a Beta error distribution (Brooks et al., 2017) to model leaf water content as a function of forest fragment area, hostplant species, collection date and their two- and three-way interactions. Separate intercepts for collection site were modeled as normally distributed random effects. As refrigerated storage did not alter leaf water content, we pooled measurements from leaves taken across 5 days of storage.

The probability of mortality from parasitoids was modeled as a function of forest fragment area, diet breadth, and their two-way interaction using a generalized linear mixed-effects model (Bates et al., 2015) assuming a binomial error distribution. Separate intercepts for block and collection site (nested within block) were modeled as normally distributed random effects. All records of parasitism were pooled across years and tree species to increase sample sizes. Preliminary analyses confirmed that neither days from collection to pupation nor collection date had any effect on the probability of parasitism. Consequently, these terms were not included in the final model. We confirmed the lack of spatial autocorrelation in the residuals by examining semi-variograms of the residuals (no trend observed) and computing Moran's I auto-correlation coefficient (I = 𢄠.03, P = 0.635).

Estimating confidence intervals and making formal inferences from generalized linear mixed-models (GLMMs) is complicated by the absence of a standard method to calculate the denominator degrees of freedom associated with reference distributions. One flexible and robust approach for constructing confidence intervals (CIs) around the parameter estimates from GLMMs is parametric bootstrapping (Davison and Hinkley, 1997 Gelman and Hill, 2007). We simulated 1,000 sets of response data from the posterior distribution of the parameter estimates, refitted the model to each simulated data set and calculated the 2.5 and 97.5% quantiles of the parameter estimates across the refitted models to obtain their 95% confidence intervals. We estimated approximate, two-tailed P-values following the methodology of Bagchi et al. (2011). We present parameter estimates on the scale of the linear predictor with 95% CIs and approximate P-values.


Discussion

Seed predation rates by Penthobruchus germaini varied considerably across Australia and between years, but even the highest predation rates were similar to other seed mortality factors within the pod. Mean predation rates were less than 30% in all regions and years, despite egg densities averaging almost two eggs per seed in some regions. Modelling of the demographic effects of the observed seed predation rates was beyond the scope of this study, but effects would be expected to be limited, based on results from other studies (see Introduction). Relatively low predation has also been observed for all other bruchid species that have been released and evaluated as biological control agents ( Julien & Griffiths 1998 Impson, Moran & Hoffmann 1999 Radford, Nicholas & Brown 2001 Paynter 2005 Raghu et al. 2005 ). The only exception we could find was the uni-voltine bruchid accidentally released on scotch broom (Cytisus scoparius (L.) Link) in north-west USA, which destroyed over 80% of the seeds ( Redmon, Forrest & Markin 2000 ).

We draw three main conclusions regarding factors limiting seed predation rates: (i) the ability of seed-feeders to regulate host populations can be constrained by even modest aggregation of eggs and commonly recorded levels of insect mortality on or in the seed (ii) seed-feeders, especially multi-voltine species, commonly fail to track within-season fluctuations in resource and (iii) with the possible exception of egg parasitism, the effects of these factors on seed predation rates are likely to be predictable prior to the release of seed-feeders into new environments. These conclusions have important implications for the use of specialist seed-feeders to regulate invasive plants.

The effect of oviposition pattern and beetle mortality on seed predation

Egg distributions within seed populations were consistently aggregated across northern Australia, and across surveys and years. The observed egg distribution suggested that eggs were laid singly and the number of visits by ovipositing females per seed was random (because the mean was similar to the variance at low egg densities), but that the seeds differed in attractiveness to the egg-layer, and/or seeds differed in their exposure times to the egg-layer. Egg aggregation was relatively slight compared with some other species, but it still resulted in a considerable increase in the egg densities required to achieve high egg coverage compared to if eggs had been randomly distributed. The importance of aggregated distributions and clumping on discrete hosts has received considerable attention as a potential mechanism for avoiding inter-specific competition ( Rohlfs & Hoffmeister 2003 ), but in the case of seed-feeders, and from the perspective of the host, its effect is reduced seed predation.

Egg hatch rates for unparasitized eggs did not differ statistically between regions, but was lowest when egg parasitism was the highest, suggesting that some egg mortality may be the result of failed parasitism. Field egg hatch rates compare well with those recorded in a laboratory study in Argentina where adults were fed on an ideal diet of honey and pollen (c. 92·1%, n = 4173 Briano et al. 2002 ). Larval and/or pupal mortalities (c. 62%) were surprisingly constant across the surveyed regions and years. Furthermore, substantial unexplained egg, larval and pupal mortalities appears to be common among seed-feeders. Failure of eggs to hatch is commonly around 20% ( de Steven 1981 Siemens & Johnson 1992 Sagnia 1994 ), although it can be as high as 50% ( Traveset 1991 ). This does not include eggs that fall off the seed, which can be high ( Traveset 1991 ), but is probably insignificant for P. germaini which glues its eggs firmly to the seed. Unexplained larval or pupal mortalities are frequently between 30 and 60% ( Janzen 1977 de Steven 1981 Traveset 1991 Sagnia 1994 ). These widely reported low egg hatch rates and high unexplained larval mortalities suggest that egg densities for many seed-feeding species would need to be over eight per seed (assuming an egg distribution as for P. germaini) to result in predation of at least 80% of seeds. The required egg density would increase considerably with increasingly aggregated egg distributions, and for seed-feeders that require more than one individual to consume a seed. The unexplained mortality of immature beetle stages can therefore seriously limit the proportion of seeds that many seed-feeder populations will consume.

Egg parasitism was the only mortality factor detected in our study that was dependent on egg density. A very similar result was found for the egg parasitoid Uscana semifumipennis Girault on the seed-feeding bruchid Stator limbatus (Horn) ( Siemens & Johnson 1992 ). Strong density dependence of egg parasitoids will act to dampen any increase in larval emergence, and hence seed predation, resulting from increases in egg density, even at the relatively low egg densities observed in our study. Indeed, in our study system, it means that unrealistic mean egg densities are required to achieve 80% seed predation. High egg parasitism will also reduce the ability of P. germaini populations to track seed populations ( van Huis et al. 1998 ). Egg parasitoids are rarely considered in seed predator studies. However, high parasitism rates have been recorded for other species ( Traveset 1991 Siemens & Johnson 1992 Sagnia 1994 Coetzer & Hoffmann 1997 ), if not universally so ( Wang & Kok 1986 ).

Ability to track fluctuating resources

Within-season variation in egg density was strongly coupled to fluctuations in seed availability, highlighting the importance of understanding within-season resource dynamics, and the ability of seed predators to track those resources, when determining seed-feeder impacts ( Solbrech & Sillen-Tullberg 1986 van Klinken 2005 Raghu et al. 2005 ). Seed dynamics on trees is particularly important as P. germaini beetles showed a strong oviposition preference for pods on the tree (Fig. 1 van Klinken 2005 ). Maturation of parkinsonia pods was relatively synchronous at any one site, occurred approximately 6 weeks prior to pod drop ( van Klinken 2005 , unpublished data) and was consistently correlated with a drop in egg density, suggesting predator satiation. Egg densities therefore failed to peak at times when most seeds were available to seed-feeders, thereby limiting total annual seed loss to predation ( van Klinken 2005 ). A similar outcome has been observed where the host of multi-voltine seed-feeding species are consumed by vertebrate herbivores soon after maturation ( Impson et al. 1999 Baes, de Viana & Saravia 2001 Radford et al. 2001 ). Multi-voltine seed-feeders therefore appear poorly equipped to effectively track sharp within-season fluctuations, which prevents high seed predation of the annual seed crop. However, multi-voltine seed-feeders may be better at tracking between-year and between-site variation in the timing of resource fluctuations in our study, variation in the seasonal timing of pod maturation with climate zone had no apparent effect on the ability of P. germaini to track fluctuations in seed availability. In contrast, synchronisation between uni-voltine insects and their host allows them to exploit sharp within-season peaks in resource availability, but they are often less able to deal with between-year and between-site variations ( Redmon et al. 2000 Russell & Louda 2005 ). Indeed, all the examples that we could find of seed-feeding biological control agents that regulated host populations were uni-voltine (e.g. Hoffmann & Moran 1998 Dennill et al. 1999 Redmon et al. 2000 ).

Recommendations

To be an effective biological control agent, a seed predator needs to reach sufficiently high egg densities at the right time of the year so as to predate the greatest proportion of the annual seed crop ( van Klinken 2005 ). Our modelling showed that the egg density that is required to achieve a target seed predation rate is determined by the multiplicative effect of the way in which eggs are distributed across seeds, and a wide range of mortality factors of immature beetle life stages. In our study, egg parasitism and unexplained larval/pupal mortality were the most important factors, but this will vary with the study system. However, even without high immature beetle mortality, an inability to track within-season fluctuations in seed availability meant seed predation would still have been quite low at a time when most seeds were available (5–56%). With the exception of egg parasitism, each of the factors we considered that limited seed predation rates acted independently of environmental conditions and their effects in the target environment should therefore be predictable. If this is commonplace, then it should simplify the selection of effective seed-feeding biological control agents.

The inability of seed predators to track fluctuations in seed resources through time was the key factor limiting seed predation in our study system. Strict oviposition preferences, such as for seeds on trees, will have the effect of increasing within-season resource fluctuations. Our results suggest that multi-voltine insects will become less effective the greater the fluctuations in within-season resource are, and that the converse might apply to uni-voltine seed-feeders. The relative efficacy of multi-voltine and uni-voltine seed-feeders may therefore be predictable by considering oviposition preference for seed age and position, and the spatial and temporal fluctuations in resource availability within and between seasons.

The ability of seed predator populations to track fluctuating resources will be dampened by the population effects of both the way eggs are distributed across seeds, and mortality of immature life stages. Although we did not consider their population effects directly, the impact of egg parasitism is likely to be particularly important as it was the only density-dependent mortality factor. Although parasitism is often lower in the introduced range because of a lack of specialist natural enemies ( Torchin et al. 2003 ), this is clearly not always the case. Also, predicting parasitism rates is more difficult than simply predicting parasitoid diversity ( van Klinken & Burwell 2005 ). Nonetheless, predictions should improve as our knowledge of the parasitoid fauna, and their abundance, in the target distribution of potential biological control agents improves. For example, any new seed-feeders being considered as biological control agents for invasive plants in arid and semi-arid Australia should possess mechanisms to avoid known egg parasitoid risks.

Overall, given the multiple inter-relating factors limiting seed predation rates, it is not surprising that seed-feeders frequently do not reach the densities required to regulate host populations. This suggests caution when prioritizing seed-feeders for biological control, and when advocating their use as companion species in agro-forestry. It does, however, suggest that detailed pre-release studies which quantify factors that can limit herbivory will be useful for identifying the most efficacious species for biological control, especially where the interactions between herbivore, environment and plant damage are well understood ( Raghu & van Klinken 2006 ).


Discussion

So far, only a few studies have shown that ion channel-forming peptides of fungal origin may act as inducers of an early step in plant defence signal transduction resulting in defence responses of plants against different attackers. For example, treatment of Nicotiana tabacum with chrysospermin (produced by Apiocrea sp.) resulted in increased resistance against tomato mosaic virus infection (Kim et al., 2000), and two peptides from Trichoderma virens induced systemic protection against leaf bacteria in cucumber (Viterbo et al., 2007). ALA induces volatile emission in Lima bean (Phaseolus lunatus) and A. thaliana, as well as an increase in endogenous levels of plant hormones such as JA and SA (Engelberth et al., 2001 Chen et al., 2003). So far, only one study addressed the effect of ALA treatment on arthropod behaviour (M Dicke and H Dijkman, described in Dicke and Van Poecke, 2002). They showed that predatory mites (Phytoseiulus persimilis) prefer ALA-treated over control Lima bean plants. The induced volatiles in ALA-treated Lima bean plants: TMTT, DMNT, MeSA, and a trace amount of linalool (Engelberth et al., 2001), have been shown to be important for prey-searching behaviour of predatory mites (Dicke et al., 1990 De Boer et al., 2004). However, another compound attractive to predatory mites, the monoterpene (E)-β-ocimene, and transcript levels of a (E)-β-ocimene synthase are not induced by ALA in the leguminous species Lima bean and Lotus japonicus (Arimura et al. 2004, 2008).

The parasitoid C. glomerata responds to herbivore-induced plant volatiles from Brassicaceous plants (Blaakmeer et al., 1994 Geervliet et al., 1996) and is also attracted to B. oleracea plants that are artificially induced with JA (Bruinsma et al., 2009). In this study, treatment of Brussels sprouts plants with ALA induces the emission of volatiles that attract parasitoid wasps. The parasitoid wasp C. glomerata preferred ALA-treated Brussels sprouts plants over control plants in three out of four concentrations tested. ALA treatment of Brussels sprouts plants did not result in higher emission rates of TMTT, DMNT, and MeSA as it did in Lima bean ( Table 1 Engelberth et al., 2001). Because of the large variation in volatile emission after ALA treatment of Brussels sprouts plants recorded here, it is difficult to determine which compounds are responsible for the difference in preference of the parasitoids. It is not known whether the parasitoids respond to specific attractive compounds, or to ratios of attractive and repellent compounds, and whether responses increase with concentration above a certain threshold. Several studies suggest that green leaf volatiles, such as (Z)-3-hexen-1-ol, (E)-2-hexenal, and (Z)-3-hexenyl acetate, are important for the attraction of C. glomerata, but also other compounds such as terpenes have been suggested as attractants, and sulphur compounds as repellents (Smid et al., 2002 Fatouros et al., 2005 Scascighini et al., 2005 Shiojiri et al., 2006a, b Soler et al., 2007). The total volatile emission of JA- and JA+ALA-treated plants was larger than that of control and ALA-treated plants. Possibly, the higher volatile emission rate of JA+ALA-treated plants is responsible for the preference of the parasitoids for these plants over ALA-treated plants. Yet, a higher volatile emission rate cannot explain the observed parasitoid choices in all tests. An unexpected result relative to the composition of the volatile blends is the similar response of the parasitoids to ALA- and JA-treated plants, especially so in view of the fact that ALA was applied at a molar dose 20 times lower than that of JA. The total volatile emission and composition differed significantly between these two treatments a range of compounds were emitted at higher rates by JA-treated plants compared with ALA-treated plants ( Table 1 ). However, several compounds were emitted at similar rates in the two treatments these compounds might be sufficient for the attraction of the parasitoids to the plants. Compounds that occurred in similar amounts and had the least influence on the statistical separation of the groups are TMTT, 3-pentanone, MeSA, and (Z)-3-hexen-1-ol.

In Lima bean, both JA and SA are induced by ALA treatment (Engelberth et al., 2000). There is growing evidence that the JA and SA pathways can negatively interact with each other, e.g. in tomato (Pe༚-Cortes et al., 1993 Doares et al., 1995 Thaler et al., 2002b), tobacco (Niki et al., 1998 Felton et al., 1999 Rayapuram and Baldwin, 2007), and A. thaliana (Gupta et al., 2000 Traw et al., 2003 Cipollini et al., 2004). However, other studies show that the interactions between signalling pathways are not always negative, depending on the dose and timing of application of the inducing compound, and the response measured (Niki et al., 1998 Schenk et al., 2000 Thaler et al., 2002a, b). For the Brassicaceous plant A. thaliana it was shown that both JA and SA are involved in the induced attraction of the parasitoid C. rubecula to P. rapae-infested plants (Van Poecke and Dicke, 2002).

An increase in SA due to ALA treatment inhibits the octadecanoid pathway between OPDA and JA in Lima bean plants however, due to the slow increase in SA, inhibition occurs only after several hours, and thus after the typically transient JA burst (Engelberth et al., 2001). If ALA treatment would have a similar effect on Brussels sprouts plants, addition of JA to ALA-treated plants could compensate for the inhibition of the octadecanoid pathway by ALA. Indeed, in the present experiments, addition of JA to ALA treatment of plants generally increased the attractiveness of plants to the parasitoids compared with ALA-treated plants, significantly so at two ALA concentrations (5 μg ml 𢄡 and 20 μg ml 𢄡 ALA) in combination with 0.05 mM JA ( Fig. 3 ) and marginally significantly (0.058 <P π.088) in the other four combinations. Comparison of the behavioural responses in dual-choice tests with JA+ALA-treated plants versus JA-treated plants, however, did not yield such a clear-cut result. Only in the combination of JA and the highest concentration of ALA (50 μg ml 𢄡 ), did ALA increase attractiveness, although less strongly at the lower JA concentration (0.05 mM) than at the higher JA concentration (0.5 mM) ( Fig. 3C, F ). These data indicate that ALA increased parasitoid attraction at a molar dose 20 times lower than the JA dose to which it was added.

Phenotypic manipulation through the use of fungal inducers as well as phytohormones can increase our understanding of the signal transduction of plant defence responses and can provide more insight into the use of volatile cues in host searching by carnivorous arthropods. This is clear for the use of ALA in the studies described earlier with Lima bean, in which ALA induces a qualitatively different volatile blend from control plants, and the induced compounds were shown to be attractive to predatory mites (Dicke et al., 1990 Engelberth et al., 2001 Dicke and Van Poecke, 2002 De Boer et al., 2004). For Brussels sprouts plants, the regulatory network seems to differ from that of Lima bean as well as from that of A. thaliana, and results in quantitative rather than qualitative differences. In this study, ALA treatment induced a volatile blend in Brussels sprouts plants different from that induced by mechanical damage alone. The parasitoids were attracted to the ALA-treated plants, demonstrating that ALA, as an elicitor of an early step in induced plant defence, induces a volatile blend that is attractive to parasitoids. Although JA treatment induced higher volatile emissions than ALA treatment, this resulted in equal attractiveness to parasitoids yet JA was applied at a substantially higher dose. A combination of ALA and JA further increased the attractiveness of the plants to parasitoids at 20 μg ml 𢄡 or 5 μg ml 𢄡 ALA and 0.05 mM JA. Combining different treatments as presented here allows comparisons of the relative importance of specific steps of the signal transduction pathways for both plant volatile emission and indirect induced defence provided by parasitoid attraction.


6: Week 6: Pests, Predators, and Parasitoids, Pt. II - Biology

The information presented in this newsletter

is not to be used in any form without the

consent of the specific author(s).

Edited by C. Michael Smith, Professor, and John C. Reese, Professor, Department of Entomology, Kansas State University, Manhattan, Kansas. Clerical assistance by Evelyn Kennedy.

Welcome from the Department of Entomology at Kansas State University to volume 26 of the International Plant Resistance to Insects Newsletter (IPRIN). We think the present format of the newsletter is helping plant resistance researchers continue to move into the world of 21st century digital communications. To all of you who continue to offer suggestions for further improvement, thank you very much.

For those of you reading the newsletter for the first time, we welcome your comments and contributions. If you wish to contribute items to future newsletters, they should be Word or WordPerfect files of two pages or less of text in length (tables are not printed) and can be submitted as e-mail file attachments to [email protected], or on 3.5" computer diskette to Evelyn Kennedy, Department of Entomology, Kansas State University, Manhattan, KS 66506-4004.

Other types of plant resistance to insects information continue to be accessible also. The KSU Plant Resistance to Pests listserv, established by Donna Schenck-Hamlin of the KSU Hale Library and now administered by John Reese ([email protected]), is intended for continuous information exchange among individuals globally interested in plant resistance to pests about professional meetings, conferences and research grants, as well as new research developments concerning plant resistance to arthropods and plant pathogens. To subscribe to the bulletin board, send an e-mail message to: [email protected]>, with the subject line blank, and the message "SUB PRP firstname lastname."

Use the e-mail address [email protected]>to send a message to the entire bulletin board group. Kansas State University plant resistance to insects information is available on the Worldwide Web at http://www.oznet.ksu.edu/dp_entm/welcome.htm. Items available include the Painter Reprint Collection, archive editions of IPRIN, and new this year links to related websites including the Crop Science Society of America, CGIAR (Consultative Group for International Agricultural Research), and the Technology ISB Monthly News Report. Information is also available on how to subscribe to Plant Breeding News.

Thank for your interest in the IPRIN 2000. Please send your suggestions for improvement to Mike Smith at [email protected] or Mike Smith, Department of Entomology, Kansas State University, Manhattan, KS 66506-4004. Your continued support, through contributions and/or financial assistance is much appreciated. Financial contributions may be sent to LaVona Francis, Department of Entomology, Kansas State University, Manhattan, KS 66506-4004, Attention IPRIN.

14 th Biennial International Plant Resistance to Insects Workshop

Items from the United States

Kramer, Morgan, Throne, Bailey, Howard

Reese, Reeck, Kofoid, Nagaraj, Campbell, Ma, Girma, Zhang

Flinn, Smith, Malik, Liu, Harvey, Starkey, Gill, Brown-Gudeira, Tolmay, Havlickova, Holubec

Baker, Burd, Elliot, Greenstone, Kindler, Mornhinweg, Porter, Shufran, Webster, Chen.

Reinert, George, Mackay, Smith, Davis, Read, Busey, Engelke

Balasubramani, Muthukrishnan, Sadakathulla, Subramanian, Ramanathan

14 th Biennial Int'l Plant Resistance to Insects Workshop

Colorado State University -- Fort Collins, Co

Dates Held: 2/28/2000 to 3/2/2000

Abstracts of presentations made during the Graduate Student Symposium: Tri-Trophic Interactions and the Impact of Host Plant Resistance on Non-Target Organisms.

14 th Biennial, INTERNATIONAL PLANT RESISTANCE TO INSECTS WORKSHOP, Feb. 29 - Mar. 2, 2000, Fort Collins, Colorado.

Organizer/Moderator: Kevin A. Shufran, USDA-ARS, 1301 N. Western Rd., Stillwater, OK 74075

Bold lettering indicates the presenting author.

Tritrophic Interactions Among Tobacco Budworm, (Heliothis virescens, Lepidoptera: Noctuidae), a Parasitoid of the Budworm (Campoletis sonorensis, Hymenoptera: Ichneumonidae), and Budworm Resistant Tobaccos . Juba, T. R., Sorenson, C. E., Southern, P. S. Department of Entomology, North Carolina State University, Raleigh, NC 27695

Effective management of pests of flue-cured tobacco requires several components including insecticidal sprays, baits, beneficial insects, and, recently, host-plant resistance. Understanding interactions among different management strategies facilitates integration of them into one system. Tobaccos CU 263 and CU 370 were bred for resistance to the tobacco budworm (Heliothis virescens), which feeds upon the developing vegetative growth of the plant. Campoletis sonorensis, a significant natural enemy of the budworm larvae in North Carolina, parasitizes the second and third instars of the budworm. Using the variety K 326 as a susceptible standard, three experiments were performed to evaluate how host-plant resistance may effect the parasitoid in the laboratory and field. In the first experiment, H. virescens that had been reared on the different tobaccos were offered for parasitization to C. sonorensis. The larvae and any parasitoids that developed in them were maintained until emergence of adult parasitoids or pupation of the larvae. Measurements included weight of the budworms at parasitization, weight of the parasitoid pupae in cocoons, weight of the parasitoid adults, length of time from parasitization until parasitoid pupation, and length of time from parasitoid pupation until adult parasitoid emergence. The only significant difference in these parameters was a higher weight of pupae in cocoons from K 326 and CU 263 than CU 370 (the more resistant line). The objective of the second experiment was to determine whether there were any differences in parasitoid orientation to the host-plant in a wind tunnel assay. In addition to the three tobaccos, there were three treatments. Plants were uninjured, injured mechanically, or injured by budworm feeding with the larval budworm present in the wind tunnel. While no differences existed among the tobaccos within each treatment, the parasitoid females responded most to the plants injured by the budworm feeding, then the mechanically injured plants, and least to the uninjured tobacco. Finally, the interaction between resistant host-plant and parasitoid was evaluated in the field. Rows of each tobacco variety were planted in the field and infested with laboratory-reared H. virescens of an appropriate size. After three or four days, the plants were searched for surviving budworms. Recovered larvae were maintained on artificial diet in an incubator. The experiment was repeated 6 times over time. Significantly more budworms were recovered in K 326 than CU 370 recovery rates in CU 263 were similar to both other varieties. There was no clear significant trend over time. Early in the season significantly more of the recovered larvae had been parasitized than those recovered later in the season. No differences in proportion of larvae parasitized occurred among the varieties. Similarly, if total mortality is defined as unrecovered budworms plus parasitized budworms, then significantly more mortality occurred earlier in the season than later. Greater mortality also occurred on the resistant tobaccos than K 326. Finally, significantly more parasitized budworms from K 326 yielded adult parasitoids than the resistant tobaccos. The lower percent emergence in the resistant varieties may reflect a fitness cost of the lower pupal weight in cocoons in the first experiment. While there may be a fitness cost to the parasitoid, the second and third experiments demonstrate that parasitoid efficacy is unhindered and total mortality of budworms may be enhanced in the resistant tobaccos.

Effects of plant morphological complexity on the efficacy and efficiency of Coccinella septempunctata L. as a predator of the pea aphid Acyrthosiphon pisum Harris. Ana Legrand and Pedro Barbosa. Department of Plant Science, 1376 Storrs Road, U-67, University of Connecticut, Storrs, CT 06269 and Department of Entomology, Plant Science Building, University of Maryland College Park, MD 20742.

Host plant resistance relies on both chemical and physical plant traits. At the same time as these traits deter or harm insect herbivores, they can also have an effect on insect natural enemies. Physical plant characters that have been shown to impact the effectiveness of insect natural enemies include non-glandular trichomes, surface waxes and the size and shape of plant organs and protective structures. Another physical character that could influence the interaction between a herbivore and its natural enemies is plant morphological complexity. Plant complexity could provide a physical refuge to the prey or could interfere with foraging activities of a natural enemy. Andow and Prokym (1990) and Lukianchuk and Smith (1997) showed that egg parasitism was reduced when wasps searched for hosts on complex rather than on simple surfaces. Thus, the objective of this research was to test the hypotheses that increased plant morphological complexity reduces the area search efficiency and predation efficacy of Coccinella septempunctata L. a predator of the pea aphid Acyrthosiphon pisum Harris. Essential to testing these hypotheses is the use of near-isogenic lines of the pea plant. The Normal, tl and aftl near-isogenic lines were selected because they represented changes in morphological complexity that could be ranked from low to high complexity. Further, the use of these genetic isolines allowed for the control, as much as possible, of non-morphological plant characters such as phytochemicals and surface waxes.

The first step was to establish how plant morphological complexity might influence the herbivore. Changes in plant morphology did not have a significant effect on pea aphid total fecundity or intrinsic rate of increase. Moreover, plant morphology did not affect the choice of settling location by the pea aphid. Therefore it is unlikely that changes in plant morphological complexity have indirect effects on the predator via the aphid prey. While there were no significant effects on the prey, plant morphological complexity had a significant effect on the foraging efficiency of the coccinellid. Plant complexity influenced the foraging time of the predator and as a consequence residence time was longest on the most complex leaves (aftl plants), regardless of aphid presence. Due to the localized movements within a small fraction of the most complex leaf, coccinellids had a significantly reduced area search efficiency. Although the predation efficacy of the beetle was not affected by the morphology of the plants, plant complexity had a significant effect on the degree of prey disturbance by the predator. More aphids dropped or moved from their original position when the predator searched the tl plants which were intermediate in complexity. The results from separate experiments showed that the predator achieves the highest area search efficiency on tl leaves. This might explain why the coccinellid disturbed more prey on this plant type. The results presented in this study support the notion that plant complexity can interfere with the foraging activity of an insect predator.

Andow, D.A. and D.R. Prokym. 1990. Plant structural complexity and host finding by a parasitoid. Oecologia 82: 162-165.

Lukianchuk, J. L. and S. M. Smith.1997. Influence of plant structural complexity on the foraging success of Trichogramma minutum: a comparison of search on artificial and foliage models. Entomologia Experimentalis et Applicata 84: 221-228.

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Tritrophic effects of volatile chemicals associated with induced resistance in solanaceous plants. Ahnya M. Redman, Jack C. Schultz, and James H. Tumlinson. Entomology Department, Pennsylvania State University, 501 Agricultural Sciences and Industries Bldg., University Park, PA 16802 Entomology Department, Pennsylvania State University, Pesticide Research Laboratory, University Park, PA 16802 and USDA- ARS, Center for Medical and Veterinary Entomology, 1700 SW 23rd Drive, Gainesville, FL 32608.

There has been a flurry of interest recently in tritrophic interactions and the potential use of herbivore-induced volatile compounds in agriculture. But, a critical question that has not been nswered is whether the release of these compounds actually benefits plants, and thus growers utilizing these chemicals for biological control, by reducing pest populations. This question is equally important to ecologists interested in whether damage-induced volatiles have evolved to protect plants from herbivore-damage. Laboratory demonstrations of parasitoid-attraction to volatiles abound, but nothing is known about the function of these compounds in nature. We attempted to determine if natural enemies were attracted to volatile compounds in the field, using two solanaceous plants, tomato and eastern black nightshade, as well as the herbivore Manduca sexta (Lepidoptera: Sphingidae). First, we measured parasitoid-recruitment to tomato plants induced with natural damage (imposed at night, with herbivores removed each morning) to plants induced with 5 mM jasmonic acid (JA), a natural plant elicitor, biweekly to untreated plants and to plants treated with the solvent used to dissolve JA. Plants were protected from background herbivory by hand-picking, and parasitoid-recruitment was measured by recruitment to sticky traps and by parasitism of sentinel M. sexta caterpillars confined in mesh bags near treated plants. Parasitism of sentinels was significantly elevated on the induced plants over the two controls, and sticky traps showed a similar pattern, indicating that plants, not larvae themselves, attracted parasitoids. Parasitioids included some unidentified tachinids (Diptera), but were primarily Cotesia congregata (Hymenoptera: Braconidae).

The following field season, another experiment was conducted, utilizing both nightshade and tomato, to ascertain whether the same pattern could be detected when plants were exposed to background herbivory in addition to our treatments, and also to compare the effect of M. sexta regurgitant with the other two means of inducing resistance in plants. Parasitism of sentinels was measured on tomato plants treated with natural damage, JA, M. sexta regurgitant, no damage, solvent, or mechanical damage (the control for regurgitant). Natural damage received the highest level of parasitism, followed by JA and regurgitant, and all three differed from untreated, solvent-treated, and mechanically damaged plants. Nightshade plants were subjected to the same treatments, except for regurgitant and mechanical damage. Natural damage elevated parasitism compared to untreated plants, and although JA increased parasitism somewhat as well, it did not differ from either of the two controls.

In addition, we found in a census of arthropods on the foliage of treated tomato plants, that the relative composition of three functional feeding guilds (natural enemies herbivores and miscellaneous arthropods, which were primarily nectar-feeders) differed between treatments. The relative proportions of natural enemies and miscellaneous arthropods were higher than expected on naturally damaged and JA-treated plants, and proportions of herbivores were lower.

Headspace-sampling of plants grown in a greenhouse revealed increased levels of myrcene, á-terpinene, 2-carene, â-phellandrene, caryophyllene, and á-humulene released by plants treated with M. sexta damage v. untreated plants, as well as slightly (but significantly) increased levels of these same compounds by regurgitant-treated plants v. mechanically damaged plants.

Effect of Bt corn on the predator Orius insidiosus (Say) . Mohammad A. Al-Deeb * (Presenter) and Gerald E. Wilde

Laboratory feeding studies were conducted to determine the effect of feeding Orius insidiosus nymphs on 1 day old European corn borer Ostrina nubilalis (Hbn) larvae which had ingested diet containing Bt toxins (Dipel ES). A commercial formulation of Bacillus thuringiensis subsp Kurstaki (Dipel ES) was incorporated into a meridic diet used to feed European corn borer larvae they were then offered as food to Orius nymphs. Immediately after eclosion Orius adult sex was determined, body weight and length were measured, and developmental time was calculated. Another feeding study was conducted to determine the effect of Bt corn silk on immature mortality of O. insidiosus. Fresh corn silks of Bt and non-Bt corn plants were offered to Orius nymphs till they reached maturity. Mortality counts were made daily. Finally, visual counts of O.insidiosus were made on Bt and non-Bt corn at three locations in Kansas (Abilene, Clay Center 1, 2). Number of Orius nymphs and adults were recorded on 40 plants per location on 2 sampling dates.

There was no significant difference in developmental time, body weight, body length of mature Orius, and immature mortality of Orius when reared on ECB larvae fed a diet containing Dipel ES. Orius nymphs feeding only on Bt and non-Bt corn silk suffered 100% mortality. There was no significant difference in immature mortality when Orius nymphs were fed a day on Bt and non-Bt silk and the other day on corn earworm eggs. Numbers of Orius adults and nymphs in Bt corn fields did not significantly differ from those of non-Bt fields. Our results suggest that Bt corn does not have a significant effect on the predator O.insidiosus (Say).

Biotypic and genotypic variation of greenbug populations collected from non-cultivated grass hosts. James A Anstead, John D Burd, Kevin A Shufran

The greenbug is an important pest of small grains in sorghum in North America. Resistant varieties have been deployed to control greenbug damage, but biotypes able to overcome this resistance have continued to cause significant loses. Very little is known about the biotypic or genotypic makeup of greenbug populations on grass hosts. It is hypothesized that non-cultivated grasses serve as a reservoir of diversity in the greenbug and that greenbugs move locally from non-cultivated hosts to exploit crops. It is also hypothesized that greenbug biotypes are in fact host specific races that evolved on non-cultivated grasses.

Greenbugs collected from a number of non-cultivated hosts and nearby cultivated hosts were tested for virulence against standard differentials to determine their biotype. Biotypic diversity was then compared between the cultivated and non-cultivated hosts.

The COI gene has been used to elucidate the relationships between the known greenbug biotypes (Shufran et al. unpublished data). They were found to fall into 3 clades the biotypes predominantly found on sorghum (C, E, I and K) and J formed a single clade biotypes B and the Canada Wild Rye isolate formed a single clade the New York isolate (a possible example of biotype A) and biotypes F and G formed a separate clade. Biotype H diverged completely separately to the rest of the biotypes and was the most divergent.

The genetic relationship amongst isolates collected in this study were estimated by the same molecular phylogenetic techniques. A dendogram, based on a 1kb section of the COI mtDNA gene, and including sequence data from the laboratory biotype colonies and field collected colonies was produced. The relationships between host, biotype and genotype will be discussed.

"Plant Allocation to Secondary Defensive Compounds: Testing the Carbon/Nutrient Balance Hypothesis in Elevated CO2". Carlos E. Coviella (1,2) and John T. Trumble (1), (1)University of California Riverside (2)Universidad Nacional de Lujan, Argentina

Plant resistance to herbivorous insects depends in part on plant allocation to defensive secondary compounds. The Carbon/Nutrient Balance Hypothesis (CNB) predicts that, when grown in elevated CO2, plants should allocate relatively more resources to carbon-based defenses as compared to plants grown in ambient CO2 levels. On the other hand, concentrations of nitrogen-based defenses should decline. We tested the CNB using a system that allowed us to simultaneously assess CO2 and nitrogen fertilization effects on plant total carbon and nitrogen, allocation to carbon-based and nitrogen-based defenses, and relating these results with potential impacts on herbivorous insects. We used transgenic Bt cotton plants as well as a near isogenic line without the Bt gene, grown in both ambient (370 L/L) and elevated (900 L/L) CO2 levels. We selected a split-plot design with CO2 level as whole plots, and with a 2 x 2 factorial for two levels of nitrogen fertilization and two levels of nitrogen-based defenses. We measured the effects of both elevated CO2 and nitrogen fertilization on total plant Carbon, and total plant Nitrogen. The nitrogen-based compound (the Bt toxin) and the carbon-based compounds in cotton (total phenolics, condensed tannins, and gossypol) were analyzed and quantified. We also examined the response of the insect herbivore Spodoptera exigua (Hbner) using foliar bioassays. The performance of the CNB hypothesis and the biological significance of the observed changes in plant resistance to insects are discussed.

Molecular Markers Linked to Greenbug (Homoptera: Aphididae) Biotype I Tolerance in Aegilops tauschii . Michael Flinn 1 , C. Michael Smith 1 , John C. Reese 1 , and Bikram Gill 2
1 Department of Entomology, Kansas State University, Manhattan, KS 66506-4004
2 Department of Plant Pathology, Kansas State University, Manhattan, KS 66506-5502

New advances in molecular biology are being used to enhance the future development of insect resistant lines of wheat. In developing insect resistance molecular markers, the categories of resistance the marker identifies must be identified. Aegilops tauschii accession TA 1675 (resistant donor), 'Wichita' (susceptible wheat cultivar), and line 97-85-3 (resistant offspring), were investigated and the category of resistance determined in each. Antibiosis was determined by calculating and comparing the intrinsic rate of increase of aphid population on 'Wichita', TA1675, and 97-85-3. Antixenosis was determined by measuring the number of aphids moving to each line of wheat planted around the perimeter of a 12cm pot. TA1675 exhibited antixenosis, but this resistance was not passed on to 97-85-3. Comparisons of SPAD meter readings and proportional dry plant weights were used to determine tolerance in each line. TA1675 and 97-85-3 were found to be highly tolerant compared to 'Wichita'. This tolerance provides a unique opportunity for it to be combined with biocontrol techniques as effective alternatives to insecticides.

Preliminary evaluations indicate polymorphism between 'Wichita', compared to TA1675 and 97-85-3 genomic DNA when amplified by PCR with wheat microsatellite (WMS) 428, and primers developed from the wheat resistance gene analog (RGA)1 gene and the barley chitinase (Cht)1b gene. These putative linkages will be determined by genotypic and phenotypic evaluation of F2 progeny from the cross TA1675 x 'Wichita'. When confirmed, these molecular markers will help wheat breeders, geneticists, and entomologists quickly and efficiently screen segregating wheat populations and new accessions of wheat for greenbug resistance.

Morphological and Molecular Quantification of the Hessian Fly/Wheat Interaction, Luke Gumaelius and Roger Ratcliffe, Department of Entomology, Purdue University, West Lafayette Indiana 47907

The Hessian Fly (HF), Mayetiola destructor (Say),has been a economically significant insect wheat pest since its introduction to the United States in the late 1700s, causing massive crop losses throughout wheat growing regions of the country. Cultural controls and the institution of intensive resistance breeding programs have reduced, but not eliminated crop loss. The fly's life cycle begins in the fall with the emergence of pupating adults. The short-lived adults mate, lay eggs and die within 2-3 days. Upon hatching, the first instar larvae crawl down the leaf surface into the growing point where a series of feeding sites are established. The feeding process causes localized cell permeability and stunting of the developing third leaf. The eventual effect of this feeding is a severely stunted main stem that gradually turns darker green. Uninfested tillers visually appear to be unaffected by main stem infestation. This phenotype often persists throughout the plant's life. Although stereotypic, the aforementioned phenotype is not absolute. To the contrary, HF associated phenotypes are highly variable due to abiotic and biotic mediation.

My research is aimed at quantifying the range of morphological and molecular effects associated with HF feeding. Specifically, I have investigated: protein titre and size, chlorophyll titer, photosystem health, amino acid ratios, sugar pool sizes, root structure and whole plant morphometrics. Maggot size, infesting number and subsequent growth rate have been coupled with the plant measurements. Together these measures will indicate the relative sink strength of the infesting maggots and a biomass conversion ratio. This study will provide a baseline for future studies involving mechanisms of resistance and resistance gene introgression.

Phylogenetic Relationships Among Greenbug Biotypes, Andrea B. Jensen, J. Spencer Johnston, and George L. Teetes, Dept. of Entomology, Texas A&M Univ., College Station, TX 77843

The family Poaceae, the grasses, comprises 90% of the world's food crops. Greenbug, Schizaphis graminum, infests 70 species in this family, including wheat, barley, and sorghum. Understanding biotype development has application to sustainable production of sorghum, small grains, and many other crops for which insect-resistant varieties are available but resistance is periodically lost due to resistance-breaking biotypes. Determining biotype relatedness among greenbugs contributes to an understanding of pest-host plant relationships. Biotype relatedness was determined by sequencing 640 bp from the mitochondrial cytochrome oxidase II (COII) and 530 bp from the 16S ribosomal RNA (16S rRNA) subunits from multiple individuals of each greenbug biotype. Sequence data is examined as phylogenetic relationships (gene trees) using maximum parsimony. Gene fragments from the COII and 16S rRNA subunits show congruence. Significant diversity exists that gene trees are resolved and results are compared to biotypes and biogeography.

Antibiosis and tolerance of Canadian spring wheats to cereal aphids, S.M. Migui, Department of Entomology, University of Manitoba, Winnipeg, Manitoba R3T 2N2

Cereal aphids are pests of adult, spring-sown wheat plants in Canada. Previous research on resistance to cereal aphids concentrated on young winter wheat plants. To initiate research on identification and incorporation of resistance to aphids for Canadian wheats, the susceptibility of young and adult plants were compared for commonly grown wheats and pest aphids. Cultivars of three wheat classes were exposed to three aphid species, Rhopalosiphum padi (L.), Schizaphis graminum (Rondani) and Sitobion avenae (Fabricius). Antibiosis was measured as the change in aphid biomass during infestation. For young and adult plants, antibiosis to aphids was similar among wheat cultivars, but R. padi produced more biomass on young plants and Sc. graminum and Si. avenae produced more biomass on adult plants. The impact of the aphids on plants was measured as differences in biomass between control and infested plants. Aphid infestation reduced biomass production of young plants equally among cultivars, but R. padi and Sc. graminum reduced biomass of all cultivars more than Si. avenae. The foliage biomass of adult plants did not differ between infested and control plants, although infestation greatly reduced seed yield. Schizaphis graminum and Si. avenae caused the greatest yield reduction for all cultivars, but some cultivars were more tolerant than others. To compare tolerance levels for the three aphids and two plant growth stages, specific impacts were estimated based on a biomass conversion ratio (units of biomass lost by plants per unit gained by aphids). The specific impacts ranged from 1.0 to 3.5 for young and 3.3 to 20.7 for adult plants, with young plants more tolerant of aphids than adult plants. Young wheat plants cannot be used as a model for antibiosis or tolerance of adult plants for these aphids. Adult plants of some Canadian cultivars are more tolerant to infestation by aphids than others.

Effect of leaf color on growth and development of armyworms in cotton, D. Jones 1 , G.O. Myers 1 , and B.R. Leonard 2 1 Louisiana State University, Department of Agronomy, Baton Rouge, LA 70803, 2 Louisiana State University Agricultural Center, Macon Ridge Research Center, Winnsboro, LA 71295

In cotton, both the fall armyworm (Spodoptera frugiperda) and the beet armyworm (Spodeptera exigua) aresporadic but economically important pests. Traditional control measures rely on the use of costly insecticides. Little research has been done on possible host plant resistance mechanisms. In 1998 it was observed that cotton germplasm expressing the red leaf color phenotype showed less foliar damage than normal green leaf color genotypes. In 1999 studies were performed to assess the effect of leaf color on armyworm growth and development. Fresh leaves of closely related green and red cotton genotypes were placed in petri dishes and infested with 2 nd instar larvae of laboratory reared cultures of both armyworm species. Larval mortality and weight gain were recorded at 2 day intervals for a period of 12 days (or until pupation). The possible utility of cotton leaf color as a host plant resistance mechanism which functions by suppressing armyworm feeding and subsequent development will be discussed.

Host Plant Preference and Performance of Bemisia argentifolii(Homoptera:Aleyrodidae) on poinsettia (Euphorbia pulchirrima) in relation to cultivar. Laura O. Petro and Richard A. Redak, Department of Entomology, University of California, Riverside, CA 92521, USA

We investigated the resistance qualities of seven economically important red cultivars of poinsettias against its major pest, the silverleaf whitefly, Bemisia argentifolii, Bellows and Perring. Additionally, two cultivars selected on the basis of previous adult preference studies (representing preferred and non-preferred) were monitored for nymphal development and survivorship. After 6 d of exposure, the cultivars "Red Velvet", "Supjibi", and "Pepride" were less preferred as oviposition sites than the other 4 cultivars evaluated. "Peterstar" was the most preferred host for ovipostion. After 21 days of exposure, there were significantly fewer eggs and nymphs observed on "Pepride " and "Red Velvet", and "Peterstar" again had significantly more eggs than the other preferred cultivars. The "Success" and "Petoy" had a significantly greater number of surviving nymphs than the other cultivars evaluated Total numbers of all live stages observed were significantly lower on "Freedom Red", "Red Velvet" and "Pepride". These latter cultivars demonstrated the greatest potential for resistance against the silverleaf whitefly. Observed plant morphology in addition to plant chemistry may explain the differences in suitability among the poinsettia cultivars. The population dynamics of silverleaf whiteflies on the most preferred and non-preferred poinsettia hosts are represented as life tables. The wider implications of the mechanisms of poinsettia resistance to whiteflies and future uses in integrated pest management for greenhouse cropping systems will be discussed.

Potato Leafhopper Resistance in Glandular-haired Alfalfa: A Comparative Study, Floyd W. Shockley and Elaine A. Backus, Dept. of Entomology, 1-87 Agriculture Building, University of Missouri, Columbia, MO 65211

Comparisons were made among seven different genotypes of glandular-haired alfalfa supplied by two different companies, Cal/West Seeds and Forage Genetics, in order to: 1) determine the relative resistance to hopperburn and the potato leafhopper, and 2) suggest possible physiological mechanisms of that resistance. A bioassay was designed to collect data on leafhopper mortality, number of excretory droplets (a gross measure of feeding), settling on various plant parts, hopperburn symptoms and severity, plant stunting under constant leafhopper pressure, and glandular trichome density on stems. A second bioassay was developed that would determine whether the physical presence of intact glandular trichomes changed the responses of the leafhoppers. This bioassay involved removing the stem glandular trichomes by rubbing them off with a Kleenex ® tissue and then infesting those plants with leafhoppers. Three of the seven genotypes showed increased leafhopper settling with trichome removal, an expected response if the resistance factor was located primarily in the trichomes. However, four of the genotypes showed decreased leafhopper settling, suggesting that the insects are responding to something other than physical contact with the intact hairs. In order to ascertain whether morphological differences in the glandular trichomes could explain variations in resistance, scanning electron micrographs were taken of all of the genotypes. The trichomes showed little difference from genotype to genotype all appeared as a simple ball atop a multicellular stalk. Further observational evidence to be discussed suggests that the glandular trichomes produce some type of chemical, either in the form of a volatile repellent or a contact deterrent. Future studies will involve testing of some of these genotypes for volatility and contact deterrency in the trichomes.

Induction of resistance in the black mustard Brassica nigra depends upon resistance trait and herbivore , Brian Traw Section of Ecology and Systematics, Corson Hall, Cornell University, Ithaca, NY 14853

Plant resistance occupies a continuum from traits which are generally effective against most herbivores to traits which are only effective against a small proportion of herbivores. On the one end is allylglucosinolate, a chemical produced by the black mustard Brassica nigra which deters generalists but actually attracts specialists to oviposit and/or feed. On the other end are trichomes, which at high densities deter both generalist and specialist herbivores of mustards. We are interested in how the environment influences plant allocation of resources between these two resistance traits. We compared leaf allylglucosinolate concentration and trichome density in black mustard plants damaged by three different herbivore species. Our primary question was whether these plant resistance traits would be induced. We predicted that leaf trichome density would be more likely than leaf allylglucosinolate concentration to be induced by the herbivores, especially when the feeding was by a specialist herbivore, because the production of allylglucosinolate might attract more specialists. Two specialists Pieris rapae and Phyllotreta cruciferae and one generalist Trichoplusia ni were each applied to 44 Brassica nigra seedlings at the four leaf stage. We recorded herbivory and removed the herbivores after 12 hours. Plants were later harvested after reaching 8, 10, 12, or 14 leaves (n_ per plant developmental stage). Pieris rapae triggered a doubling of trichome density in subsequent leaves, whereas neither Trichoplusia ni nor Phyllotreta cruciferae had a significant effect on trichome density. The increase in leaf trichome density was the result of more trichomes being produced, rather than a smaller leaf area. Allylglucosinolate concentration was not induced by the three herbivores. The specificity of the trichome induction to Pieris rapae suggests that the plant receives a signal more specific than damage alone, perhaps including some constituent of the saliva.

Chromosome Localization and Genetic Mapping of Russian Wheat Aphid Resistance Genes Dn1, Dn2, and Dn5i in Wheat Using Molecular Markers, Xuming Liu and C. Michael Smith, Department of Entomology Bikram S. Gill,

Department of Plant Pathology, Kansas State University, Manhattan, KS 66506, USA and Vicki Tolmay, Small Grain Institute, Private Bag, Bethlehem, Republic of South Africa

The Russian wheat aphid (RWA), Diuraphis noxia Mordvilko, is a serious economic pest of wheat and barley in the western United States and South Africa. Aphid resistant cultivars have proven to be a viable tactic for RWA management. Several dominant resistance genes have been identified in wheat, Triticum aestivum, germplasm, including Dn1 in PI 137739, Dn2 in PI 262660, and at least two resistance genes (Dn5i) in PI 294994. To determine the chromosome locations of these genes, genomic DNA of several near isogenic lines (BC 5+), as well as segregating F2 populations from crosses between the resistant PIs and four susceptible wheat cultivars, was amplified via PCR with molecular markers of known chromosome location. Results revealed that the locus for wheat microsatellite (WMS) 111, located on wheat chromosome 7DS (short arm), was tightly linked to Dn1, Dn2, and Dn5a. These results confirm that Dn1, Dn2, and Dn5a are tightly linked to each other, and provide new information about their location being 7DS, near the centromere, instead of as previously reported on chromosome 7DL (long arm). WMS 635 (near the distal end of 7DS) clearly marked the location of the previously suggested resistance gene Dn5b, and WMS 642 (located on 1DL) marked and identified a new gene Dn5c, which is located in a defense gene-rich region of wheat chromosome 1DL. Based on analyses of isogenic line data, the genetic distance between the Dn genes and their respectively linked WMS markers was estimated to be <3.2 cM [1 x 100 / 2 5 ]. Exact genetic linkage distances are being determined using F2 populations. These markers will prove very useful for the further study of RWA resistance genes and in marker-assisted breeding for aphid resistant wheat.

Key words: Russian wheat aphid, wheat, molecular marker, Dn resistance genes

Isolation of the Nucleotide Binding Site Family of Resistance Gene Analogs from Alfalfa, J.C. Cordero and D.Z. Skinner, Kansas State University & USDA-ARS

Many disease resistance genes from different plant genera that confer strong resistance against a wide range of pathogens have been found to share sequence homology at specific regions. Furthermore, the NBS region of homology from the NBS-LRR group of R genes share conserved motifs - P-loop, Kinase-2, Kinase 3-a, and a putative membrane-spanning domain. The objective of this study was to isolate the NBS regions from Medicago sativa in order to evaluate the variability and to facilitate the future cloning of complete disease resistance genes.

PCR with degenerate primers designed from the P-Loop and the putative membrane-spanning domains was used to amplify a 500 bp fragment. The 500 bp product was cloned and sequence diversity was analyzed. Sequence analysis from 94 individual clones showed that fifteen significantly different types of NBS regions exist in alfalfa. Each possessed the conserved domains Kinase-2 and Kinase-3a, characteristic of the NBS region. The fifteen sequences were compared to the most similar NBS genes found with a BLAST search of the GenBank database.

Dendrogram analysis showed that three major clusters of families exist in alfalfa that seem to have different evolutionary origins. This suggests that further research evaluating the evolution of disease resistance genes in alfalfa is possible. Additionally, the confirmed existence of such a wide family of NBS regions in alfalfa might make it possible to clone R genes using this approach in combination with Serial Analysis of Gene Expression (SAGE) or differential display.

Department of Plant, Soil and Entomological Sciences 1
University of Idaho
Moscow, ID 83844-2339

Daniel E. Cervantes, Nilsa A. Bosque-Perez and Sanford D. Eigenbrode

Hessian fly oviposition preference on winter wheats varying in surface waxes

Damage due to the Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), has been increasing in northern Idaho for the last decade. The use of resistant varieties has been a principal control measure for this pest. Resistance to Hessian fly in wheat has relied on antibiosis, but in other parts of the USA this has resulted in the evolution of Hessian fly biotypes capable of overcoming resistance. Antixenosis, which focuses on non-preference by the ovipositing female, has the potential to reduce selection for new biotypes.

Free choice tests were conducted in the greenhouse to evaluate winter wheats for possible antixenosis to Hessian fly. Comparisons were made between Avalon and Avalon reduced wax, and in a separate experiment, between Virtue and Virtue reduced wax. Genotypes were tested separately at the seedling stage and the flag-leaf stage. There were no significant differences in number of eggs laid per female when the genotypes were tested at the seedling stage.

Significant differences in mean number of Hessian fly eggs were detected between the wheat genotypes when plants were tested at the flag-leaf stage. Female Hessian flies preferred reduced wax genotypes for oviposition compared to normal wax genotypes. Scanning electron microscopy of the winter wheats showed less crystal density on reduced wax compared to normal wheat genotypes. Gas chromatography was performed on the surface waxes in order to characterize the genotypes. Differences in surface wax components between normal and reduced wax genotypes were evident only at the flag-leaf stage. Nonacosane, hentriacontane, and octacosanol were greater in percentage of total constituents in the reduced wax genotypes, whereas these components were considerably lower in percentage in the normal wax genotypes. Some of the constituents identified may have influenced oviposition preference by the Hessian fly.

USDA-ARS North Central Regional
Plant Introduction Station
Ames, IA

Richard L. Wilson and Sharon G. McClurg

During 1999, we evaluated 500 maize accessions (introductions) for resistance to leaf feeding by European corn borer (Ostrinia nubilalis (Hübner)). A 1 - 9 visual rating scale (1=no damage, 9=heavy damage) was used to evaluate the accessions in the field. Four accessions rated 3 or less (resistant). We also evaluated 509 accessions during 2000 and found 13 accessions to be resistant.

In 1999, we evaluated 189 maize accessions for resistance to stalk boring by European corn borer. Data were obtained by splitting stalks and measuring length of feeding tunnels. These data were compared to a resistant check inbred, B52. Fourteen accessions were as good as, or better than the resistant check. Data for 2000 are not available at this writing.

The Brassica collection is being field evaluated for cabbage aphid (Brevicoryne brassicae (L.)) resistance at Hermiston, Oregon (Gary Reed, Oregon State University, is cooperating on this project). A 1 - 5 visual rating scale (1=no damage, 5=heavy damage) was used to evaluate the accessions. During 1999, 24 of 500 accessions tested rated 2 or less (resistant) and in 2000, 31 of 581 accessions tested rated resistant.

Data from these evaluations will be made available to the public via the Germplasm Resources Information Network (GRIN). The web site to view this data is http://www.ars-grin.gov/npgs/or you may contact our station directly via our web site, http://www.ars-grin.gov/nc7/.

Recent publications dealing with plant resistance to insects:

1 Wilson, R. L. and S. G. McClurg. 1999. Evaluation of sunflower germplasm for resistance to sunflower moth. Abs. Submitted Papers, N. Cent. Br., Entomol. Soc. Am. 54, 16.

2 Binder, B. F., J. C. Robbins, R. L. Wilson, C. A. Abel, and P. N. Hinz. 1999. Effects of Peruvian maize extracts on growth, development, and fecundity of the European corn borer. J. Chem. Ecol. 25, 1281-1294.

3. Wilson, R. L. 1999. Acquisition and Maintenance of Resistant Germplasm. In: Handbook of Pest Management. (Ed: Ruberson, J. R.) Marcel Dekker, Inc., New York, 239-262.

4. Abel, C. A. and R. L. Wilson. 1999. Evaluation of 11 maize populations from Peru for mechanisms of resistance to leaf feeding by European corn borer. J. Kan. Entomol. Soc. 72, 149-159.

5. Abel, C. A., R. L. Wilson, B. R. Wiseman, W. H. White, and F. M. Davis. 2000. Conventional resistance of experimental maize lines to corn earworm (Lepidoptera: Noctuidae), fall armyworm (Lepidoptera: Noctuidae), southwestern corn borer (Lepidoptera: Crambidae), and sugarcane borer (Lepidoptera: Crambidae). J. Econ. Entomol. 93, 982-988.

USGMRL/ARS-USDA
1515 College Avenue
Manhattan, KS 66502
K.J. Kramer, T.D. Morgan, J.E. Throne, M. Bailey and J.A. Howard

Results of collaborative research between ARS-USDA (Manhattan, KS) and ProdiGene, Inc. (College Station, TX) demonstrated that a new type of transgenic corn (maize) is insect-resistant. This corn contains the protein avidin, which results in kernels that have nutritional resistance to many stored-product insects because avidin binds the essential vitamin biotin. Insects feeding on this corn develop a biotin deficiency that leads to delayed development and toxicity. Avidin is a rather unique biopesticide because it is a protein found in one of nature's most nutritious creations, the chicken egg. Avidin occurs in the transgenic grain at only a fraction of the level present in eggs. This is one of the very few new ideas for use of transgenic plant biotechnology for insect pest management and has exciting possibilities.

Kramer, K. J., Morgan, T. D., Throne, J. E., Bailey, M. and Howard, J. A. 2000. Transgenic maize expressing avidin is resistant to storage pests. Nature Biotech. 18, 670-674.

Department of Entomology
Kansas State University
Manhattan, KS 66506

Sorghum Tolerance to Greenbug Feeding Damage

John C. Reese, G. R. Reeck, Ken Kofoid, Nandi Nagaraj, Leslie R. Campbell, Runlin Z. Ma, and Melaku Girma, Yu Zhang

In order to decrease any possible selection pressure for yet more virulent biotypes of the greenbug, Schizaphis graminum (Rondani), we have focused our efforts on the development of sorghum germplasm that exhibits tolerance to greenbug feeding damage, rather than antibiosis or antixenosis. We have emphasized the reduction of chlorophyll loss due to greenbug feeding damage. A chlorophyll meter was utilized to nondestructively measure chlorophyll of areas fed upon four days by greenbugs. Four accessions that showed only low levels of resistance to biotype I were utilized in a recurrent selection scheme to make a large number of crosses. Selections were screened for tolerance and many promising ones were returned to the scheme, thus the label recurrent selection.

We are continuing to screen a group of 1,017 selections for tolerance to biotype I greenbugs, and then screen those tolerant selections for tolerance to biotype K. We have completed screening a total of 315 selections for tolerance to biotype K. Sixty-one selections from the most recent group lost significantly less chlorophyll than the susceptible check.

The damage response elicited by feeding greenbugs appears to be caused mainly by pectinases such as polygalacturonase via a two-step process involving the release of cell wall fragments. Pectinases from various sources, including greenbugs, caused significant chlorophyll losses in susceptible sorghum plants. Cell wall fragments released by the actions of pectinases on pectin from various sources, including sorghum, also caused significant reductions in chlorophyll.

In the area of molecular genetics of pectinases, Yu Zhang is completing his M. S. thesis, Comparative Studies on Pectin Methylesterases of Sitophilus oryzae, S. zeamais, and S. granarius.

We are just starting a project on the relationships between chlorophyll loss and photosynthetic capabilities. Preliminary experiments suggest that greenbug feeding activities actually elicit a very rapid and dramatic drop in photosynthetic rates.

Barbehenn, R. V., J. C. Reese, and K. S. Hagen. 1999. The food of insects. In, Ecological Entomology (Second Edition). C. B. Huffaker and A. P. Gutierrez (eds.). John Wiley and Sons. New York. Pp. 83-121.

Girma, M., K. D. Kofoid, and J. C. Reese. 1998. Sorghum germplasm tolerant to greenbug (Homoptera: Aphididae) feeding damage as measured by reduced chlorophyll loss. J. Kansas Entomol. Soc. 71: 108-115.

Ma, R. Z., J. C. Reese, W. C. Black IV, and P. Bramel-Cox. 1998. Chlorophyll loss in a greenbug-susceptible sorghum due to pectinases and pectin fragments. J. Kansas Entomol. Soc. 71: 51-60.

Reese, J. C., W. F. Tjallingii, M. van Helden, and E. Prado. 2000. Waveform comparisons among AC and DC electronic monitoring systems for aphid (Homoptera: Aphididae) feeding behavior. In, Principles and Applications of Electronic Monitoring and Other Techniques in the Study of Homopteran Feeding Behavior. G. P. Walker and E. A. Backus (eds.). Thomas Say Publ. In Entomol.: Proceedings. Entomol. Soc. Am. Pp. 71-101.

1 Department of Entomology
2 Department of Plant Pathology
3 USDA/ARS & Department of Agronomy
Kansas State University, Manhattan, KS 66506

4 Department of Entomology, Kansas State University,
Agricultural Research Center - Hays, Hays, KS 67601

5 Small Grain Institute, Bethlehem, Republic of South Africa
6 Czech Research Institute of Crop Protection, Prague, Czech Republic

Michael Flinn 1 , C. Michael Smith 1, Renu Malik 1 , Xuming Liu 1 , Tom Harvey 4 , Sharon Starkey 1 , Bikram Gill, 2 Gina Brown-Gudeira 3 , Vicki Tolmay 5 Helena Havlickova 6 , and Vojtech Holubec 6
Microsatellite Markers Linked to Six Russian Wheat Aphid Resistance Genes in Wheat

Xuming Liu, C. Michael Smith, Bikram Gill and Vicki Tolmay

The Russian wheat aphid (RWA), Diuraphis noxia Mordvilko, is a serious economic pest of wheat and barley in North America, South America, and South Africa. Using aphid resistant cultivars has proven to be a viable tactic for RWA management. Several dominant resistance genes have been identified in wheat, Triticum aestivum, including Dn1 in PI 137739, Dn2 in PI 262660, and at least three resistance genes (Dn5+) in PI 294994. The identification of RWA-resistant genes and the development of resistant cultivars may be accelerated through the use of molecular markers. DNA of wheat from near isogenic lines and segregating F2 populations was amplified with microsatellite primers via PCR.

Results revealed that the locus for wheat microsatellite GWM111 (Xgwm111), located on wheat chromosome 7DS (short arm), is tightly linked to Dn1, Dn2, and Dn5, as well as Dnx in PI 220127. Segregation data indicate RWA resistance in wheat PI 220127 is also conferred by a single dominant resistance gene (Dnx). These results confirm that Dn1, Dn2, and Dn5 are tightly linked to each other, and provide new information about their location being 7DS, near the centromere, instead of as previously reported on 7DL. Xgwm635 (near the distal end of 7DS) clearly marked the location of the previously suggested resistance gene in PI 294994, here designated as Dn8. Xgwm642 (located on 1DL) marked and identified another new gene Dn9, which is located in a defense gene-rich region of wheat chromosome 1DL. The locations of markers and the genes linked to them were confirmed by ditelosomic and nulli-tetrasomic analyses. Genetic linkage maps of the above RWA resistance genes and markers have been constructed for wheat chromosomes 1D and 7D.

Molecular Markers Linked to a New Gene for Wheat Curl Mite Resistance in Wheat

Renu Malik, C. Michael Smith, Tom Harvey, Sharon Starkey, and Gina Brown-Gudeira

Over 200 molecular markers have been evaluated to map the location of the gene(s) in the WGRC40 germplasm responsible for resistance to the wheat curl mite, Aceria toschilla Keifer. Initial phenotypic evaluations indicated that this resistance is expressed by a dominant gene. However, preliminary genotypic results indicate that resistance is expressed by the previously identified Cmc1 resistance gene from Aegilops tauschii, as well as a new gene, also from Ae. tauschii. Both appear to be located on the short arm of chromosome 6D.

Molecular Markers in Wheat Linked to Tolerance to Greenbug Feeding Damage

C. Michael Smith, Sharon Starkey, John Reese and Gina Brown-Gudeira

Plants containing the greenbug resistance genes Gb3, Gb4, Gb5, and Gb6 were evaluated for tolerance to chlorophyll loss from greenbug feeding in SPAD index experiments. The SPAD indices of wheats containing the Gb3, Gb5, and Gb6 genes were significantly less than those of the susceptible cultivar 'Thunderbird'. SPAD indices of two uncharacterized biotype I resistance sources from Aegilops tauschii , WGRC 04 and KSU94U306, were intermediate in phenotypic response. The resistance of these sources appears to be controlled by genes expressing a category of resistance other than tolerance.

DNA isolated from 'Amigo' (Gb3) and 'Thunderbird' (Gb0) was amplified with wheat microsatellite (WMS) primers with loci on chromosome 7D and evaluated for putative polymorphisms. Preliminary results of these experiments indicated that WMS primers 44 & 111 (7DS) and 130 (7AS) all differentially amplified 'Amigo' and 'Thunderbird' DNA in such a way to reveal putative polymorphisms. WMS primers with loci on chromosome 1A, specific to rye, were evaluated for putative polymorphisms between DNA containing 'GRS 1201' (Gb6) and 'Thunderbird'. Preliminary results of these experiments indicate that WMS primers 33 and 136 each differentially amplify the DNA of resistant and susceptible cultivars in such a way to reveal putative polymorphisms.

Evaluation of Aegilops Germplasm with Multiple Aphid Resistance in Wheat

C. Michael Smith, Bikram Gill, Helena Havlickova, and Vojtech Holubec

Afterwards, 20 Aegilops species from the Gene Bank Collection of RICP, all possessing some level of resistance the bird cherry-oat aphid or the English grain aphid were evaluated for resistance to the Russian wheat aphid and the greenbug (biotype I) at KSU. Aegilops tauschii accession 7096 was similar in level of greenbug resistance to A. tauschii 1675, a standard greenbug resistant control in aphid evaluations at KSU. Both A. tauschii accessions were significantly less damaged than the susceptible variety 'Wichita'.Two Aegilops cylindrica accessions (4059 & 4062) and an Aegilops markgrafi accession were highly susceptible and similar to 'Wichita' in response to greenbug feeding. A. neglecta accession (8052) was moderately resistant to Russian wheat aphid and greenbug. Sixty-seven pest-resistant Aegilops accessions from the KSU Wheat Genetic Resource Center were evaluated for resistance to bird cherry-oat aphid and accessions TA36, TA4, and TA 168 were highly resistant.

A Molecular Marker Linked to Tolerance in Aegilops tauschii Accession 1675 to Greenbug, (Homoptera: Aphididae). Michael B. Flinn, Kansas State University, Manhattan, Kansas. 2000.

The greenbug is a serious aphid pest of wheat and sorghum throughout the world. Its ability to overcome both resistant plant cultivars and insecticides make it a serious problem to crop producers. Nevertheless, traditional plant breeding techniques to produce insect resistant cultivars are an economical and environmentally sound way of managing greenbugs in sorghum production.

The categories of resistance to greenbug, Schizaphis graminum (Rondani), biotype I, were determined in Aegilops tauschii (goatgrass) accession #1675 (Ae. tauschii 1675) (resistant donor parent), 'Wichita' (susceptible wheat parent), and an Ae. tauschii derived resistant offspring, line 97-85-3 ('A97-85-3'). Antibiosis was determined using the intrinsic rate of increase of populations of aphids confined to each of the three wheats. Neither parent nor the resistant progeny expressed antibiosis. Antixenosis was determined by allowing aphids a choice to feed on plants of each of the three wheats. Ae. tauschii 1675 exhibited antixenosis, but this resistance was not inherited and expressed in 'A97-85-3'. Comparisons of SPAD meter readings and proportional dry plant weight loss were used to determine tolerance to greenbug feeding. Ae. tauschii 1675 and 'A97-85-3' were highly tolerant compared to 'Wichita'.

DNA from segregating F2 populations from the cross [Ae. tauschii accession 1675 x 'Wichita'] was isolated and amplified using all known wheat microsatellite PCR primers and other degenerate primers for the D genome of wheat. Segregation analyses showed that microsatellite marker XGWM44 was linked to the Ae. tauschii 1675 greenbug resistance gene(s). The location of XGWM44 was confirmed as being on the short arm of wheat chromosome 7D. A genetic linkage map was constructed for XGWM44
Recent Publications

Smith, C. M. 1998. Plant Resistance to Insects. In: Rechcigl, J. E. and Rechcigl, N. A. (Eds.) Biological and Biotechnological Control of Insects Pests. CRC Press LLC., Boca Raton, FL. pgs. 171-208.

Dhaliwal, G. S. , V. K. Dilwari, and C. M. Smith. 1999. Host Plant Defense Against Insects. In: Dhaliwal, G. S., and Arora, R. (Eds.). Environmental Stress in Crop Plants. Commonwealth Publishers, New Delhi. pp. 172-210.

Oppert, B., K. Hartzer, and C. M. Smith. 2000. Characterization of the digestive proteinases of Hypera postica Gyllenhal (Coleoptera: Curculionidae). Trans. Kansas Acad. Sci. (In Press).
Lui, X. M. , C. M. Smith, B. S. Gill, and V. Tolmay. 2000. Microsatellite markers linked to six Russian wheat aphid resistance genes in wheat. Theor. Appl. Genet. 98: (In Press).

On August 3, 2000, after 32 years of service, Dr. James A. Webster will retire from the USDA-ARS, Plant Science and Water Conservation Research Laboratory, Stillwater, Oklahoma.

Jim received his B.S. in Zoology and M.S. in Entomology from the University of Kentucky, and then went on to earn a Ph.D. in Entomology from Kansas State University in 1968. He immediately came to work for ARS in East Lansing, Michigan, working on the cereal leaf beetle plant resistance program. After the successful development and release of CLB-resistant wheat and barley germplasm lines, the ARS phase of the program was discontinued, and in 1981 Jim transferred to Stillwater to work primarily on plant resistance to cereal aphids in the Wheat and Other Cereal Crops Research Unit. From 1993 to 1999 he served as Research Leader for that Unit, as well as Laboratory Director for the Plant Science and Water Conservation Research Laboratory.

Jim is best known for his leadership role during the initial detection of the Russian wheat aphid in the United States. His background knowledge on the insect allowed ARS to immediately distribute information to U.S. researchers and extension personnel. It is estimated that this advance information cut a year off the time required to develop management strategies for this new pest. For this work, Jim was awarded the Entomological Society of America Recognition in Entomology Award for Outstanding Contributions to Agriculture for 1996.

Jim is an active member in the Entomological Society of America, and has held numerous offices and committee chair positions in the Southwestern Branch. He is also a member of the American Society of Agronomy, the Kansas (Central States) Entomological Society, and the Southwestern Entomological Society. He participates in activities of the International Plant Resistance to Insects group, the Hard Red Winter Wheat Improvement Committee, and the Western Coordinating Committee for "Integrated Management of Russian Wheat Aphid and Other Cereal Aphids." He was the ARS co-organizer for an international ARS/Oklahoma State University aphid symposium held in Stillwater in 1990. He also was invited to serve as an outside reviewer of the South African Russian Wheat Aphid Research Program by the South African Department of Agriculture. During his career he authored or co-authored over 150 articles and book chapters, and he co-edited the 1999 Thomas Say Publications in Entomology book "Economic, Environmental, and Social Benefits of Resistance in Field Crops."

Because many of the people who have worked with Jim over the years will be attending this year's ESA annual meeting in Montreal in December, plans are in the works for a nice reception there. Information on that can be obtained from Dave Porter ( [email protected] ). As part of that event, we will present him with a book of congratulatory and memory letters. These can be sent to Ruth Treat, USDA-ARS, 1301 N. Western Road, Stillwater, OK 74075, by November 15.

A small, informal reception by the Stillwater group is also planned for Jim's last day, August 3. Any of Jim's coworkers who happen to be in the vicinity that afternoon are certainly welcome to stop by for coffee and cake.

Plant Science Research Laboratory, USDA-ARS
1301 N. Western St.,
Stillwater, OK 74075-2714, USA
http://www.pswcrl.ars.usda.gov

C.A. Baker, J.D. Burd, N.C. Elliot, M.H. Greenstone, S.D. Kindler, D.W. Mornhinweg, D.R. Porter, K.A. Shufran, J.A. Webster, and Y. Chen.

Russian wheat aphid, Diuraphis noxia (Mordvilko)

Efforts are ongoing to develop Russian wheat aphid (RWA)-resistant wheat germplasm. Advanced wheat lines derived from 13 different RWA resistance sources were planted for seed increase, evaluation, and purification in preparation for germplasm release these include 61 hard white winter lines, 87 hard red winter lines, 36 hard red spring lines, 63 soft white spring lines, and 42 hard white spring lines. Topcrossed seed was screened for resistance to RWA, and resistant plants were transplanted to the greenhouse for increase and progeny testing. Homozygous RWA-resistant lines will be selected for germplasm release. Field evaluations of winter RWA-resistant wheat lines continue to be made in Stillwater.

Durum wheats maintained by USDA -ARS GRIN have been evaluated for resistance to RWA. Resistant plants were identified, rescued, and grown for seed increase. Purified selections will be reintroduced to the GRIN collection, and crosses will be made with agronomically acceptable durum wheats.

Development of resistant X resistant populations continued in order to study genetic diversity of RWA resistance in wheat. Genetic diversity studies are ongoing for all resistant lines to determine if these lines carry different genes for resistance to RWA.

Efforts continue to develop adapted RWA-resistant germplasm lines for all barley producing areas of the U.S. 2,500 spring and 450 winter BC3F3/F4 barley observation lines were evaluated in Aberdeen, ID with the cooperation of Phil Bregitzer and Darrell Wesenberg, USDA-ARS, Aberdeen, ID and head/row selections made for further analysis in 2001 headrows/preliminary yield trials. These lines include 20 susceptible backgrounds and 25 resistant sources. Seventy lines were evaluated in preliminary yield trials and selections earmarked for advanced replicated yield trials in 2001. These lines included 7 susceptible backgrounds and 24 resistant sources. Approximately 16 lines were evaluated in replicated advanced yield trials in several locations Idaho and Colorado for potential release as adapted germplasm lines. These lines include 3 susceptible backgrounds and 3 resistant sources. Other lines developed in conjunction with Phil Bregitzer were also evaluated in advanced yield nurseries at several locations in Idaho, Colorado and Nebraska. Crossing still continued to bring more resistant sources into adapted barley backgrounds.

Development of genetic populations to study genetic diversity among all 109 RWA-resistant barley lines identified and selected at Stillwater continued.

Data analysis is ongoing from a study conducted in 1998 and 1999 in Idaho and Colorado, with the cooperation of Phil Bregitzer and Frank Peairs, to determine the affect of early and late RWA feeding on malting quality of malting barley cultivars and adapted RWA-resistant barley lines.

Greenbug, Schizaphis graminum (Rondani)

Greenbugs were a serious pest on winter wheat in the central Oklahoma wheat growing area (north of I-40) in autumn of 1999. Intensity of infestations appeared to increase as one headed north towards the Kansas border. Early planted fields appeared to suffer less damage than later-planted fields, suggesting that fields were colonized by greenbugs primarily from mid-September through mid-October. Seriously damaged fields first became evident in late-October. Autumn weather was mild and dry, making conditions ideal for greenbug population growth. The majority of winter wheat fields in central Oklahoma were treated with insecticide in autumn of 1999 (mostly during November). Greenbug populations in untreated fields in central Oklahoma declined during winter, primarily due to the activity of parasitoids. Parasitism levels by L. testaceipes exceeded 90% in some fields. Most such fields had probably already suffered economic damage.

Wheat fields in the Oklahoma panhandle also developed serious greenbug infestations, but they developed later than in central Oklahoma, peaking in January or February. This was the result of low parasitism levels and mild weather. Much of the wheat acreage in the panhandle was treated with insecticide during January and February, but we believe that a smaller proportion of fields were treated than in central Oklahoma. Parasitism levels increased from late January through February and greenbug populations in untreated fields eventually crashed as the result however not before economic damage occurred. Greenbugs were sparse in southwestern Oklahoma (south of I-40). The bird cherry-oat aphid was present in fields throughout the state, but generally occurred at low levels.

A regional field study to assess the overwintering ability and the success of the greenbug to undergo sexual reproduction is now in its third year. Research locations include Brookings, SD, Hays and Manhattan, KS, Stillwater, OK, and Bushland, TX. Greenbugs have produced sexual morphs at all locations, and except for the Bushland site, eggs have been collected and successfully hatched. Future plans include studies to optimize the process of artificially generating the greenbug holocycle and improving egg-hatch success.

A molecular phylogenetic analysis based on the cytochrome oxidase I mitochondrial gene was conducted on all greenbug biotypes found in the United States (B, C, E, F, G, H, I, J and K). In addition, three unique isolates, one from a New York colony (NY) that has been in culture since 1959, another that was collected from Canada wild rye (CWR) in Oklahoma, and an isolate from Germany (EUR) were used in the analysis. Genetic distances among greenbug biotypes ranged from 0.08% to 6.17% difference in nucleotide substitutions. Phylogenetic analyses produced dendrograms revealing three clades clade 1 contained the 'agricultural biotypes' commonly found on sorghum and wheat (C, E, I, K, plus J), clade 2 contained F, G, and NY, and clade 3 contained B, CWR, and EUR, which are rarely found on crops. Biotype H fell outside these clades and may represent another Schizaphis species. Greenbug biotypes are a mixture of genotypes belonging to three clades and likely have diverged as host-adapted races on wild grasses as opposed to resistant crop cultivars. Biotype, as defined for the greenbug, does not appear to have any evolutionary or taxonomic status.

Information was developed that sheds new light on a theory of breeding plants with resistance to insects. Older, classical concepts of resistance breeding have dictated that "pyramiding" genes (combining more than one resistance gene) into a single wheat plant provided durable protection to insect pests and thwarted the development of new damaging biotypes. Experimental wheat germplasms were developed using various combinations of resistance genes and subsequently tested with an array of greenbug biotypes. Results of these experiments clearly show that pyramiding resistance genes in wheat does not provide additional protection against greenbug biotypes.

Rice root aphid, Rhopalosiphum rufiabdominalis (Sasaki)

An obscure aphid found on wheat in Oklahoma was identified as the rice root aphid. Rather high numbers of this aphid were found on wheat beginning in October and continued through the middle of January. During October this was the most numerous aphid found on wheat. The aphid feeds at the base of the wheat plant. It is believed the aphid can cause economic damage to wheat, although losses have apparently never been quantified. The rice root aphid may be a particularly important pest of cereals in the southern Great Plains (Susan Halbert personal communication), where in addition to direct feeding damage, it can also transmit barley yellow dwarf disease. Interspecies similarities between the bird cherry-oat aphid and the rice root aphid often lead to visual misidentification, and damage to cereals often attributed to the bird cherry-oat aphid may sometimes be caused by the rice root aphid. A key distinguishing feature is that the bird cherry-oat aphid has six antennal segments whereas the rice root aphid only has five antennal segments. Other, non-diagnostic characteristics can often be used to separate the species, including presence of dense setae on the antennal segments, and the slight differences in coloration.

James Anstead (Cambridge, UK) has completed his MS degree at Oklahoma State University (Thesis: Genotypic and Biotypic Diversity of Greenbug, Schizaphis graminum (Rondani), on Non-cultivated Hosts).

Hays, D.B., D.R. Porter, J.A. Webster, and B.F. Carver. 1999. Feeding behavior of biotypes E and H greenbug (Homoptera: Aphididae) on previously infested near-isolines of barley. J. Econ. Entomol. 92:1223-1229.

Lukaszewski, A.J., D.R. Porter, E.F. Antonelli, and J. Dubcovsky. 2000. Registration of UCRBW98-1 and UCRBW98-2 wheat germplasms with leaf rust and greenbug resistance genes. Crop Sci. 40:590.

Porter, D.R. and J.A. Webster. 2000. Russian wheat aphid-induced protein alteration in wheat. Euphytica 111:199-203.

Porter, D.R., J.D. Burd, K.A. Shufran, and J.A. Webster. 2000. Efficacy of pyramiding greenbug (Homoptera: Aphididae) resistance genes in wheat. J. Econ. Entomol. (in press).

Webster, J.A. and D.R. Porter. 2000. Reactions of four aphid species on a Russian wheat aphid resistant wheat. Southwest. Entomol. (in press)

Webster, J.A. and D.R. Porter. 2000. Plant resistance components of two greenbug (Homoptera: Aphididae) resistant wheats. J. Econ. Entomol. 93:1000-1004.

Shufran, K.A., Burd, J.D., Anstead, J.A., and Lushai, G. 2000. Mitochondrial DNA sequence divergence among greenbug (Homoptera: Aphididae) biotypes: evidence for host-adapted races. Insect Molecular Biology 9:179-184.

Name: James Anstead Date of Degree: July, 2000

Institution: Oklahoma State University Location: Stillwater, Oklahoma

Title of Study: Genetic And Biotypic Diversity of Greenbug Schizaphis Graminum (Rondani) Populations on Non-Cultivated Hosts

Pages in Study: 103 Candidate for the Degree of Master of Science

Scope and Method of Study: The purpose of this study was to determine the biotypic and genetic diversity of Schizaphis graminum on non-cultivated hosts. Collections made from non-cultivated hosts were screened against resistant crop lines to determine their biotype. A 1043 base pair region of the mitochondrial DNA, cytochrome oxidase I gene was sequenced to measure genetic diversity. The evolutionary and taxonomic status of biotype was also investigated.

Findings and Conclusions: There was significant biotypic diversity on non-cultivated grasses. We found biotypes E, I and K on non-cultivated grasses but we also found biotype G at higher than previously recorded densities. An isolate with a unique virulence profile was also found (i.e. a new biotype). Our study indicates non-cultivated grasses are a reservoir of biotypic diversity. This study supports previous conclusions that biotype formation was not driven by the development of resistant crop varieties. Biotypes, as defined in the greenbug (by virulence against resistant hosts) do not appear to have any evolutionary and taxonomic status. Rather this study confirms the presence of three genetically distinct clades in S. graminum. The distances between clades indicate one to two million years have passed since they had shared a common mitochondrial ancestor. These clades are likely to represent host-adapted races, with only one of the three containing greenbugs commonly found on crop hosts.

U.S. Department of Agriculture
Northern Grain Insects Research Laboratory
Crops and Entomology Research Unit
2923 Medary Avenue
Brookings, SD 57006

Nutrient Solution Nitrogen Form and Bird Cherry-Oat Aphid Resistance in Wheat

Bird cherry-oat aphids (Rhopalosiphum padi L.) are common insect pests of wheat (Triticum aestivum L.) in the northern Great Plains. Heavy spring infestations of seedling spring wheat can reduce yield by about 80 % while fall infestations in winter wheat can reduce yield from 20 to 75 %. The nutritional status of wheat crops modifies cereal aphid biology and life cycle and plays an important role in allowing plants to compensate for insect damage. Fungal, bacterial, and viral disease infestation severity and crop disease symptom intensity were shown to be strongly influenced by the form of N (NH4-N or NO3-N) provided to plants. It is not known if differences in fertilizer N form provided to wheat would impact plant resistance to bird cherry-oat aphids. The availability of specialized fertilizer products and the development of nitrification inhibitors that block the conversion of NH3 to NO3 in the soil provides reasons for reexamination of the relative merits of NH4 and NO3 nutrition especially with respect to potentially improving aphid resistance in small grains.

The research reported here examined the impact of nutrient solutions with different forms of N (either all NO3-N or all NH4-N) on aphid population growth and plant growth in wheat. The objectives of our growth chamber experiments were to determine if the form of nitrogen provided in plant nutrient solutions affected aphid population growth parameters or the ability of wheat to withstand infestation. Aphid population growth characteristics (development time, number of aphids produced, and intrinsic rate of increase) were not significantly affected by nutrient solution N form treatments. Plants grown with NH4-N nutrient solutions had significantly less shoot fresh weight. Aphid infestation also significantly reduced shoot fresh weight. There were no significant interactions between nutrient solution N form and aphid treatments for shoot fresh weight. Aphid treatment did not reduce root fresh weight in plants given NO3-N nutrient solution, but did in plants given NH4-N nutrient solution. Thus, while N form given to wheat plants had no effect on aphid population growth characteristics, plants given NH4-N nutrient solution showed less root growth than plants given the NO3-N nutrient solutions. The results of this study suggest that use of NH4-containing fertilizer and soil nitrification inhibitors likely would not improve wheat resistance to aphids.

Riedell, W.E. and L.S. Hesler. 2000. Nutrient solution nitrogen form and bird cherry-oat Aphid resistance in wheat. Cereal Res. Commun. Accepted for publication 19 April 2000

Texas A&M University Research & Extension Center
17360 Coit Road
Dallas, TX 75252-6599
Ph: 972/231-5362 FAX: 972/952-9216
[email protected]

Lantana Lace Bug, Teleonemia scrupulosa Stal, resistance among Lantana Cultivars for the Landscape - James A. Reinert, Steve W. George, Wayne A. Mackay, Erin Smith & Tim D. Davis . Lantana lace bug, Teleonemia scrupulosa Stal, (Hemiptera: Tingidae) is a primary insect pest of lantana, a tender perennial landscape plant that is commonly grown across the Southern United States for its heat and drought tolerance. Most of the literature on T. scrupulosa refers to its potential use worldwide as a biocontrol agent for several Lantana spp. that were introduced as ornamental plants from their native North and South America and had become major weed pests. Twenty-eight cultivars of three lantana species [Lantana montevidensis (K. Spreng.) Briq., L. camara L. and L. hybrida] were evaluated for resistance to the lantana lace bug in replicated field plantings exposed to natural infestations. Lace bug populations began to develop in mid July 1996, and were dispersed across the replicates within 30 days. Populations of nymphs and adults were sampled bi-weekly from Sep. - Nov. 1996 (5 sample dates). Highest mean populations for the 5 sample dates were present on 'Patriot Desert Sunset' (40.3 nymphs and adults/3-leaf sample/plant), 'Pink Frolic' (20.6) and 'Patriot Sunburst' (19.4), with 19 of the cultivars exceeding 4 lace bugs per 3-leaf sample. Plants of 'Weeping White', 'White Lightning' and 'Weeping Lavender' were never observed to have any lace bugs on them throughout the test period and 'Imperial Purple', 'Patriot Rainbow' and 'Denholm Dwarf White' had means of 0.1 total lace bugs per sample and never exceeded more than 0.7 per sample. The Resistance Performance Index shows that the aforementioned cultivars and additionally, 'Radiation', 'Dallas Red', 'Gold Mound', 'New Gold' and 'Lemon Swirl' occurred either 9 or 10 (out of 10) times in the top statistical groupings. When cultivars are grouped and analyzed by species, L. montevidensis (four cultivars with a mean of 0.02 lace bugs/3 leaf sample) is highly resistant whereas, L. camara and L. hybrida (6.73 and 9.54, respectively) are susceptible to the lantana lace bug. All of the L. montevidensis have flower color of either white or purple. Cultivars were also separated by flower color for analysis. Cultivars with purple or white flower color (primarily L. montevidensis) had far fewer lantana lace bugs (means of 0.03 and 1.73, respectively) developing on them than did cultivars with other flower colors. Additionally, cultivars with either gold or red flowers and the aforementioned purple- or white-flowered cultivars had far fewer lace bugs than did cultivars with either orange/red, yellow or a bicolor of yellow with another color. It appears that cultivars with either yellow or yellow bicolor flowers are among the most susceptible to the lantana lace bug. These results indicate that within most flower colors or bicolors, there exists a range of resistance among the cultivars.

Host Resistance to White Grubs (Phyllophaga spp.) among Genotypes of Poa arachnifera X P. pratensis Hybrids - James A. Reinert & James C. Read. White grubs are annual pests of both the cool- and warm season turfgrasses in the U.S. A 3-yr-old replicated planting of two genotypes of Texas bluegrass, Poa arachnifera Torr., and five of its hybrids with Kentucky bluegrass, P. pratensis L., was evaluated for resistance to white grub damage. A field population of Phyllophaga spp. (prob. P. congrua LeConte) had established and was causing significant damage across the replicated plots. On 31 May 1996, a visual rating (scale of 1-9 (turf damage, 9 = most damage with loss of stand, yellowing and loss of root anchoring 1 = no damage or loss of turf quality) of white grub damage to the grass in each turf plot was taken. Grass in each plot was visually examined for wilting and loss of stand and the leaves of 4 to 5 randomly selected plants within the plot were pinched and pulled to indicate potential root damage and loss of anchoring. Based upon these results from randomized planting in field plots exposed to natural Phyllophaga adult selection, it appears that the two Texas bluegrass selections, Syn1 and Syn2, and three Texas bluegrass X Kentucky bluegrass hybrids, TXKY-90-13-16, TXKY-90-13-8 and 'Reveille' (evaluated as TXKY-90-16-1), have considerable resistance to white grub damage. TXKY-90-15-6 and TXKY-92-35-1 are susceptible and sustained significant damage (ca. 4 ranking) and loss of stand.

Host Resistance to Tawny Mole Cricket, Scapteriscus vicinus, in Bermudagrass, Cynodon spp. - James A. Reinert & Philip Busey. Three species of Scapteriscus mole crickets were introduced to the southeastern USA and have become major pests of turfgrasses, especially bermudagrass, Cynodon spp. The objective of the study was to evaluate genetic resistance among vegetatively propagated Cynodon genotypes to damage by tawny mole cricket, S. vicinus Scudder (Orthoptera: Gryllotalpidae). Genotypes of bermudagrass, including commercial cultivars, were evaluated for their response to the tawny mole cricket, in field screen cages. Adult tawny mole crickets were introduced into replicated cages in which bermudagrass plants were planted. Cage sidewalls extended below the soil line and extended with a soil erosion fabric to a depth of 75 cm, to prevent migration of the highly mobile mole crickets. Damage estimates were based on visual ratings and relative reduction in clippings mass of harvested plants in inoculated cages compared with the same genotypes in adjacent noninfested cages. The four cage pairs, mole-cricket-infested and noninfested, thus represented the main plots of a split-plot experiment in four replications. Differences were observed (P < 0.05) in tawny mole cricket damage among 26 genotypes evaluated across two experiments. 'Tifdwarf', 'Tifgreen', 'Sunturf', 'Texturf-10' and 'Texturf-1F' were the most susceptible and sustained more tunneling and feeding damage than any of the other genotypes. All bermudagrass selections tested were damaged, but 'Ormond', FL-2400, PI-290659 and PI-291586 showed the least overall damage. Resistance scores (83 to 99) were high for each of these genotypes. 'Tifway' and 'FLoraTeX', were common to both studies, and each received similar intermediate damage and growth reduction ratings. Whereas, conflicting results were produced with Tifgreen and Sunturf, which were also common to both experiments. The field screen cages provided an excellent environment to evaluate plant materials against a highly mobile soil insect such as the tawny mole cricket.

Resistance in Zoysiagrass, Zoysia spp., to the Tropical Sod Webworm, Herpetogramma phaeopteralis, Guenee - James A. Reinert & M. C. Engelke. The tropical sod webworm, Herpetogramma phaeopteralis Guenee (Lepidoptera: Pyralidae) is a primary pest of turfgrass especially in the southern states of the USA and many islands of the Caribbean Archipelago. Twenty cultivars and genotypes of zoysiagrass, Zoysia spp., were evaluated for resistance to tropical sod webworm adult preference for oviposition and larval feeding. Adults expressed a preference among the zoysiagrass genotypes for egg deposition as expressed by the resulting larval feeding. 'Cavalier', DALZ8501 and JZ-1 exhibited high resistance (rankings < 7) with low feeding damage while 'Meyer' and DALZ8516 (ranking >1.5) sustained near complete defoliation. When neonate larvae were allowed to develop on each zoysiagrass in a no-choice experiment, a similar ranking was produced. Cavalier, DALZ8501, 'Korean Common' and 'El Toro' exhibited high resistance in the form of much smaller larvae (6.3-7.5 mg) at the 15-day evaluation. Conversely, larvae developing on 'Diamond', Meyer and DALZ8516 were significantly larger (36.4 to 41.0 mg). Additionally, larvae developing on the resistant Cavalier, Korean Common, El Toro and DALZ8501 required more than a week longer to reach pupation compared to larvae feeding on Diamond, Meyer and DALZ8516, which required only 19.1-19.7 days. Compared to the industry standard, Meyer (19 days), Cavalier required 12 days longer to pupation. During this period, larvae were much smaller, eating far less and they would be more vulnerable to predation. The highest mortality was recorded on Cavalier. In contrast, larvae feeding on the three most susceptible genotypes had an accumulated mortality of 6.7 to 13.4% at adult emergence.

Cultivar releases by Texas Agric. Exp. Stn.

Engelke, M. C., V. G. Lehman, K. B. Marcum, P. F. Colbaugh, J. A. Reinert, B. A. Ruemmele, & R. H. White. 1996. Release of 'Mariner' (Reg. No. CV-8, PI 599032) a creeping bentgrass with good salt tolerance.

Engelke, M. C., P. F. Colbaugh, J. A. Reinert, K. Marcum, R. H. White, B. A. Ruemmele & S. J. Morton. 1996. Release of 'Diamond' or DALZ8502 a dwarf type zoysiagrass.

Engelke, M. C., J. A. Reinert, P. F. Colbaugh, R. H. White, B. A. Ruemmele, K. Marcum & S. J. Morton. 1996. Release of 'Cavalier' or DALZ8507 a zoysiagrass with good water stress tolerance and good insect and disease resistance.

Engelke, M. C., R. H. White, P. F. Colbaugh, J. A. Reinert, K. Marcum, B. A. Ruemmele & S. J. Morton. 1996. Release of 'Crowne' or DALZ8512 a zoysiagrass with excellent water stress tolerance and good insect and disease resistance.

Engelke, M. C., R. H. White, P. F. Colbaugh, J. A. Reinert, K. Marcum, B. A. Ruemmele & S. J. Morton. 1996. Release of 'Palisades' or DALZ8514 a zoysiagrass with excellent water stress tolerance and good insect and disease resistance.

Read, J. C., J. A. Reinert, P. F. Colbaugh & W. B. Knoop. 1999. Release of 'Reveille' bluegrass.

Agriculture and Agri-Food Canada
Potato Research Centre, P.O. Box 20280
Fredericton, New Brunswick, Canada, E3B 4Z7

Accessions from seven wild Solanum species were evaluated in the field for their resistance to the Colorado potato beetle (Leptinotarsa decemlineata (Say)). The multivariate insect population density data were analysed using factorial analysis. The factors extracted corresponded to relevant phases of the life cycle of the insect and provided information on the mode of resistance (antixenosis and antibiosis) of the plant species. S. berthaultii, S. capsicibaccatum, S. jamesii, S. pinnatisectum and S. trifidum demonstrated both antixenosis and antibiosis but had different level of resistance. The mode of resistance of S. polyadenium seems to be caused by an antibiotic effect and the resistance of S. tarijense by an antixenotic effect. Genetic variability and heritability of insect resistance trait within accession was trivial or inconsistent for all Solanum species studied.

Annamalai University
Tamilnadu 608 002
India

V. Selvanarayanan
Lecturer In Entomology
Faculty of Agriculture

Greetings from India. I am new member to the PRP group and I wish to thank all the members for their patience to go through this mail. I am a Lecturer in Agricultural Entomology working at Annamalai University, Tamilnadu situated in the southern peninsula of India.

I have just completed my doctoral research on Host Plant Resistance in Tomato against fruit borer, Helicoverpa armigera. In the process, I have collected and screened around 320 exotic and indigenous/ native /tribal tomatoes and isolated five accessions which are resistant to the borer both under field and glasshouse conditions. I am planning to work on those selected accessions in depth and many other wild accessions, I hold, with reference to their mechanisms of resistance, future scope in breeding programmes and other related areas.

I wish to pursue my post-doctoral research in this venture and if any of the distinguished member is willing to utilize my services, I will much thankful to him. I request all the learned members to mail me their suggestions and help in this regard.

Hope to receive fruitful information from the members.

Tamil Nadu Rice Research Institute
Aduthurai - 612 101
Tamil Nadu
India

Screening Rice Entries of AICRIP in ADVANCED Yield Trial for Resistance to Insect Pests of Rice

V. Balasubramani, S. Sadakathulla, M. Subramanian and S. Ramanathan

Under all India Co-ordinated Rice Improvement Programme (AICRIP), 183 and 178 advanced yield trial entries of rice were screened during 1997-98 and 1998-99 respectively, for their reaction to insect pests under natural conditions. Damage score was recorded as per Standard Evaluation System (SES) of IRRI, Philippines and AICRIP protocol. In 1997-98, out of 183 entries fourteen entries viz., IET 14829, IET 14833, IET 14834, IET 14806, IET 14807, IET 14867, IET 14350, IET 14359, EIT 14584, IET 14935, IET 14955, IET 14956, IET 14657, and IET 14338 were found to be resistant against gall midge (Orseolia oryzae) throughout the crop stand. In 1998-99, out of 178 entries, IET 15177, IET 15178 and IET 15179 against gall midge, IET 15742 and IET 15072 against yellow stem borer (Scirpophaga incertulus) and IET 16120 against rice leaf folder (Cnaphalocrosis medinalis) were found to be moderately resistant.

Varying Level of Natural Incidence of Rice Leaf Folder

V. Balasubramani, P. Muthukrishnan, S. Sadakathulla, M. Subramanian and S. Ramanathan

Cnaphalocrosis medinalis Guenee was observed in Tamil Nadu Rice Research Institute, Aduthurai, India during August-September 1999. Variation among different medium duration varieties was found with respect to leaf folder damage. Damage score was recorded as per Standard Evaluation System (SES) of IRRI, Philippines in 0-9 scale. Among the 24 medium duration varieties/cultures screened, seven (ADT 38, ADT 39, ADT 40, Improved white Ponni, AD 95319, Bhavani and TPS 3) were found to be resistant, seven (AD 94010, AD 92215, CO 46, MDU 4, IR 20, TRY-1 and Paiyur 1) scored moderately resistant reaction, three (AD 94016, ASD 19, MDU 3) were found to be moderately susceptible and seven (AD 90072, CO 43, CO 45, MDU 2, PY-1, Red Ponni and PTS 2) were found to be susceptible.

Reaction of Short and Medium Duration Rice Varieties Entries to Tetranychid mite Oligonychus oryzae

V. Balasubramani, P. Muthukrishnan, S. Sadakathulla, M. Subramanian and S. Ramanathan

Twenty-five short duration and twenty-four medium duration rice varieties and cultures under advanced stage of yield trials were screened for their reaction to rice mite Oligonychus oryzae under in vivo condition during Kuruvai 1999 season (June-July sowing). Mite damage score was done on 0-9 scale as per Sridharan et al., 1992 (APRINL 18:66). When the natural incidence was high, out of 25 short duration rice, three varieties (ADT 41, ASD 8 and IR 50) recorded score 1, nineteen (ADT 36, ADT 37, ADT 42, AD 95010, AD 95078, AD 95104, AD 95106, ADTRH 1, DRRH 1, Pro Agro 6201, PHB 71, ASD 16, ASD 17, ASD 18, IR 36, IR 64, IR 72, TKM 9, and MDU 5) recorded score 3 and three varieties (ADT 43, ASD 20, and IR 66) recorded score 5. Among the medium duration varieties, ten (Improved white Ponni, AD 95319, AD 94016, ASD 19, CO 43, Red Ponni, Bhavani, Paiyur 1, TPS 2 and TPS 3) recorded score 1, tweleve (ADT 38, ADT 39, ADT 40, AD 90072, AD 92215, CO 45, CO46, MDU 2, MDU 3, MDU 4, IR 20, and PY 1) recordedd score '3' and two (AD 94010 and TRY 1) recorded score 5, showing their resistant, moderately resistant and moderately susceptible nature respectively.

Reaction of Popular Varieties of Medium Duration Rice in Nursery to Rice Thrips Stenchaetothrips biformis

V. Balasubramani, P. Muthukrishnan, S. Sadakathulla, M. Subramanian and S. Ramanathan

Twenty-six medium duration rice varieties/cultures were screened under natural conditions, 20 days after sowing in the nursery during Thaladi season 1999 (Sept-Oct sowing). Reaction score of 0-9 scale was adopted as per Standard Evaluation System (SES) or IRRI, Philippines. Three varieties viz., ADT 39, ADT 40, and Improved white Ponni recorded 1 (resistant), three cultures (AD 92215, AD 90072, and AD 94016) and two varieties (Pondy 1 and Red Ponni) recorded score 3 (moderately resistant), six varieties (ADT 38, CO 43, CO46, MDU2, TRY1, and ASD 19) recorded score 5 (moderately susceptible), Bhavani and AD 94010 recorded score 7 (Susceptible) and nine varieties (CO 45, MDU3, MDU 4, IR 20, Paiyur 1, TPS 2, TPS 3, BPT 5204 and ADRH 8) and a culture (AD 95319) recorded score 9 (highly suscpetible).

Scoring of Medium Duration Rice Varieties Against Yellow Stem Borer Scirpophaga incertulus (Walker) Attack

V. Balasubramani, P. Muthukrishnan, S. Sadakathulla, M. Subramanian and S. Ramanathan

Twenty-one varieties and five cultures of medium duration rice were screened for their reaction against the yellow stem borer Scripophaga incertulus (Walker) under natural conditions, based on dead heart counts on 30, 50 DAT (Days After Transplanting) and white ear counts on 80 DAT, during Thaladi season 1999 (Sept-Oct sowing). Based on the mean score (0-9 scale as per SES of IRRI, Philippines) nine varieties and two cultures (ADT 38, ADT 40, CO 43, CO 45, MDU 3, Pondy 1, ASD 19, Red ponni, Bhavani, AD 95319 and AD 92215) were found to be resistant with score 1. Twelve of the total varieties/cultures (Improved white ponni, AD90072, AD94010, CO 46, MDU 2, MDU 4, IR 20, Trichy 1, Paiyur 1, TPS 2, TPS 3 and ADRH 8) stored score 3 revealing their moderately resistant reaction. Only there viz. ADT 39, AD94016, and BPT 5204 were found to be moderately susceptible with score '5'.

Screening Banana Germplasm for Resistance to Lacewing Bug Stephanitis typicus

V. Balasubramani, P. Sundararaju and H.P. Singh

A total of 278 accessions from the banana germplasm maintained at National Research Centre on Banana (NRCB), Tiruchirappalli were screened for their reaction to lacewing bug Stephanitis typicus under natural condition, 7-8 months after planting. Of them five accessions viz., Kalibale (0286), Malaivazhai (0290), Dole (0459), Gandevi (0370) and Chakkarakel (0093) were found to be free from the incidence of S. typicus. The remaining 273 accessions had infestation of S. typicus which ranged from 10-40 percent infested leaves.

Horticulture Research International,
Wellesbourne,
Warwick, CV35 9EF,
United Kingdom

Studies continued on the high levels of resistance to the cabbage aphid, Brevicoryne brassicae discoveredin certain lines of Brassica fruticulosa (n=8). F1 and F2 families have been produced from crosses between selected individual plants representing the extremes of the range of resistance. These families have been evaluated in a controlled environment. Resistance was found to be quantitative, with no mendelian segregation ratios observed.

In an earlier report, the results of evaluating about 400 Brassica accessions against B. brassicae were presented. The most promising gene pool was found to be the kales. Four of the kale accessions were selected for breeding work. In order to study the genetics of resistance these kales were crossed with a double haploid line derived from the calabrese 'Marathon' and with the Brussels sprouts 'Oliver', which had been used a susceptible standard in all field, glasshouse and laboratory experiments. One of the objectives of the project was to 'bank' genes for resistance in a rapid cycling brassica genotype so that they could be exploited in future breeding programmes with different horticultural brassica crops. The rapid cycling Brassica oleracea CRGC 121 has been shown to be highly susceptible to B. brassicae and was considered to be a suitable recipient of genes for resistance. The four kales were therefore crossed with this rapid cycling accession. F1 and F2 families were produced in 1997 and 1998 from crosses between all four kales and the different brassicas described above. Progeny from three of the crosses were evaluated in 1999. The results indicated that resistance was multigenic, the response to selection was poor, the susceptible brassica genetic background significantly influenced resistant phenotype and environmental affects influenced the expression of resistance. Microspore culture will be used to produce double haploid lines which can be assessed more thoroughly in replicated experiments. This should make it possible to partition environmental and genetic components of resistance and to identify true-breeding resistant lines.

A project has begun to search for resistance in Arabidopsis thaliana to three important aphid pests, B. brassicae, cabbage aphid, Lipaphis erysimi, the mustard aphid and Myzus persicae, the peach-potato aphid. About 110 different Arabidopsis accessions have been obtained and a series of experiments designed to evaluate material. For both B. brassicae and M. persicae several different clones of aphid have been collected and used in preliminary experiments to identify the most vigorous ones for use in subsequent screening work. Antibiosis resistance has been identified to B. brassicae in 2 accessions, with some putative resistance to L. erysimi also being identified in a separate accession.

A UK MAFF-funded project on lettuce continued in 2000 to investigate the resistance to Myzus persicae in the lettuce variety 'Iceberg', a Batavian type of lettuce. Six clones of the aphid collected from different locations in the UK have been established at Wellesbourne. The performance of these clones on a susceptible lettuce variety, 'Saladin' has been compared. Antixenosis and antibiosis screening techniques have been developed for the evaluation of resistance. Preliminary laboratory experiments have confirmed that the Batavian 'Iceberg' variety possesses moderate levels of antibiosis resistance to aphid attack. It is planned to investigate the biological and genetical basis of this resistance and to determine the performance of inbreds produced in a single seed descent programme bred from a cross between susceptible and resistant lettuce material.

A review has been written on the resistance of carrot to carrot fly, Psila rosae (see below). The team continues to offer seed companies and other organisations a service for screening breeding lines for resistance to carrot fly, Psila rosae. A new carrot fly-resistant variety, 'Resistafly', was released by A.L. Tozer (seed company) in the spring of 2000 as a result of the collaboration with Horticulture Research International.

ELLIS, P.R. (1999). The identification and exploitation of resistance in carrots and wild Umbelliferae to the carrot fly, Psila rosae (F.). Integrated Pest Management Reviews4, 256-268.

ELLIS, P.R., PINK, D.A.C., BARBER, N.E., & MEAD, A. (1999). Identification of high levels of resistance to cabbage root fly, Delia radicum, in wild Brassica species. Euphytica 110, 207-214.

ELLIS, P.R., KIFT, N.B., PINK, D.A.C., JUKES, P.L., LYNN, J. & TATCHELL, G.M. (2000). Variation in resistance to the cabbage aphid (Brevicoryne brassicae) between and within wild and cultivated Brassica species. Genetic Resources and Crop Evolution 47, 395-401.

ELLIS, P.R., PINK, D.A.C., McCLEMENT, S.J., SAW, P.L. PHELPS, K., VICE, W.E. & KIFT, N.B. (2000). Identification of sources of resistance in lettuce to the lettuce root aphid, Pemphigus bursarius. Euphytica. (Submitted)

KIFT, N.B., PINK, D.A.C., ELLIS, P.R. & TATCHELL, G.M. (2000). The influence of genetic background on the use and manipulation of resistance to the cabbage aphid (Brevicoryne brassicae) in kale (Brassica oleracea var. acephala). Annals of Applied Biology (In press)

ELLIS, P.R. (1999). Breeding the fly-free carrot. Grower 131 (12), pp. 18 & 20.

COLLIER, R.H., TATCHELL, G.M., ELLIS, P.R., & PARKER, W.E. (1999). Strategies for the control of aphid pests of lettuce. IOBC/WPRS Bulletin 22, (5), 25-35.

ELLIS, P.R. & ESTER, A. (1999). Possible reasons for the decline in carrot fly (Psila rosae (F.) infestations in western Europe. IOBC/WPRS Bulletin 22, (5), 83-87.

KIFT, N.B., ELLIS, P.R. & SINGH, R. (1999). Interpretation of aphid performance data in quantifying resistance. IOBC/WPRS Bulletin 22, (10), 65-70.

ELLIS, P.R. (1999). Exploiting the resistance in carrots and wild umbelliferae to the carrot fly, Psila rosae (F.). IOBC/WPRS Bulletin 22, (10), 45-52.

ELLIS, P.R. & KIFT, N.B. (2000). The exploitation of plant resistance in controlling insect pests of vegetable crops. IOBC/WPRS Bulletin. (Submitted).

ELLIS, P.R. & DERRIDJ, S. (1999) (Editors). Breeding for Resistance to Insects and Mites. IOBC

Ecotoxicology Research Group
Department of Agricultural and Environmental Science
Newcastle University, Newcastle upon Tyne
NE1 7RU, UK

R.M. Wilkins, ([email protected]) Senior Lecturer & Supervisor Fazalluah M. Bughio ([email protected]) Miss A.S. Petrova (A.S. [email protected]) Ovais S. Pathan ([email protected]) Ecotoxicology Group, Department of Agricultural & Environmental Science, University of Newcastle, Newcastle upon Tyne, NE1 7RU, UK.

Inhibition of gut proteolytic enzymes of Tribolium castaneum (Hbst.) (Coleoptera: Tenebrionidae) by albumin proteins isolated from insect-resistant and susceptible rice flours.

Fazalullah M. Bughio and Richard M. Wilkins

Seeds, especially those of cereals contain large quantities of protein and are major source of dietary protein. However, some are extremely toxic to animals and insects. Albumin protein was extracted from two forms of rice grain (brown and milled) of Dawn and DR82 cultivars, which are resistant and susceptible respectively to the stored product insect Tribolium castaneum. The aqueous extract of each grain form was divided and part was heat-treated for 10 min at 80°C. The concentrations of both heat-treated and untreated proteins of Dawn cultivar were significantly higher than DR82 in brown and milled forms except in the unheated brown form of the cultivars. The heat-treated proteins of both forms of the grains were the most effective in inhibiting the proteolytic activity of the insect gut. The effects of the heat-treated and untreated proteins of the two forms of Dawn cultivar on the proteolytic activity of Tribolium castaneum were significantly higher than the forms and treatments of DR82 cultivar.

Brown planthopper Nilaparvata lugens as a stress factor in rice plants

Adelina Petrova and Richard M. Wilkins

Phloem sugars and free amino acids are known to influence the feeding behaviour of many phloem feeding homopteran pests. Brown planthopper (BPH) also has the ability to modify plant nutritional physiology. Heavy infestations of BPH on rice plants induce proteolysis and a 30-fold increase in levels of several amino acids (arginine, asparagine, lysine, proline, and tryptophan), whereas free sugars and moisture content decrease (Sogawa, 1971 Cagampang et al., 1974).

Three rice varieties have been chosen on the basis of resistance to the BPH, Rathu Heenati (resistant), Bg300 (medium), TN1 (susceptible), and they have been grown under two nitrogen regimes. The total amount of amino acids of 8- and 6-week old plants infested with BPH have been measured and compared to that of the control plants. The ninhydrin method has been used for the determination of the amino acids.

Mechanisms of plant resistance in crops to the leafworm Spodoptera littoralis: role of gut detoxifying enzymes

Ovais Safdar Pathan and Richard M. Wilkins
The cotton leafworm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) is an important polyphagous insect pest attacking a wide variety of crops in tropical and temperate areas of Africa, Asia and Europe. The choice and combination of the methods for control depend on the pest complex, infestation and the costs of implementation. Much control is achieved through integrated pest management including insecticides and mating disruption.

In contrast to monophagous pests, it is difficult to develop varietal resistance for polyphagous pests in the crops attacked. However, an understanding of the reasons for susceptibility of the various crops to attack may help in the development of resistant varieties. In the case of S. littoralis, dicotyledonous crops are preferred to monocots. An understanding of the mechanisms that contribute to this preference could have a role in improving crop resistance and biological control.

The objectives of this study were to compare feeding on selected crops (maize, wheat, sunflower and cabbage) and the consequential response from the insect in terms of detoxification activities. Larvae were reared on the crops until the last instar and their weight gains, food intake and cytochrome P450 enzymes (CYP1A1 and CYP2B1) activities measured. Food consumption and CYP1A1 activity was low on wheat and maize. In sunflower and cabbage both enzyme activities were significantly increased. The role of these enzymes in the insect's response to the crops will be discussed in terms of the food utilisation and in the comparison of the four crops.

Bughio, F. M., and R. M. Wilkins. 1997. Effect of rough rice cultivars on larval period and F1 emergence time of the red flour beetle Tribolium castaneum (Hbst.) and confused flour beetle Tribolium confusum (Duv.). International Plant Resistance to Insects Newsletter. 23: 55-56.

Bughio, F. M. and R. M. Wilkins. 1998. Influence of various types of flour of resistant and susceptible rice cultivars on biology of Tribolium species. International Plant Resistance to Insects Newsletter. 24: 11-12

Bughio, F. M., and R. M. Wilkins. 1998. Response of insecticide-resistant and susceptible strains of Tribolium castaneum to various types of grains flour of rice cultivars, pp. 4B-048. In Proceedings: 9th International Congress: Pesticide Chemistry, 2-7 August 1998, London. Royal Society of Chemistry, Cambridge, UK.

Bughio F. M., and R. M. Wilkins. 1999. Post-harvest pest management: resistant rice varieties in control of stored product insect pests, pp. 221-225. In Proceedings: 5 th International Conference on Plant Protection in the Tropics, 15-18 March 1999, Kuala Lumpur, Malaysia. Malaysian Plant Protection Society (MAPPS).

Bughio F. M., and R. M. Wilkins. 2000. Influence of Malathion Resistance Status on Survival and Growth of Tribolium spp. (Coleoptera: Tenebrionidae), when Fed on Flour from Resistant and Susceptible Rice Cultivars. J. Econ. Entomol. In press.

Rauf, A., F. M. Bughio, and R. M. Wilkins. 1997. Insecticide resistance in Tribolium castaneum Herbst and Sitophilus granarius L.: comparing residual film and topical application methods. Tribolium Information Bull. 37: 163-169.

Fruit and Grape Research Centre
32 000 Cacak
Yugoslavia

Strawberry Resistance to the Aphid Chaetosiphon Fragaefolii (Cockerell) (Homoptera, Aphididae)

The paper presents the results of the studies on the resistance of the strawberry Fragaria x ananassa Duchesne and 652 hybrids of Fragaria ananassa x Fragaria chiloensis clone Del Norte. Moderately resistant hybrids from the cross Senga Fructarina x Del Norte (zf/1/94/96 and 2/11/95/97) and Dana x Del Norte (da/17/94/96) were singled out on the basis of testing in the glasshouse and in the field. Fifteen strawberry genotypes were used for studying survival and fertility (a five-day test), longevity, fertility and production of honeydew on filter paper with bromine cresol green in apterous parthenogenetic females. Significant differences were recorded in all the evaluated parameters by genotypes, with the lowest values obtained on the moderately resistant hybrids and Del Norte. The population density of Chaetosiphon fragaefolii in the field on the standard cultivars and moderately resistant hybrids shows year-to-year variations. However, on the moderately resistant hybrids it does not exceed 20% of the density recorded on the sensitive cultivars. Strawberry genotype affects morphometric characters of parthenogenetic apterous females. The smallest dimensions of the body and the apical segment of the rostrum were observed in the females reared on Del Norte and moderately resistant hybrids. Dimethoate and delthametrine are more toxic to the individuals from the Ch. fragaefolii population reared on the moderately resistant hybrid zf/1/94/96 compared to the population reared on the highly sensitive selection ^a

anska Rana, particularly at LC90 level. The cross-section of the leaf blade and leaf petiole in strawberry genotypes showing different resistance to Ch. fragaefolii was studied by the paraffin method and by staining it with safranine, crystal violet and light green SF. In more resistant genotypes, besides thicker cell walls of the primary bark collenchyma and a greater share of the collenchyma in relation to the parenchyma in the primary bark, the main vascular bundles are encircled by a ring of more intensely stained lignified cells forming a mechanical ring. This stained reaction of cells to safranine and crystal violet also occurs in smaller-sized vascular bundles, as well as in the leaf palisade tissue. The tissue cross-sections in the sensitive genotypes reveal the predominance of the green colour on the cellulose cell walls and protoplasts due to the reaction to light green SF, whereas the stained reactions to safranine and crystal violet are absent.

Key words: Chaetosiphon fragaefolii, Fragaria ananassa, Fragaria chiloensis, resistance, fertility, longevity, honeydew, morphometric ch


Results

Experiment 1: unrewarded experience

The residence time of T. brochymenae wasps was significantly affected by the treatment × experience interaction (χ 2 = 7.46 df = 3 P < 0.001). Among each of the four treatments, experience status had a large and statistically significant effect on the wasps’ residence time (Fig. 1). Wasps experienced with host female chemical residues spent less time on the arena when re-encountering the same type of chemical cue (group FF: χ 2 = 13.88 df = 1 P < 0.001). A similar effect was found for those parasitoids that were experienced on female walking traces and re-tested on male walking traces (group FM: χ 2 = 16.24 df = 1 P < 0.001). Naïve parasitoids that were tested on host male traces displayed a reduced residence time when re-tested on the same type of chemical cue (group MM: χ 2 = 13.31 df = 1 P < 0.001). On the contrary, wasps experienced on male traces and re-tested on female traces increased the time spent on the arena (group MF: χ 2 = 11.90 df = 1 P < 0.001) (Fig. 1).

Behavioural response of Trissolcus brochymenae with unrewarded experience.

Mean (±SE) residence time of Trissolcus brochymenae females encountering for the first time (naïve, white bars) or re-encountering (experienced, grey bars) Murgantia histrionica adult walking traces adsorbed on cabbage leaf disks. MM = experienced and tested on male traces, N = 31 MF = experienced on male traces and tested on female traces, N = 29 FM = experienced on female traces and tested on male traces, N = 27 FF = experienced and tested on female traces, N = 26. Asterisks indicate significantly different means within each pairwise combination (GLMM, *P < 0.05).

Experiment 2: rewarded experience

The residence time of T. brochymenae wasps when tested in arenas contaminated by host chemical cues was significantly affected by previous successful oviposition experience (GLM, χ 2 = 38.14 df = 3 P < 0.001) (Fig. 2). Rewarded parasitoids re-encountering host female residues (group F_o_F) showed longer arena residence time compared to rewarded parasitoids re-encountering host male residues (group M_o_M) (GLM, z = 2.83, P < 0.05). The influence of oviposition experience per se on residence time could be excluded because wasps with successful oviposition experience did not stay longer when re-tested on untreated arenas (Fig. 2). In fact, the arrestment response of rewarded wasps in the presence of host female residues was significantly different from controls (group F_o_B) (z = −7.56, P < 0.001). Similarly, the residence time of rewarded wasps on host male chemical cues was significantly different than controls (group M_o_B) GLM, z = −5.43, P < 0.001).

Behavioural response of Trissolcus brochymenae with rewarded experience.

Mean (±SE) residence time of Trissolcus brochymenae females allowed to oviposit on a host egg mass in the presence of either host female or male traces and then tested according to different conditions: F_o_F = oviposition on female traces and tested on female traces, N = 32 M_o_M = oviposition on male traces and tested on male traces, N = 31 F_o_B = oviposition on female traces and tested on uncontaminated cabbage leaf disks, N = 35 M_o_B = oviposition on male traces and tested on uncontaminated cabbage leaf disks, N = 34. Different letters above bars indicate significantly different means (GLM, *P < 0.05).

Experiment 3: hierarchical value of host traces

The residence time of experienced wasps was significantly affected by the host gender (χ 2 = 5.42 df = 1 P < 0.01) and by the time interval (χ 2 = 3.32 df = 2 P < 0.05) whereas the host gender × time interval interaction was not significant (χ 2 = 0.15 df = 2 P = 0.705). The residence time of T. brochymenae wasps experienced on female traces and re-tested on female traces was significantly affected by the time interval × experience interaction (χ 2 = 6.08 df = 2 P < 0.01) (Fig. 3a). Within each time interval treatment, the arena residence time was significantly different between naïve and experienced wasps as long as the time interval was shorter than 48 h (group F_24_F, χ 2 = 9.46 df = 1 P < 0.01 group F_48_F, χ 2 = 9.01 df = 1 P < 0.01 group F_72_F, χ 2 = 0.27 df = 1 P = 0.601) (Fig. 3a). The residence time of T. brochymenae wasps was also significantly affected by time interval × experience interaction when parasitoids were experienced on male traces and re-tested on male traces (χ 2 = 3.27 df = 2 P < 0.05) (Fig. 3b). However, within each time interval treatment, the arena residence time was significantly different between naïve and experienced wasps only when the time interval was not longer than 24 h (group M_24_M, χ 2 = 8.46 df = 1 P < 0.01 group M_48_M, χ 2 = 2.01 df = 1 P = 0.106 group M_72_M, χ 2 = 0.55 df = 1 P = 0.462) (Fig. 3b).

Behavioural response of Trissolcus brochymenae for evaluation of hierarchical value of host traces.

Mean (±SE) residence time of Trissolcus brochymenae females trained and tested on 2 consecutive leaf disk arenas contaminated with traces of Murgantia histrionica adults (combination “female-female, F_F” in figure A or “male-male, M_M” in figure B) at intervals of 24, 48, or 72 h (experienced, grey bar), F_24 h_F, N = 30, F_48 h_F, N = 28, F_72 h_F, N = 29 M_24 h_M , N = 27, M_48 h_M, N = 28, M_72 h_M, N = 30. As controls, T. brochymenae females tested at the same times as experienced females were used (white bars naïve females). Asterisks indicate significantly different means within each pairwise combination (GLM, *P < 0.05).


Conclusion

The Lygaeidae offer a variety of opportunities for evolutionary and behavioral ecologists, and we hope this review will make the super-family better known and encourage more groups to begin working with them. They are often easy to keep in the laboratory, and in the age of next-generation sequencing and subthousand dollar genomes, any species can relatively easily become a fully fledged genetic model organism (for an example of this see Zhen et al. 2012 ). While our own interests focus on sexual selection, sexual conflict, and reproductive interference, we would also like to emphasize: (1) the fascinating pattern of coevolution between the bugs and their endosymbionts, including the evolution of specialized structures and the remarkable diversity within genera (2) the opportunities to explore individual variation in chemical defence and how this variation might influence within- and among-population and species patterns of mimicry (3) the patterns of cannibalism that remain poorly studied, including egg- and sib-cannibalism, and the opportunities for testing kin selection theory (4) the lack of precopulatory mate choice and the likely importance of postcopulatory sexual selection and (5) the ease with which these species can be used to study fundamental aspects of life history evolution, including diet specialization, wing polymorphisms, and diapause.


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