XIII International Entomophagous Insects Workshop

July 27-31, 2003, Tucson, Arizona

ORGANIZERS

Molly Hunter, Department of Entomology, University of Arizona, Tucson, AZ
James Hagler, USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ

Abstracts are listed in alphabetical order by the last name of the senior author.

Can plants affect the genetic structure of parasitoids populations? The case of beans and parasitoids of bruchids

Alexandre Aebi and Betty Benrey

University of Neuchâtel, Institute of Zoology, Laboratoire d'Ecologie Animale et Entomologie

Alexandre.Aebi@unine.ch

A growing number of studies suggest that plants can dramatically influence the interactions between herbivorous insects that feed on them and the natural enemies of these herbivores. Features of plants, such as morphology, nutritional quality, and allelochemistry can affect herbivore-enemy interactions. Although these studies provide ample evidence for the role of plants in determining the performance of parasitoids, no study has established an effect of plant characteristics on their genetic population structure and genetic differentiation of the third trophic level. In this study we examined the influence of host plant species and habitat characteristics on parasitoid genetic population structure. The model system comprises beans of the genus Phaseolus (P. vulgaris, P. coccineus and P. lunatus), two bruchid beetles (Zabrotes subfasciatus and Acanthoscelides obtectus), and a complex of three hymenopteran parasitoids, Horismenus sp. (Eulophidae), that attack these beetles. Molecular markers (microsatellites) were developed and used to estimate the genetic heterogeneity within and among parasitoid populations from different habitats and on the three bean species. Geographic isolation and plant species appeared to be the most important factors influencing the genetic structuring of parasitoid populations. Additionally, the parasitoid species composition varied greatly between plant species, suggesting a high degree of specialisation of the parasitoids on the first trophic level.

Effects of host age, female parasitoid age and host plant, on parasitism of Ceratogramma Etiennei (Hymenoptera: Trichogrammatidae)

Divina M. Amalin¹, Jorge E. Peña, Rita E. Duncan

University of Florida, Tropical Research and Education Center, 18905 SW 280^th St., Homestead, FL 33031
¹Current Address: USDA-APHIS, 13601 Old Cutler Rd., Miami, FL 33158

red@mail.ifas.ufl.edu

The parasitism of Diaprepes abbreviatus (L.) eggs by Ceratogramma etiennei Delvare as influenced by host age, age of the parasitoid, and host plant preference was evaluated. Percent parasitism of D. abbreviatus eggs by C. etiennei decreased as eggs matured under laboratory and greenhouse tests. One to 2 d old C. etiennei females parasitized more hosts than older females. Host plant leaf thickness, leaf pubescence and plant strata affected parasitism by C. etiennei. This parasitoid is diurnal and spends approximately 5 min probing, 46 min in actual parasitism per egg mass and 24 min resting.

Natural enemies and the evolution of host range expansion in herbivorous insects

D. A. Andow

Department of Entomology, 219 Hodson Hall, University of Minnesota, St. Paul, MN 55108, USA

dandow@umn.edu

Some recent theoretical research has suggested that natural enemies can retard or accelerate the rate of evolution of host range expansion in an herbivorous insect. Other theoretical results imply that natural enemy induced mortality may have little influence on the rate of evolution of host range expansion. This issue has attracted some interest when considered in the context of the evolution of resistance to transgenic Bt crops. I provide an overview to the various theoretical approaches to the problem and outline a set of circumstances where natural enemies could exert considerable selection pressure on an herbivorous insect to expand its host range.

Colorado potato beetle hemolymph effects on the parasitic nematode Heterorhabditis marelatus

Christine A. Armer¹, Sujaya Rao², Ralph E. Berry³

¹Center for Population Biology, 2320 Storer Hall, University of California, Davis, CA 95616
²Department of Crop and Soil Science, 109 Crop Science Building, Oregon State University, Corvallis, OR 97331
³Department of Botany and Plant Pathology, 2082 Cordley Hall, Oregon State University, Corvallis, OR 97331

Christine_Armer@qmail.com

The Colorado potato beetle (Leptinotarsa decemlineata Say) (CPB) is the key pest of potatoes and other solanaceous crops in the United States and much of Europe. The beetle rapidly develops resistance to most pesticides used against it, and transgenic crops are not currently favored by the general public for pest control. Hence, we examined biological control of the beetle, using the entomopathogenic nematode Heterorhabditis marelatus Liu & Berry and its symbiotic bacteria. The nematode kills nearly 100% of beetles in field trials, but does not reproduce in the beetle. Previous research indicated the symbiotic bacteria switched rapidly to a secondary form when placed in CPB hemolymph. Unlike the primary form of the bacteria, the secondary form does not provide nutrients or protection against competing pathogens for the nematode. The research discussed here examines the host's immune system and hemolymph chemistry effects on the nematode and its symbiotic bacteria. We found that the immune system rarely inhibits bacterial or nematode growth. However, a toxic protein, which may be the previously identified 57kD leptinotarsin, appears to cause the bacterial switch to the secondary form. When the protein is denatured, the nematodes still cannot reproduce. Addition of a variety of lipids indicates that a lipid source is not available to the nematodes or the symbiotic bacteria in CPB hemolymph, limiting reproduction. We hypothesize that the glycoalkaloids from the plants on which the CPB feeds bind to the lipid-transport proteins in the hemolymph, halting the movement of cholesterol in the hemolymph, and thus negatively affecting the nematodes.

Ecological and evolutionary implications of oosorption by Eretmocerus eremicus (Hymenoptera: Aphelinidae)

Mark K. Asplen and David N. Byrne

Dept. of Entomology, 410 Forbes Building, University of Arizona, Tucson, AZ 85721, USA

masplen@ag.arizona.edu

Oosorption (egg resorption) in parasitic wasps is thought to be limited to strongly synovigenic taxa due to the high time cost associated with the process. We have discovered, however, that the strongly pro-ovigenic species Eretmocerus eremicus resorbs oocytes linearly between 2 and 8 d of adult life. Furthermore, it appears that the oosorption mechanism in this wasp differs ultrastructurally from those previously reported in hymenopterans. While the mechanism of yolk degradation follows the general “islands of degeneration” model, it is unusual in that this process begins and progresses while the chorion and vitelline membranes remain as barriers to contact by the follicular epithelium. The egg membranes, which in previous studies are completely digested by enzymes from the follicle cells prior to yolk breakdown, are instead broken down concurrently. The synchrony between these two phases of the oosorption process of E. eremicus may be an adaptation to decrease the time required to resorb each oocyte, thus lowering the time cost of the process to this short-lived insect. Additionally, this is the first unequivocal example of an ultrastructural mechanism for autolytic oosorption in insects. From an evolutionary perspective, this may explain how many members of the Encyrtidae and at least one ichneumonid are capable of resorbing oocytes with no apparent breakdown of the chorion.

Impact of Eretmocerus eremicus (Hymenoptera: Aphelinidae) on open-field Bemisia tabaci (Hemiptera: Aleyrodidae) populations

David E. Bellamy and David N. Byrne

Department of Entomology, University of Arizona, Tucson, AZ 85721, USA

dbellamy@ag.arizona.edu

The effect of three different release rates (1x, 10x, and 20x the recommended rate of 25,000/ha) of Eretmocerus eremicus Rose and Zolnerowich on Bemisia tabaci (Gennadius) populations found in open-field cantaloupe, Cucumis melo L., was evaluated against populations in untreated control plots. Parasitoids were released from a point source in the center of each of nine treatment plots. Whitefly population growth, encompassing all developmental stages, and rates of parasitism were monitored within a 10-m annulus surrounding the center point in all 12 plots over a 52-d period. The rates of B. tabaci population increase during this time were equivalent regardless of the parasitoid release rate. Whitefly densities were not limited in any of our treatment plots when compared to those found in the control plots. Moreover, mean rates of parasitism did not increase with time nor did they differ among the three treatments or control plots. Finally, estimated rates of parasitism were density dependent responding positively to increasing host numbers. The ineffectiveness of this parasitoid in controlling whitefly populations in the field may be due to its high propensity to disperse at low host densities or to influxes of immigrating whiteflies. Hence, the use of E. eremicus alone is not an efficient means to reduce whitefly populations in melon crops in the southwestern United States.

Inter-population variation in performance of insects in a tri-trophic system

Betty Benrey¹, Alicia Callejas², and Erick Campan¹

¹Institute of Zoology, University of Neuchatel, Rue Emile-Argand 11, Neuchatel, Switzerland
²Institute of Ecology, Universidad Nacional Autónoma de México (UNAM), Apartado. Postal 70-275, México, DF 04510, México.

Betty.Benrey@unine.ch

Many species of parasitoids are distributed over populations in a variety of habitats in which they may experience different environmental conditions. If gene flow among these populations is limited and natural selection operates differently in the different habitats, this should lead to genetic divergence and local adaptation. Our study examines the effects of plant variation and the existence of local adaptation in a tri-trophic interaction. The system comprises four wild populations of the bean Phaseolus vulgaris, the bruchid beetle Zabrotes subfasciatus and the braconid parasitoid Stenocorse bruchivora. Transplant experiments revealed that bruchid performance varies among bean populations. Beetles from one site performed better on the seeds of their original site than on seeds of the other populations. A nutritional analysis of the seeds showed that seeds from this site are nutritionally superior as they have a higher nitrogen content. We then examined the consequences of bruchid variation on the performance and potential for local adaptation of the parasitoid. The results did not show evidence for local adaptation, but they showed behavioural and performance differences among parasitoid populations with respect to their origin and the origin of the seeds in which they developed. We currently study the role of the plant in determining genetic differences among populations.

Patch quality, life expectancy and patch residence time in female egg parasitoids

Guy Boivin¹ and Eric Wajnberg²

¹Horticultural Research and Development Center, Agriculture and Agrifood Canada, 430 Boul. Gouin, St-Jean-sur-Richelieu, Quebec, Canada J3B 3E6
²Station d'Antibes, INRA, 37 Boul. du Cap, 06600 Antibes, France

guy.boivin@agr.gc.ca

The Marginal Value Theorem predicts that female parasitoids should exploit host patches until their instantaneous rate of gain reaches a marginal value. Patch residence time was measured in an egg parasitoid, Anaphes victus (Hymenoptera: Mymaridae), when patch quality and travel time varied. The effect of female age on patch residence time was also tested while keeping travel time constant. The females Anaphes stayed longer and exploited the patch to a higher level when patch quality and travel time increased. However, the marginal value at which females left the patch decreased with these parameters. Contrarily to Trichogramma species, Anaphes females appear to base their patch quality estimate on the first patch encountered rather than on a fixed innate estimate. Such strategy may be optimal when inter-generation variability in patch quality is high. Independently of travel time, the age of females influenced their patch residence time. Patch residence time increased exponentially as the life expectancy of females decreased. The probability of finding another patch diminishes with a female life expectancy and it is therefore adaptive to exploit the current patch to a higher level.

The molecular phylogenetics of the Figitidae (Hymenoptera: Cynipoidea)

Matthew L. Buffington

Dept. of Entomology, University of California, Riverside, CA 92521, USA

mbuff@citrus.ucr.edu

The figitids are a diverse assemblage of parasitic cynipoids. Intense systematic research over the past two decades has revealed much about this ubiquitous group, both taxonomically and phylogenetically. To aid in the study of figitid phylogenetics, I have sequenced the 28S D2+D3, COI and 16S gene regions while placing a premium on taxon sampling that represents the maximum diversity of the Figitidae. Additionally, several members of other cynipoid families have been included. The results to date find the majority of figitid subfamilies monophyletic. The goal of this research is a robust phylogeny that future studies on the classification and evolution of this group can be based upon.

Migration by the sweet potato whitefly, Bemisia tabaci, and its aphelinid parasitoid Eretmocerus eremicus

David N. Byrne and David E. Bellamy

Department of Entomology, University of Arizona, Tucson, AZ 85721

byrne@ag.arizona.edu

Information has been gathered for several years on the migration habits of the sweet potato whitefly, Bemisia tabaci. Empirical evidence demonstrates that this relatively small insect is easily capable of migrating several kilometers during a single morning. Anecdotal evidence indicates it can disperse much farther. Contrastingly, one of its principle natural enemies in the Southwest, Eretmocerus eremicus, seems less capable of moving even these modest distances. Regardless, an examination of their flight behavior has provided useful information. For example, when examined in the laboratory the ability of E. eremicus to sustain flight is linked to gender and mating status. Unmated females fly for significantly longer periods of time that do unmated females and females fly for significantly longer periods than males. Conclusions concerning flight behavior were substantiated in field trials where female dispersal had a strong directional component while males apparently diffused away from release points. Taken collectively (see Bellamy presentation) these data provide insight into host/parasitoid relationships.

The induction of volatiles in bean plants by feeding and oviposition of Nezara viridula that attract the egg parasitoid Trissolcus basalis: Behavioral and chemical ecology investigations

Stefano Colazza^*+ and Jocelyn Millar⁺

^*S.En.Fi.MI.Zo. Department – Entomology, Zoology and Acarology – University of Palermo – Palermo 90128, Italy
⁺Department of Entomology – University of California – Riverside, CA 92521, USA

colazza@unipa.it

The ability of parasitic arthropods to locate and attack hosts, and consequently their efficacy, is a result of sequential host selection steps that are regulated by physical, infochemical, and biochemical factors. A series of cues mediate the host selection process, and among them, volatile compounds emitted by plants as a consequence of herbivore activities play a significant role. When these volatiles recruit natural enemies, they have been termed host-induced synomones and they are regarded as an indirect chemical defense reaction by the plants. The ability of hymenopteran parasitoids to locate their hosts using these induced synomones has been well documented for adult and larval parasitoids, i.e., for those host instars whose feeding activities induce qualitative and quantitative changes in the plant's volatile profile. However, variations in plant volatiles are not only induced by insects that damage plant tissues while they feed, but also by egg deposition, and these volatiles also serve as host-induced synomones for their egg parasitoids. Previous investigations showed that broad bean leaves (Vicia faba) damaged by feeding activity of Nezara viridula (Heteroptera: Pentatomidae) and on which an egg mass had been laid, produced host-induced synomones that attracted the egg parasitoid Trissolcus basalis (Hymenoptera: Scelionidae). In contrast, undamaged leaves or leaves damaged only be feeding did not attract wasp females. Comparisons of the headspace analysis of broad bean plants revealed differences in the blends emitted by undamaged plants and feeding damaged plants carrying an egg mass. Dichloromethane extracts of feeding damaged plants carrying an egg mass attracted T. basalis females in Y-olfactometer tests, and after preparative gas chromatography fractionation of these extracts, we obtained a terpenoid fraction that was attractive to the parasitoid.

Identification of synomones induced by feeding and oviposition of Nezara viridula on bean plants

Stefano Colazza^*+, J. Steven McElfresh⁺ and Jocelyn Millar⁺

^*S.En.Fi.MI.Zo. Department – Entomology, Zoology and Acarology – University of Palermo – Palermo 90128, Italy
⁺Department of Entomology – University of California – Riverside, CA 92521, USA

colazza@unipa.it

Several studies have demonstrated that herbivores can induce host plants to produce volatiles that can attract arthropod natural enemies which parasitize or prey on the herbivores, reducing further damage to the plants. To date, studies that have investigated herbivore-induced volatiles have primarily focused on defoliating insects that damage plants by chewing. There is much less information available about volatiles induced by herbivores having phloem-feeding or stylet-sheath-feeding habits, such as Heteroptera. Furthermore, volatiles may be produced in response to insect egg deposition and these volatiles also may serve as host-induced synomones for egg parasitoids. Here we present results of analyses of headspace odors from broad bean (Vicia faba) and French bean (Phaseolus vulgaris) plants induced by adults of Nezara viridula (Heteroptera: Pentatomidae) as a result of their feeding activity, oviposition activity, and feeding and oviposition activity combined. Undamaged plants produced relatively small amounts of “green leaf volatiles” (hexanal, (Z)-3-hexenol and (Z)-3-hexenyl acetate) and traces of monoterpenes and sesquiterpenes (linalool, -caryophyllene and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene). Feeding and oviposition by adults of N. viridula induced a significance increase in terpenoids, reaching a peak during the first day after bug feeding and oviposition. No differences were detected in the volatiles profiles of undamaged plants and plants on which bugs were allowed only to lay eggs. Furthermore, water extracts of N. viridula salivary glands induced the emission of the same volatile blend produced by plants damaged by both feeding and oviposition. Bioassays revealed that the volatiles blend produced by plants damaged by both stink bug feeding and oviposition was more attractive to the egg parasitoid Trissolcus basalis than volatiles from undamaged plants, or plants with only feeding damage.

Provisioning of an enemy-free space for an oligophagous insect herbivore: Direct effect of a recently acquired host plant on parasitoids

Moshe Coll¹ and Bayeh Mulatu Aregay^1,2

¹Dept. of Entomology, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel
²Ethiopian Agricultural Research Organization, P.O. Box 2003, Addis Ababa, Ethiopia

coll@agri.huji.ac.il

Enemy-free space (EFS) is a potentially important factor affecting host plant use by phytophagous insects. In this study we first tested whether tomato plants provide Phthorimaea operculella larvae with an EFS. Compared to potato, tomato is a sub-optimal host for P. operculella. Yet in a few areas, high population densities of P. operculella were reported on tomato plants in the last 15 years or so. Berdegue et al. (1996) proposed three conditions for EFS. Through field experiments in Ethiopia, we demonstrated that natural enemies are an important mortality factor on the potato host; a significantly higher proportion of larvae survive on caged potato plants than on exposed ones. We then found that in the presence of natural enemies, larval survival was significantly higher on tomato than potato plants, implying that the herbivore is more protected from its enemies on tomato than potato plants. Finally, we found that larval survival was significantly higher on caged potato than caged tomato plants. Yet the cost involved in feeding on the sub-optimal novel host (Berdegue et al.'s third condition) was observed only on one of the three tested tomato genotypes and only at the preblossom stage. These variations were not related to trichome density or tomatine concentration. Results however show for the first time that a lack of fitness cost may not necessarily be due to herbivore adaptation to feed on the novel host but may also depend on plant genotype and phenology. We conclude that tomato plants provide EFS for this oligophagous herbivore because all of Berdegue et al.'s conditions were met in our system. Laboratory experiments show that the EFS is due primarily to the direct and negative effect of tomato plants on Diadegma larval parasitoids. An intensive field survey provides further support for this conclusion; unlike larvae on nearby potato, P. operculella larvae on tomato plants were not parasitized.

Consequences of intraspecific interference for competitive displacement and biological control in a community of Hawaiian fruit-fly parasitoids

Timothy Collier¹, Russell Messing², and Cheryl Briggs³

¹Dept. of Renewable Resources, University of Wyoming, Laramie, WY 82071
²Dept. of Entomology, University of Hawaii, Kauai Agricultural Research Center, Kapaa, HI 96746
³Department of Integrative Biology, University of California, Berkeley, CA 94720

tcollier@uwyo.edu

Using a laboratory experiment and a stage-structured population dynamic model, we attempted to explain a historic pattern of competitive displacement in tephritid parasitoids in Hawaii. We sought to understand the simultaneous occurrence of three phenomena following the introduction of the egg parasitoid Fopius arisanus: (1) a 10-fold decline in tephritid densities, (2) decline in abundance of four previously established larval parasitoids in the genus Diachasmimorpha, and (3) current and historic coexistence of three of the Diachasmimorpha species with F. arisanus. In a laboratory experiment with F. arisanus, we investigated a form of intraspecific interference that arose from “host-egg killing” by adult female F. arisanus. We hypothesized that this mechanism of intraspecific interference might explain coexistence, whereas other aspects of F. arisanus' biology would explain competitive displacement. We developed a stage-structured population-dynamic model that incorporated the results of our study and other studies of the system. Contrary to our expectations, the model failed to predict the pattern of competitive displacement observed in Hawaii. Competitive displacement, coexistence and enhanced biological control of fruit flies never occurred for the same set of parameter values. The model probably does not incorporate additional competitive advantages of F. arisanus and/or other important coexistence-promoting mechanisms.

Nutritional implications and differential gene expression in the wing morph differentiation of Melittobia digitata

Fernando L. Consoli, H.S. Tian, S.B. Vinson, and C. Coates

Department of Entomology, Texas A&M University, College Station, TX 77843-2475, USA

f-consoli@tamu.edu

Wing morph development is a developmental plasticity associated with species inhabiting unpredictable or unstable environments. It is a widespread phenomenon among insects and it represents a trade-off between dispersal or migratory behavior and reproduction. The concept of the existence of trade-offs among traits that dictate shifts in the organismal life history has been one of the central paradigms for evolutionary biologists and wing dimorphism is considered a strategy to maximize the development of the reproductive organs by diverting nutrient resources that would be otherwise allocated to the development and maintenance of flying structures. A variety of environment-derived cues such as crowding, host plant condition, temperature and photoperiod, are among the most common factors to elicit wing form differentiation. However, density, especially if coupled to an unsuitable nutritional medium, has been described as the trigger for the development of wing morphs of several species. Although diverse cues may trigger wing morph development, changes in hormone levels is considered to be the underlying mechanism and is likely to be evolutionarily conserved. An increase in titers of juvenile hormone (JH) is the most accepted mechanism to lead to short wing morph (SWM) development through the blockage of changes normally induced by ecdysone-mediated metamorphosis. We discuss the nutritional implications and the differential gene expression in the morph differentiation of the ectoparasitoid Melittobia digitata.

Expression and molecular characterization of a putative chitinase from teratocytes of Toxoneuron nigriceps

Fernando L. Consoli and S.B. Vinson.

Department of Entomology, Texas A&M University, College Station, TX 77843-2475, USA

f-consoli@tamu.edu

Parasitoids are a very diverse group in which their nutritional and physiological interactions will depend on the evolutionary history of a particular host-parasitoid association. They have a natural arsenal to help them to subdue the host immune response, alter and regulate host metabolism, development, and synthesis of host proteins, such as maternally-born secretions (venom, calyx fluids), larval secretions, associated symbiotic virus (PDVs), and/or secretions from teratocytes (a particular cell type derived from the developing embryo). Teratocytes are cells derived from the serosal membrane of parasitoids eggs that may have a dual function in the parasitoid-host interaction serving not only as a source of substances that alter the host internal environment, but also of proteins that might have a nutritional role for the developing parasitoid. Toxoneuron nigriceps is a larval endoparasitoid in which teratocytes were shown to secrete several proteins into the host hemocoel and regulate the host endocrine system. In here we analyze the expression pattern, provide the molecular characterization of a putative chitinase produced by teratocytes and released into the host hemolymph, and discus its possible implications for the developing parasitoid.

Strategies involved in host location of Telenomus busseolae and Trichogramma turkestanica, egg parasitoids of Sesamia nonagrioides

Eric Conti¹, Gianandrea Salerno¹, Ahmet Bayram² and Ferdinando Bin¹

¹Dept. of Arboriculture and Plant Protection – Entomology, University of Perugia, Borgo XX Giugno, Perugia 06121, Italy
²Dept. of Plant Protection, Faculty of Agricultural Sciences, Çukurova University, 01330 Adana, Turkey

econti@unipg.it

The noctuid stemborer Sesamia nonagrioides (Lepidoptera: Noctuidae) is an important pest of maize in the Mediterranean Basin. The egg clusters of S. nonagrioides, concealed under the leaf sheaths or the ear bracts, are attacked by Telenomus busseolae (Hymenoptera: Scelionidae) and Trichogramma spp. (Hymenoptera: Trichogrammatidae), but only T. busseolae exerts an effective natural control. A possible explanation is based on the different strategies used to reach and parasitize the concealed host eggs. T. busseolae is dorso-ventrally flattened (depressed) and crawls under the leaf sheath or ear bracts, whereas Trichogramma spp. does not show any specialized adaptation. Bioassays were conducted to verify whether such difference of efficacy can be explained also by a different response to semiochemical cues from S. nonagrioides. Behavioral responses of T. busseolae, reared on S. nonagrioides, and Trichogramma turkestanica, reared on S. nonagrioides or Ephestia kuehniella for 1, 5 and 10 generations, were compared. In olfactometer, T. busseolae females where attracted by the sex pheromone of S. nonagrioides as already reported. Instead, none of the two strains of T. turkestanica reared on S. nonagrioides and E. kuehniella responded to S. nonagrioides. In an open arena, T. busseolae and both strains of T. turkestanica showed an arrestment response to host scales. Specifically, T. busseolae response was higher compared to that of both T. turkestanica strains. Finally, response by T. turkestanica reared on both hosts declined with increasing number of generations. The potential of T. busseolae as biological control agent of noctuid stemborers is discussed.

Parasitoid and host movement and population dynamics in a heterogeneous prairie landscape

James T. Cronin and Kyle J. Haynes

Department of Biological Sciences, 206 Life Sciences Bldg., Louisiana State University, Baton Rouge, LA 70803, USA

jcronin@lsu.edu

Landscape-level experiments with insect hosts and their parasitoids are virtually non-existent. Here, we studied an egg parasitoid (Anagrus columbi) of a planthopper (Prokelisia crocea) that exists among discrete patches of prairie cordgrass (Spartina pectinata); the sole food source for the planthopper. We experimentally tested the effects of the landscape matrix (i.e., non host-plant habitat) on the movement and population dynamics of the planthopper and parasitoid. Based on a small-scale experiment in which cordgrass patches were embedded in three different matrix types (3 m between patches), we found that emigration and immigration of planthoppers were highest in a matrix composed of the introduced grass smooth brome, intermediate in native grasses, and lowest in mudflats. The egg parasitoid exhibited an identical response to the three matrix types at this spatial scale. Moreover, the parasitoid's pattern of movement through the matrix was fundamentally different between mudflat and non-host grasses. Adult parasitoids spread diffusively through non-host grasses but exhibited highly directional outward movement in a mudflat. A larger scale field experiment ( 25 m between patches), corroborated these smaller scale results: Brome facilitates higher connectivity than mudflat. Finally, preliminary data from this large-scale field experiment suggest that local planthopper and parasitoid populations are more prone to extinction in a mudflat and have significantly more asynchronous population densities in space than populations embedded in a brome matrix. These results are expected from metapopulation theory and suggest that the invasion of brome into the tall-grass prairie may greatly affect the stability of this host-parasitoid interaction.

Systematics of an enigmatic wasp family: Evaniidae (Hymenoptera)

Andrew R. Deans and James B. Whitfield

Department of Entomology, University of Illinois, 320 Morrill Hall, 505 S. Goodwin Ave, Urbana, IL 61801, USA

adeans@life.uiuc.edu

Ensign wasps (Hymenoptera: Evaniidae) develop as solitary egg predators within the oothecae of cockroaches. This interesting family encompasses 20 genera and more than 450 described species, but evaniids have long been neglected taxonomically. The generic relationships within Evaniidae (Hymenoptera) are explored for the first time using both morphological and molecular (16S, 28S) data. We also examined relationships within Apocrita using mixed models in MrBayes; these analyses revolved around Sharkey and Roy's (2002) morphological matrix and Dowton and Austin's (2001) molecular (16S, COI, 28S) dataset, with several new taxa added. Our results demonstrate that Evanioidea is monophyletic and sister to Ceraphronoidea + Proctotrupoidea + Platygastroidea + Cynipoidea + Chalcidoidea.

Early nutrition and embryonic development in two congeneric parasitoids, Encarsia formosa and E. pergandiella (Hymenoptera: Aphelinidae)

David M. Donnell^* and Lisa M. Nagy

Interdisciplinary Program in Insect Science, University of Arizona, Tucson, AZ 85721, USA
^*Current address: Department of Entomology, University of Georgia, Athens, GA 30601, USA

donnell@bugs.ent.uga.edu

The availability of amino acids was analyzed in the eggs of the endoparasitoids Encarsia formosa and E. pergandiella after oviposition and near the end of embryonic development. Newly laid eggs of E. formosa appear to contain the full complement of amino acids required for embryonic development while those of E. pergandiella absorb greater than 30-fold more amino acids from host hemolymph during embryonic development than are present at the time of oviposition in the host. Only E. pergandiella eggs were capable of absorbing and utilizing [¹⁴C]-labeled lysine in an in vitro system. An analysis of embryonic development in the two species revealed that E. pergandiella embryos become surrounded by a multinucleate, syncytial membrane early in development while E. formosa embryos do not. The membrane around E. pergandiella embryos contains large numbers of golgi, mitochondria and rough endoplasmic reticulum. The precise role of the membrane in the development of the embryo is unclear at present, however, the tremendous growth observed in E. pergandiella during embryonic development suggests the membrane plays a major role in nutrient acquisition from the host.

The role of the germ cell line in caste determination in the polyembryonic wasp, Copidosoma floridanum (Hymenoptera: Encyrtidae)

David M. Donnell¹, Laura S. Corley², and Michael R. Strand¹

¹Dept. of Entomology, 413 Bio Science Building, University of Georgia, Athens, GA 30602, USA
²Dept. of Entomology, Washington State University, Pullman, WA 99164, USA

donnell@bugs.ent.uga.edu

A single egg of the polyembryonic wasp, Copidosoma floridanum, gives rise to thousands of embryos. These embryos develop into two distinct larval castes. Reproductive larvae possess germ cells and develop into adult wasps, while precocious larvae lack germ cells and function as soldiers that defend the host from competitors. Germ line determinants localize to a single blastomere at the four-cell stage of development. To determine if inheritance of germ cells plays a role in caste formation, we compared development of eggs in which we ablated the progenitor germ cell to eggs in which we ablated other blastomeres. Our results indicate that inheritance of germ cells is a key factor involved in caste formation in C. floridanum.

Predator and parasitoid response to sequestered secondary compounds

Lee A. Dyer, Grant L. Gentry, and Angela M. Smilanich

Department of Ecology and Evolutionary Biology; Tulane University; New Orleans, LA 70118

ldyer@tulane.edu

Lepidopteran larvae possess a diverse array of defenses against predators and parasitoids. Among these protective features, chemical defenses appear to be the most effective against predators but do not function as well against parasitoid wasps and flies. Our multiple-species comparisons in both temperate and tropical caterpillar rearing studies support this pattern. Thus, chemically defended caterpillars can provide enemy free space for parasitoids. But how do parasitoids avoid toxins that are clearly defensive to predators? Our studies on specific caterpillar-parasitoid interactions provide preliminary support for several complementary toxin-avoidance hypotheses. Parasitoids may develop on tissues where toxins are not sequestered or they may process toxins using metabolism very similar to caterpillar adaptations to plant toxins. In addition to these potential responses to a toxic host, sequestered toxins may also compromise encapsulation in caterpillar hosts, leading to greater parasitism success on toxic caterpillars.

Biological control of obscure scale in northern California

L. E. Ehler

Department of Entomology, University of California, One Shields Avenue, Davis, CA 95616-8584, USA

leehler@ucdavis.edu

One of the oldest controversies in classical biological control of insects concerns the need for ecological investigations in the native home of a target pest in order to determine an appropriate introduction strategy for the pest in the exotic home. However, there has been limited progress on this issue because of the sense of urgency that often attends exotic pest problems. Over twenty years ago, I found an exceptional case: An infestation of obscure scale (Melanaspis obscura [Comstock]), an exotic diaspidid on native and introduced oaks (Quercus spp.) in Sacramento, California that was localized and not expected to spread. Because there was no “need for speed,” I conducted pre-introductory investigations in the native home of the pest (eastern USA), with emphasis on the structure of the scale's parasite guild. This information was used to derive an introduction strategy designed to maximize the ecological impact of one particular natural enemy--i.e., the aphelinid Encarsia aurantii (Howard). The parasite was released in 1988-89; it established, increased in numbers from year to year, and now has reduced the obscure-scale population to a level that no longer requires chemical control (i.e., complete biological control). This case illustrates how “guild analysis” can be used to derive introduction strategies in biological control.

Evidence of conserved genes involved in host physiological regulation in bracoviruses

E. Espagne¹, E. Huguet¹, B Provost¹, L. Cattolico², C. Dupuy¹ and J-M Drezen¹

¹Institut de Recherche sur la Biologie de l'Insecte, Tours (France)
²Centre National de Séquençage Génoscope, Evry (France)

drezen@univ-tours.fr

Bracoviruses are obligatorily associated with at least 17500 species of endoparasitoid wasps that constitute a clade -the microgastroid complex. They are essential for successful parasitism. Mature virions are produced in the ovaries, and injected by female wasps during oviposition into the host lepidopteran larvae. The virus particles enter host cells where viral genes are expressed, causing several alterations to the host physiology, comprising disruption of the immune defenses, retarded growth and inhibition of metamorphosis. We have undertaken the characterization of Cotesia congregata viral genes expressed in the parasitized host Manduca sexta and the sequencing of the virus genome. The analysis of the DNA sequences obtained so far and the screening of a cDNA library of parasitized M. sexta have allowed us to characterize several multigenic families. Some of the genes recently identified genes contain conserved protein domains found in other parasites or pathogens which are known to be involved in the suppression of the immune response of mammals. This suggests a convergent evolution between parasitoids, bacterial pathogens, and parasitic nematodes (filariae) to face the host cellular response. The characterization of genes conserved in the virus genome of different parasitoid species will also be an essential tool to understand the role played by bracoviruses in the tremendous diversification of the microgastroid complex.

Nutritional quality of aphid-produced honeydew for non-aphid parasitoids

Cristina Faria¹, Felix Wackers², Ted C.J. Turlings¹

¹LEAE-Zoology Institute, University of Neuchâtel, 2007 Neuchâtel, Switzerland
²CTE-NIOO, 6666 Heteren, The Netherlands

waeckers@cto.nioo.knaw.nl
cristina.faria@unine.ch
ted.turlings@unine.ch

Aphid-produced honeydew might be an alternative food source of fundamental importance for adult parasitoids in the context of biological control. Honeydew is likely to be particularly important in crops where nectar is not available, and is expected to increase longevity and fecundity, as well as attraction and retention of adult parasitoids in a target area. We studied the importance of honeydew produced by the aphid Rhopalosiphum maidis for the longevity of the solitary larval endoparasitoids Cotesia marginiventris, Campoletis sonorensis, and Microplitis rufiventris, natural enemies of important lepidopteran pests. Honeydew-fed females of all three species lived longer than females provided only with water, but significantly shorter than females that were fed with sucrose. When investigating the effect of honeydew feeding on the parasitism rate of C. marginiventris over eight days we found that honeydew-fed females parasitized significantly more caterpillars than non-fed females. Further experiments demonstrated that C. marginiventris is able to learn honeydew associated odours. Females that had 2x 15seconds feeding experience with honeydew on aphid-infested barley were more attracted to odours of such plants compared to naïve females and females that had experience with the odour of infested plants only. The results show that aphid-produced honeydew has the potential to serve as a food source for parasitoids and increases longevity and fecundity. Furthermore, parasitoids can learn to respond to honeydew associated odours, which should increase their foraging efficiency.

Mass production of Coccus spp. and Saissetia spp. and their parasitoids

L. D. Forster, P. G. Pacheco, R. F. Luck, and A. P. Flores.

Department of Entomology, University of California, Riverside, CA 92521, USA

lforster@citrus.ucr.edu

Reduction of organophosphate and carbamate use in traditional citrus pest management has allowed a secondary pest, citricola scale, Coccus pseudomagnoliarum (Kuwana), to re-emerge as a key pest in San Joaquin Valley citrus. Currently, we are evaluating augmentative biological control as a potential alternative pest management tactic to maintain citricola scale populations below economic concern. Commercial methods currently used to produce its parasitoids are uneconomic and cannot meet existing demand. Thus, we have developed an alternative method for rearing the scale and its parasitoids using detached yucca leaves as the host substrate. The leaves are inoculated passively (crawlers freely walk onto new leaves) and are maintained hydroponically while the scales develop. When the scales are 26-30 days old, a portion of them are exposed to the parasitoids for 96 hrs. We collect the emerging parasitoids from these leaves on days 14, 17, and 24 post-exposure, using a specially designed “sting box” which yields 160 female Metaphycus sp. per leaf on average. The remaining scale-infested leaves are retained for crawler production to infest additional leaves for subsequent parasitoid production.

Synchronized development of Encarsia scapeata and its univoltine whitefly host, Trialeurodes lauri

Dan Gerling¹, Eyal Erel¹, Dale B. Gelman², and Moshe Inbar³

¹Department of Zoology, Tel Aviv University, Ramat Aviv, Israel
²Insect Biocontrol Laboratory, Bldg. 011A, Rm. 214, BARC West Beltsville, MD 20705, USA
³Department of Biology, Haifa University at Oranim, Israel

dangr@post.tau.ac.il
gelmand@ba.ars.usda.gov

Previous life history studies of Encarsia species were conducted on multivoltine host species. The present work deals with the developmental adaptations of Encarsia scapeata, which develops on a univoltine whitefly host, Trialeurodes lauri on Arbutus andrachne trees inhabiting the Mediterranean hills of central and northern Israel. The tree has one flush of leaves each year during April and May and the whiteflies respond by emerging during that time, laying eggs and within ca. 3 weeks, developing to the 4^th instar. The whiteflies pass the next 10-11 months of the year as 4^th instar nymphs (in diapause), rather than as pharate adults. Parasitoid emergence occurs at two separate times. Some female emergence occurs in the fall (group 1) whereas most females and all males emerge in the spring (group 2). The mated females of group 2 lay female-producing eggs in the new whitefly generation during May. A few of these will emerge in the fall and give rise to group 1 females which are virgins and will lay male-producing eggs in parasitized hosts. Most female parasitoids develop to adults only from January through April, probably after inducing premature development of their hosts. These parasitoid females will constitute group 2 and will emerge in the spring together with the males that develop from the eggs laid by group1 females. Thus, there is considerable developmental synchrony between the parasitoid and its host requiring a complex series of interactions between the two insects.

Confirming the role of yeast symbionts in green lacewings, Chrysoperla spp. (Neuroptera: Chrysopidae)

Cara M. Gibson and Martha S. Hunter

University of Arizona, Department of Entomology, 410 Forbes Hall, Tucson, AZ

cgibson@ag.arizona.edu

As larvae, lacewings in the genus Chrysoperla are voracious predators of aphids and other soft-bodied insects. Unlike many other lacewings, Chrysoperla spp. adults are non-predaceous and feed on pollen, nectar and aphid honeydew. Earlier studies observed that Chrysoperla spp. adults house symbiotic yeasts in their crops and indicated that the yeast may supplement amino acids missing in the largely carbohydrate diet (Hagen KS et al. 1970. Bolletino Laboratorio di Entomologia Agraria Filippo Silvestri 28:113-34; Hagen KS, RL Tassan. 1972. In J.G. Rodriguez (ed.) Insect and Mite Nutrition. North Holland, Amsterdam, The Netherlands). They suggested that lacewings eclose without their yeast symbionts and must obtain them from the environment. In our research, attempts to cure adult Chrysoperla spp. of yeast using Hagen et al.'s (1970) protocol, as well as several other fungicides and heat treatment, have been unsuccessful. Furthermore, preliminary data suggests that yeast may also be vertically transmitted. Our research indicates that the functional significance of yeast in green lacewings requires further study.

Parthenogenesis-inducing microorganisms in Encarsia parasitic wasps: Different mechanisms of sex manipulation

Massimo Giorgini¹, and Emilio Caprio²

¹Istituto per la Protezione delle Piante, CNR, Sezione di Portici, 80055, Italy
²Dipartimento di Entomologia e Zoologia agraria, Università di Napoli Federico II, Portici, Italy

giorgini@ipp.cnr.it

In the genus Encarsia (Hymenoptera: Aphelinidae) thelytokous reproduction appears to be caused by two different groups of maternally inherited bacteria, namely an proteobaceria, Wolbachia, and members of the Cytophaga–Flexibacter–Bacteroid (CFB) group, that are located in the reproductive tissues. Although several karyological studies have been performed on thelytokous and arrhenotokous species of Encarsia, no data are available on the ploidy level of males obtained by treating parthenogenetic females with antibiotics, in order to eliminate sex determining symbionts. In this study, male larvae of E. hispida, a species with CFB, and E. formosa, the only species of Encarsia infected by Wolbachia, were karyotyped. Chromosome preparations revealed diploid complements (2n=10) in the former species and haploid complements (n=5) in the latter (in which diploid nuclei were also present). These results suggest that parthenogenesis-inducing microorganims manipulate sex in two different ways. Wolbachia alters the ploidy level of unfertilized eggs in E. formosa, whilst CFB does not in E. hispida. Consequently, E. formosa follows the general haplodiploid sex determination mechanism of Hymenoptera and the genic balance model could apply, as for other microbe-associated thelytokous species of chalcidoids. Conversely, in E. hispida diploidy has became fixed in both sexes and unfertilized eggs are feminized by CFB probably through a genomic imprinting.

Molecular differentiation of closely related Encarsia species (Hymenoptera: Aphelinidae) based on mitochondrial COI gene

Massimo Giorgini, and Maurilia Maria Monti

Istituto per la Protezione delle Piante, CNR, Sezione di Portici, 80055, Italy

giorgini@ipp.cnr.it

The genus Encarsia includes species that are parasitoids of whiteflies and armored scale insects. Many species are considered effective natural enemies of agricultural pests and their correct identification is fundamental for successful biological control programmes. Recently, due to unreliability of morphological characters in separating closely related species of Encarsia, new identification techniques are being investigated. In this study, a 850 bp long region of the mitochondrial COI gene was sequenced from 5 species of Encarsia belonging to luteola (E. formosa, E. luteola and E. hispida) and strenua (E. protransvena and two strains of E. sophia, from Pakistan and Spain respectively) species groups. A parsimony analysis resolved two monophyletic clades supporting the two groups of species considered. The nucleotide sequence divergence between the two E. sophia strains was greater than that found among the species of the luteola group, suggesting that the two strains could be actually sibling species. PCR-RFLP analysis produced restriction patterns which discriminate E. formosa from E. luteola (DraI and TaqI), that are similar morphologically, and the Pakistani from the Spanish strain of E. sophia (DraI and XhoI), that are indistinguishable morphologically. In conclusion, the COI region could be a useful marker to characterize and separate species within the genus Encarsia otherwise indistinguishable on a morphological basis.

Inter-clone conflicts in the parasitoid wasp C. floridanum: Do precocious larvae mediate competition between broods in a single host?

David Giron and Michael R. Strand

Entomology Department, University of Georgia-Athens, USA

giron@bugs.ent.uga.edu

When should interacting organisms compete and when should they cooperate? This has been an enduring topic in many areas of evolutionary ecology. Cooperation will be favored when there are material benefits to both parties but not when they are material costs. However, the balance between cooperation and competition will be more complex if interacting individuals experience both costs and benefits. Our study aims to explore proximate mechanisms underlying the evolution of conflicts in the polyembryonic wasp C. floridanum by testing the importance of two key components of evolutionary conflicts among individual: Mating opportunities and genetic relatedness. C. floridanum is obligately polyembryonic with each egg laid into a host developing clonally into an average of 1200 adults. The majority of embryos develop into ‘reproductive’ larvae that develop into adults, while a minority of embryos develop into ‘soldiers’ larvae (precocious larvae) that always die when the host is consumed by the reproductive larvae. Previous studies investigating brood responses to completely unrelated competitors showed that soldiers protect the evolutionary interests of their clone mates by attacking the competitor but with no influence of genetic relatedness or other benefits such as mating opportunities. Here, by injecting intraspecific competitors labeled with a vital tracer into hosts parasitized by C. floridanum and by conducting in vitro experiments, we characterize the behavioral response of resident soldiers to conspecifics. The genetic background and the sex of the introduced brood are manipulated in order to study how ‘soldiers’ larvae respond to these two different factors and if precocious larvae are able to mediate competition between two conspecifics broods.

The adaptive significance of sibling egg cannibalism in the Coccinellidae: Comparative evidence from three species

Angela K. Grant and J.P. Michaud

Agricultural Research Center, Kansas State University, Hays, KS

jpmi@ksu.edu

Egg cannibalism is common among aphidophagous coccinellids that lay clustered eggs. Neonate larvae may improve their survival probability by cannibalizing sibling eggs prior to dispersal in search of prey. Egg-clustering facilitates sibling egg cannibalism and may represent a form of maternal care that improves the survival of early-hatching larvae at the expense of late-hatching larvae. We examined sibling egg cannibalism behavior in three aphidophagous coccinellid species that lay clustered eggs: Cycloneda sanguinea L., Harmonia axyridis Pallas, and Olla v-nigrum Mulsant. Newly hatched larvae of all three species delayed dispersal from clusters when sibling eggs were available for cannibalism and consumed all late-hatching and/or non-viable eggs within clusters before dispersing. There was significant variation among species in 1) the proportion of eggs laid singly versus in clusters, 2) the proportion of eggs cannibalized by early-hatching larvae and, 3) the physiological consequences of egg cannibalism for developing larvae. Both male and female larvae that cannibalized eggs molted to the second instar sooner than did their non-cannibalizing counterparts in all three species, and this translated into reduced total developmental time for both sexes in H. axyridis, but only for males in C. sanguinea and only for females in O. v-nigrum. Adult females weighed significantly more than adult males in all three species and increases in adult weight as a consequence of egg cannibalism were sex-specific. Female cannibals were heavier as adults than were non-cannibalizing females in H. axyridis and O. v-nigrum, but males had similar weights. Egg cannibalism had no detectable effect on adult weight in C. sanguinea. Therefore, our results revealed substantial life history benefits for sibling egg cannibalism behavior in all three species, although in many cases the benefits were sex-specific.

Flight response of Aphidius ervi to tomato plant volatiles

Emilio Guerrieri¹, Maria Cristina Digilio², Giandomenico Corrado³, Francesco Pennacchio⁴ and Rosa Rao³

¹Istituto per la Protezione delle Piante, CNR, sez. di Portici, Portici (NA), Italy
²Dipartimento di Entomologia e Zoologia Agraria, Università di Napoli, Portici (NA), Italy
³Dipartimento di Scienze del Suolo, della Pianta e dell'Ambiente, Università di Napoli, Portici (NA), Italy
⁴ Dipartimento di Biologia, Università della Basilicata, Potenza, Italy

e.guerrieri@ipp.cnr.it

Plants can be attractive towards natural enemies of insects that attack them. This common feature is termed indirect resistance and can be exploited to increase biological control of insect pests. The attractiveness of two tomato ecotypes towards Aphidius ervi has been studied in wind tunnel bioassay. This parasitoid has proved to be the most effective biocontrol agent of Macrosiphum euphorbiae, the key pest of tomato grown in open field in Southern Italy. It has been found that a high level of attractiveness can be either constitutive (ecotype AN5), i.e. recorded in absence of infestation by M. euphorbiae, or induced (ecotype AN7), i.e. produced after several days of aphid infestation. In AN5, aphid infestation did not enhance attractiveness towards A. ervi, probably due to its higher level of direct resistance to aphids. The F1 obtained by crossing AN5xAN7 followed the response recorded for AN7, suggesting that the inducibility of high level of attractiveness is inherited according to dominant fashion. As a consequence, it appears that this character may be introgressed efficiently into commercially valuable varieties of tomato.

Foraging behavior, host stage selection and gut content analysis of field collected Drapetis nr. divergens (Diptera: Empididae): A predatory fly of Bemisia argentifolii

James R. Hagler

Western Cotton Research Laboratory, USDA-ARS, 4135 E. Broadway Road, Phoenix, AZ 85040, USA

jhagler@wcrl.ars.usda.gov

Little information is published about the biology of the predatory fly, Drapetis nr. divergens Loew. A laboratory investigation of the foraging behavior and host stage selection of field collected D. nr. divergens presented with a surfeit of silverleaf whitefly, Bemisia argentifolii Bellows & Perring eggs, nymphs and adults was undertaken. The foraging behavior of D. nr. divergens resembled that of an ambush attack strategist, frequently exhibiting motionless behavior and feeding exclusively on mobile adults. A gut content evaluation of D. nr. divergens using a whitefly-specific enzyme-linked immunosorbent assay (ELISA) was conducted on field collected flies. The analysis revealed that 15% of the individuals collected contained whitefly remains in their guts.

Impacts of exotic parasitoid foraging strategies on a native Hawaiian community: A detailed simulation

M. Laurie Henneman¹ and Eric G. Dyreson²

¹Department of Environmental Sciences, University of Montana-Western, 710 S. Atlantic St., Dillon, MT 59725
²Department of Mathematics, University of Montana-Western, 710 S. Atlantic St., Dillon, MT 59725

l_henneman@umwestern.edu

A quantitative food webs and simulation modeling are useful tools in the study of community structure and dynamics. We used these tools to examine the ways in which exotic species invasions can affect an entire food web, both qualitatively and quantitatively. Starting with detailed life-history data from a plant-moth-parasitoid quantitative food web from the Alaka Swamp, Kaua, we constructed a detailed simulation model which allows us to reveal potential dynamical consequences for species invasions. We included insect behavior as part of the model, which is not generally done in simulations of complex food webs. The simulations indicate that the ability of exotic parasitoids to use learning to enhance foraging success has repercussions throughout the food web.

Field oviposition rates of sugar-fed and sugar-starved parasitoids

George E. Heimpel, Jana C. Lee & Zhishan Wu

Dept. of Entomology, University of Minnesota, 1980 Folwell Ave., St. Paul, MN 55108, USA

heimp001@tc.umn.edu

We compared estimates of fecundity of parasitoids foraging freely in the field that were either sugar-fed or sugar-starved. Fecundity was estimated by first tracking changes in egg loads of parasitoids captured throughout the day to obtain a rate of change in the egg load. This rate was then adjusted using egg load changes of parasitoids kept in field cages that contained either sugar sources or not, but no hosts, throughout the foraging day. The result is an estimate of oviposition rate that takes into account egg maturation and resorption. This estimate was applied to samples of field-caught parasitoids that were classified as either sugar-fed or not using the cold anthrone test. We made this comparison for three species of parasitoid Hymenoptera: Diadegma insulare (Ichneumonidae), which attacks diamondback moth, Macrocentrus grandii (Braconidae), which attacks European corn borer, and Aphelinus albipodus, which attacks soybean aphid. Our results from D. insulare and A. albipodus are consistent with a higher oviposition rate for sugar-fed parasitoids. Results for M. grandii have not been analyzed at the time of this writing.

How parasitoids can estimate habitat quality and respond to information cues within and between patches

Thomas S. Hoffmeister, Andra Thiel, Munjong Kolß, Ulf Tölch, and Mônica Frank Kersch

Zoological Institute, Dept. of Animal Ecology, Christian-Albrechts-University, 24098 Kiel, Germany

thoffmeister@zoologie.uni-kiel.de

Patch time allocation in insect parasitoids has mainly been studied as a function of host density and host encounters in single-patch experiments. From such experiments we know that parasitoids respond to host kairomones and encounters with unparasitized hosts. Whether they should and do respond to encounters with parasitized hosts has been debated, but experimental evidence has been equivocal. Moreover, whether host density of a given patch and patch encounter rate influence the patch time allocation on subsequent patches has largely remained unanswered. Using the Drosophila parasitoids Leptopilina heterotoma and Asobara tabida, we investigated behavioral responses of wasps to information cues for estimating patch quality and habitat quality. In our patch-quality experiments we tested responses towards staged encounters with unparasitized vs. parasitized hosts. Corresponding with predictions, we found that wasps use information from encounters with both, unparasitized and parasitized hosts, to allocate their patch time. Moreover, we found that host-encounters influenced the walking speed of wasps within and outside of patches, and thus presumably impact the probability of host and patch encounters. In our habitat-quality experiments we found that wasps did not respond on test patches to variation in host density experienced on pre-test patches. However, wasps responded strongly to variation in patch encounter rates in their patch time allocation and patch exploitation level.

Host patch exploitation by competing parasitoids: An asymmetric generalized war of attrition?

Gijs Hoogendoorn¹, Nicolette Snijders¹, Gé Boskamp¹, Patsy Haccou², and Jacques van Alphen¹

¹Section of Animal Ecology, Institute of Biology, Leiden University, Kaiserstraat 63, 2311 GP Leiden, The Netherlands
²Section of Theoretical Biology, Institute of Biology, Leiden University, Kaiserstraat 63, 2311 GP Leiden, The Netherlands

hoogendoorn@rulsfb.leidenuniv.nl

A recent study used a game theoretical approach to model patch leaving and oviposition behavior of two solitary parasitoid females depleting one patch. Optimal decisions on when to start superparasitizing and when to leave the patch were addressed in terms of a war of attrition. Superparasitism causes the reward of foraging on a patch to change in time, which makes the game a generalized war of attrition. In addition, differences in arrival time between the two females induce superparasitism to affect their expected payoffs from the patch asymmetrically. Predictions from the model are that a female arriving later on a patch will start superparasitizing and leave a patch sooner than a female arriving earlier on a patch. To study a similar problem empirically, we allowed pairs of females of the solitary braconid parasitoid Asobara persimilis to compete for hosts in standardized patches, while we assessed patch residence time and oviposition behavior. Treatments consisted of varying the difference in arrival time and the number of competitors simultaneously present in a patch. The results will be presented and discussed referring to the model.

Evolution of host use and courtship in sibling species of parasitoids

Keith Hopper¹, James B. Woolley², Angela Farias³, John Heraty⁴, and Jung Wook Kim⁴

¹USDA-ARS-BIIR, Newark, DE 19713, USA
²Dept. of Entomology, Texas A&M University, College Station, TX, 77843-2475, USA
³Departemento de Zoologia, CCB, Universidade Federal de Pernambuco, Pernambuco 50670-420, Brasil
⁴Department of Entomology, University of California, Riverside, CA 92521, USA

khopper@UDel.edu

Aphelinus varipes is reported to have a wide host range, attacking more than 40 species of aphids, and a wide geographic distribution, being endemic throughout Eurasia and perhaps in North America. However, we found that Aphelinus varipes from different hosts (Aphis glycines, Diuraphis noxia, Rhopalosiphum padi) and countries (France, Georgia, Israel, China, and Japan) showed different patterns of parasitism when exposed to seven aphid species on four host plant species. Some host species were not attacked at all by some wasp populations. When we attempted to cross these populations, most females from most populations rejected males from other populations. The only crosses where some females accepted alien males involved those from allopatric populations. Although these populations are very similar morphologically, they differ subtly morphometrically, and there are small, fixed differences in DNA sequences among them (see companion paper by Woolley et al.). Together our data suggest that these populations are sibling species that have diverged greatly in host use and courtship, but much less so in morphology and putatively highly variable DNA sequences. Despite a weak phylogenetic signal from molecular data, host use and mate acceptance do map well on the molecular phylogeny, with a pattern of increasing specialization in host use and with females more likely to mate with males from more closely related species.

Host finding abilities increased by cleptoparasitism in bark beetle parasitoids

Evelyne Hougardy¹ and Jean-Claude Grégoire

Biologie des Communautés animales, CP 160/12, Université Libre de Bruxelles, 50 av. F.D. Roosevelt, B-1050 Brussels, Belgium
¹Present address: ESPM - Insect Biology, Wellman Hall 310, University of California, Berkeley, CA 94720-3112

ehougard@nature.berkeley.edu

The braconid Coeloides bostrichorum and the pteromalid Rhopalicus tutela are two ectoparasitoid wasps attacking the late instar of the spruce bark beetle Ips typographus. R. tutela is a polyphagous species attacking numerous bark beetles on pine and spruce while C. bostrichorum has been reported as the most efficient parasitoid of Ips typographus. Both species search for hosts from the bark surface, preferentially in the upper section on tree. Therefore interspecific encounters between foraging females might be frequent. The host searching efficiency of each species, alone or in the presence of the other, was investigated in the laboratory using the “phloem sandwich” technique. When the females searched alone for hosts, C. bostrichorum had better host searching abilities than R. tutela. In the presence of C. bostrichorum, R. tutela increased its host finding abilities through direct displacement and stealing of hosts discovered by C. bostrichorum. This cleptoparasitic behavior did not seem to affect the success in host location and parasitism of C. bostrichorum. However, cleptoparasitism had a disturbing influence on C. bostrichorum as the females only probed at bark locations without a host in the presence of R. tutela and as they were observed to fly away from the bark after several acts of aggression from R. tutela. This study suggests that cleptoparasitism could partly explain the success of the polyphagous R. tutela in coexisting with the specialist C. bostrichorum.

Feeding behavior of Lygus hesperus and L. lineolaris on whitefly life stages

Charles G. Jackson, James R. Hagler, Daniel R. Langhorst, Scott A. Machtley, and Livy Williams, III

USDA-ARS, Western Cotton Research Laboratory, 4135 East Broadway Road, Phoenix, AZ 85040, USA

gjackson@wcrl.ars.usda.gov

Lygus spp. are known to feed on, and cause economic loss to a number of important agriculture crops, including cotton alfalfa, vegetables, fruits, and ornamentals. However, they are also facultative predators on insect eggs, aphids, whiteflies, lepidopterous larvae, and other insects. We made observations on instars 3 – 5 and adults of Lygus hesperus and L. lineolaris in leaf arenas in the laboratory to quantify the behavior and predation on whitefly life stages. Feeding occupied 23 – 60% of the total activity budget for L. hesperus and 51 – 64% of the time for L. lineolaris. Feeding on the cotton leaves was 70 – 84% of the feeding budget for the different stages of L. lineolaris and 34 – 84% for L. hesperus. When we reared L. hesperus on a meridic diet, more than 50% of the feeding budget was eating whiteflies. The amount of time that Lygus spp. spent on each type of behavior occurred in the following order; fed on plants > fed on whitefly adults (mostly dead or disabled) > fed on nymphs > rested > groomed > walked > fed on eggs > probed adults = probed nymphs = probed eggs. Lygus spp. fed 3.3 times on the cotton leaves for each time they fed on whiteflies (all stages combined). All stages of both Lygus spp. ate more whitefly nymphs than adults. Very few whitefly eggs were consumed.

The effect of Phloxine B and Spinosad combined with protein baits on three species of fruit fly parasitoids

Ekhlass A. Jarjees¹, Marshall W. Johnson², and Russell H. Messing¹

¹Dept. of PEPS, University of Hawaii at Manoa, Honolulu HI 96822
²Dept. of Entomology, Riverside, CA 92521

ekhlass@hawaii.edu

Laboratory bioassays were conducted to evaluate the effect of Phloxine B and spinosad bait (GF-120) on three species of tephritid fruit fly parasitoids, Fopius arisanus (Sonan), an egg-larval parasitoid of oriental fruit fly, Bactrocera dorsalis (Hendel), Diachasmimorpha tryoni (Cameron), larval parasitoid of Ceratitis capitata (Wiedemann), and Dirhinus giffardii Silvestri pupal ectoparasitoid of Bactrocera cucurbitae (Coquillet). The first 2 braconids were more susceptible to phloxine B than the third one. Results suggest that rates of 0.017%, 0.023% and 0.025% of phloxine B were enough to kill 50% of male and female D. tryoni and F. arisanus after 24 hours of exposure, respectively. Testing GF-120 showed that 12.5 ppm, 14.1 ppm, 13.9 ppm, 12.6 ppm of spinosad were enough to kill 50& of female and male D. tryoni and F. arisanus after 24 hours of exposure, respectively. These results may have important implications for decisions concerning best chemicals suited for reducing pest damage while conserving natural enemies in agricultural systems.

Brochosomes: A novel defense mechanism deterring egg parasitism of the glassy-winged sharpshooter

Walker A. Jones

Beneficial Insects Research Unit, ARS, USDA, 2413 E. Hwy. 83, Weslaco, TX 78596, USA

wjones@weslaco.ars.usda.gov

Brochosomes are lipo-protein particles produced in the Malpighian tubules of certain Cicadellidae. In several genera of Proconiini, these particles are produced by sexually mature females that collect them in reservoirs as conspicuous white spots on each forewing. Following oviposition, females use their hind legs to transfer the white particles around and on their egg masses. The proposed function of brochosomes applied to eggs has been a source of speculation. While observing oviposition behavior of the native egg parasitoid, Gonatocerus triguttatus Girault (Hymenoptera: Mymaridae) on the eggs of the glassy-winged sharpshooter, Homalodisca coagulata (Homoptera: Cicadellidae; Proconiini), it was observed that the brochosome particles readily adhered to the tarsi and antennae of the parasitoids during examination of the host eggs. Large brochosome accumulations caused the parasitoids to stop parasitization behavior, leave the egg mass, and spend much time preening in attempts to remove the particles. Experiments demonstrated that little or no time was spent grooming when brochosomes were removed prior to exposure to parasitoids. SEMs of parasitoids showed large accumulations of brochosome particles adhering to tarsi, antennae, mandibles and other body parts. Since the morphology of brochosomes can differ dramatically between sharpshooter genera and even species, there may be limitations to the efficiency of egg parasitoids currently being imported from other host genera for possible release for management of H. coagulata in California. The effects of H. coagulata brochosomes on native and exotic parasitoids will be compared.

Microsatellites illustrate tritrophic relationships of the parasitoid, Cotesia congregata (Say) [Hymenoptera: Braconidae]

Karen M. Kester, M. Kathleene Jensen, Alexandra Sledd and Bonnie L. Brown

Department of Biology, Virginia Commonwealth University, Richmond, VA 23284

kmkester@mail1.vcu.edu

Eight microsatellite loci were developed and tested for usefulness in determining population structure by assaying two groups of the insect parasitoid, Cotesia congregata (Say) [Hymenoptera: Braconidae]. One group originated from Manduca sexta L. and Manduca quinquemaculata (Haworth) on tomato and tobacco (“solanaceous group”) and the other from Ceratomia catalpae (Boisduval) on catalpa (“catalpa group”). One locus was monomorphic and seven were polymorphic. Allelic distributions differed significantly between the solanaceous and catalpa groups (P=0 for each locus and overall, Fisher's exact test). F_ST was < 1 for within-group comparisons across all loci; F_ST was > 0.47 for between-group comparisons across all loci. These results lend support to the hypothesis that host plant association is a significant factor influencing population structure of this species. Wasps from the solanaceous and catalpa groups were examined further for mtDNA and rDNA variation to investigate their status as sibling species. One conserved mtDNA gene (16S) showed considerable population genetic variation and a single fixed nucleotide difference between the two groups. Investigation of the more variable mtDNA D-loop is now underway to evaluate the possibility that these groups are incipient species.

Olfactory responses by Metaphycus sp. nr. flavus to semiochemicals released from one of its hosts, Coccus hesperidum

P. Lo Bue^1,2, L. D. Forster², J. Millar², S. Collazza¹, R. F. Luck²

¹S. En. Fi. Mi. Zo. Department, sez. Entomology, University of Palermo, Viale delle Scienze, 13, Palermo 90128, Italy
²Department of Entomology, University of California, Riverside, Riverside, CA 92521, USA

lforster@citrus.ucr.edu

Successful parasitoid-host associations depend on a parasitoid's ability to locate and recognize its hosts in a complex and heterogeneous environment, and to produce offspring from those hosts it locates and accepts. In 1996, we imported Metaphycus sp. nr. flavus (Howard) (Hymenoptera: Encyrtidae) into California from Turkey for release against citricola scale, Coccus pseudomagnoliarum (Kuwana) (Hemiptera: Coccidae), in San Joaquin Valley citrus as a classical and/or augmentative biological control agent. We rear M. sp. nr. flavus on excised Yucca sp. leaves infested with brown soft scale, Coccus hesperidum L. The infested leaves are maintained hydroponically in the University of California, Riverside, Insectary. To improve our mass rearing, we sought to determine whether M. sp. nr. flavus recognizes soft brown scale as a host. Using a Y-olfactometer, we tested whether M. sp. nr. flavus was attracted to; 1) leaves infested with 26, 27, 28, 29, or 30 d-old scale versus uninfested leaves, 2a) leaves previously infested with brown soft scale but with the scale removed and the leaves washed with distilled water versus leaves infested with brown soft scale, 2b) unwashed versus washed leaves after the brown soft scale had been removed and 3) filter paper disks impregnated with the wash water from the preceding bioassay versus filter paper disks impregnated with distilled water. The bioassays showed that M. sp. nr. flavus was preferentially attracted to; 1) leaves infested with 26, 27, 28 and 29 d-old scale but not to leaves infested with 30 d-old scale; 2) leaves infested with soft brown scale or their residue, but not to leaves from which the scale had been removed and the leaves washed with distilled water; and 3) to filter paper disks impregnated with distilled water used to wash off the scale residue after the brown soft scale had been removed from the leaf but not to disks impregnated with distilled water. We conclude that M. sp. nr. flavus is equally attracted to 26 to 29 d-old brown soft scale or their residues. These are the scale ages we use to mass-produce the parasitoid in the insectary.

Host habitat location mediated by olfactory stimuli by Anaphes iole (Hymenoptera: Mymaridae), an egg parasitoid of Lygus hesperus (Hemiptera: Miridae)

Veronica Manrique¹, Walker Jones², Livy Williams III³, and Julio Bernal¹

¹Dept. of Entomology, 412 Heep Center, Texas A&M University, College Station, TX 77843
²USDA-ARS Kiki de la Garza, Subtropical Agricultural Research Center, Beneficial Insects Research Unit, Weslaco, TX 78596
³USDA-ARS Southern Insect Management Research Unit, Stoneville, MS 38776

veronicman@neo.tamu.edu

Anaphes iole Girault is the most commonly encountered parasitoid of Lygus eggs in the U.S. Chemicals derived from adult hosts, and physical properties of protruding eggs are used as host recognition and acceptance cues by this parasitoid. However, it is unknown whether A. iole relies on volatile cues to locate hosts. Therefore, olfactometer and flight chamber experiments were conducted to assess the attractiveness of A. iole towards volatiles derived from various host plant complexes. The responses of female parasitoids to odors emanating from host plants harboring Lygus hesperus eggs (infested plants) were measured in a four-arm olfactometer, and their attraction to cotton plants harboring different numbers of eggs were measured in a flight chamber. The olfactometer was similar to that described by Vet et al. (1983), and the flight chamber consisted of a rectangular Plexiglas cage (65 x 35 x 40cm) with two compartments at one end where infested and uninfested plants were placed. Results showed that A. iole females spend significantly more time in odor fields corresponding to infested host plants (common groundsel, annual ragweed, redroot pigweed, alfalfa and cotton) compared to control odor fields in the olfactometer, though differences were not detected among host plant species. Significantly more wasps arrived to cotton plants with medium (48.4 eggs) and high (95.9 eggs) infestation levels compared to uninfested plants, while similar numbers were recovered on cotton plants with low infestation (8.7 eggs) compared to uninfested plants. These results represent the first report indicating that A. iole are attracted at a distance to plants harboring Lygus eggs.

Key predators of Helicoverpa armigera in Australian cotton crops

Sarah Mansfield

Australian Cotton CRC, CSIRO Entomology, Narrabri NSW, Australia

Sarah.Mansfield@ento.csiro.au

Australian cotton crops have a significant community of native insect predators with potential to control the key pest Helicoverpa armigera. The abundance of predatory arthropods increases over the growing season (November to February) when the use of broad-spectrum insecticides is avoided. The rising costs of chemical control and widespread development of insecticide resistance have led to increased interest in conservation biological control. However for biological control to be successful, the key predators of H. armigera must be identified and their impact on pest populations measured. The development of a serological test (ELISA) to detect predation on H. armigera eggs and larvae has played a major role in this process. Protocols have been developed for a predatory beetle, Dicranolaius bellulus (Melyridae), and the predatory bug, Pristhesancus plagipennis (Reduviidae). Predators were collected from commercial cotton farms in northern NSW during the 2001-02 and 2002-03 seasons and predation of H. armigera quantified for D. bellulus. This technique will be extended to additional predator species in the future.

Olfactory responses of Dicyphus hesperus Knight (Heteroptera: Miridae) to prey and plant odors

Robert R. McGregor¹ and David R. Gillespie²

¹Department of Biology, Douglas College, P.O. Box 2503, New Westminster, B.C., V3L 5B2, Canada
²Pacific Agri-Food Research Centre, Agriculture and Agri-food Canada, P.O. Box 1000, Agassiz, B.C., V0M 1A0, Canada

r_mcgregor@douglas.bc.ca

Dicyphus hesperus Knight (Heteroptera: Miridae) is an omnivorous generalist predator that is being developed for biological control of arthropod pests of greenhouse-grown tomatoes and peppers in British Columbia, Canada. Responses of female D. hesperus to pairs of odor sources were determined in the laboratory using a y-tube olfactometer. Females chose the odor of greenhouse whitefly (Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae)) on tomato foliage significantly more frequently than the odor of clean tomato foliage. However, no differences in the number of responses were recorded when the odors of two-spotted spider mites (Tetranychus urticae Koch (Acari: Tetranychidae)) on tomato foliage and clean tomato foliage were compared or the odors of whitefly on tomato foliage and mites on tomato foliage were compared. Females also chose the odor of green-peach aphids (Myzus persicae (Sulzer) (Homoptera: Aphididae)) on pepper foliage significantly more frequently than the odour of clean pepper foliage. No differences in the number of responses were recorded when the odors of cabbage looper eggs (Trichoplusia ni (Huebner) (Lepidoptera: Noctuidae)) on pepper foliage and clean pepper foliage were compared or the the odours of green-peach aphids on pepper foliage and cabbage looper eggs on pepper foliage were compared. These results are discussed as they relate to the use of D. hesperus for biological control in vegetable greenhouses.

The adaptive significance of sibling egg cannibalism in the Coccinellidae: Comparative evidence from three species

J.P. Michaud and A.K. Grant

Agricultural Research Center – Hays, Kansas State University, Hays, KS, USA

jpmi@ksu.edu

We examined sibling egg cannibalism behaviour and its consequences in three aphidophagous coccinellid species that all lay clustered eggs: Cycloneda sanguinea L., Harmonia axyridis Pallas, and Olla v-nigrum Mulsant. There was variation among species in the proportion of eggs laid singly versus in clusters (C. sanguinea > H. axyridis = O. v-nigrum), the synchronicity of egg hatch within clusters (H. axyridis > C. sanguinea = O. v-nigrum) and the proportion of eggs cannibalised by early-hatching larvae (O. v-nigrum > C. sanguinea > H. axyridis). The dispersal of neonate larvae from their egg clusters was delayed by the availability of sibling eggs for cannibalism. Egg cannibals survived to adulthood at the same rate as control larvae in H. axyridis and O. v-nigrum, and at a higher rate in C. sanguinea, suggesting that the Ephestia egg diet was sub-optimal for this species. In all three species, larvae that cannibalised eggs as neonates molted to the second instar sooner than did their non-cannibalising counterparts, regardless of gender. This translated into reduced total developmental time for both sexes in H. axyridis, but only for males in C. sanguinea and only for females in O. v-nigrum. Adult females weighed significantly more than adult males in all three species and female cannibals were heavier as adults than were non-cannibalising females in H. axyridis and O. v-nigrum, whereas males had similar weights. Egg cannibalism had no effect on adult weight in C. sanguinea. We hypothesize that the benefits of sibling egg cannibalism accrue in a gender-specific manner such that females potentially gain more than males, but only if the subsequent larval diet is of high quality.

The developmental strategy of an aphidiine parasitoid: Is host quality influenced by temperature or endosymbionts?

Nick Mills¹ and Baoping Li²

¹Insect Biology, Wellman Hall, University of California, Berkeley, CA 94720-3112, USA
²Department of Entomology, Nanjing Agricultural University, Nanjing 210095, P.R. China

nmills@nature.berkeley.edu

Host size is commonly considered to be an important determinant of host quality for insect parasitoids. While this is clearly the case for idiobionts parasitoids, host size at the time of oviposition would seem a less predictable indicator of host quality for koinobiont parasitoids. Aphidiine parasitoids are unusual among koinobionts in that they can attack the full range of host developmental stages, and thus a very broad range of host sizes, and frequently show a pattern of increasing progeny size and sex ratio with host instar (and size). These characteristics are more typical of idiobiont parasitoids. By manipulating aphid size in relation to stage of development through rearing Aphis fabae at either 15°C or 30°C, cohorts of 30 aphids of each instar were exposed to parasitism by individual mated female Aphidius transcaspicus at 22.5°C for a period of 5 h. Parasitized aphids were subsequently reared at the intermediate temperature of 22.5°C until parasitoid progeny emerged. We show that at an initial rearing temperature of 15°C parasitoid progeny sex ratio and size increased linearly with the fresh weight of the successive aphid instars at the time of attack. In contrast, at a rearing temperature of 30°C, this pattern was reversed, with both progeny sex ratio and size declining with fresh weight at the time of attack. The effect of temperature on the nutritional status of aphids, the activity of their obligate endosymbionts, and their future growth potential following parasitism are considered as possible determinants of host quality in aphid hosts for aphidiine parasitoid development.

Glassy-winged sharpshooter biological control in California – research and application

David J. W. Morgan¹, Greg Simmons², Patrina Brennan¹, and Humesh Kumar³

¹California Department of Food and Agriculture, Mount Rubidoux Field Station, 4500 Glenwood Drive, Riverside, CA 92501, USA
²USDA-APHIS, 3645 E. Wier Avenue, Phoenix, AZ 85040, USA
³California Department of Food and Agriculture, Oswell Street Biological Control Facility, 601 Oswell Street, Bakersfield, CA 93307, USA

dmorgan@cdfa.ca.gov
Gregory.S.Simmons@aphis.usda.gov

The biological control of the glassy-winged sharpshooter, Homalodisca coagulata, has received considerable attention over the past three years. Much of the research into biological control has now been applied and ongoing research is being employed to optimize biological control efficacy. Work carried out in conjunction with the California Department of Food and Agriculture has lead to the release of four species of Mymarid parasitoid into California. The current status and future directions for improving biological control are also presented.

Avoidance of intraguild predators by parasitoids: Chemically mediated behavioural mechanisms and field evaluation

Yoshitaka Nakashima^1,2, Michael A. Birkett³, and Wilf Powell¹

¹Plant and Invertevrate Ecology Division, Rothamsted Research, Harpenden, Herts. AL5 2JQ, UK
²Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, 080-8555, Japan
³Biological Chemistry Division, Rothamsted Research, Harpenden, Herts, AL5 2JQ, UK

nksm@obihiro.ac.jp

In the parasitoid-predator-herbivore system, intraguild (IG) predators can affect parasitism in two ways: Firstly, IG predators prey on parasitized hosts, i.e. intraguild predation (IGP), and secondly, parasitoid females avoid oviposition in host patches where IG predators are present. Some studies on parasitoid-predator interactions have reported that IGP leads to a reduction of parasitism. However, the effects of IG predator avoidance on parasitism and characteristics of chemical compounds which mediate the avoidance behaviour of parasitoids have not clearly been determined. We investigated the effect of IGP by the seven-spot ladybird, Coccinella septempunctata, on aphids parasitised by Aphidius ervi, and the effect of IG predator avoidance by adult female A. ervi on parasitism rates of the pea aphid, Acyrthosiphon pisum. To estimate the effects of IGP and IG predator avoidance, we conducted both field and laboratory experiments. In the field, we found that parasitism rates were lower in patches containing larger IG predator populations. Laboratory experiments showed that parasitoid females avoided plant surfaces on which IG predators had recently foraged. Non-volatile fractions in chemical trails left by foraging ladybirds on plant surfaces significantly induced avoidance behaviour by A. ervi. Parasitism rates of aphids on broad bean plants that had been sprayed with a mixture of the chemicals were significantly lower than those on control plants. IGP is not likely to affect parasitism rates negatively, because IG predators didn't show preference for either unparasitized or parasitized hosts. Thus, we conclude that in this system IG predator avoidance by parasitoid females may have more important effects o