Priming and filtering of antiherbivore defences among Nicotiana attenuata plants connected by mycorrhizal networks

Arbuscular mycorrhizal fungi (AMF) establish symbiotic associations with a majority of terrestrial plants to form underground common mycorrhizal networks (CMNs) that connect neighbouring plants. Because Nicotiana attenuata plants do not respond to herbivory-elicited volatiles from neighbours, we used this ecological model system to evaluate if CMNs function in interplant transmission of herbivory-elicited responses. A mesocosm system was designed to establish and remove CMNs linking N. attenuata plants to examine the herbivory-elicited metabolic and hormone responses in CMNs-connected "receiver" plants after the elicitation of "donor" plants by wounding (W) treated with Manduca sexta larval oral secretions (OS). AMF colonization increased constitutive jasmonate (JA and JA-Ile) levels in N. attenuata roots but did not affect well-characterized JAs-regulated defensive metabolites in systemic leaves. Interestingly, larger JAs bursts, and higher levels of several amino acids and particular sectors of hydroxygeranyllinalool diterpene glycoside metabolism were elevated in the leaves of W + OS-elicited "receivers" with CMN connections with "donors" that had been W + OS-elicited 6 hr previously. Our results demonstrate that AMF colonization alone does not enhance systemic defence responses but that sectors of systemic responses in leaves can be primed by CMNs, suggesting that CMNs can transmit and even filter defence signalling among connected plants.

Upper thermal limits differ among and within component species in a tritrophic host-parasitoid-hyperparasitoid system

Understanding how climate change affects host-parasite systems and predicting the consequences for ecosystems, economies, and human health has emerged as an important task for science and society. Some basic insight into this complex problem can be gained by comparing the thermal physiology of interacting host and parasite species. In this study, we compared upper thermal tolerance among three component species in a natural host-parasitoid-hyperparasitoid system from Virginia, USA. To assess the ecological relevance of our results, we also examined a record of maximum daily air temperatures collected near the study site in the last 124 years. We found that the caterpillar host Manduca sexta had a critical thermal maximum (CTmax) about 4°C higher than the parasitic wasp, Cotesia congregata, and the hyperparasitic wasp, Conura sp., had a CTmax about 6°C higher than its host, C. congregata. We also found significant differences in CTmax among instars and between parasitized and non-parasitized M. sexta. The highest maximum daily air temperature recorded near the study in the last 124 years was 42°C, which equals the average CTmax of one species (C. congregata) but is several degrees lower than the average CTmax of the other two species (M. sexta, Conura sp.) in this study. Our results combined with other studies suggest that significant differences in thermal performance within and among interacting host and parasite species are common in nature and that climate change may be largely disruptive to these systems with responses that are highly variable and complex.

Innate and Learned Olfactory Responses in a Wild Population of the Egg Parasitoid Trichogramma (Hymenoptera: Trichogrammatidae)

Parasitoid insects face the fundamental problem of finding a suitable host in environments filled with competing stimuli. Many are deft sensors of olfactory cues emitted by other insects and the plants they live on, and use these cues to find hosts. Using olfactory cues from host-plants is effective because plants release volatile organic compounds (VOCs), in response to herbivory or oviposition, that contain information about the presence of hosts. However, plant-produced cues can also be misleading because they are influenced by a variety of stimuli (abiotic variation, infection and multiple sources of induction via herbivory or oviposition). Flexible behavior is one strategy that parasitoids may use to cope with variation in olfactory cues. We examine the innate and learned responses of a natural population of wasp egg parasitoids (Trichogramma deion and Trichogramma sathon) using a series of laboratory and field Y-olfactometer experiments. Wasps typically attack eggs of the hawkmoth Manduca sexta and Manduca quinquemaculata on native Datura wrightii plants in the southwestern United States. We show that Trichogramma wasps responded innately to VOCs produced by D. wrightii and could distinguish plants recently attacked by M. sexta from non-attacked plants. Furthermore, adult Trichogramma wasps were able to learn components of the VOC blend given off by D. wrightii, though they did not learn during exposure as pupae. By further exploring the behavioral ecology of a natural population of Trichogramma, we gain greater insight into how egg parasitoids function in tri-trophic systems.

Transcriptomic response of Manduca sexta immune tissues to parasitization by the bracovirus associated wasp Cotesia congregata

During oviposition, Cotesia congregata parasitoid wasps inject into their host, Manduca sexta, some biological factors such as venom, ovarian fluid and a symbiotic polydnavirus (PDV) named Cotesia congregata bracovirus (CcBV). During parasitism, complex interactions occur between wasp-derived factors and host targets that lead to important modifications in host physiology. In particular, the immune response leading to wasp egg encapsulation is inhibited allowing wasp survival. To date, the regulation of host genes during the interaction had only been studied for a limited number of genes. In this study, we analysed the global impact of parasitism on host gene regulation 24 h post oviposition by high throughput 454 transcriptomic analyses of two tissues known to be involved in the host immune response (hemocytes and fat body). To identify specific effects of parasitism on host transcription at this time point, transcriptomes were obtained from non-treated and parasitized larvae, and also from larvae injected with heat-killed bacteria and double stimulated larvae that were parasitized prior to bacterial challenge. Results showed that, immune challenge by bacteria leads to induction of certain antimicrobial peptide (AMP) genes in M. sexta larvae whether they were parasitized or not prior to bacterial challenge. These results show that at 24 h post oviposition pathways leading to expression of AMP genes are not all inactivated suggesting wasps are in an antiseptic environment. In contrast, at this time point genes involved in phenoloxidase activation and cellular immune responses were globally down-regulated after parasitism in accordance with the observed inhibition of wasp egg encapsulation.

Nancy E. Beckage (1950-2012): pioneer in insect host-parasite interactions

Nancy E. Beckage is widely recognized for her pioneering work in the field of insect host-parasitoid interactions beginning with endocrine influences of the tobacco hornworm, Manduca sexta, host and its parasitoid wasp Apanteles congregatus (now Cotesia congregata) on each other's development. Moreover, her studies show that the polydnavirus carried by the parasitoid wasp not only protects the parasitoid from the host's immune defenses, but also is responsible for some of the developmental effects of parasitism. Nancy was a highly regarded mentor of both undergraduate and graduate students and more widely of women students and colleagues in entomology. Her service both to her particular area and to entomology in general through participation on federal grant review panels and in the governance of the Entomological Society of America, organization of symposia at both national and international meetings, and editorship of several different journal issues and of several books is legendary. She has left behind a lasting legacy of increased understanding of multilevel endocrine and physiological interactions among insects and other organisms and a strong network of interacting scientists and colleagues in her area of entomology.

Indirect routes to reproductive success

By comparing wild-type and transgenic tobacco plants in a natural ecosystem, researchers have confirmed that the indirect defence mechanisms employed by plants to fend off herbivorous insects can increase Darwinian fitness.

Herbivory-induced volatiles function as defenses increasing fitness of the native plant Nicotiana attenuata in nature

From an herbivore's first bite, plants release herbivory-induced plant volatiles (HIPVs) which can attract enemies of herbivores. However, other animals and competing plants can intercept HIPVs for their own use, and it remains unclear whether HIPVs serve as an indirect defense by increasing fitness for the emitting plant. In a 2-year field study, HIPV-emitting N. attenuata plants produced twice as many buds and flowers as HIPV-silenced plants, but only when native Geocoris spp. predators reduced herbivore loads (by 50%) on HIPV-emitters. In concert with HIPVs, plants also employ antidigestive trypsin protease inhibitors (TPIs), but TPI-producing plants were not fitter than TPI-silenced plants. TPIs weakened a specialist herbivore's behavioral evasive responses to simulated Geocoris spp. attack, indicating that TPIs function against specialists by enhancing indirect defense.DOI:http://dx.doi.org/10.7554/eLife.00007.001.

Differential inhibition of BmRelish1-dependent transcription in lepidopteran cells by bracovirus ankyrin-repeat proteins

In the tripartite parasitization system of the lepidopteran host Manduca sexta, the endoparasitoid wasp Cotesia congregata and its endosymbiotic virus, C. congregata Bracovirus (CcBV), the expression of viral proteins is necessary for successful parasitization. Here we have examined the in vitro effects of six members of the ankyrin-repeat protein family (Ank) of CcBV, which are thought to interfere with the host's induced innate immune responses, on the transcriptional activity of a heterologous lepidopteran Rel/NFκB transcription factor, Relish1 of Bombyx mori. Using as transcriptional activator BmRelish1-d2 (R1d2), a constitutively active mutant of the major regulator of the Imd pathway, BmRelish1, in conjunction with a reporter gene controlled by a B. mori antimicrobial peptide gene promoter, we have found that 5 of the 6 examined Anks suppress R1d2-dependent transcriptional activity to various degrees. Immunofluorescence studies have also revealed that while some of the Ank proteins have a rather strict cytoplasmic localization, others are detected both in the cytoplasm and the nucleus of the expressing cells and that colocalization with R1d2 occurs exclusively in the nucleus. Thus, our results suggest that functional and spatial differences among the various CcBV Ank family members may be responsible for the observed differential inhibition of R1d2 activity.

Effects of starvation and parasitism on foregut contraction in larval Manduca sexta

Larvae of Manduca sexta are parasitised by the braconid wasp, Cotesia congregata. In this study we examined whether contraction activity of the semi-isolated foregut was affected by parasitism. Parasitised larvae fed significantly less compared with unparasitised control larvae, therefore starved unparasitised animals were used as controls. Rate and force of foregut contraction in control caterpillars significantly increased with days of starvation. However, only contraction force in foreguts of parasitised larvae increased over time following infection. The presence of food in the foregut of caterpillars starved 7 days suggested that food moved anteriorly from the midgut and that contraction became antiperistaltic, but only normal peristalsis occurred in parasitised caterpillars. Rate and force of gut contractions may be controlled independently and starvation did not truly mimic the effects of the parasitoids. Dissection of caterpillars with emerged wasps indicated that 47% had a single wasp larva wedged between the brain and foregut. Removal of this wasp caused an increased rate of foregut contraction of the caterpillar. Brain removal resulted in an increased rate of foregut contraction only for unparasitised insects. Sectioning of the recurrent nerve temporarily eliminated foregut contraction, but the contraction began again in 250 s in parasitised caterpillars prior to wasp emergence, compared with over 500 s for unparasitised controls and parasitised caterpillars following wasp emergence.

Innate immunity: eggs of Manduca sexta are able to respond to parasitism by Trichogramma evanescens

So far, it was unknown whether immune responses of insect eggs are inducible or suppressed by parasitism. We investigated whether transcription of immune related genes in eggs of Manduca sexta changed in response to parasitism by Trichogramma evanescens. First, using DDRT-PCR, several cDNA elements known to represent immune related M. sexta genes inducible by bacterial challenge were isolated from eggs. In addition, two novel cDNAs were found: (a) immulectin-V (IML-V) suggested to be involved in recognition of foreign bodies, and (b) a new like-moricin protein with possible antimicrobial effects (L-Mor). Quantitative real time RT-PCR analyses revealed enhanced transcription in parasitized eggs compared to unparasitized ones for IML-V, prophenoloxidase (ProPO), prophenoloxidase activating protease I (PAP I), and proparalytic peptide (ProPP). No significant differences between parasitized and unparasitized eggs were detected for sequences encoding the antimicrobial peptides L-Mor, leureptin Leu, and attacin II Att II. Transcript levels of other antibacterial peptides were suppressed after parasitization for 3d (cecropin 6, Cec 6) and 2d (gloverin, Glov). While nearly 100% of the Manduca eggs contained Trichogramma specimens 1d after exposure to parasitoids, only 64% of the host eggs harbored parasitoid larvae 4d after parasitization. Our data demonstrate that the immune system of Manduca eggs shows differentiated responses to parasitization and suggest that insect eggs can defend against parasitization.

Nicotine moderates the effects of macronutrient balance on nutrient intake by parasitized Manduca sexta L

Effects of dietary nicotine and macronutrient ratio on M. sexta larvae were examined. Larvae were fed a carbohydrate-biased, protein-biased or diet having equal amounts of casein and sucrose, with and without nicotine. Without nicotine, larvae displayed compensatory feeding on the low protein diet, but despite consuming more, grew least on this diet. Nicotine at 0.5% had no effect on nutrient consumption. Nicotine at 1.0 and 2.0% reduced overall consumption and thereby also reduced nicotine consumption. Larvae parasitized by C. congregata displayed reduced nutrient intake and growth on all diets. Parasitized larvae responded to 1% nicotine similarly to unparasitized larvae. At 0.5% nicotine, they displayed reduced consumption on all diets, possibly due to altered chemoreceptor sensitivity to nicotine. When offered a choice of two diets having different macronutrient ratios, one with and the other without 0.1% nicotine, all larvae preferred the diet lacking nicotine and failed to regulate nutrient intake such that the nutrient intake target, a ratio of nutrients supporting optimal growth, was achieved. Parasitized larvae consumed less nicotine on a fresh weight basis than unparasitized insects, suggesting that the feeding response of parasitized larvae to nicotine minimizes the exposure of nicotine to developing parasites.

Increased melanizing activity in Anopheles gambiae does not affect development of Plasmodium falciparum

Serpins are central to the modulation of various innate immune responses in insects and are suspected to influence the outcome of malaria parasite infection in mosquito vectors. Three Anopheles gambiae serpins (SRPN1, -2, and -3) were tested for their ability to inhibit the prophenoloxidase cascade, a key regulatory process in the melanization response. Recombinant SRPN1 and -2 can bind and inhibit a heterologous phenoloxidase-activating protease and inhibit phenoloxidase activation in vitro. Using a reverse genetics approach, we studied the effect of SRPN2 on melanization in An. gambiae adult females in vivo. Depletion of SRPN2 from the mosquito hemolymph increases melanin deposition on foreign surfaces such as negatively charged Sephadex beads. As reported, the knockdown of SRPN2 adversely affects the ability of the rodent malaria parasite Plasmodium berghei to invade the midgut epithelium and develop into oocysts. Importantly, we tested whether the absence of SRPN2 from the hemolymph influences Plasmodium falciparum development. RNAi silencing of SRPN2 in an An. gambiae strain originally established from local populations in Yaoundé, Cameroon, did not influence the development of autochthonous field isolates of P. falciparum. This study suggests immune evasion strategies of the human malaria parasite and emphasizes the need to study mosquito innate immune responses toward the pathogens they transmit in natural vector-parasite combinations.

Evaluation of a commercially available beneficial insect habitat for management of lepidoptera pests

A field study was conducted in 2003 and 2004 at the Center for Environmental Farming Systems in Goldsboro, NC, to evaluate the effectiveness of a commercially available beneficial insect habitat in decreasing pest caterpillar populations in organically managed tomato, Lycopersicon esculentum Mill., plots. Six pairs of tomato plots were established and a commercial beneficial insect habitat seed mix (Peaceful Valley's Good Bug Blend) transplanted around the perimeter of treatment plots, whereas a brown-top millet, Brachiaria ramose (L.) Stapf., border was planted around control plots. Egg predation, egg parasitism by trichogrammatid wasps, and larval parasitism by braconid wasps was monitored throughout the growing season to determine whether habitat increased their activity. In both years of this study, the density of Helicoverpa zea (Boddie) and Manduca spp. eggs was not significantly different between treatment and control plots. Although parasitism was the most important component of egg mortality (19-49%), parasitism was not significantly different between habitat types. Identifiable predation was a minor component (3-9%) of egg fate; it is possible that unidentified predation may be part of the approximately 35-52% of eggs that met unknown fates. Larval parasitism levels ranged from approximately 10 to 90% but was not significantly influenced by the presence of beneficial insect habitat in either year of the study. These results demonstrate that natural enemy activity in organic tomatoes was not amplified, and pest populations were not reduced by the presence of a commercially available beneficial insect habitat.

Analysis of the PixA inclusion body protein of Xenorhabdus nematophila

The symbiotic pathogenic bacterium Xenorhabdus nematophila produces two distinct intracellular inclusion bodies. The pixA gene, which encodes the 185-residue methionine-rich PixA inclusion body protein, was analyzed in the present study. The pixA gene was optimally expressed under stationary-phase conditions but its expression did not require RpoS. Analysis of a pixA mutant strain showed that PixA was not required for virulence towards the insect host or for colonization of or survival within the nematode host, and was not essential for nematode reproduction. The pixA gene was not present in the genome of Xenorhabdus bovienii, which also produces proteinaceous inclusions, indicating that PixA is specifically produced in X. nematophila.

Host refractoriness of the tobacco hornworm, Manduca sexta, to the braconid endoparasitoid Cotesia flavipes

Cotesia flavipes (Hymenoptera:Braconidae) is a gregarious endoparasitoid of several pyralid stemborer larvae of economic significance including the sugarcane borer, Diatraea saccharalis. In this study, the ability of this parasitoid to develop in a sphingid host, Manduca sexta, was tested. First, second, third, fourth, and even pharate fifth instar host tobacco hornworm larvae were readily parasitized by the female C. flavipes parasitoids but no wasp larvae hatched from the eggs in this refractory host. Instead, the parasitoid eggs were invariably encapsulated by the host's hemocytes and, ultimately, no parasitoids emerged from tobacco hornworm hosts. The first stages of encapsulation were evident at 2 h post-parasitization of the host M. sexta larvae, when the beginning stages of capsule formation were seen. The developmental fate of the host larvae with encapsulated parasitoids was variable. Most succumbed as abnormally small fifth instars or as post-wandering prepupal animals, while a few developed normally to the pupal stage. Dissection of all the larvae or pupae with encapsulated wasp eggs showed evidence of hemocytic encapsulation and melanization of the C. flavipes eggs. This report describes the association between C. flavipes and M. sexta, which appears to be an excellent model system for studying the physiological processes accompanying wasp egg encapsulation that result in death of the host as well as the parasitoid. Since the parasitoid egg never hatches, the system offers an excellent opportunity to identify and study the effects of parasitoid-injected polydnavirus and venom on host physiology.

Parasitic suppression of feeding in the tobacco hornworm, Manduca sexta: parallels with feeding depression after an immune challenge

The parasitic wasp, Cotesia congregata, suppresses feeding in its host Manduca sexta. Feeding suppression in the host coincides with the emergence of the wasps through the host's cuticle. During wasp emergence, host hemocyte number declined, suggesting that the host mounts a wound/immune response against the exiting parasitoids and/or resulting tissue damage. Eliciting a different type of immune response by injecting heat-killed Serratia marcescens also resulted in a decline in feeding and a reduction in hemocyte number. Both the emerging wasps and the bacteria induced an increase in hemolymph octopamine concentration and a decrease in foregut peristalsis in M. sexta. The emerging parasitoids produced the largest changes. The source of the additional octopamine appeared to be the host in both cases. S. marcescens was found to contain no detectable amounts of octopamine. The parasitoids had insufficient octopamine to account for the amount found in host hemolymph and they did not secrete octopamine in vitro. One cause for the high concentration of octopamine in parasitized M. sexta was that octopamine was removed from the hemolymph approximately 23 times more slowly after the wasps emerged than prior to wasp emergence. The striking similarity between the effects of parasitoids and bacteria on M. sexta feeding, hemocyte number, hemolymph octopamine concentration, and foregut peristalsis supports the possibility that the immune/wound reaction induced by the emerging wasps could play a role in the suppression of host feeding. These results also support the hypothesis that M. sexta exhibit an immune-activated anorexia.

Feeding behaviour and nutrient selection in an insect Manduca sexta L. and alterations induced by parasitism

Manduca sexta L. larvae exhibit broad food acceptance with regard to nutrient content during the first 3 days of the last stadium. Larvae fed diets with a constant combined level of casein and sucrose, but variable ratios, display a linear relationship between protein and carbohydrate intake. Larvae grow best on a diet with equal nutrients, but will consume an excess of one nutrient in order to obtain an adequate amount of the other, as nutrient ratio shifts. Parasitized larvae feed similarly, but the nutrient ratio does not affect growth. Unparasitized larvae regulate intake of protein and carbohydrate when offered choices of protein-biased and carbohydrate-biased diets having combined nutrient levels of 120 g/l, but with variable ratios. Larvae normally consume equal amounts of nutrients, regardless of ratio, and grow similarly. As combined nutrient level is reduced in one diet, larvae abandon regulation and feed randomly. Parasitized larvae offered choice diets with 120 g/l combined nutrients do not regulate nutrient intake. Consumption of nutrients varies widely, but growth is unaffected. Larvae offered choices of diets having equal amounts of casein and sucrose but variable fat (corn oil), fail to regulate fat intake, although both unparasitized and parasitized larvae prefer a diet containing higher fat.

A virus essential for insect host-parasite interactions encodes cystatins

Cotesia congregata is a parasitoid wasp that injects its eggs in the host caterpillar Manduca sexta. In this host-parasite interaction, successful parasitism is ensured by a third partner: a bracovirus. The relationship between parasitic wasps and bracoviruses constitutes one of the few known mutualisms between viruses and eukaryotes. The C. congregata bracovirus (CcBV) is injected at the same time as the wasp eggs in the host hemolymph. Expression of viral genes alters the caterpillar's immune defense responses and developmental program, resulting in the creation of a favorable environment for the survival and emergence of adult parasitoid wasps. Here, we describe the characterization of a CcBV multigene family which is highly expressed during parasitism and which encodes three proteins with homology to members of the cystatin superfamily. Cystatins are tightly binding, reversible inhibitors of cysteine proteases. Other cysteine protease inhibitors have been described for lepidopteran viruses; however, this is the first description of the presence of cystatins in a viral genome. The expression and purification of a recombinant form of one of the CcBV cystatins, cystatin 1, revealed that this viral cystatin is functional having potent inhibitory activity towards the cysteine proteases papain, human cathepsins L and B and Sarcophaga cathepsin B in assays in vitro. CcBV cystatins are, therefore, likely to play a role in host caterpillar physiological deregulation by inhibiting host target proteases in the course of the host-parasite interaction.

Parasitization of Manduca sexta larvae by the parasitoid wasp Cotesia congregata induces an impaired host immune response

During oviposition, the parasitoid wasp Cotesia congregata injects polydnavirus, venom, and parasitoid eggs into larvae of its lepidopteran host, the tobacco hornworm, Manduca sexta. Polydnaviruses (PDVs) suppress the immune system of the host and allow the juvenile parasitoids to develop without being encapsulated by host hemocytes mobilized by the immune system. Previous work identified a gene in the Cotesia rubecula PDV (CrV1) that is responsible for depolymerization of actin in hemocytes of the host Pieris rapae during a narrow temporal window from 4 to 8h post-parasitization. Its expression appears temporally correlated with hemocyte dysfunction. After this time, the hemocytes recover, and encapsulation is then inhibited by other mechanism(s). In contrast, in parasitized tobacco hornworm larvae this type of inactivation in hemocytes of parasitized M. sexta larvae leads to irreversible cellular disruption. We have characterized the temporal pattern of expression of the CrV1-homolog from the C. congregata PDV in host fat body and hemocytes using Northern blots, and localized the protein in host hemocytes with polyclonal antibodies to CrV1 protein produced in P. rapae in response to expression of the CrV1 protein. Host hemocytes stained with FITC-labeled phalloidin, which binds to filamentous actin, were used to observe hemocyte disruption in parasitized and virus-injected hosts and a comparison was made to hemocytes of nonparasitized control larvae. At 24h post-parasitization host hemocytes were significantly altered compared to those of nonparasitized larvae. Hemocytes from newly parasitized hosts displayed blebbing, inhibition of spreading and adhesion, and overall cell disruption. A CrV1-homolog gene product was localized in host hemocytes using polyclonal CrV1 antibodies, suggesting that CrV1-like gene products of C. congregata's bracovirus are responsible for the impaired immune response of the host.

Host nutrition determines blood nutrient composition and mediates parasite developmental success: Manduca sexta L. parasitized by Cotesia congregata (Say)

This investigation examined the influence of dietary protein and carbohydrate balance in a chemically defined artificial diet for Manduca sexta larvae on development of the gregarious parasite Cotesia congregata. Normal unparasitized larvae and larvae superparasitized in the fourth stadium were reared to the end of the fifth stadium on six diets, each having the same total amount of casein and sucrose but with different ratios ranging from high protein/no carbohydrate through to low protein/high carbohydrate. Levels of blood protein nitrogen and trehalose, nutrients supporting growth and development of C. congregata, varied with diet and were influenced by parasitism. Different levels of blood metabolites reflected differences in diet consumption, and the relationships between protein nitrogen and trehalose were very similar to those for protein and carbohydrate intake by parasitized and normal larvae on various diets. Dietary nutrient ratio had a significant effect on parasite burden, the numbers of parasites developing in individual host larvae and on parasite biomass. Parasites included individuals that developed and eventually emerged as second instar larvae, moulted to third instars and pupated. Many apparently mature second instar parasites, however, failed to emerge. The proportion of non-emerging individuals varied with diet, and in some cases, parasites failing to emerge were greater in number and total biomass than those that did emerge to complete development. On most diets, the mass of individual parasites was similar regardless of dietary nutrient ratio. Three dimensional models developed to demonstrate the relationships between blood protein nitrogen and trehalose levels and parasite burden and biomass established that the levels of both metabolites are important for supporting growth and development of emerged and non-emerged parasites. In the case of emerged parasites, however, the relationships are linear, and a quadratic function best describes the relationships with non-emerged parasites. Blood metabolite levels supporting the greatest parasite burden and biomass of emerged and non-emerged parasites occupy a region of two dimensional space corresponding to approximately 60-200 mg per insect of protein nitrogen and 60-100 mg per insect of trehalose. Despite the differences in the response of emerged and non-emerged parasites to host nutrition, the present results indicate that host nutrition is not the critical factor determining parasite emergence. The significance of these findings to the biology of C. congregata is discussed.

Nutrition interacts with parasitism to influence growth and physiology of the insectManduca sextaL

The influence and interaction of dietary protein:carbohydrate balance and parasitism by Cotesia congregata on nutrient intake and growth were examined over the last two larval stadia of Manduca sexta. Effects of nutritional status on host blood metabolite concentrations were also determined. Six fat-free chemically defined diets were tested, each having the same total level of casein and sucrose, but with casein to sucrose ratios varying from low protein/high carbohydrate to equal levels of both nutrients through to high protein/no carbohydrate. Nutrient ratio and parasitism each affected nutrient consumption and growth. Feeding responses differed between normal and parasitized larvae, as illustrated by nutrient arrays,two-dimensional plots of protein and carbohydrate consumption on diets having different nutrient ratios. Normal larvae consumed more nutrients and took longer to develop as dietary nutrient ratio was displaced from equal levels of both nutrients. Except on the diet having the same amount of protein and carbohydrate, parasitized larvae consumed less nutrients than normal larvae,although on all diets parasitized larvae took longer to develop. When the contribution of parasite biomass was excluded, parasitized larvae showed lower mass gain than normal larvae on all diets. Total mass gain by normal and parasitized larvae with parasite biomass included, however, was similar on diets having intermediate nutrient ratios. Differences in mass gain between diets relative to nutrient consumption were evident from multi-dimensional representations of mass gain with protein and carbohydrate consumption. Three-dimensional plots and contour maps of normal and parasitized larvae were different. When differences in nutrient consumption between diets were taken into account, protein consumption had a greater effect on growth than carbohydrate consumption and normal larvae generally displayed greater mass gain than parasitized larvae on the same diets. Utilization efficiency, the efficiency of conversion of ingested food to body mass, was, therefore,generally reduced in parasitized insects. Concentrations of blood protein,total free amino acids and trehalose were each influenced by dietary nutrient ratio and parasitism. Concentrations of protein and free amino acids generally increased and trehalose concentration decreased as dietary protein increased and carbohydrate decreased. The opposite was the case as dietary carbohydrate increased and protein decreased. Dietary nutrient ratio, however, affected normal and parasitized larvae differently. Parasitized larvae had higher overall trehalose concentrations while normal larvae had higher protein and total free amino acid concentrations. When differences in nutrient consumption between diets were accounted for, protein consumption had a greater effect on blood protein and free amino acid concentrations than did dietary nutrient ratio or parasitism. Protein consumption, however, did not affect trehalose concentration. Carbohydrate consumption had no effect on the concentration of any of the metabolites after differences in nutrient consumption were taken into account. Effects of nutrient consumption on trehalose concentration,therefore, were due to dietary nutrient ratio and parasitism. The potential relevance of the above findings to the biology of parasitized M. sexta larvae is discussed.

Genome sequence of a polydnavirus: insights into symbiotic virus evolution

Little is known of the fate of viruses involved in long-term obligatory associations with eukaryotes. For example, many species of parasitoid wasps have symbiotic viruses to manipulate host defenses and to allow development of parasitoid larvae. The complete nucleotide sequence of the DNA enclosed in the virus particles injected by a parasitoid wasp revealed a complex organization, resembling a eukaryote genomic region more than a viral genome. Although endocellular symbiont genomes have undergone a dramatic loss of genes, the evolution of symbiotic viruses appears to be characterized by extensive duplication of virulence genes coding for truncated versions of cellular proteins.

Immulectin-2, a pattern recognition receptor that stimulates hemocyte encapsulation and melanization in the tobacco hornworm, Manduca sexta

In insects, encapsulation followed by melanization is a major defense mechanism against metazoan parasites. However, insects must recognize and differentiate nonself before they mount an immune response. Recognition of pathogens in insects is accomplished by a set of pattern recognition receptors (PRRs). Binding of PRRs to pathogens is linked to a variety of immune responses including phagocytosis, nodule formation, encapsulation, and prophenoloxidase activation. So far, little is known about how recognition of pathogens by PRRs triggers different immune responses. In this article, we report that immulectin-2, a C-type lectin, enhances encapsulation and melanization processes in the tobacco hornworm, Manduca sexta. Coating of agarose beads with recombinant carboxyl-terminal carbohydrate-recognition domain (CRD2-II) of immulectin-2 enhanced encapsulation of the beads in vitro by hemocytes and melanization of the beads in vivo in M. sexta larvae. Recombinant CRD2-II also directly bound to granular cells and oenocytoids, but not to plasmatocytes or spherule cells. Immulectin-2 in hemolymph of M. sexta larvae bound to the surface of a nematode, Caenorhabditis elegans, and recombinant CRD2-II directly bound to C. elegans and a human filarial nematode, Brugia malayi. Binding of CRD2-II to C. elegans enhanced melanization of the nematode in vivo. Our results suggest that binding of immulectin-2 to the surface of parasites can trigger encapsulation and melanization responses in M. sexta.

Herbivore-induced plant vaccination. Part I. The orchestration of plant defenses in nature and their fitness consequences in the wild tobacco Nicotiana attenuata

A plant's responses to attack from particular pathogens and herbivores may result in resistance to subsequent attack from the same species, but may also affect different species. Such a cross-resistance, called immunization or vaccination, can benefit the plant, if the fitness consequences of attack from the initial attacker are less than those from subsequent attackers. Here, we report an example of naturally occurring vaccination of the native tobacco plant, Nicotiana attenuata, against Manduca hornworms by prior attack from the mirid bug, Tupiocoris notatus (Dicyphus minimus), which results from the elicitation of two categories of induced plant responses. First, attack from both herbivore species causes the plants in nature to release predator-attracting volatile organic compounds (VOCs), and the attracted generalist predator, Geocoris pallens, preferentially attacks the less mobile hornworm larvae. Second, attack from both mirids and hornworms increases the accumulation of secondary metabolites and proteinase inhibitors (PIs) in the leaf tissue, which is correlated with the slow growth of Manduca larvae. Mirid damage does not significantly reduce the fitness of the plant in nature, whereas attack from the hornworm reduces lifetime seed production. Consequently, plants that are attacked by mirids realize a significant fitness advantage in environments with both herbivores. The combination of growth-slowing direct defenses and predator-attracting indirect defenses results in greater hornworm mortality on mirid-attacked plants and provides the mechanism of the vaccination phenomenon.

Parasitoid-host endocrine relations: self-reliance or co-optation?

High titers of juvenile hormone (JH) maintain developmental arrest in Manduca sexta larvae parasitized by Cotesia congregata. Parasitized hosts exhibit up to 9.5 times greater amounts of total hemolymph JH (from 0.6+/-0.09 to 2.51+/-0.43ng/ml) compared to non-parasitized controls. Elevated titers are observed throughout the fifth instar, even beyond egression of the parasitoids on day 5. GC-MS analysis revealed that in hemolymph of unparasitized control larvae, JH I is the major homolog and levels of JH III are negligible; in parasitized individuals the amounts of JH I, II, and III rise, and JH III predominates. Neck ligation ensured separation of M. sexta's corpora allata from the posterior section, which contained most of the parasitoids in the infected insects. When the posterior region was sampled, JHs were not detected in the non-parasitzed larvae, but in those parasitized, JH III was found (1.98+/-0.29ng/ml, 24 h post-ligation). JH III was the only homolog produced and secreted by the parasitoid in in vitro culture. This is the first report stating that a parasitoid secretes JH III and may contribute, at least in part, to the circulating titer in the host hemocoel, concurrently promoting host production of JH I and II.

The glucogenic response of a parasitized insect Manduca sexta L. is partially mediated by differential nutrient intake

Induction of gluconeogenesis is accelerated in larvae of the insect Manduca sexta L. parasitized by Cotesia congregata (Say), maintaining the concentration of the blood sugar trehalose, an important nutrient for parasite development. Investigation has demonstrated that when host larvae are offered a choice of diets with varying levels of sucrose and casein, parasitized insects consume a different balance of these nutrients, principally due to a decrease in protein consumption. The result is metabolic homeostasis, with normal unparasitized and parasitized larvae exhibiting similar levels of gluconeogenesis and blood sugar level. In the present study, normal unparasitized and parasitized larvae were maintained on individual chemically defined diets having the balance of protein and carbohydrate consumed by each when offered a dietary choice. Total dietary nutrient, the sum of carbohydrate and protein, was provided at six levels, composed of three pairs of diets. Each diet pair consisting of diets having equivalent overall nutrient ratios of 2:1 and 1:1 casein/sucrose. Host growth and diet consumption were significantly affected by dietary nutrient level and the magnitude of these effects was influenced by parasitism. Due to the effects of dietary nutrient level on diet consumption, none of the unparasitized and parasitized larvae within any of the three diet pairs consumed protein and carbohydrate at the levels predicted by the earlier choice experiments. Among insects on all of the diets, however, two groups of unparasitized and parasitized larvae consumed the expected levels of protein and carbohydrate. In each case, gluconeogenesis, as measured by 13C nuclear magnetic resonance spectroscopy (NMR) analysis of pyruvate cycling and trehalose synthesis from [2-13C]pyruvate, was evident in unparasitized and parasitized insects, confirming the conclusions of the earlier experiments. Generally, all larvae that consumed less than approximately 250 mg of sucrose over the 3-day feeding period, were gluconeogenic, regardless of diet. Differential carbohydrate consumption, therefore, was an important factor in inducing gluconeogenesis in both unparasitized and parasitized insects. The selective 13C enrichment in trehalose displayed by non-gluconeogenic larvae on some diets demonstrated trehalose formation from [2]pyruvate. The absence of net carbohydrate synthesis in these insects was likely due to an elevation of glycolysis. There was no significant effect of diet consumption or parasitism on blood trehalose level. Parasitized larvae displayed higher levels of gluconeogenesis than did unparasitized insects, a finding consistent with the conclusion that blood sugar is rapidly sequestered by developing parasites. The parasite burden, the total number of parasites developing within host larvae, as well as the number of parasites emerging from host larvae to complete development, was significantly less at the lowest dietary nutrient level, but was otherwise similar at all dietary nutrient levels. Moreover, the number of parasites that emerged increased with increasing diet consumption as reflected by host final weight.

Restriction of nutrient intake results in the increase of a specific Manduca sexta allatotropin (Manse-AT) mRNA in the larval nerve cord

The Manduca allatotropin (Manse-AT) gene is expressed as three mRNAs that differ from each other by alternative splicing. The level of one of these mRNAs (RNA-3) is specifically increased in the nerve cord of last instar larvae that were starved, parasitized, or fed the ecdysteroid agonist RH-5992. Each of these treatments results in reduction of feeding and increased levels of juvenile hormone (JH). The normal decline in JH biosynthesis by the corpora allata does not occur in starved or RH-5992-fed larvae. The increase in RNA-3 levels has the capacity to increase the production of Manse-AT and two related peptides that may be part of the complex response of larvae to nutrient deprivation.

Altered dietary nutrient intake maintains metabolic homeostasis in parasitized larvae of the insect Manduca sexta L

Manduca sexta larvae exhibited altered food selection over a 2- or 3-day feeding period when parasitized by Cotesia congregata, and offered a choice of two chemically defined diets, one containing casein without sucrose and a second with sucrose but no casein. While normal larvae consumed the diets in a ratio of approximately 2:1 protein:carbohydrate (w/w), parasitized insects consumed a ratio of approximately 1:1. The altered nutrient ratio consumed by parasitized insects was principally due to a decrease in consumption of the protein diet, and was only partially explained by their lower growth. Conditioning larvae for 1 day to either one of the choice diets had little effect on subsequent dietary intake over a 2-day feeding period. Conditioned larvae, regardless of parasitism, initially fed on the opposite diet immediately after conditioning. Although this suggests that the altered nutrient intake displayed by parasitized insects was not due to any failure in their capacity for dietary selection, these results do not definitively demonstrate an altered nutrient intake target by parasitized larvae. Rather, parasitism may compromise dietary selection, resulting in random feeding. When parasitized larvae were maintained on several isocaloric diets with a varying ratio of casein and sucrose, those larvae feeding on the diet with a ratio of 1:1 of these nutrients supported the largest parasite population. Previous investigation of larvae maintained on a single artificial diet established that parasitized insects display an aberrant induction of gluconeogenesis, so that haemolymph trehalose is maintained at a level equivalent to that of normal insects. In contrast, the present results demonstrated that parasitized larvae offered a choice of diets, and feeding at the altered nutrient ratio above, maintain haemolymph sugar but have the same level of gluconeogenesis as normal larvae given the same dietary choice. These investigations suggest that altered food selection by parasitized M. sexta larvae maintains metabolic homeostasis and, moreover, may be adaptive for C. congregata, potentially maximizing the number of parasites developing in a single host larva.

Parasitism enhances the induction of glucogenesis by the insect, Manduca sexta L

Metabolic alterations that accompany parasitism of invertebrate animals can play an important role in parasite development. Employing 13C NMR, this study examined pyruvate cycling from (2-(13)C)pyruvate in the lepidopteran insect Manduca sexta, and the effects of parasitism by the hymenopteran Cotesia congregata on the gluconeogenic formation of trehalose, the haemolymph or blood sugar of insects. Larvae were maintained on a semi-synthetic sucrose-free diet, or on the same diet with sucrose at 8.5 g/l. Pyruvate cycling was evident from the 13C enrichment in C3 of alanine, derived following carboxylation to oxaloacetate, and was similar in parasitized and normal insects regardless of diet. Trehalose was formed following de novo synthesis of glucose, and net synthesis was estimated from the 13C distribution in trehalose and alanine. The 13C-enrichment ratio [2trehalose C6/alanine C3] is an indicator of the level of gluconeogenesis relative to glycolysis, both enrichments were derived from (2-(13)C)pyruvate in the same manner. The ratio was greater than unity in all insects, regardless of diet, but was significantly greater in parasitized larvae, demonstrating an enhanced level of gluconeogenesis. This was confirmed by analysis of the 13C distribution in trehalose and glutamine derived from (3-(13)C)alanine. Despite enhanced de novo trehalose formation in parasitized insects, the haemolymph sugar level was similar to that of normal larvae. Because haemolymph trehalose regulates dietary carbohydrate intake, but not gluconeogenesis, the results suggest that accelerated induction of gluconeogenesis is an adaptive response to parasitism that provides increased carbohydrate for parasite growth and simultaneously maintains nutrient intake.

Octopamine mimics the effects of parasitism on the foregut of the tobacco hornworm Manduca sexta

The parasitic braconid wasp Cotesia congregata lays its eggs inside the body of the larval stage of its host, the moth Manduca sexta. The Cotesia congregata larvae develop within the hemocoel of their host until their third instar, when they emerge and spin cocoons and pupate on the outer surface of the caterpillar. From this time until their death approximately 2 weeks later, the Manduca sexta larvae show striking behavioral changes that include dramatic declines in spontaneous activity and in the time spent feeding. Coincident with these behavioral changes, it is known that octopamine titers in the hemolymph of the host become elevated by approximately 6.5-fold. Octopamine is an important modulator of neural function and behavior in insects, so we examined hosts for neural correlates to the behavioral changes that occur at parasite emergence. We found that, in addition to the changes reported earlier, after parasite emergence (post-emergence), Manduca sexta larvae also showed marked deficits in their ability to ingest food because of a disruption in the function of the frontal ganglion that results in a significant slowing or the absence of peristaltic activity in the foregut. This effect could be produced in unparasitized fifth-instar larvae by application of blood from post-emergence parasitized larvae or of 10(−6)mol l(−1)d,l-octopamine (approximately the level in the hemolymph of post-emergence larvae). In contrast, blood from parasitized larvae before their parasites emerge or from unparasitized fifth-instar larvae typically had no effect on foregut activity. The effects of either post-emergence parasitized blood or 10(−6)mol l(−1) octopamine could be blocked by the octopamine antagonists phentolamine (at 10(−5)mol l(−1)) or mianserin (at 10(−7)mol l(−1)).

Inactivation of a novel gene produces a phenotypic variant cell and affects the symbiotic behavior of Xenorhabdus nematophilus

Xenorhabdus nematophilus is an insect pathogen that lives in a symbiotic association with a specific entomopathogenic nematode. During prolonged culturing, variant cells arise that are deficient in numerous properties. To understand the genetic mechanism underlying variant cell formation, a transposon mutagenesis approach was taken. Three phenotypically similar variant strains of X. nematophilus, each of which contained a single transposon insertion, were isolated. The insertions occurred at different locations in the chromosome. The variant strain, ANV2, was further characterized. It was deficient in several properties, including the ability to produce antibiotics and the stationary-phase-induced outer membrane protein, OpnB. Unlike wild-type cells, ANV2 produced lecithinase. The emergence of ANV2 from the nematode host was delayed relative to the emergence of the parental strain. The transposon in ANV2 had inserted in a gene designated var1, which encodes a novel protein composed of 121 amino acid residues. Complementation analysis confirmed that the pleiotropic phenotype of the ANV2 strain was produced by inactivation of var1. Other variant strains were not complemented by var1. These results indicate that inactivation of a single gene was sufficient to promote variant cell formation in X. nematophilus and that disruption of genetic loci other than var1 can result in the same pleiotropic phenotype.

Blood sugar formation due to abnormally elevated gluconeogenesis: aberrant regulation in a parasitized insect, Manduca sexta Linnaeus

Alterations of carbohydrate metabolism associated with parasitism were examined in an insect, Manduca sexta L. In insect larvae maintained on a low carbohydrate diet gluconeogenesis from [3-13C]alanine was established from the fractional 13C enrichment in trehalose, a disaccharide of glucose and the blood sugar of insects and other invertebrates. After transamination of the isotopically substituted substrate to [3-13C]pyruvate, the latter was carboxylated to oxaloacetate ultimately leading to de novo glucose synthesis and trehalose formation. Trehalose was selectively enriched with 13C at C1 and C6 followed by C2 and C5. 13C enrichment of blood sugar in insects parasitized by Cotesia congregata (Say) was significantly greater than was observed in normal animals. The relative contributions of pyruvate carboxylation and decarboxylation to trehalose labeling were determined from the 13C distribution in glutamine, synthesized as a byproduct of the tricarboxylic acid cycle. The relative contribution of carboxylation was significantly greater in parasitized larvae than in normal insects providing additional evidence of elevated gluconeogenesis due to parasitism. Despite the increased gluconeogenesis in parasitized insects the level of blood sugar was the same in all animals. Because de novo glucose synthesis does not normally maintain blood sugar level in insects maintained under these dietary conditions the findings suggest an aberrant regulation over gluconeogenesis. The 13C labeling in trehalose was nearly symmetric in all insects but the mean C1/C6 13C ratio was higher in parasitized animals suggesting a lower activity of the pentose phosphate pathway that brings about a redistribution of 13C in trehalose following de novo glucose synthesis. Additional studies with insects maintained on a high carbohydrate diet and administered [1,2-13C2]glucose confirmed a decreased level of pentose cycling during parasitism consistent with a lower level of lipogenesis. It is suggested, however, that the pentose pathway may facilitate the synthesis of trehalose from dietary carbohydrate by directing hexose phosphate cycled through the pathway to the production of energy.

Identification of neuropeptides in the midgut of parasitized insects: FLRFamides as candidate paracrines

Parasitism of Manduca sexta (Lepidoptera: Sphingidae) larvae by the braconid wasp Cotesia congregata (Hymenoptera: Braconidae) leads to accumulation of peptides in host neurons and neurosecretory cells of the central nervous system (CNS) and neurons and endocrine/paracrine cells of the midgut. This accumulation has now facilitated the characterization of two new members of the FLRFamide family from midguts of parasitized larvae. The peptides, given the names F24 and F39, are 24 and 39 amino acids in length with the sequences VRDYPQLLDSGMKRQDVVHSFLRFamide and YAEAAGEQVPEYQALVRDYPQLLDSGMKRQDVVHSFLRFamide. The sequence of F24 is identical to the C-terminal 24 amino acids of F39. The C-terminal 10-mer of each is identical to a previously characterized decapeptide neurohormone (F10). This sequence is preceded by a potential processing site. In nonparasitized insects F39 was present at several-fold the amount of F24. In parasitized insects F24 and F39 accumulate in the middle and posterior regions of the midgut, which are enriched in endocrine/paracrine cells reacting with FLRFamide antisera. In the combined brain and subesophageal ganglion F39 was not detected and the amount of F24 never exceeded 2 fmol per Br/SEG. Of the three peptides, only F10 was found in the hemolymph. Thus, F24 and F39 may be intermediates in the biosynthesis of F10 and may themselves be released locally from endocrine/paracrine cells in the midgut epithelium.

Parasitism-induced accumulation of FMRFamide-like peptides in the gut innervation and endocrine cells of Manduca sexta

Manduca sexta larvae that are parasitized by the braconid wasp Cotesia congregata enter a state of developmental arrest following emergence of the wasp larvae from the host. These fifth instar hosts linger for 2 to 3 weeks without resuming feeding, molting, or metamorphosis once the wasps emerge. Immunohistochemical staining with antiserum against FMRFamide revealed dramatic accumulation of FMRFamide-like peptide(s) in the gut nervous and endocrine systems of the developmentally arrested larvae when compared to that observed in unparasitized feeding or starved larvae. Specifically, the number of immunopositive cells and the intensity of staining was enhanced in the neurons of the frontal ganglion, the axons and axon terminals on the midgut surface, and in the gastric endocrine cells. These results were confirmed using ELISA to show that the relative amounts of FMRFamide-like peptides in midgut extracts were highly elevated in the parasitized larvae relative to the fed or starved unparasitized larvae. These data suggest that FMRFamide-like peptides in developmentally arrested larvae are produced in a significantly larger number of gastric endocrine cells, and that the rate of release of the peptides may be suppressed, or the rate of their synthesis may be elevated. Localization of FMRFamide-like peptides in the gastric endocrine cells of C. congregata is also described.

Accumulation of neuropeptides in the cerebral neurosecretory system of Manduca sexta larvae parasitized by the braconid wasp Cotesia congregata

Fifth instar larvae of Manduca sexta that were parasitized by the braconid wasp Cotesia congregata failed to develop after the parasitoid larvae emerged, and these host larvae lingered for 2-3 weeks in a quiescent, nonfeeding state without initiating a larval molt or metamorphosis. This study was focused on the neuroendocrine changes associated with the host's developmental arrest. Immunohistochemical studies suggested that the host brain neurosecretory cells as well as their axon terminals in the corpora cardiaca-corpora allata complex accumulated multiple neuropeptides. The extent of accumulation in cells and axons increased with time, so that hosts examined 7-14 days after the wasps emerged showed the most intense staining with antibodies against prothoracicotropic hormone, bombyxin, allatotropin, allatostatin, diuretic hormone, eclosion hormone, proctolin, and FMRFamide. Increased levels of prothoracicotropic hormone and FMRFamide-like peptides in the brains of parasitized larvae were confirmed using Western blots and enzyme-linked immunosorbent assay (ELISA), respectively. Starvation of the unparasitized larvae induced some accumulation of the neuropeptides; however, the intensity of staining and number of immunopositive cells and axons were in most cases clearly higher in the parasitized larvae. Our results suggest that accumulation of the neuropeptides is associated with developmental arrest of parasitized larvae. Because a similar developmental arrest occurs in a wide range of parasitized insects, our findings may have relevance for many other species. Moreover, these data illustrate the potential value of using parasitized M. sexta larvae as a model for studying the mechanisms governing the rates of neuropeptide expression, processing, packaging, and release, as well as providing a rich source of neuropeptides, thus facilitating their isolation and characterization.

An abundantly expressed hemolymph glycoprotein isolated from newly parasitized Manduca sexta larvae is a polydnavirus gene product

Cotesia congregata polydnavirus (CcPDV) is essential for successful parasitism of Manduca sexta larvae by the braconid wasp C. congregata. CcPDV virions are present in large numbers in the oviducts of C. congregata and injected with eggs into the hemocoel of M. sexta larvae during parasitization. Injection of sucrose density purified virions into nonparasitized larvae causes several of the parasitism-induced alterations in the physiology of host larvae that occur as a result of natural parasitism, including the synthesis of novel hemolymph proteins and abrogation of the host's immune response against the developing parasites. One of these proteins, early-expressed protein 1 (EP1), is a 190-kDa molecule which constitutes up to 5% of the total hemolymph protein by 24 hr following oviposition by the wasp. Using N-terminal sequence data for EP1 to construct primers for use in the polymerase chain reaction, we amplified and cloned a cDNA corresponding to the gene encoding EP1. This cDNA hybridized to DNA of the CcPDV genome, but not to DNA isolated from M. sexta larvae, suggesting that EP1 is a CcPDV gene product. A cDNA clone was isolated from an expression library generated from RNA extracted from newly parasitized M. sexta larvae. Sequence analysis of the cDNA clone revealed the presence of an open reading frame of 819 bp encoding a protein of 30.7 kDa. In vitro transcription/translation of the cDNA clone produced a protein of approximately 31 kDa, which was immunoprecipitated by EP1-specific polyclonal antiserum generated against purified deglycosylated EP1. EP1-like sequences also were amplified from male wasp genomic DNA, suggestive of integration of EP1-like sequences in the genome. This report constitutes the first evidence that a specific protein isolated from a parasitized host insect is a wasp polydnavirus gene product.