Parasitoid Venom Research Articles

Regulation of melanization in aphids by parasitoid wasp venom proteins enhances mummification.

Interactions between parasitic insects and their hosts demonstrate the complexity of evolutionary processes. Specifically, the parasitoid wasp Aphidius ervi manipulates its host, the pea aphid Acyrthosiphon pisum, through strategic venom injection to enhance mummification. This study explores how this venom affects the aphid's immune system, particularly targeting the activity of the phenoloxidase (PO) enzyme. Following the injection of venom from A. ervi, significant changes were observed in the expression of immune-related genes in A. pisum, especially notable expression changes of ApPPOs and a reduction of PO activity. Multi-omics sequencing identified 74 potential venom proteins in the venom gland of A. ervi, including serine protease homolog 1 (AeSPH1) and serine protease inhibitor (AeSPN1), hypothesized to regulate PO activity. The injection of recombinant protein AeSPH1 and AeSPN1 into the A. pisum hemocoel selectively reduced the expression of ApPPO1, without affecting ApPPO2, and effectively suppressed melanization. Moreover, RNAi targeting AeSPH1 significantly reduced the mummification rate in A. pisum population parasitized by A. ervi. Our findings clarify the complex biochemical mechanisms underlying host-wasp interactions and highlight potential avenues for developing targeted biological control strategies. © 2024 Society of Chemical Industry.

The venom of Habrobracon hebetor induces alterations in host metabolism.

The ability of parasitic wasps to manipulate a host's metabolism is under active investigation. Components of venom play a major role in this process. In the present work, we studied the effect of the venom of the ectoparasitic wasp Habrobracon hebetor on the metabolism of the greater wax moth host (Galleria mellonella). We identified and quantified 45 metabolites in the lymph (cell-free hemolymph) of wax moth larvae on the second day after H. hebetor venom injection, using NMR spectroscopy and liquid chromatography coupled with mass spectrometry. These metabolites included 22 amino acids, nine products of lipid metabolism (sugars, amines and alcohols) and four metabolic intermediates related to nitrogenous bases, nucleotides and nucleosides. An analysis of the larvae metabolome suggested that the venom causes suppression of the tricarboxylic acid cycle, an increase in the number of free amino acids in the lymph, an increase in the concentration of trehalose in the lymph simultaneously with a decrease in the amount of glucose, and destructive processes in the fat body tissue. Thus, this parasitoid venom not only immobilizes the prey but also modulates its metabolism, thereby providing optimal conditions for the development of larvae.

Extracting Venom from the Parasitoid Wasp Trichogramma dendrolimi using an Artificial Host.

Parasitoid wasps are a diverse group of hymenopteran insects that serve as invaluable resources for pest biocontrol. To ensure successful parasitism, parasitoid wasps inject venom into their hosts to suppress their hosts' immunity, modulate hosts' development, metabolism, and even behavior. With over 600,000 estimated species, the diversity of parasitoid wasps surpasses that of other venomous animals, such as snakes, cone snails, and spiders. Parasitoid wasp venom is an underexplored source of bioactive molecules with potential applications in pest control and medicine. However, collecting parasitoid venom is challenging due to the inability to use direct or electrical stimulation and the difficulty in dissection because of their small size. Trichogramma is a genus of tiny (~0.5 mm) egg parasitoid wasps that are widely used for the biological control of lepidopteran pests in both agriculture and forests. Here, we report a method for extracting venom from T. dendrolimi using artificial hosts. These artificial hosts are created with polyethylene film and amino acid solutions and then inoculated with Trichogramma wasps for parasitism. The venom was subsequently collected and concentrated. This method enables the extraction of large amounts of Trichogramma venom while avoiding contamination from other tissues caused by dissection, a common issue in venom reservoir dissection protocols. This innovative approach facilitates the study of Trichogramma venom, paving the way for new research and potential applications.

Comparative Analysis of the Venom Proteins from Two Eupelmid Egg Parasitoids Anastatus japonicus and Mesocomys trabalae.

Parasitic wasps are abundant and diverse Hymenoptera insects that lay their eggs inside or on the external surface of the host and inject venom into the host to create a more favorable environment for the larvae to survive and regulate the host's immunity, metabolism, and development. But research on the composition of egg parasitoid venom is very limited. In this study, we used a combination of transcriptomic and proteomic approaches to identify the protein fractions of the venom in both eupelmid egg parasitoids, Anastatus japonicus and Mesocomys trabalae. We identified 3422 up-regulated venom gland genes (UVGs) in M. trabalae and 3709 in A. japonicus and analyzed their functions comparatively. By proteome sequencing, we identified 956 potential venom proteins in the venom pouch of M. trabalae, of which 186 were contained in UVGs simultaneously. A total of 766 proteins were detected in the venom of A. japonicus, of which 128 venom proteins were highly expressed in the venom glands. At the same time, the functional analysis of these identified venom proteins was carried out separately. We found the venom proteins in M. trabalae are well known but not in A. japonicus, which may be related to the host range. In conclusion, identifying venom proteins in both egg parasitoid species provides a database for studying the function of egg parasitoid venom and its parasitic mechanism.

Aphidius ervi venom regulates Buchnera contribution to host nutritional suitability

The association between the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), and the endophagous parasitoid wasp Aphidius ervi Haliday (Hymenoptera: Braconidae) offers a unique model system for studying the molecular mechanisms underlying the complex interactions between the parasitoid, its host and the associated primary symbiont. Here, we investigate in vivo the functional role of the most abundant component of A. ervi venom, Ae-γ-glutamyl transpeptidase (Ae-γ-GT), which is known to induce host castration. Microinjections of double-stranded RNA into A. ervi pupae stably knocked down Ae-γ-GT1 and Ae-γ-GT2 paralogue genes in newly emerged females. These females were used to score the phenotypic changes both in parasitized hosts and in the parasitoid’s progeny, as affected by a venom blend lacking Ae-γ-GT. Ae-γ-GT gene silencing enhanced growth both of host and parasitoid, supported by a higher load of the primary bacterial symbiont Buchnera aphidicola. Emerging adults showed a reduced survival and fecundity, suggesting a trade-off with body size. This demonstrates in vivo the primary role of Ae-γ-GT in host ovary degeneration and suggests that this protein counterbalances the proliferation of Buchnera likely triggered by other venom components. Our study provides a new approach to unravelling the complexity of aphid parasitoid venom in vivo, and sheds light on a novel role for Ae-γ-GT in host regulation.

ECR Spotlight – Amit Rana

ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology during our centenary year but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Amit Rana is an author on ‘ Parasitoid wasp venom re-programs host behavior through downmodulation of brain central complex activity and motor output’, published in JEB. Amit is a PhD student in the lab of Frederic Libersat at Zlotowski Center for Neurosciences, Ben Gurion University of the Negev, Beer Sheva, Israel, investigating neuroparasitoids, nociception, navigation and hibernation.

Parasitoid wasp venom re-programs host behavior through downmodulation of brain central complex activity and motor output.

The parasitoid wasp Ampulex compressa hunts down its host, the American cockroach (Periplaneta americana), and envenomates its brain to make it a behaviorally compliant food supply for its offspring. The primary target of the wasp sting is a locomotory command center called the central complex (CX). In the present study, we employ, for the first time, chronic recordings of patterned cockroach CX activity in real time as the brain is infused with wasp venom. CX envenomation is followed by sequential changes in the pattern of neuronal firing that can be divided into three distinct temporal phases during the 2h interval after venom injection: (1) reduction in neuronal activity for roughly 10 min immediately after venom injection; (2) rebound of activity lasting up to 25 min; (3) reduction of ongoing activity for up to 2 h. Long-term reduction of CX activity after venom injection is accompanied by decreased activity of both descending interneurons projecting to thoracic locomotory circuitry (DINs) and motor output. Thus, in this study, we provide a plausible chain of events starting in the CX that leads to decreased host locomotion following brain envenomation. We propose that these events account for the onset and maintenance of the prolonged hypokinetic state observed in stung cockroaches.

In Silico Analysis of a Drosophila Parasitoid Venom Peptide Reveals Prevalence of the Cation-Polar-Cation Clip Motif in Knottin Proteins.

As generalist parasitoid wasps, Leptopilina heterotoma are highly successful on many species of fruit flies of the genus Drosophila. The parasitoids produce specialized multi-strategy extracellular vesicle (EV)-like structures in their venom. Proteomic analysis identified several immunity-associated proteins, including the knottin peptide, LhKNOT, containing the structurally conserved inhibitor cysteine knot (ICK) fold, which is present in proteins from diverse taxa. Our structural and docking analysis of LhKNOT's 36-residue core knottin fold revealed that in addition to the knottin motif itself, it also possesses a Cation-Polar-Cation (CPC) clip. The CPC clip motif is thought to facilitate antimicrobial activity in heparin-binding proteins. Surprisingly, a majority of ICKs tested also possess the CPC clip motif, including 75 bona fide plant and arthropod knottin proteins that share high sequence and/or structural similarity with LhKNOT. Like LhKNOT and these other 75 knottin proteins, even the Drosophila Drosomycin antifungal peptide, a canonical target gene of the fly's Toll-NF-kappa B immune pathway, contains this CPC clip motif. Together, our results suggest a possible defensive function for the parasitoid LhKNOT. The prevalence of the CPC clip motif, intrinsic to the cysteine knot within the knottin proteins examined here, suggests that the resultant 3D topology is important for their biochemical functions. The CPC clip is likely a highly conserved structural motif found in many diverse proteins with reported heparin binding capacity, including amyloid proteins. Knottins are targets for therapeutic drug development, and insights into their structure-function relationships will advance novel drug design.

Editor's Choice: October 2022

Parasitoid venom alters the lipid composition and development of microorganisms on the wax moth cuticle – V. Y. Kryukov, E. I. Chernyak, N. Kryukova, M. Tyurin, A. Krivopalov, O. Yaroslavtseva, I. Senderskiy, O. Polenogova, E. Zhirakovskaia, V. V. Glupov & S. V. Morozov (https://doi.org/10.1111/eea.13219). Parasitoid venom alters the lipid composition and development of microorganisms on the wax moth cuticle – V. Y. Kryukov, E. I. Chernyak, N. Kryukova, M. Tyurin, A. Krivopalov, O. Yaroslavtseva, I. Senderskiy, O. Polenogova, E. Zhirakovskaia, V. V. Glupov & S. V. Morozov (https://doi.org/10.1111/eea.13219) Parasitoids are in a continuous arms race with their host for survival. This battle has led to numerous evolutionary innovations, including the recruitment of additional parties, such as the host microbiome. Kryukov and colleagues demonstrate that parasitization by Habrobracon brevicornis (Hymenoptera: Braconidae) leads to differences in the microbial composition of larvae of the wax moth, Galleria mellonella (Lepidoptera: Pyralidae). They envision that the parasitoid's venom alters the lipid composition of the host larval cuticle, which increases its susceptibility to infection, thereby putting an extra challenge on the host immune system, which in turn may increase the survival chance of the parasitoid's offspring. This study is an intriguing example of the intricate interactions between parasitoids and their hosts.

Parasitoid venom alters the lipid composition and development of microorganisms on the wax moth cuticle

AbstractEctoparasitoids may change host metabolism, making the environment more favorable for the development of their larvae. These alterations may also be suitable for growth and proliferation of commensal microorganisms and pathogens. This is especially important in relation to cuticular microbiota, with which ectoparasitoids interact directly. However, biochemical and microbiological changes occurring on insect cuticles in response to parasitoid venoms are insufficiently understood. We assayed the biochemical and microbiological changes in cuticles of larvae of the wax moth,Galleria mellonella(L.) (Lepidoptera: Pyralidae), after envenomation byHabrobracon brevicornis(Wesmael) (Hymenoptera: Braconidae).In particular, lipid composition in the epicuticle, total nitrogen (N) and carbon (C) amounts in the cuticle, bacterial colony‐forming unit (CFU) counts, and bacterial community structure (16S rRNA gene‐based metagenomics) on the insect surface were analyzed. The susceptibility of wax moth larvae to the entomopathogenic fungus (EPF)Metarhizium robertsiiJ.F. Bisch., S.A. Rehner & Humber (Hypocreales: Clavicipitaceae) was also assessed.Envenomation led to an increase in the hydrocarbon amount, as well as alterations in the fatty acid composition of the epicuticle; in particular, a large decrease in the amount of ω‐1 hydroxy fatty acids. The total N and C amounts in the cuticle also slightly increased after envenomation. These changes were correlated with a decrease in bacterial diversity and an increase inEnterococcusabundance on the surface of envenomated larvae. Envenomation also led to a substantial increase in larval susceptibility toM. robertsiiinfection; differences between the LC50values of envenomated and control larvae were 505 000‐fold. We suggest that the hyper‐lipidation of the cuticle is related to processes occurring in the host’s hemocoel after envenomation by the parasitoid. The effects of the changes in the lipid composition on the proliferation and development of microorganisms are discussed.

Suppression of host nocifensive behavior by parasitoid wasp venom.

The parasitoid wasp Ampulex compressa envenomates the brain of its host the American cockroach (Periplaneta americana), thereby making it a behaviorally compliant food supply for its offspring. The target of venom injection is a locomotory command center in the brain called the central complex. In this study, we investigate why stung cockroaches do not respond to injuries incurred during the manipulation process by the wasp. In particular, we examine how envenomation compromises nociceptive signaling pathways in the host. Noxious stimuli applied to the cuticle of stung cockroaches fail to evoke escape responses, even though nociceptive interneurons projecting to the brain respond normally. Hence, while nociceptive signals are carried forward to the brain, they fail to trigger robust nocifensive behavior. Electrophysiological recordings from the central complex of stung animals demonstrate decreases in peak firing rate, total firing, and duration of noxious-evoked activity. The single parameter best correlated with altered noxious-evoked behavioral responses of stung cockroaches is reduced duration of the evoked response in the central complex. Our findings demonstrate how the reproductive strategy of a parasitoid wasp is served by venom-mediated elimination of aversive, nocifensive behavior in its host.

Evaluation of the Potential Anti-inflammatory Effects of Endoparasitoid Pimpla turionellae L. (Hymenoptera: Ichneumonidae) venom on Mammalian Cell Lines

Parasitic wasps inject their eggs, together with a complex venom mixture, in or on other insects. Parasitoid venoms use various mechanisms to manipulate the physiology and suppress the immune system of their hosts, thus enabling the growth and development of their offspring. Since the major mechanisms of innate immunity in insects are homologous to the Nuclear Factor kappa B (NF-κB) pathway in mammalian immunity, this study hypothesized that venom related immune suppression observed in host insects could also be observed in mammalian cells. Therefore, an NF-κB-dependent luciferase assay was used to determine the effects of P. turionellae venom on murine fibrosarcoma L929sA cells. Results from an MTT assay showed that venom from P. turionellae has no cytotoxic effects on L929sA cell lines when taking into account a defined range of exposure time and concentrations. Also, the present study indicated that endoparasitoid P. turionellae venom has potential to inhibit NF-κB signaling in cells of mammals at nontoxic concentrations. In conclusion, venom components from ecto- or endoparasitoid wasps have anti-inflammatory potential on increased immune responses of mammalian cells.

Impact of Temperature on the Immune Interaction between a Parasitoid Wasp and Drosophila Host Species.

Simple SummaryGlobal warming affects most species and their interaction s. Insects are ectotherms, meaning their body temperature is affected by the ambient temperature. This is particularly important for koinobiont parasitoids, insects that keep their host insect alive during development of their eggs and larvae, the host eventually being consumed before adult parasitoids emerge. Temperature changes could therefore affect parasitoids directly and/or indirectly through their impact on the host. Here, we tested the effect of temperature on the parasitic success of two parasitoid lines on two host species, and on each partner independently, to determine whether the host immune response and/or the parasitoid venom proteins, injected with the egg to counteract the host immune response, were affected. The host’s immune defense consists of forming a capsule surrounding the parasitoid egg. In half of the interactions tested, the parasitic success increased with temperature. For one, the increase appeared to result solely from an increased capacity of the parasitoid to escape from a capsule, while for the second, it also appeared to involve a decrease in host encapsulation capacity. Finally, we observed a strong change in venom composition depending on the rearing temperature which may partially explain the change in parasitic success.Temperature is particularly important for ectotherms, including endoparasitoid wasps that develop inside another ectotherm host. In this study, we tested the impact of three temperatures (20 °C, 25 °C and 30 °C) on the host–parasitoid immune interaction using two Drosophila host species (Drosophila melanogaster and D. yakuba) and two parasitoid lines of Leptopilina boulardi. Drosophila’s immune defense against parasitoids consists of the formation of a melanized capsule surrounding the parasitoid egg. To counteract this response, Leptopilina parasitoids rely on the injection of venom during oviposition. Here, we tested the effect of temperature on parasitic success and host encapsulation capacity in response to a parasitoid egg or other foreign body. Increased temperature either promoted or did not affect the parasitic success, depending on the parasitoid–host pairs considered. The mechanisms behind the higher success seemed to vary depending on whether the temperature primarily affected the host immune response or also affected the parasitoid counter-immune response. Next, we tested the effect of parasitoid rearing temperature on its success and venom composition. Venom composition varied strongly with temperature for both parasitoid lines, partially consistent with a change in their parasitic success. Overall, temperature may have a significant impact on the host–parasitoid immune interaction.

Annotation and Comparison of Parasitoid Wasp GAPDH Gene

Endoparasitoid wasps are members of the hymenoptera superfamily that are dependent on other arthropod species for reproduction, consisting of the host's exploitation after the first sting for the preparation of egg insertion. The element that allows the manipulation of host biology is the introduction of venom gland derived proteins into their host. This venom has the ability to alter the host's gene expression and paralyze the arthropod to allow the wasp's eggs to develop inside the host without a fight. Once the eggs begin to develop, they become completely dependent on the host for their nourishment and development, meaning that the host will lack its nourishment and what is needed to continue living. A painful and quiet death awaits the host while it is being eaten alive from the inside out for the benefit of the parasitoid wasp. This research project focuses on the evolutionary relationships between venom proteins from three different endoparasitoid wasps: Leptolina. heterotoma, L. boulardi, and Ganaspis. The genes aligning to the venom transcriptome of the following species were identified with the help of the University of California Santa Cruz Genome Browser, allowing easy identification of precise and accurate coding regions through comparison with other insect orthologs. The goal of this research project is the annotation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the three parasitoid species. GAPDH is a glycolytic enzyme that has significant cellular functions in glycolysis and gluconeogenesis, responsible for the interconversion of 1,3-diphosphoglycerate and glyceraldehyde-3-phosphate. This enzyme catalyzes the conversion of glyceraldehyde 3-phosphate to 1,3-diphosphoglycerate, producing ATP and pyruvate in the Cytoplasm of the cell through anaerobic glycolysis. RNA-seq data from the venom transcriptome suggests that the three GAPDH orthologs have a similar gene structure and are highly homologous to the Nasonia vitripennis predicted GAPDH peptide sequence. The GAPDH peptide from Ganapsis species has shares 93% identity and 97% similarity to N. vitripennis ortholog, whereas the L. boulardi ortholog is more divergent with 88.4% identity and 93.1% identity. These gene models will be used in a comparative genomics study to investigate parasitoid wasp venom evolution.

What makes a parasite successful? Parasitoid wasp venoms evolve rapidly in a host-specific manner

A recommendation of: Fanny Cavigliasso, Hugo Mathé-Hubert, Jean-Luc Gatti, Dominique Colinet, Marylène Poirié Parasitic success and venom composition evolve upon specialization of parasitoid wasps to different host species https://doi.org/10.1101/2020.10.24.353417

An integrated transcriptomic and proteomic approach to identify the main Torymus sinensis venom components

During oviposition, ectoparasitoid wasps not only inject their eggs but also a complex mixture of proteins and peptides (venom) in order to regulate the host physiology to benefit their progeny. Although several endoparasitoid venom proteins have been identified, little is known about the components of ectoparasitoid venom. To characterize the protein composition of Torymus sinensis Kamijo (Hymenoptera: Torymidae) venom, we used an integrated transcriptomic and proteomic approach and identified 143 venom proteins. Moreover, focusing on venom gland transcriptome, we selected additional 52 transcripts encoding putative venom proteins. As in other parasitoid venoms, hydrolases, including proteases, phosphatases, esterases, and nucleases, constitute the most abundant families in T. sinensis venom, followed by protease inhibitors. These proteins are potentially involved in the complex parasitic syndrome, with different effects on the immune system, physiological processes and development of the host, and contribute to provide nutrients to the parasitoid progeny. Although additional in vivo studies are needed, initial findings offer important information about venom factors and their putative host effects, which are essential to ensure the success of parasitism.

Characterization of a cell death‐inducing endonuclease‐like venom protein from the parasitoid wasp Pteromalus puparum (Hymenoptera: Pteromalidae)

Parasitoid wasps are valuable natural enemies for controlling pests. To ensure successful parasitism, these wasps inject venoms along with their eggs that are deposited either into or on their hosts. Parasitoid venoms regulate host behaviors, development, metabolism and immune responses. Pteromalus puparum is a pupal endoparasitoid that parasitizes a number of butterflies, including the worldwide pest cabbage butterfly, Pieris rapae. Venom from P. puparum has a variety of effects on host hemocytes, including alteration of absolute and relative hemocyte counts, and inhibition of hemocyte spreading and encapsulation. In particular, P. puparum venom causes hemocyte cell death in vivo and in vitro. Using assay-guided chromatography, a cell death-inducing venom fraction was identified and defined as P. puparum endonuclease-like venom protein (PpENVP). It belongs to the DNA/RNA nonspecific endonuclease family, which contains two conserved endonuclease activation sites. We analyzed its expression profiles and demonstrated that PpENVP inhibits gene expression in transfected cells relying on two activation sites. However, RNA interference of PpENVP did not significantly reduce P. puparum venom cytotoxicity, suggesting that PpENVP may not be the sole cytotoxic factor present. Our results provide novel insight into the function of the P. puparum venom cocktail and identify a promising insecticide candidate endonuclease that targets insect hemocytes.

CYTOTOXICITY OF VENOM FROM ENDOPARASITOID PIMPLA TURIONELLAE L. (HYMENOPTERA: ICHNEUMONIDAE) ON GLIOBLASTOMA CELLS

In the treatment of brain cancer, the inhibition of cancer cell proliferation using anti-cancer agents is a priority approach. Venom of endoparasitoid wasps also may be a candidate for the development of new therapeutic agents. In this context, endoparasitoid Pimpla turionellae L. (Hymenoptera: Ichneumonidae) venom may have an anti-carcinogenic effect on glioblastoma that resists traditional therapies by various mechanisms. Therefore, we aimed to investigate endoparasitoid venom cytotoxicity on glioblastoma cells. For this purpose, the cytotoxic potential of venom from P. turionellae was evaluated on rat C6 glioblastoma cell lines with methyl thiazolyl tetrazolium assay (MTT assay). P. turionellae venom was isolated from 15±2 day-old females. Different concentrations of P. turionellae venom (176.6-1.83 μg/ml) were applied to C6 rat glioblastoma cells in vitro. Results of MTT assay showed that the viability of C6 cells in vitro significantly decreased depending on the parasitoid venom concentrations. Therefore, P. turionellae venom showed cytotoxic activity in a time- and dose-dependent manner. In conclusion, the results from this research could be used as primary data of venom cytotoxicity for investigation of new chemotherapeutic agents against malignant tumors.

Mechanism and consequences for avoidance of superparasitism in the solitary parasitoid Cotesia vestalis

A parasitoid’s decision to reject or accept a potential host is fundamental to its fitness. Superparasitism, in which more than one egg of a given parasitoid species can deposit in a single host, is usually considered sub-optimal in systems where the host is able to support the development of only a single parasitoid. It follows that selection pressure may drive the capacity for parasitoids to recognize parasitized hosts, especially if there is a fitness cost of superparasitism. Here, we used microsatellite studies of two distinct populations of Cotesia vestalis to demonstrate that an egg laid into a diamondback moth (Plutella xylostella) larva that was parasitized by a conspecific parasitoid 10 min, 2 or 6 h previously was as likely to develop and emerge successfully as was the first-laid egg. Consistent with this, a naive parasitoid encountering its first host was equally likely to accept a healthy larva as one parasitized 10 min prior, though handling time of parasitized hosts was extended. For second and third host encounters, parasitized hosts were less readily accepted than healthy larvae. If 12 h elapsed between parasitism events, the second-laid egg was much less likely to develop. Discrimination between parasitized and healthy hosts was evident when females were allowed physical contact with hosts, and healthy hosts were rendered less acceptable by manual injection of parasitoid venom into their hemolymph. Collectively, these results show a limited capacity to discriminate parasitized from healthy larvae despite a viability cost associated with failing to avoid superparasitism.

Competitive interactions between entomopathogenic nematodes and parasitoid venom

AbstractEntomopathogenic nematodes and parasitoid larvae of some wasps play important roles in the natural control of the pest insects. However, it has not been excluded that competition between nematodes and wasps may in some cases reduce their efficacy in the pest control. Using caterpillars of Spodoptera littoralis, we examined interactions between the nematode Steinernema carpocapsae and the venom of the parasitoid Habrobracon hebetor. The survival of S. littoralis caterpillars was reduced in a dose‐dependent manner when 5 to 500 nematodes or 0.005–0.1 venom units were applied to single caterpillars. High doses of either nematodes or the venom caused death within 1–3 days in all treated hosts. The low doses of nematodes killed caterpillars within a week, in some cases when they attempted to pupate. Caterpillars receiving low venom doses were characterized by extended survival time terminated with death due to starvation. Combined treatment of nematodes and the venom were mutually synergistic and elicited severe lethal effects. The nematodes were fully resistant to the venom and can feed and grow on the symbiotic bacteria in vitro. The venom impairs food processing and causes death of caterpillars due to starvation. Disruption of the hormonal regulation of metamorphosis by ecdysteroids and juvenile hormone could be responsible for defective moults block at different stages of the moulting process, regionally restricted moulting, moults to “intermediates” combining regions of newly secreted larval and pupal cuticles.