VENOM FROM THE ECTOPARASITIC WASP Habrobracon hebetor ACTIVATES CALCIUM‐DEPENDENT DEGRADATION OF Galleria mellonella LARVAL HEMOCYTES

Ectoparasitoids inject venom into hemolymph during oviposition. We determined the influence of envenomation by the parasitoid, Habrobracon hebetor, on the hemocytes of its larval host, Galleria mellonella. An increase in both intracellular Са²⁺ content and phospholipase C activity of the host hemocytes was recorded during 2 days following envenomation by the parasitoid. The decreased hemocyte viability was detected 1, 2, and 24 h after the envenomation. Injecting of the crude venom (final protein concentration 3 μg/ml) into the G. mellonella larvae led to the reduced hemocyte adhesion. The larval envenomation caused a decrease in transmembrane potential of the hemocytes. These findings document the suppression of hemocytic immune effectors in the parasitized host larvae.     

Passive vectoring of entomopathogenic fungus Beauveria bassiana among the wax moth Galleria mellonella larvae by the ectoparasitoid Habrobracon hebetor females

Females of the ectoparasitoid Habrobracon hebetor attack and envenomate numerous host individuals during oviposition. The vectoring of the entomopathogenic fungus Beauveria bassiana during the adhesion stage by ectoparasitoid females among the wax moth larvae Galleria mellonella was explored under laboratory conditions. Vectoring occurred both from infected parasitoids to wax moth larvae and from infected to healthy wax moth larvae by parasitoids. The efficacy of vectoring in both cases was dose dependent. Parasitoid females were unable to recognize infected larvae in a labyrinth test. In addition, the presence of H. hebetor females significantly (1.5–13 fold) increased the mycoses level in clusters of G. mellonella, with 40% of the larvae infected with fungal conidia. Envenomation by H. hebetor increased conidia germination on the cuticles of the wax moth larvae by 4.4 fold. An enhanced germination rate (2 fold) was registered in the n‐hexane epicuticular extract of envenomated larvae compared to that of healthy larvae. Both envenomation and mycoses enhanced the phenoloxidase (PO) activity in the integument of G. mellonella and, in contrast, decreased the encapsulation rate in hemolymphs. We hypothesize that changes in the integument property and inhibition of cellular immunity provide the highest infection efficacy of entomopathogenic fungi with H. hebetor.     

Venom of ectoparasitoid,Euplectrus sp near plathypenae (Hymenoptera: Eulophidae) regulates the physiological state of Pseudaletia separata (Lepidoptera: Noctuidae) host as a food resource

Euplectrus sp. near plathypenae is an ectoparasitoid that can parasitize from 3rd to day 0-6th instar Pseudaletia separata. The developmental period of the parasitoid from the egg to the pupal stage is about 13 days. Parasitized hosts are developmentally arrested and never molt to the next stadium. The injection of venom fluid results in similar effects on P. separata larvae as does parasitization. The inhibitory effect of the venom on molting was dose dependent. Injection of 0.3 female equivalents of venom into day 0-5th host instar resulted in a similar developmental arrest as seen in parasitized hosts. The amount of total lipid in the hemolymph of the host increased as a function of the amount of venom injected, while the lipid content of the fat body was similar to lipid levels in the fat body of parasitized larvae. The amount of total protein in the hemolymph also increased when venom was injected, whereas the protein level of the fat body did not increase. The lipid concentration within the parasitoid larva was maintained at the same level throughout larval development, but increased before pupation. We conclude that the injected venom increased the hemolymph content of lipid and protein to support the growth and development of the ectoparasitoid larva.     

The effect of Habrobracon hebetor venom on the activity of the prophenoloxidase system, the generation of reactive oxygen species and encapsulation in the haemolymph of Galleria mellonella larvae

The cellular and humoral immune reactions in haemolymph of the wax moth Galleria mellonella larvae naturally injected by venom of ectoparasitic wasp Habrobracon hebetor were analyzed. A strong decline of phenoloxidase (PO) activity in the haemolymph and the number of haemocytes with PO activity of envenomated wax moth was observed. In addition, it has been shown that the rate of capsule melanization in the envenomated larvae was half that of the control. Also production of reactive oxygen species (ROS) in the haemolymph of envenomated larvae decreased. The obtained data casts light on the suppression of the main immune reactions in G. mellonella larvae during natural envenomation by H. hebetor.     

Microsporidiosis in the wax moth Galleria mellonella (Lepidoptera: Pyralidae) caused by Vairimorpha ephestiae (Microsporidia: Burenellidae)

An experimental microsporidiosis of the wax moth caterpillars from laboratory population had been caused by oral infecting of early stages larvae and by intracavity injections of the spores of the microsporidian species Vairimorpha ephestiae. Peculiarities of microsporidiosis proceeding, manifestations of host defence reactions, and also an effect of the temperature of caterpillars cultivation and conditions of spores keeping on liability of the insects to the infection were studied. The effect of the microsporidia on the host organism was the early death or the delay of larvae development, but in several cases external manifestations of the effect of the parasite on the host were absent. The development of the parasites from the moment of infecting to the appearing of the mature spores congestions in the host organism proceeded 6 days. Microsporidia invaded insect fat body and caused its hypertrophy and disappearance of lipid granules. In the intestine and salivary glands microsporidia were not observed in the period from 6 to 16 day of the development. On the final stage of microsporidiosis the all contents of fatty tissue cells were replaced by spores of microsporidia. Under microscope only diplocaryotic spores of the Nozema type had been found in infected and died specimens, but not octospores. The spores threw out polar tubes under the change of pH in incubating solution from neutral to alkaline. The effects of microsporidiosis on the wax moth haemolymph were the increased rate of prohaemocytes, appearing of multinuclear free-circulating cells at 6 day after infection, and suppression of the reaction of haemolymph melanization with the mass sporogenesis of the parasite. The characteristic symptom of the wax moth microsporidiosis had been revealed, accumulation of black points and small spots of irregular form under cuticle ("reaction of attretization"). Increase of the temperature of insect cultivation up to 32 degrees C during 3 days after infection contributed to the full deliverance of the insects from the infection in first and second generations. It can be considered as a method of treatment of wax moth laboratory colonies from microsporidiosis. Oral infection of III and IV stage caterpillars by the spores being kept during 3-6 months under 4 degrees C in form of water suspension caused the death of 63.0-61.5 and 91% of caterpillars being cultivated under 25 and 21 degrees C respectively. Under the temperature of cultivation equal 30 degrees C the mortality did not differ from the control sample (8-10%). The spores extracted from dried bodies of caterpillars lost their vitality. It was demonstrated by the test on infectious ability in vivo and by acridine orange staining. This host-parasite system appears to be perspective in investigations of resistance mechanisms in insects and immunosuppressive features of entomopathogen microsporidia.     

Influences of host size and host species on theinfectivity and development of Heterorhabditismegidis (strain NLH-E87.3)

The infectivity, time to first emergence of infective juveniles (IJs), total number of IJs per insect and IJs body length of the entomopathogenic nematode Heterorhabditis megidis (strain NLH-E87.3) after development in larvae of two insect hosts, Galleria mellonella (greater wax moth) and Otiorhynchus sulcatus (vine weevil) was studied. At a dose of 30 IJs, larvae of G. mellonella show to be significantly more susceptible than O. sulcatus larvae. At a dose of one IJ, vine weevil larvae were more susceptible. The number of invading infective juveniles (IJs) increased with host size while the host mortality at a dose of one IJ decreased with the increase of host size. Time to first emergence was longer at a dose of one IJ per larva and increased with the increase of host size in both insect species. Reproduction of IJs differed between host species, host sizes and doses of nematodes. Generally, the IJs body size increased with an increasing host size. The longest infective juveniles were produced at the lowest IJ doses. Results are discussed in relation to the influence of different host species and their different sizes on the performance of H. megidis (strain NLH-E87.3) as a biological control agent.     

Performance of Sclerodermus brevicornis,a parasitoid of invasive longhorn beetles,when reared on rice moth larvae

Biological control efficiency can be improved by developing effective mass‐rearing systems to produce large numbers of high‐quality parasitoids. This study explored an alternative host for rearing Sclerodermus brevicornis (Kieffer) (Hymenoptera: Bethylidae), a potential biocontrol agent for the suppression of exotic and invasive wood‐boring longhorn beetle (Coleoptera: Cerambycidae) populations in the European agroforestry ecosystems. We tested larvae of the rice moth, Corcyra cephalonica Stainton (Lepidoptera: Pyralidae), as host for the parasitoid. We quantified the probability and timing of host attack and parasitism as well as reproductive success, offspring production, and the characteristics of adult offspring. As S. brevicornis is a quasi‐social species (multiple females, communally produced offspring broods), we also explored the effects of varying the number of females to which individual hosts were presented, with the aim of determining the optimal female‐to‐host ratio. As time to host attack can be a limiting factor in S. brevicornis rearing protocols, we tested the use of adult females of another bethylid species, Goniozus legneri Gordh, to paralyse C. cephalonica larvae prior to presentation. We identified the conditions within our experiment that maximized offspring production per host and offspring production per adult female parasitoid. We found that C. cephalonica is suitable as a factitious host and, as it is considerably more straightforward for laboratory rearing than cerambycid species, it is a good candidate for adoption by future S. brevicornis mass‐rearing and release programmes.     

Food utilization values of gypsy moth Lymantria dispar (Lepidoptera: Lymantriidae) larvae infected with the microsporidium Vairimorpha sp. (Microsporidia: Burenellidae)

Infection of the gypsy moth, Lymantria dispar, with the microsporidium Vairimorpha sp. strongly influences the development of the host in ways typical of many species of terrestrial entomopathogenic Microsporidia; growth is reduced while development time is extended in infected insects. The appearance of the different stages of the parasite in the host relative to the elapsed time after oral infection, as well as the influence of the parasite proliferation on food utilization of the host, were examined. At 3 days postinfection, midgut muscle cells were infected with primary spores, and the fat body tissues contained meronts, sporonts, and primary spores. Many more fat body cells contained vegetative stages and primary spores at 4 and 5 days postinfection, and diplokaryotic spores and immature octospores were also present. Approximate digestibility of infected larvae increased during this time period, whereas the conversion of ingested and digested food to body substance decreased. The relative growth rate of infected and uninfected groups did not differ significantly between 4 and 5 days postinfection, although the relative consumption rate in infected L. dispar larvae was higher. Between 8 and 10 days postinfection, the relative growth rate of uninfected larvae increased. The infected group did not demonstrate this increase at a time period characterized by maturation of diplokaryotic spores and octospores in larval fat body tissues. Total body weight of uninfected larvae remained higher than that of infected larvae after 8 days postinfection.     

VENOM COMPONENTS OF Asobara japonica IMPAIR CELLULAR IMMUNE RESPONSES OF HOST Drosophila melanogaster

The endoparasitoid wasp Asobara japonica has highly poisonous venom: the host Drosophila larvae are killed by envenomation at a dose that is naturally injected by the female wasp at parasitism. This insecticidal venom is neutralized, however, because A. japonica introduces lateral oviduct components soon after venom injection at oviposition. Although the venom and lateral oviduct components of this parasitoid have been partially characterized, how the venom components favor successful development of wasp eggs and larvae in the host remains ambiguous. Here, we demonstrated that A. japonica venom did not affect host humoral immune responses, determined as expression of antimicrobial peptide (AMP) genes, but significantly diminished two cellular responses, spreading and phagocytosis, by host hemocytes. Moreover, venom components drastically elevated a serine protease‐like activity 4 h after its injection. The lateral oviduct components did not negate the detrimental effects of the venom on host cellular immunities, but significantly reduced the venom‐induced elevation of protease activity. Both active factors in venom and lateral oviduct components were roughly characterized as heat‐labile substances with a molecular mass of at least 10 kDa. Finally, venom of A. japonica, with a wide host range, was found to be much more toxic than that of Asobara rossica, which has a limited host range. These results reveal that A. japonica venom toxicity allows exploitation of a broader range of host insects because it is essential to overcome cellular immune responses of the host for successful parasitism.     

Cytotoxic effects of parasitism and application of venom from the endoparasitoid Pimpla turionellae on hemocytes of the host Galleria mellonella

In parasitoid species devoid of polydnaviruses and virus‐like particles, venom appears to play a major role in suppression of host immunity. Venom from the pupal endoparasitoid Pimpla turionellae L. (Hymenoptera: Ichneumonidae) has previously been shown to contain a mixture of biologically active components, which display potent paralytic, cytotoxic, and cytolytic effects toward lepidopteran and dipteran hosts. The current study was undertaken to investigate if parasitism and/or envenomation by P. turionellae affects the frequency of apoptotic and necrotic hemocytes, hemocyte viability and mitotic indices in Galleria mellonella L. (Lepidoptera: Pyralidae) pupae and larvae. Our study indicates that parasitism and experimental envenomation of G. mellonella by P. turionellae resulted in markedly different effects on the ratio of apoptotic hemocytes circulating in hemolymph depending on the host developmental stages. The ratio of early and late apoptotic hemocytes increased in G. mellonella pupae and larvae upon parasitization and at high doses of venom when compared to untreated, null and Phosphate Buffered Saline (PBS) injected controls. In contrast, an increase in necrotic hemocytes was only observed in parasitized pupae at 24 h and no difference was observed in larvae. The lowest hemocyte viability values were observed with pupae as 69.87%, 69.80%, and 72.47% at 4, 8, and 24 h post‐parasitism. The ratio of mitotic hemocytes also decreased in pupae and larvae upon parasitization and at high doses of venom. Staining of hemocytes with annexin V‐FITC revealed green fluorescent ‘halos’ along the plasma membranes of venom treated cells within 15 min following exposure to venom. By 1 h post‐venom – treatment, the majority of hemocytes displayed binding of this probe, indicative of early stage apoptosis. These same hemocytes also displayed a loss of plasma membrane integrity at the same time points as evidenced by accumulation of propidium iodide in nuclei.     

Venom of Euplectrus separatae causes hyperlipidemia by lysis of host fat body cells

Although the lepidopteran larva Pseudaletia separata is attacked by the gregarious ectoparasitoid Euplectrus separatae, it continues to feed and grow. Lipid concentration in the hemolymph of the parasitized host was higher than that of the nonparasitized host from 3 to 8 days after parasitization. Artificial injection of parasitoid venom also elevated lipid concentration in the host hemolymph. One day after venom injection the host's fat body contained many lipid particles, but most of the lipid particles disappeared 7 days later. Light microscopy and transmission electron microscopy showed the lipid particles leaving the fat body cells as a result of the lysis of the fat body cells. These results suggest that the venom elevated the lipid concentration in the host hemolymph by provoking the release of lipid particles from the fat body. Though most of the lipid particles were freely floating in the host hemolymph, a portion of the released lipid particles were phagocytized by hemocytes. The amount of lipid that was loaded to lipophorin in the hemolymph of the venom-injected host was measured, but it was not sufficient to explain the high lipid titer in the hemolymph of parasitized and venom-injected host larvae. The fact that parasitoid larva consumed many hemocytes as evidenced by their presence in the midgut supported the hypothesis that the parasitoid larvae fed on the host hemolymph containing the free lipid particles, the hemocytes phagocytizing the lipid particles, and the lipid-loaded lipophorin. The possibility of the venom contribution to the disruption of the intercellular matrix was examined. The venom showed high activity of matrix metalloproteinase (MMP), especially when it was mixed with the hemolymph of non-parasitized 5th instar larvae. We suggest that the MMP in the venom was activated by some components of the host hemolymph. On the other hand, the venom mixed with hemolymph could not decompose gelatin on zymography, suggesting that the venom-MMP is a different type from gelatinase. Activity of phospholipases A(2), B, C and hyaluronidase were measured with agar plates. High activities of phospholipase B and hyaluronidase were detected. These results suggest that the venom-MMP initially attacked the specific site of the intercellular-matrix of the fat body, and then the hyaluronidase and the phospholipase B cause lysis of the fat body cell, allowing lipid particles to be released into the host hemolymph.     

Histopathology of Aedes aegypti (Diptera: Culicidae) larvae parasitized by Reesimermis nielseni (Nematoda: Mermithidae)

Histological observations were made of Aedes aegypti larvae parasitized for 2, 4, and 6 days by Reesimermis nielseni. Little difference was detected between the tissues of uninfected and nematode-parasitized larvae 4 days after infection, at which time most hosts were in the early fourth instar and their fat bodies were well developed containing abundant storage materials. Nematodes grew most rapidly between day 4 and day 6 of parasitism, depleting host metabolites, reducing the fat body and other host storage tissues while accumulating storage material in their trophosomes. Development of host imaginal discs was inhibited during this period. The severity of the nematodes upon host tissues depended upon intensity of infection. Dry weight measurements of nematode and host supported histological observations that the nematode developed most rapidly 4–6 days post-infection, thus causing most serious effects upon the host at that time.     

Parasitization of Lacanobia oleracea (Lepidoptera: Noctuidae) by the ectoparasitc wasp,Eulophus pennicornis. Effects of parasitization,venom and starvation on host haemocytes

In contrast to the situation with endoparasitic wasps, little is known about the effects of ectoparasitoids and their secretions on the haemocytes of their insect hosts. To address this deficit, a study has been made of the ectoparasitic wasp, Eulophus pennicornis, and it's host, the tomato moth, Lacanobia oleracea. Using light microscopy, it was determined that L. oleracea has five main haemocyte types, namely, plasmatocytes, granular cells, spherule cells, oenocytoids and pro-haemocytes, representing 56%, 30%, 10%, 2% and 2% of the population, respectively. Parasitization by E. pennicornis, resulted in an increase in the number of circulating haemocytes up to day three, followed by a decrease towards day eight; the latter being associated with changes to the morphology and viability of the cells. For example, on day five after parasitization, plasmatocytes and granular cells had become more rounded and put out pseudopods less readily compared with those from non-parasitized controls, whilst from day seven onwards there was a significant decrease in haemocyte viability and by day nine, extensive haemocyte damage and disintegration was evident. These changes were not observed when larvae were injected with E. pennicornis venom, or when haemocytes were exposed directly to venom in vitro, neither did they occur in starved larvae. Thus, although the observed effects on L. oleracea haemocytes are definitely associated with parasitization they are not due to wasp venom components, nor are they a non-specific effect resulting from nutritional deprivation. The possibility that the feeding wasp larvae produce factors which perturb host haemocytes in order to help condition the host to ensure that successful parasitization occurs, is discussed.     

Correlation between concentration of hemolymph nutrients and amount of fat body consumed in lightly and heavily parasitized hosts (Pseudaletia separata)

Two states of parasitization in the Pseudaletia separata-Cotesia kariyai system were examined: one that was lightly parasitized and one that was heavily parasitized. We predicted that the consumption of fat body and hemolymph nutrients depends on the number of parasitoid larvae in the host. Lightly parasitized hosts (average clutch size+/-S.E.: 42.5+/-16.2, N=15) and heavily parasitized hosts (average clutch size+/-S.E.: 230.2+/-8.8, N=15) were prepared artificially. Eight days after parasitization, perivisceral fat body was depleted in the heavily parasitized host, although peripheral fat body was not yet consumed, but by day 10 most of the peripheral fat body was consumed. In lightly parasitized hosts, perivisceral fat body was not consumed by day 10. The parasitoid larvae deplete the perivisceral fat body first and then consume the peripheral fat body in the heavily parasitized host. The amount of trehalose, the major carbohydrate in the hemolymph, was related to the number of parasitoid larvae developing in the host. In a heavily parasitized host, trehalose concentrations remained low. However, in lightly parasitized hosts, the amount of trehalose increased 8 days after parasitization and then decreased by day 10. Protein and total lipid concentrations in the hemolymph of the heavily parasitized host were significantly lower than in lightly parasitized host on day 10, suggesting that the large number of parasitoid larvae depleted the fat body and hemolymph nutrients by day 10. High concentrations of total lipid on day 8 and 10 in lightly parasitized hosts and on day 8 in heavily parasitized host are likely to be attributed to the teratocytes.     

Comparing the physiological effects and function of larval feeding in closely‐related endoparasitoids (Braconidae: Microgastrinae)

Abstract The larvae of most endoparasitoid wasps consume virtually all host tissues before pupation. However, in some clades, the parasitoid larvae primarily consume haemolymph and fat body and emerge through the side of the host, which remains alive and active for up to several days. The evolutionary significance of this host‐usage strategy has attracted attention in recent years. Recent empirical studies suggest that the surviving larva guards the parasitoid broods against natural enemies such as predators and hyperparasitoids. Known as the ‘usurpation hypothesis’, the surviving larvae bite, regurgitate fluids from the gut, and thrash the head capsule when disturbed. In the present study, the ‘usurpation hypothesis’ is tested in the association involving Manduca sexta, its parasitoid Cotesia congregata, and a secondary hyperparasitoid Lysibia nana. Percentage parasitoid survival is higher and hyperparasitism lower when cocoons of C. congregata are attached to the dorsum of M. sexta caterpillars. Fat body contents in several associations involving solitary and gregarious parasitoids feeding on haemolymph and fat body are also compared. The amount of fat body retained in parasitized caterpillars varies considerably from one association to another. In M. sexta and Pieris brassicae, considerable amounts of fat body remain after parasitoid emergence whereas, in Cotesia kariyai and Cotesia rufricus, virtually all of the fat body is consumed by the parsasitoid larvae. The length of post‐egression survival of parasitized caterpillars differs considerably in several tested associations. In Pseudeletia separata, most larvae die within a few hours of parasitoid emergence whereas, in M. sexta, parasitized larvae live up to 2 weeks after parasitoid emergence. Larvae in other associations parasitized by gregarious and solitary endoparasitoids live for intermediate periods. The results are discussed in relation to the adaptive significance of different feeding strategies of immature parasitoids and of the costs and benefits of retaining the parasitized caterpillar in close proximity with the parasitoid cocoons.     

Fungal infection dynamics in response to temperature in the lepidopteran insect Galleria mellonella

This study examines how the dynamics of fungus–insect interactions can be modulated by temperature. The wax moth, Galleria mellonella, is a well‐studied and important model insect whose larvae in the wild develop optimally at around 34 °C in beehives. However, surprisingly little research on wax moths has been conducted at relevant temperatures. In this study, the entomopathogenic fungus Metarhizium robertsii inflicted rapid and substantial mortality on wax moth larvae maintained at a constant temperature of 24 °C, but at 34 °C a 10 fold higher dose was required to achieve an equivalent mortality. The cooler temperature favored fungal pathogenicity, with condial adhesion to the cuticle, germination and hemocoel invasion all significantly enhanced at 24 °C, compared with 34 °C. The wax moth larvae immune responses altered with the temperature, and with the infective dose of the fungus. Enzyme‐based immune defenses (lysozyme and phenoloxidase) exhibited enhanced activity at the warmer temperature. A dramatic upregulation in the basal expression of galiomicin and gallerimycin was triggered by cooling, and this was augmented in the presence of the fungus. Profiling of the predominant insect epicuticular fatty acids revealed a 4–7 fold increase in palmetic, oleic and linoleic acids in larvae maintained at 24 °C compared with those at 34 °C, but these failed to exert fungistatic effects on topically applied fungus. This study demonstrates the importance of choosing environmental conditions relevant to the habitat of the insect host when determining the dynamics and outcome of insect/fungus interactions, and has particular significance for the application of entomopathogens as biocontrol agents.     

Inhibition of juvenile hormone esterase activity in Lymantria dispar (Lepidoptera, Lymantriidae) larvae parasitized by Glyptapanteles liparidis (Hymenoptera, Braconidae)

Glyptapanteles liparidis is a gregarious, polydnavirus (PDV)-carrying braconid wasp that parasitizes larval stages of Lymantria dispar. In previous studies we showed that parasitized hosts dramatically increase juvenile hormone (JH) titers, whereas JH degradation is significantly inhibited in the hemolymph. Here we (i) quantified the effects of parasitism on JH esterase (JHE) activity in hemolymph and fat body of penultimate and final instars of L. dispar hosts and (ii) assessed the relative contribution of individual and combined wasp factors (PDV/venom, teratocytes, and wasp larvae) to the inhibition of host JHE activity. The effects of PDV/venom was investigated through the use of gamma-irradiated wasps, which lay non-viable eggs (leading to pseudoparasitization), while the effects of teratocytes and wasp larvae were examined by injection or insertion of these two components in either control or pseudoparasitized L. dispar larvae. Parasitism strongly suppressed host JHE activity in both hemolymph and fat body irrespective of whether the host was parasitized early (premolt-third instar) or late (mid-fourth instar). Down-regulation of JHE activity is primarily due to the injection of PDV/venom at the time of oviposition, with only very small additive effects of teratocytes and wasp larvae under certain experimental conditions. We compare the results with those reported earlier for L. dispar larvae parasitized by G. liparidis and discuss the possible role of JH alterations in host development disruption.     

Venom is beneficial but not essential for development and survival of Nasonia

1. Parasitoid wasps sting and inject venom into arthropod hosts, which alters host metabolism and development while keeping the host alive for several days, presumably to induce benefits for the parasitoid young. 2. This study investigates the consequences of host envenomation on development and fitness of wasp larvae in the ectoparasitoid Nasonia vitripennis, by comparing wasps reared on live unstung, previously stung, and cold‐killed hosts. Developmental arrest and suppression of host response to larvae are major venom effects that occur in both stung and cold‐killed hosts, but not in unstung hosts, whereas cold‐killed hosts lack venom effects that require a living host. Thus, cold‐killed hosts mimic some of the effects of venom, but not others. 3. Eggs placed on live unstung hosts have significantly higher mortality during development; however, successfully developing wasps from these hosts have similar lifetime fecundity to that of wasps from cold‐killed or stung hosts. Therefore, although venom is beneficial, it is not required for wasp survival. 4. While wasps developing on both cold‐killed and stung hosts have similar fitness levels, rearing multiple generations on cold‐killed hosts results in significant fitness reductions of wasps. 5. It is concluded that the largest benefits of venom are induction of host developmental arrest and suppression of host response to larva (e.g. immune responses), although more subtle benefits may accrue across generations or under stressful conditions.     

Phenology of Parasetigena silvestris (Diptera: Tachinidae), gypsy moth (Lymantria dispar) (Lepidoptera: Lymantriidae) larval parasitoid and its efficiency for parasitisation

Parasetigena silvestris is a univoltine, solitary, larval endoparasitoid which lays its eggs on the surface of gypsy moth larvae. Field collection of the host larvae (2nd through 5th instar) from an artificially established gypsy moth population were made to compare stage specific parasitism between larvae without and with P. silvestris tachinid eggs. The tachinid oviposition rate detected was highest in second instar larvae, and then decreased as larvae developed toward full maturity. The opposite was true for tachinid parasitoid emergence which had no emergence from second through third host instar larvae. Fourth instar gypsy moth larvae, however, experienced significantly higher parasitism by P. silvestris in the larvae with eggs than those without the eggs. The braconid wasp Cotesia melanoscelus caused significantly higher parasitism in early instar larvae with P. silvestris eggs than in those without the eggs. The tachinid prefers to lay more eggs on parasitised larvae by the braconid even though the braconid is a superior competitor to the fly during multiparasitism. Factors influencing parasitism rates by P. silvestris such as host-parasitoid synchronisation and the multiparasitism interaction with C. melanoscelus are discussed.