Host regulation and release of parasitism-specific proteins in the system Toxoneuron nigriceps-Heliothis virescens

The braconid wasp Toxoneuron nigriceps induced qualitative and quantitative changes in the protein composition of the moth Heliothis virescens host hemolymph. Total protein concentration was found to be higher in parasitized host 4 days after parasitism as compared to control hosts, mainly due to changes in a particular group of proteins. Host proteins with a molecular mass of 173 and 72 kDa were found in higher levels in the hemolymph of parasitized larvae as control hosts approached pupation, while an 80 kDa peptide was found in reduced concentration in the hemolymph of parasitized hosts. Levels of these three peptides were maintained throughout parasitoid development, while two of them (173 and 72 kDa) were cleared from the host hemolymph close to pupation. Besides the regulation of host proteins, three parasitism-specific proteins (PSPs) were released into the host hemolymph. Two of them (PSP1-MW=116 kDa, pI=6.3; PSP2-MW=114 kDa, pI=6.2) first appeared in the hemolymph of parasitized hosts soon after pupation of control host and increased in concentration as the parasitoid developed. The third PSP (PSP3-MW=56 kDa, pI=5.8) was produced towards the end of parasitoid larval development, close to parasitoid egression. Database searches based on the amino acid composition and amino terminal sequence of PSP1 and PSP2 did not produce any significant matches, while PSP3 was identified as a putative chitinase. Incubation of host derived tissues, parasitoid larvae and teratocytes in 35S conditioned media suggested PSPs were a product of teratocytes. The role of the regulation of host proteins and release of PSPs by teratocytes for the successful development of T. nigriceps are discussed.     

Symbiotic bracovirus of a parasite manipulates host lipid metabolism via tachykinin signaling

Parasites alter host energy homeostasis for their own development, but the mechanisms underlying this phenomenon remain largely unknown. Here, we show that Cotesia vestalis, an endoparasitic wasp of Plutella xylostella larvae, stimulates a reduction of host lipid levels. This process requires excess secretion of P. xylostella tachykinin (PxTK) peptides from enteroendocrine cells (EEs) in the midgut of the parasitized host larvae. We found that parasitization upregulates PxTK signaling to suppress lipogenesis in midgut enterocytes (ECs) in a non-cell-autonomous manner, and the reduced host lipid level benefits the development of wasp offspring and their subsequent parasitic ability. We further found that a C. vestalis bracovirus (CvBV) gene, CvBV 9–2, is responsible for PxTK induction, which in turn reduces the systemic lipid level of the host. Taken together, these findings illustrate a novel mechanism for parasite manipulation of host energy homeostasis by a symbiotic bracovirus gene to promote the development and increase the parasitic efficiency of an agriculturally important wasp species.     

Expression of a parasitism-specific protein in lepidopteran hosts of Chelonus sp.

The hemolymph of each noctuid species successfully parasitized by Chelonus near curvimaculatus possessed a parasitism-specific protein (PSP) previously identified in host T. ni (Insect Biochem. 19:445; 21:845). Expression of PSP occurred in a stage-specific manner in the stadium during which the host undergoes precocious metamorphosis. The appearance of the protein was not due to nutritional stress associated with parasitism of hosts, since starved nonparasitized larvae did not produce the protein, or to low juvenile hormone titers occurring in precociously metamorphosing hosts, but rather was dependent on the presence of the endoparasite larva. Results of in vivo incorporation experiments with [³⁵S]-methionine showed that synthesis and subsequent appearance of the protein in the hemolymph of parasitized hosts was abrogated by prior surgical removal of endoparasite. Immunoprecipitation analysis of proteins from C. near curvimaculatus larvae cultured in vitro using antibodies specific to PSP indicated that the source of the protein was the endoparasite. Synthesis of PSP by the endoparasitic larvae with its subsequent secretion into the hemocoel of hosts was specific to the advanced stages of parasite development prior to its egression from the host. © 1993 Wiley-Liss, Inc.     

一种中红侧沟茧蜂畸形细胞分泌的寄生特异蛋白

SDS-PAGE电泳表明,黏虫Pseudaletia separa-ta、棉铃虫 Helicoverpa armigera、小地老虎 Agrotisypsilon的幼虫受中红侧沟茧蜂Microplitis mediator寄生后,血淋巴中都出现一个98.6 kDa的寄生特异蛋白(p98.6)。畸形细胞(teratocytes)的体外培养发现,p98.6是由来自中红侧沟茧蜂胚胎浆膜层的畸形细胞分泌的。这一结果将为研究寄生蜂的寄生生理和畸形细胞在协调寄生蜂和寄主关系中的作用打下基础。     

Growth and development of the endoparasitic wasp Apanteles congregatus: dependence on host nutritional status and parasite load

ABSTRACT. Previously we have shown that the number of Apanteles congregatus Say (Hymenoptera, Braconidae) larvae developing in Manduca sexta (L.) (Lepidoptera, Sphingidae) larvae that are parasitized in the first instar determines the timing of emergence of the parasites from the host. Here we show that the first larval ecdysis of the wasps occurs after the host ecdyses to the terminal stage, regardless of whether that stage is the host's fourth, fifth or supernumerary sixth instar. Starvation of newly ecdysed terminal stage host larvae prevents emergence of the parasites. When starvation is begun at progressively later times, then an increasing proportion of the hosts have parasites that emerge, suggesting a period of indispensable host nutrition exists during which the host must feed to satisfy the developmental requirements of the parasites. In hosts fed ad libitum , the weight of the host plus its parasites at the time of emergence is positively correlated with the number of parasites developing in the host. When the weight of the parasites alone is subtracted from the weight of the host—parasite complex, the data show that heavily parasitized hosts have a larger host mass than lightly parasitized larvae. In contrast, the wasp larvae, and the adult males and females that develop from them, have lower individual weights after development in heavily parasitized hosts.     

中红侧沟茧蜂寄生对寄主粘虫血淋巴糖类、脂类和蛋白质含量的影响

为揭示寄生蜂寄生对其寄主的生理调控机制, 室内对中红侧沟茧蜂Microplitis mediator寄生与未被寄生寄主粘虫Mythimna separata幼虫血淋巴中糖类、脂类和蛋白含量变化进行了测定。结果显示: 在滞育与非滞育条件下, 被寄生的粘虫血淋巴中糖原浓度均比未被寄生的粘虫高。滞育条件下寄生后12 d差异显著（P<0.05）, 被寄生粘虫糖原含量为7.93 μg/mL, 未被寄生粘虫糖原含量为4.70 μg/mL; 非滞育条件下寄生后6 d差异显著（P<0.05）, 被寄生粘虫糖原含量为14.35 μg/mL, 未被寄生粘虫糖原含量为5.47 μg/mL。海藻糖含量测定结果显示, 在滞育条件下寄生蜂对被寄生粘虫无明显影响, 而非滞育条件下影响效果差异显著（P<0.05）, 寄生后4 d被寄生粘虫海藻糖含量为46.82 μg/mL, 未被寄生粘虫含量为26.72 μg/mL。在滞育与非滞育两种条件下, 寄生与未被寄生寄主脂类和蛋白含量没有显著性差异。结果说明: 寄生蜂的存在使寄主血淋巴中的糖原含量增高; 非滞育条件是影响被寄生粘虫海藻糖含量变化主要因素; 粘虫对中红侧沟茧蜂的寄生表现相当强的适应性和忍受力。     

Relationships between polydnavirus gene expression and host range of the parasitoid wasp Campoletis sonorensis

To evaluate the relationship between immune suppression and host range six lepidopteran species were parasitized by the ichneumonid parasitoid Campoletis sonorensis. Parasitism inhibited the growth of permissive hosts (Heliothis virescens, Helicoverpa zea, and Trichoplusia ni), whereas growth of semi-permissive (Spodoptera exigua, Agrotis ipsilon) and non-permissive hosts (Manduca sexta) was not significantly affected. The 29-36 kDa ovarian protein (OP), responsible for transient immunosuppression in the permissive host H. virescens, bound to and was endocytosed by hemocytes of permissive and non-permissive hosts. Expression of the cysteine-rich polydnavirus gene, VHv1.4, was detected in all the hosts, but declined only in semi- and non-permissive hosts at later times after parasitization. The VHv1.4 protein bound to hemocytes of permissive and semi-permissive hosts, but did not bind to hemocytes of the non-permissive host, M. sexta. Melanization of larval hemolymph was severely inhibited by parasitism in permissive hosts, but was unaffected in M. sexta. In the semi-permissive host, A. ipsilon, hemolymph melanization was transiently inhibited while viral genes were expressed. In conclusion, C. sonorensis OP transiently inhibits encapsulation in all hosts that were tested. The host range of C. sonorensis seems to be determined by whether or not the C. sonorensis ichnovirus (CsIV) is able to establish persistent infections of parasitized larvae to provide long-term suppression of host immunity.     

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.     

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.     

THE PARASITOID,Cotesia flavipes (CAMERON) (HYMENOPTERA: BRACONIDAE), INFLUENCES FOOD CONSUMPTION AND UTILIZATION BY LARVAL Diatraea saccharalis (F.) (LEPIDOPTERA: CRAMBIDAE)

Parasitoids exploit host insects for food and other resources; they alter host development and physiology to optimize conditions to favor parasitoid development. Parasitoids influence their hosts by injecting eggs, along with a variety of substances, including venoms, polydnaviruses, ovarian fluids, and other maternal factors, into hosts. These factors induce profound changes in hosts, such as behavior, metabolism, endocrine events, and immune defense. Because endoparasitoids develop and consume tissues from within their hosts, it is reasonable to suggest that internal parasitization would also influence host food consumption and metabolism. We report on the effects of parasitism by Cotesia flavipes on the food consumption and utilization of its host, Diatraea saccharalis. Cotesia flavipes reduces the host food consumption, but parasitized larvae considered a unit with their parasitoid's attained the same final weight as the nonparasitized larvae. Nutritional indices, midgut activities of carbohydrases, and trypsin of parasitized and nonparasitized D. saccharalis were assessed. Parasitized larvae had reduced relative food consumption, metabolic and growth rates, coupled with higher efficiency for conversion of the digested, but not ingested, food into body mass. Parasitism also affected food flux through the gut and protein contents in the midgut of parasitized larvae. The activity of α‐amylase and trehalase in parasitized host was enhanced in the first day after parasitism relative to control larvae. Saccharase activity remained unchanged during larval development. Trypsin activity was reduced from the fifth to ninth day after parasitism. We argue on the mechanisms involved in host food processing after parasitism.     

Costs of reproduction and geographic variation in the reproductive tactics of the mosquito Aedes triseriatus

Intraspecific host discrimination is widespread in solitary parasitoids whose adult females forage for and evaluate host suitability, whereas interspecific discrimination is less common. In some parasitoid species, mostly Diptera and Coleoptera, the larva performs the last step of host searching. It has been suggested that host discrimination will rarely occur in such host-seeking larvae because their low mobility results in a low host encounter rate. We determined the extent to which the larvae of Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae), a solitary parasitoid of aggregated Diptera pupae: (1) discriminated between unparasitized hosts and hosts parasitized by conspecifics; (2) used semiochemical cues to discriminate; (3) were influenced by life expectancy, presence of conspecifics and host availability in their host acceptance decision; and the extent to which (4) A. bilineata and A. bipustulata L., a species exploiting the same hosts and occurring sympatrically, showed interspecific host discrimination. A. bilineata larvae were able to discriminate between unparasitized hosts and hosts parasitized by conspecifics in a choice experiment. Such behavior has never previously been described for a coleopteran parasitoid or for a parasitoid species whose larvae perform host searching. Host discrimination in this species was not based on the presence of visual or tactile cues (e.g., entrance holes) but rather on chemical cues. The life expectancy of A. bilineata larvae was significantly shorter in the presence than in absence of hosts, and older larvae had lower parasitism success than young larvae in a 24-h experiment. However, the host acceptance decision of A. bilineata larvae was not influenced by larval age or the presence of conspecifics when the ratio of hosts per larva was greater than or equal to 1. When hosts were scarce, the degree of superparasitism increased significantly with the number of foraging conspecifics and the age of the larvae. Both species of Aleochara showed intra- and interspecific host discrimination in a choice experiment. In contrast to A. bipustulata, A. bilineata larvae more frequently parasitized hosts parasitized by A. bipustulata than those parasitized by conspecifics. We suggest that host discrimination will be frequent in solitary parasitoids with host-seeking larvae when hosts are aggregated. Received: 4 June 1998 / Accepted: 1 September 1998     

Venom of the egg-larval parasitoid Chelonus inanitus is a complex mixture and has multiple biological effects

The egg-larval parasitoid Chelonus inanitus injects bracoviruses (BVs) and venom along with the egg into the host egg; both components are essential for successful parasitoid development. All stages of eggs of its natural host, Spodoptera littoralis, can be successfully parasitized, i.e. from mainly a yolk sphere to a fully developed embryo. Here, we show that the venom contains at least 25 proteins with masses from 14 kDa to over 300 kDa ranging from acidic to basic. The majority is glycosylated and their persistence in the host is short when old eggs are parasitized and much longer when young eggs are parasitized. Physiological experiments indicated three different functions. (1) Venom synergized the effect of BVs in disrupting host development when injected into third instar larvae. (2) Venom had a transient paralytic effect when injected into sixth instar larvae. (3) In vitro experiments with haemocytes of fourth instar larvae suggested that venom alters cell membrane permeability. We propose that venom promotes entry of BVs into host cells and facilitates placement of the egg in the embryo's haemocoel when old eggs are parasitized. The multifunctionality of the venom might thus be essential in enabling parasitization of all stages of host eggs.     

Effects of Microplitis croceipes Teratocytes on Host Haemolymph Protein Content and Fat Body Proliferation

Qualitative and quantitative changes in haemolymph proteins in Heliothis virescens were observed in larvae injected with either Microplitis croceipes teratocytes or teratocyte secreted proteins (TSP). Haemolymph protein titres in hosts receiving either 0.5 or 1 larval equivalent (LE) of teratocytes were similar to those of parasitized larvae, whereas a single injection of 4LE of TSP was required to induce a similar response. SDS-PAGE showed that the 82kDa monomer of riboflavin-binding protein and the 74/76kDa monomers of storage proteins were significantly reduced in parasitized larvae and in nonparasitized larvae treated with TSP. Concentrations of a 155kDa monomer (insectacyanin chromoprotein) also were reduced in parasitized larvae and those injected with either teratocytes or TSP. Two monomers (56 and 60kDa) were unique to parasitized larvae. Treated larvae required several days longer than controls to reach a comparable premetamorphic stage (burrowing-digging). Reductions in fat body proliferation similar to those seen in parasitized larvae were observed in larvae treated with either 1LE of teratocytes, or with 2 or 4LEs of TSP. Perivisceral fat body weights from larvae treated with either 0.25 or 0.5LE of teratocytes were significantly reduced, but less so than those which received 1LE. Thus, fat body proliferation in both teratocyte- and TSP-treated larvae was inhibited in a dose-dependent manner. Both light- and transmission electron microscopy observations revealed cytological differences in fat body tissues of larvae injected with either teratocytes or TSP from the condition observed in parasitized larvae and noninjected controls. Gross dissection of periviseral fat body from parasitized, teratocyte-injected and TSP-injected larvae showed tissue much less developed and differing considerably in appearance from controls. Observed differences included reduced size and/or number of lipid bodies and qualitative and quantitative changes in other cytoplasmic organelles.     

The function of a trypsin-like enzyme in the saliva of Euplectrus separatae larvae

Larvae of the gregarious ectoparasitoid, Euplectrus separatae, a species that parasitizes Pseudaletia separata, migrate from the dorsal to the ventral side of the host larva for pupation 7 days after parasitization. The parasitized host larvae die after the migration. The body mass of the parasitoid larvae increases while that of the host larva drastically decreases. Most of the tissue in the dead host larvae completely collapses. In this study, we examined the cause of host death and how the tissues collapse. Artificial removal of all parasitoid larvae before their migration on day 7 rescued the host larvae, but removal after parasitoid migration did not rescue the hosts. Tissues of the dead host larvae were completely liquefied. Injection of saliva from day 7 parasitoid larvae into host larvae killed the host larvae. High activity of a trypsin-like enzyme was detected in the saliva of day 7 parasitoids. Though phospholipase B and hyaluronidase were also detected in the saliva, commercial phospholipase B and hyaluronidase did not kill the hosts, whereas an injection of commercial trypsin was lethal. The trypsin-injected hosts showed the same tissue collapse as noted in parasitized and saliva-injected hosts. Leupeptin, a trypsin inhibitor, reduced mortality when injected into day 7 hosts (parasitoids were removal following migration). These observations suggest that the day 7 parasitoid larvae release saliva containing a trypsin-like enzyme to digest the host tissues following migration.     

Influence of nutrient deficiency caused by host developmental arrest on the growth and development of a koinobiont parasitoid

Koinobiont parasitoids utilize nutrients obtained from hosts that contine to feed and grow after parasitization. However, if the ecdysis of early host instars is prevented, parasitized larvae will fail to grow large enough to support the development of the parasitoid brood and both organisms will perish. When L5 instar larvae (the penultimate stage) of Pseudaletia separata were parasitized by Cotesia kariyai and injected with Euplectrus separatae venom (5PV), the development of these hosts was arrested before molting to the next stage and the caterpillars thus failed to gain weight. These hosts remained at approximately 300 mg until parasitoid emergence. In contrast, hosts parasitized as L5 but without the injection of venom (5P) exhibited an increase in weight after molting to the next stage and ultimately grew to approximately 700 mg. The inhibition of ecdysis reduced the amount of food resource (e.g. fat body) for the parasitoid larvae. On the other hand, when final (= L6) host instars were parasitized and injected with E. separatae venom (6PV), the maximum weight attained by these larvae was about 710 mg, although weight gain was depressed compared to hosts parasitized without the injection of E. separatae venom (6P). The adult weight of C. kariyai that emerged from 5PV hosts was less than conspecifics that emerged from 5P, 6P, and 6PV respectively, although the egg-pupal period of the parasitoid from 5PV hosts was extended. The offspring sex ratio (percentage males) of adult wasps did not vary significantly with treatment. Female parasitoids that eclosed from 5PV hosts laid almost the same number of eggs in day 0-6th host instars as those emerging from 5P, 6P, 6PV hosts. Their egg-pupal period was extended and the cocoon cluster mass and the parasitoid body mass on subsequent generations was lighter than those reared from 5P, 6P, 6PV hosts. The sex ratio of F2 C. kariyai wasps that eclosed from 5PV increased more than in wasps that eclosed from the other host treatments (5P, 6P, 6PV). Our results reveal that a reduction in host quality and offspring fitness in the first generation negatively impacted female fitness in the second generation. An early arrestment of host growth, mediated by the addition of E. separatae venom, has severe implications on parasitoid fitness by reducing host quality, especially in smaller hosts.     

CLP gene family,a new gene family of Cotesia vestalis bracovirus inhibits melanization of Plutella xylostella hemolymph

Polydnaviruses (PDVs) are obligatory symbionts of parasitoid wasps and play an important role in suppressing host immune defenses. Although PDV genes that inhibit host melanization are known in Microplitis bracovirus, the functional homologs in Cotesia bracoviruses remain unknown. Here, we find that Cotesia vestalis bracovirus (CvBV) can inhibit hemolymph melanization of its host, Plutella xylostella larvae, during the early stages of parasitization, and that overexpression of highly expressed CvBV genes reduced host phenoloxidase activity. Furthermore, CvBV-7-1 in particular reduced host phenoloxidase activity within 12 h, and the injection of anti-CvBV-7-1 antibody increased the melanization of parasitized host larvae. Further analyses showed that CvBV-7-1 and three homologs from other Cotesia bracoviruses possessed a C-terminal leucine/isoleucine-rich region and had a similar function in inhibiting melanization. Therefore, a new family of bracovirus genes was proposed and named as C -terminal L eucine/isoleucine-rich P rotein (CLP). Ectopic expression of CvBV-7-1 in Drosophila hemocytes increased susceptibility to bacterial repression of melanization and reduced the melanotic encapsulation of parasitized D. melanogaster by the parasitoid Leptopilina boulardi. The formation rate of wasp pupae and the eclosion rate of C. vestalis were affected when the function of CvBV-7-1 was blocked. Our findings suggest that CLP genes from Cotesia bracoviruses encoded proteins that contain a C-terminal leucine/isoleucine-rich region and function as melanization inhibitors during the early stage of parasitization, which is important for successful parasitization.     

Does superparasitism improve host suitability for parasitoid development? A case study in the Microplitis rufiventris-Spodoptera littoralis system

Superparasitism refers to the oviposition behavior of parasitoid females who lay their eggs in an already parasitized host. Recent studies have shown that allocation of additional eggs to an already parasitized host may be beneficial under certain conditions. In the present work, mortality of Microplitis rufiventris wasps was significantly influenced by both host instar of Spodoptera littoralis larvae at parasitism and level of parasitism. In single parasitization, all host instars (first through sixth) were not equally suitable. Percentage of emergence success of wasp larvae was very high in parasitized first through third (highly suitable hosts), fell to 60% in the fourth instar (moderate suitable) and sharply decreased in the penultimate (5th) instars (marginally suitable). Singly parasitized sixth (last) instar hosts produced no wasp larvae (entirely unsuitable), pupated and eclosed to apparently normal adult moths. The scenario was different under superparasitism, whereas supernumerary individuals in the highly suitable hosts were almost always killed as first instars, superparasitization in unsuitable hosts (4th through 6th) had significant increase in number of emergence success of wasp larvae. Also, significantly greater number of parasitoid larvae successfully developed in unsuitable hosts containing three wasp eggs than counterparts containing two wasp eggs. Moreover, the development of surplus wasp larvae was siblicidal in earlier instars and nonsiblicidal gregarious one in the penultimate and last “sixth” instars. It is suggested that the optimal way for M. rufiventris to deal with high quality hosts (early instars) is to lay a single egg, while the optimal way to deal with low quality hosts (late instars) might be to superparasitize these hosts.     

The ectoparasitic wasp Eulophus pennicornis (Hymenoptera: Eulophidae) uses instar-specific endocrine disruption strategies to suppress the development of its host Lacanobia oleracea (Lepidoptera: Noctuidae)

To successfully complete its development, the gregarious ectoparasitoid Eulophus pennicornis must inhibit the moult of its host, Lacanobia oleracea. In the present study, we examined the possibility that moult- and metamorphosis-associated endocrine events may be disrupted in caterpillars parasitized as newly moulted last (sixth) instars. Juvenile hormone (JH) titres on days 2 and 5 of the final stadium were significantly higher (> 100 fold) in parasitized than in non-parasitized hosts, in which JH was essentially absent. Elevated JH levels were associated with reduced haemolymph JH esterase (JHE) activity (down by 99.8%) and enhanced in vitro JH biosynthesis by the corpora allata (CA) (up to 4.5 fold). Wasp adults and/or larvae, in which we measured high levels of JH III (up to 2.7 ng/g), but little or no JH I or JH II, were not seen as likely sources of JH in parasitized hosts, in which we found mostly JH I and JH II. In addition, removal of parasitoid eggs or larvae after oviposition did not prevent the rise in JH titres seen in parasitoid-laden hosts, suggesting that wasp venom may be responsible for the observed hormonal dysfunction. Host haemolymph 20-hydroxyecdysone (20-E) levels were largely unaffected by parasitism during the final stadium although they were observed to increase earlier and decrease more rapidly in parasitized insects. We compare these results with those reported earlier for L. oleracea larvae parasitized by E. pennicornis as penultimate (fifth) instars, which display significantly depressed 20-E titres relative to control larvae. We conclude that E. pennicornis employs host endocrine-disruption strategies that differ according to whether the host is parasitized as a penultimate or final-stadium larva.     

The endoparasitoid Cotesia kariyai (Ck) regulates the growth and metabolic efficiency of Pseudaletia separata larvae by venom and Ck polydnavirus

It was previously demonstrated that parasitization by Cotesia kariyai caused a decrease in weight gain and food consumption in host larvae, resulting in a lower final weight for parasitized hosts. It is predicted that C. kariyai regulates the physiological condition of the host to obtain maximum food under restricted nutritional conditions. Approximate digestibility (AD) was higher following parasitization but the efficiency of conversion of digested food (ECD) of the parasitized hosts was lower. This suggests that resources available to the parasitoid larvae are enhanced in the parasitized hosts. We evaluated the physiological changes caused by injection of calyx fluid (polydnavirus) plus venom (C+V) in nonparasitized hosts. Injection of C+V into the nonparasitized hosts duplicated the effects of parasitism, namely it increased the AD and decreased the ECD. Furthermore, C+V injections elevated trehalose concentrations in nonparasitized host 7 to 10 d after injection (2nd stadium of the parasitoid larva). Protein content also increased on days 9 and 10 after C+V injection. These results suggest that the nutrients that parasitoid larvae require for their growth increase in the hemolymph of the host during the 2nd stadium of the parasitoid larva.     

Stage-specific effects of Campoletis sonorensis parasitism on Heliothis virescens development and prothoracic glands

Abstract The ichneumonid endoparasitoid Campoletis sonorensis Cameron (Hymenoptera: Ichneumonidae) injects a polydnavirus when it oviposits into a host. We compared the development of Heliothis virescens (F.) (Lepidoptera: Noctuidae) larvae parasitized in the penultimate (fourth) stadium with those parasitized in the last (fifth) stadium by C.sonorensis and show that hosts stung in the fifth stadium exhibited arrested or delayed development compared to the controls. Parasitoids developed normally to the point of emergence in larvae stung in the fifth stadium but most did not successfully emerge from the host. The prothoracic glands in all successfully parasitized fifth stadium hosts and most unsuccessfully parasitized fifth stadium hosts showed some degree of virally-induced degeneration. Larvae stung in the fourth stadium developed more slowly than controls and either did not moult or developed to a fifth and sometimes a supernumerary sixth stadium before parasitoid emergence. Unsuccessfully parasitized hosts were delayed in their development but eventually moulted to the fifth and, in some cases, a supernumerary sixth stadium before pupating. Hosts stung in the fourth stadium showed no signs of prothoracic gland degeneration whether successfully parasitized or not. In addition, calyx fluid injections into early fourth stadium hosts did not cause prothoracic gland degeneration even after these hosts moulted to the fifth stadium, suggesting that degeneration induced by polydnavirus is specific to the last stadium of the host.