Regulation of wing formation and adult development in an aphid host, Aphis fabae, by the parasitoid Aphidius colemani

Nymphs of presumptive winged gynoparae of Aphis fabae (Hemiptera: Aphididae), were exposed to female parasitoids, Aphidius colemani (Hymenoptera: Aphidiidae) and stung once with the ovipositor. Wing development was inhibited and, when aphids were parasitised during the early stages, they did not reach the adult stage but mummies with rudimentary or no wingbuds are observed in the host's fourth-stadium. These and previous studies have suggested that wing development may be inhibited by factor(s) from the maternal parasitoid injected into the host at the time of oviposition. In an attempt to identify such factor(s), saline extracts of whole female parasitoids, abdomens, ovaries and venom glands were prepared. When a saline extract of venom glands was injected into late-second-stadium aphids, many develop to fourth-stadium nymphs with rudimentary wingbuds, indicating an effect on wing formation but also showed developmental arrest and often died when attempting to moult to the adult stage. It appears that host death may be related to physiological/biochemical interactions of parasitoid and host rather than just late stage parasitoid larvae ingesting the host's vital organs. Injections with extracts into later host stadia gave similar results with regard to development to the adult, although aphids injected in the late-fourth-stadium develop normally to the adult stage with no effect on wing formation. The results indicate that the earlier the injection before the final moult the greater the effect of the injected extract on preventing adult development.Extracts prepared from head + thorax do not affect aphid development and the results indicate that there is an active factor(s) - likely a protein - in the female parasitoid's venom that disrupts wing development and/or inhibits development to the adult stage. Surprisingly, injections of extracts from male parasitoids have similar effects but the location and function of such a factor(s) in males are unknown.     

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.     

Host castration by Aphidius ervi venom proteins

The braconid Aphidius ervi Haliday (Hymenoptera, Braconidae) is an endophagous parasitoid of the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera, Aphididae). Parasitized host aphids show different degrees of castration, a response that is total when parasitoid oviposition takes place in first instar hosts. Deleterious effects on the host reproductive system are already evident by 24h following parasitization, before egg hatching. The effect of parasitoid venom on A. pisum ovaries has been studied by performing microinjections in non-parasitized host aphids and observing the cellular alterations of the apical germaria of ovarioles. Venom injection reproduced the same alterations observed in parasitized aphids, while injections of saline solution did not induce any detectable change. By 24h, the germarial cells of both venom-treated aphids and parasitized aphids showed the absence of the nucleolus and of electron-dense material around the nucleus, frequently referred to as "nuage material". By 48h more evident signs of degeneration were observed, suggesting the possible occurrence of apoptosis. The bioactive component of the venom was both heat- and protease-sensitive. The activity was found in purified fractions that were highly enriched in two proteins with an approximate molecular mass of 21kD and 36kD, respectively. These macromolecules are the most abundant components of A. ervi venom and, unlike many venom proteins of studied parasitic Hymenoptera, are not glycosylated and appear to be subunits of an oligomeric protein. The adaptive significance of host castration is discussed.     

Deadly venom of Asobara japonica parasitoid needs ovarian antidote to regulate host physiology

Asobara japonica (Braconidae) is an endophagous parasitoid developing in Drosophila larvae. The present study shows that A. japonica was never encapsulated in Drosophila melanogaster, and that it caused an overall inhibition of the host encapsulation reaction since injected foreign bodies were never encapsulated in parasitized hosts. Both the number of circulating hemocytes and the phenoloxidase activity decreased in parasitized larvae, and the hematopoietic organ appeared highly disrupted. We also found that A. japonica venom secretions had atypical effects on hosts compared to other braconid wasps. A. japonica venom secretions induced permanent paralysis followed by death of D. melanogaster larvae, whether injected by the female wasp during an interrupted oviposition, or manually injected into unparasitized larvae. More remarkably, these effects could be reversed by injection of ovarian extracts from female wasps. This is the first report that the venom of an endophagous braconid parasitoid can have a deadly effect on hosts, and moreover, that ovarian extracts can act as an antidote to reverse the effects of the wasp's venom. These results also demonstrate that A. japonica secretions from both venom gland and ovary are required to regulate synergistically the host physiology for the success of the parasitoid.     

The influence of parasitism on wing development in male and female pea aphids

Wing formation in presumptive alate morphs (virginoparae and males) was observed for the pea aphid, Acyrthosiphon pisum, exposed to attack by the parasitoid, Aphidius ervi, at different stages of host development. Morphological abnormalities in parasitized aphids such as complete apterization (development of a wingless form), formation of rudimentary wing buds, and deformed wings indicate a possible disruption of the endocrine system. Changes in the body shape and the number of olfactory secondary rhinaria on the antennae could indicate an influence of juvenile hormone in parasitized A. pisum but the development of fifth-stadium supernumerary larvae (indicated by an extra moult and which can be induced by exogenous juvenile hormone treatments) was not found in parasitized aphids. In addition, while apterization of virginoparae can also be induced by the pro-allatocidal compound Precocene III, this was not possible in the male. Males which survived parasitoid attack without forming aphid mummies (indicating that oviposition had not occurred) developed as wingless individuals suggesting that the reproductive-tract-fluids from the female parasitoid were important in the wing inhibition process. Teratocytes from the parasitoid appeared to promote developmental arrest in parasitized aphids.     

Pea aphid clonal resistance to the endophagous parasitoid Aphidius ervi

The physiological mechanism of resistance to the endophagous braconid Aphidius ervi Haliday (Hymenoptera, Braconidae) by a pink clone (PC) of Acyrthosiphon pisum (Harris) (Homoptera, Aphididae) has been investigated. Comparative data on parasitoid development and associated host biochemical changes in the resistant PC aphids and in a susceptible green clone (GC) of A. pisum are reported. When the PC aphids were attacked as early 4th instars, the developing parasitoid larvae showed a strongly reduced increase in size, compared to those synchronously developing in GC aphids, and were unable to produce a regular mummy. In contrast, parasitism of 2nd instar PC aphids, allowed completion of parasitoid development, but adults had a prolonged developmental time, due to a longer duration of parasitoid’s final (3rd) instar. In all cases, teratocytes, cells deriving from the A. ervi serosal membrane, and the proteins abundantly synthesised by them, were never found in the haemolymph of parasitised PC aphids. Host castration, as demonstrated by total protein incorporation into reproductive tissues, was total in the majority of early (2nd instar) parasitised host aphids, while it was limited when later instars (4th) of PC aphids were parasitised. This is partly due to the absence of the cytolytic activity of teratocytes on host embryos, which, through their persistence, may compete for nutritional resources with the developing parasitoid larvae. In parasitised PC aphids, this competitive effect is further aggravated for the parasitoid by the absence of the regulated amino acid titre increase in the host haemolymph, which is regularly observed in GC aphids. Failure of teratocyte development in the PC clone of the pea aphid is, then, the major functional constraint accounting for the reduction/inhibition of A. ervi larval growth. The reported results allow to assess in vivo the role of teratocytes in the host physiological redirection and nutritional exploitation by the parasitoid, and to integrate and validate the proposed physiological model of host-parasitoid interactions in the system A. pisum-A.ervi.     

Changes in the haemolymph proteome of Spodoptera littoralis induced by the parasitoid Chelonus inanitus or its polydnavirus and physiological implications

The egg-larval parasitoid Chelonus inanitus induces in its host Spodoptera littoralis two major developmental effects, namely a precocious onset of metamorphosis followed by a developmental arrest in the prepupal stage. Along with each egg, the wasp injects polydnavirus and venom into the host egg. The polydnavirus has been shown to play a major role in inducing the developmental arrest while the parasitoid larva is instrumental in inducing the precocious onset of metamorphosis. Here we report that experimental dilution of haemolymph of polydnavirus-containing larvae can partially prevent the developmental arrest while injection of native, but not of heat-treated, haemolymph or plasma from polydnavirus-containing larvae into nonparasitized larvae could induce developmental arrest in 14-15% of the larvae. This illustrates that heat-labile factors present in haemolymph play a role in causing developmental arrest. Injection of parasitoid medium increased the proportion of larvae entering metamorphosis precociously while injection of antibodies against a parasitoid-released protein had the opposite effect; this indicates that this protein and possibly other parasitoid-released substances are involved in inducing the precocious onset of metamorphosis. Analysis of the plasma proteome of nonparasitized, parasitized and polydnavirus-containing larvae revealed that the developmental effects are associated with only minor differences: eleven low abundant viral or virus-induced proteins and five parasitoid-released proteins were seen at specific stages of the host.     

Physiological and endocrine changes associated with polydnavirus/venom in the parasitoid-host system Chelonus inanitus-Spodoptera littoralis

As shown earlier, parasitization by the egg-larval parasitoid C. inanitus causes in its host the precocious onset of metamorphosis in the 5th instar followed by developmental arrest in the prepupal stage. Polydnavirus/venom were shown to be responsible for the developmental arrest. We investigated how polydnavirus/venom affect growth of the host larvae and found that head capsule widths were smaller from the 4th to 6th stadium and weights were lower in the 6th stadium in polydnavirus/venom-containing larvae than in non-parasitized larvae. In an attempt to identify endocrine parameters that are modified by polydnavirus/venom and might be responsible for the developmental arrest in the prepupa, we compared juvenile hormones, juvenile hormone esterase and ecdysteroids between non-parasitized and polydnavirus/venom-containing larvae from the 4th instar until pupation or developmental arrest, respectively. Obvious differences became manifest only in the 6th instar at the pupal cell formation stage, i.e. 12 days after entry of polydnavirus/venom into the host egg. Then, prothoracic glands of polydnavirus/venom-containing larvae released less ecdysteroids and ecdysteroid titres were lower than in non-parasitized larvae; this was followed by a delayed, reduced and desynchronized increase in prepupal juvenile hormones and juvenile hormone esterase and a slightly modified metabolism of ecdysone. This indicates that polydnavirus/venom affects the endocrine system of the host only after pupal commitment and that inhibition of prothoracic gland activity is the first detectable effect.     

Non‐consumptive effects of a natural enemy on a non‐prey herbivore population

1. Predator–prey interactions have traditionally focused on the consumptive effects that predators have on prey. However, predators can also reduce the abundance of prey through behaviourally‐mediated non‐consumptive effects. For example, pea aphids (Acyrthosiphon pisum Harris) drop from their host plants in response to the risk of attack, reducing population sizes as a consequence of lost feeding opportunities. 2. The objective of the present study was to determine whether the non‐consumptive effects of predators could extend to non‐prey herbivore populations as a result of non‐lethal incidental interactions between herbivores and foraging natural enemies. 3. Polyculture habitats consisting of green peach aphids (Myzus persicae Sulzer) feeding on collards and pea aphids feeding on fava beans were established in greenhouse cages. Aphidius colemani Viereck, a generalist parasitoid that attacks green peach aphids but not pea aphids, was released into half of the cages and the abundance of the non‐host pea aphid was assessed. 4. Parasitoids reduced the population growth of the non‐host pea aphid by increasing the frequency of defensive drops; but this effect was dependent on the presence of green peach aphids. 5. Parasitoids probably elicited the pea aphid dropping behaviour through physical contact with pea aphids while foraging for green peach aphids. It is unlikely that pea aphids were responding to volatile alarm chemicals emitted by green peach aphids in the presence of the parasitoid. 6. In conclusion, the escape response of the pea aphid provided the opportunity for a parasitoid to have non‐target effects on an herbivore with which it did not engage in a trophic interaction. The implication is that natural enemies with narrow diet breadths have the potential to influence the abundance of a broad range of prey and non‐prey species via non‐consumptive effects.     

Functional analysis of a fatty acid binding protein produced by Aphidius ervi teratocytes

Aphidius ervi (Hymenoptera, Braconidae) is an endophagous parasitoid of various aphid species, including Acyrthosiphon pisum (Homoptera, Aphididae), the model host used in the present study. Parasitized hosts show a marked increase of their nutritional suitability for the developing parasitoid larvae. This alteration of the biochemical and metabolic profile is due to a castration process mediated by the combined action of the venom, injected at the oviposition, and of the teratocytes, cells deriving from the dissociation of the embryonic membrane. Teratocytes produce and release in the host haemocoel two parasitism-specific proteins, which are of crucial importance for the development of their sister larvae. One of the proteins is a fatty acid binding protein (Ae-FABP), which shows a high affinity for C14-C18 saturated fatty acids (FAs) and for oleic and arachidonic acids. To better define the possible nutritional role of this protein, we have studied its immunolocalization profile in vivo and the impact on FA uptake by the epidermal and midgut epithelia of A. ervi larvae. During the exponential growth of A. ervi larvae, Ae-FABP is distributed around discrete lipid particles, which are abundantly present in the haemocoel of parasitized host aphids and in the midgut lumen of parasitoid larvae. Moreover, a strong immunodetection signal is evident on the surface of the two larval epithelia involved in nutrient absorption: the parasitoid midgut epithelium and the external epidermal layer. These two epithelia can effectively absorb radiolabelled myristic acid, but the FA transport rates are not affected by the presence in the medium of Ae-FABP. The protein appears to act essentially as a vector in the host haemolymph, transferring FAs from the digestion sites of host lipids to the growing parasitoid larvae. These data indicate that the proteins produced by A. ervi teratocytes may play complementary roles in the nutritional exploitation of the host.     

EVOLUTION OF AN APHID-PARASITOID INTERACTION: VARIATION IN RESISTANCE TO PARASITISM AMONG APHID POPULATIONS SPECIALIZED ON DIFFERENT PLANTS

The evolution of associations between herbivorous insects and their parasitoids is likely to be influenced by the relationship between the herbivore and its host plants. If populations of specialized herbivorous insects are structured by their host plants such that populations on different hosts are genetically differentiated, then the traits affecting insect-parasitoid interactions may exhibit an associated structure. The pea aphid (Acyrthosiphon pisum) is a herbivorous insect species comprised of genetically distinct groups that are specialized on different host plants (Via 1991a, 1994). Here, we examine how the genetic differentiation of pea aphid populations on different host plants affects their interaction with a parasitoid wasp, Aphidius ervi. We performed four experiments. (1) By exposing pea aphids from both alfalfa and clover to parasitoids from both crops, we demonstrate that pea aphid populations that are specialized on alfalfa are successfully parasitized less often than are populations specialized on clover. This difference in parasitism rate does not depend upon whether the wasps were collected from alfalfa or clover fields. (2) When we controlled for potential differences in aphid and parasitoid behavior between the two host plants and ensured that aphids were attacked, we found that pea aphids from alfalfa were still parasitized less often than pea aphids from clover. Thus, the difference in parasitism rates is not due to behavior of either aphids or wasps, but appears to be a physiologically based difference in resistance to parasitism. (3) Replicates of pea aphid clones reared on their own host plant and on a common host plant, fava bean, exhibited the same pattern of resistance as above. Thus, there do not appear to be nutritional or secondary chemical effects on the level of physiological resistance in the aphids due to feeding on clover or alfalfa, and therefore the difference in resistance on the two crops appears to be genetically based. (4) We assayed for genetic variation in resistance among individual pea aphid clones collected from clover fields and found no detectable genetic variation for resistance to parasitism within two populations sampled from clover. This is in contrast to Henter and Via's (1995) report of abundant genetic variation in resistance to this parasitoid within a pea aphid population on alfalfa. Low levels of genetic variation may be one factor that constrains the evolution of resistance to parasitism in the populations of pea aphids from clover, leading them to remain more susceptible than populations of the same species from alfalfa.     

Interaction of calyx fluid and venom from Microplitis croceipes (Braconidae) on developmental disruption of the natural host,Heliocoverpa zea,and two atypical hosts,Galleria mellonella and Spodoptera exigua

Polydnaviruses of many braconid and ichneumonid endoparasitoids play an important role in the successful parasitism of their hosts. The host's development is altered and its immune response is also suppressed. In this study, we compared the effects of calyx fluid and venom on the development of the natural host, Helicoverpa zea, and two atypical hosts that the parasitoid does not normally attack in nature, Galleria mellonella and Spodoptera exigua. The levels of calyx fluid and\or venom injected was 0.05, 0.1 and 0.2 female equivalents (FE)/larva. In H. zea, calyx fluid significantly reduced larval growth on day 5 post injection. Venom alone did not affect larval growth but it synergized the action of calyx fluid by reducing growth earlier and for a longer period after injection. Other effects of calyx fluid on the host, either alone or in combination with venom, were an increase in developmental period, and a reduction in percent emergence and weight of adult moths. The percentage of H. zea larvae that pupated was not affected by calyx fluid or venom. In Galleria mellonella, venom alone reduced larval growth comparable to calyx fluid and both tissues induced the effects on day 1 post injection. Other effects caused by calyx fluid or venom alone or the combination were a reduction in percent pupation and emergence, and the average adult weight. In S. exigua, high mortality occurred when 4th instar larvae were injected. Although the injection of larger fifth instars reduced overall mortality, the sham-injected larvae only gained weight during the first 24 hours after injection (from day 0 to day 1). However, adults were produced at all doses of calyx fluid or venom. The effects of the virus on development in this species were a prolongation of the larval stage and reduction of adult weight by calyx fluid in combination with venom. In conclusion, injections of calyx fluid and venom of Microplitis croceipes can differentially affect the growth and development of its natural host H. zea, and atypical host, G. mellonella, but only a minimal effect was observed in S. exigua.     

Host regulation effects on Heliothis virescens (F.) larvae inducd by teratocytes of Cardiochiles nigriceps Viereck (Lepidoptera,Noctuidae-Hymenoptera,Braconidae)

Teratocytes deriving from the serosal membrane of Cardiochiles nigriceps Viereck, obtained “in vitro” from embryos hatched on a semidefined medium, were injected at different numbers and in different developmental stages of nonparasitized Heliothis virescens (F.) last instar larvae. Host development was affected by teratocyte injections and the responses registered ranged from normal to complete inhibition of pupation, according to the number of teratocytes injected and the developmental stage of the larva at time of injection. Complete pupation failure was observed when teratocytes derived from 4C nigriceps embryos were injected into 1st day 5th instar (new-slender stage) host larvae. Complete pupation occurred when teratocytes from 2 embryos were injected into 3rd or 4th day 5th instars (burrow-digging or day 1 cell formation stage). Intermediate responses, such as the formation of pupal cuticle without ecdysis or with only partial ecdysis, were obtained with intermediate teratocyte numbers, or host developmental stages. All pupae derived from teratocyte injected larvae failed to develop into adults normally obtained from control injected larvae. The larval weight just before pupation was negatively affected only when teratocyte injections were performed on 1st day 5th instar H. virescens larvae. Teratocyte injections altered the hemolymph protein titer to a level similar to that occurring in parasitized larvae. At the same time the ecdysteroid titer was characterized by a late significant increase, which reached values almost 3 times greater than found in normally parasitized larvae, and also surpassed the highest values registered for nonparasitized larvae. Ligation of parasitized larvae between the meso- and metathorax demonstrated that when the prothoracic glands were excluded, there was almost no ecdysteroid production posterior to the ligation. Ligations performed on parasitized larvae to isolate parasitoid eggs before hatching in the last abdominal segments, demonstrated that only virus and venom determined a reduction of the ecdysteroid titer. On the basis of these results the possible role of teratocytes in affecting the biological activity of ecdysteroids is postulated and discussed in a wider context of host-parasitoid physiological interactions.     

Presence of an unsuitable host diminishes the competitive superiority of an insect parasitoid: a distraction effect

Competitive interactions between parasitoid species are traditionally evaluated when they compete for a single host species. Yet, the presence of additional host species can alter competitive interactions, even if the host is unsuitable for parasitoid development. In alfalfa of the mid-western USA, a native parasitoid species, Praon pequodorum, was once a dominant natural enemy, but it has become rare since the introduction of another parasitoid, Aphidius ervi. Despite A. ervi’s competitive superiority for their most common host, the pea aphid Acyrthosiphum pisum, P. pequodorum still persists at low densities. We performed a suite of laboratory and field studies to determine if the presence of an alternative host, the spotted alfalfa aphid Therioaphis maculata, may mitigate A. ervi’s competitive superiority and facilitate P. pequodorum’s persistence. We show that spotted alfalfa aphids reduce the foraging efficiency of both parasitoid species for pea aphids, despite spotted alfalfa aphids being an unsuitable host. This decrease in efficiency, however, was not symmetrical; the presence of spotted alfalfa aphids had a greater detrimental effect on A. ervi foraging for pea aphids. This might facilitate the persistence of the competitively inferior P. pequodorum. Our study suggests that indirect effects generated by the presence of alternative hosts are important for understanding parasitoid–host dynamics and overall insect community structure.     

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.     

Effects of female wasp accessory secretions, host fat body, and host hemolymph on protein synthesis and egg viability in Microplitis croceipes (Braconidae)

Effects of female wasp reproductive gland secretions, host fat body and hemolymph, and mechanical constriction of the parasitoid egg on protein synthesis were studied in eggs of Microplitis croceipes (Braconidae) dissected from the wasp ovary. Protein synthesis was measured by 35S-methionine incorporation in eggs held in tissue culture medium for 16 h after treatment. Synthesis was stimulated in oocytes obtained from three regions of the ovary (egg tube, reservoir, and calyx) by fat body and venom gland but not by calyx fluid. A combination of fat body, venom gland, and calyx fluid did not enhance the level of synthesis relative to that of fat body or venom gland alone. Host hemolymph inhibited protein synthesis when incubated directly with the dissected eggs but not when the eggs were collected from an artificial oviposition substrate (AOS) containing hemolymph. The inhibitory effect of the hemolymph is thought to be due to the occurrence of melanization. Mechanical constriction did not alter the rate of synthesis, confirming an earlier report that synthesis in newly deposited eggs in ongoing and is not dependent on mechanical activation during the act of oviposition. Mechanisms responsible for sustaining protein synthesis in eggs for 16 h in vitro after their exposure to host hemolymph in the AOSs or fat body and venom gland are not known. Only a small percentage (less than 2%) of dissected ovarial reservoir oocytes that were mechanically constricted and exposed to the venom gland, calyx fluid, and host fat body hatched in vitro. In contrast, an earlier study demonstrated that 38% of eggs oviposited by female wasps into AOSs developed and hatched.     

菜蛾盘绒茧蜂多分DNA病毒的特性及其对小菜蛾幼虫的生理效应

对菜蛾盘绒茧蜂Cotesia plutellae多分DNA病毒的特性及其对寄主小菜蛾Plutella xylostella幼虫的生理效应进行了研究。结果表明：菜蛾盘绒茧蜂雌蜂输卵管萼中含有大量的多分DNA病毒（polydnavirus, PDV）;一个PDV内含多个核衣壳,最多可达16个;核衣壳长40～168 nm,直径39～40 nm;PDV仅在输卵管萼细胞内复制;雌蜂产卵时,随蜂卵将PDV注入寄主血腔,并扩散到寄主的许多组织中;PDV可能先通过脱膜再侵染寄主组织。雌蜂经Co⁶⁰辐射处理后再寄生（即假寄生）小菜蛾2龄、3龄和4龄初期的幼虫,被寄生后的寄主幼虫几乎全部不能化蛹,但末龄（即4龄）幼虫期显著延长,并在寄生后期,幼虫胸部有褐色的短翅芽出现;即将化蛹的4龄末小菜蛾幼虫被假寄生后,即使每头寄主被过寄生9次,依然能正常化蛹,但不能羽化。假寄生与正常寄生后寄主的脂肪体数量和形态结构有明显的不同,推测在正常寄生的情况下蜂卵孵化时释放的畸形细胞及随后的幼蜂可能对脂肪体的结构产生了作用。     

Overview of parasitism associated effects on host haemocytes in larval parasitoids and comparison with effects of the egg-larval parasitoid Chelonus inanitus on its host Spodoptera littoralis

In the first part we review the effects of larval endoparasitoids and their polydnavirus and venom on the immune system of their hosts. In all systems investigated, haemocyte spreading and encapsulation activity was reduced; in some cases effects on total (THC) or differential (DHC) haemocyte count as well as modification of haemocyte morphology and ultrastructure were also documented. In many cases polydnavirus (and venom) were shown to play a major role in abrogation of the host's immune reaction. In the second part we present the first investigation of effects of parasitism and polydnavirus/venom on the immune system of the host for an egg-larval parasitoid, Chelonus inanitus. We observed that in 4th and 5th instar larvae, i.e. 7 to 10 days after parasitization, neither haemocyte spreading and encapsulation activity, nor DHC, nor haemocyte ultrastructure were altered. After parasitization with X-ray irradiated wasps, which inject polydnavirus and venom and infertile eggs, there was no alteration of the above mentioned parameters. Nevertheless, parasitoid larvae implanted into 4th instar larvae which developed from eggs parasitized with X-ray irradiated wasps were not encapsulated, whereas co-injected latex beads were. These results show that parasitism by this egg-larval parasitoid does not generally suppress the host's immune system but that polydnavirus/venom injected at oviposition prevent, by, as yet unknown mechanisms, encapsulation of the parasitoid larva.     

Chelonus sp. near curvimaculatus venom proteins: Analysis of their potential role and processing during development of host Trichoplusia ni

The venom that Chelonus sp. near curvimaculatus injects into each parasitized Trichoplusia ni egg is entirely injected within the first 8 s of the 19-s oviposition period, before deposition of the parasitoid egg that is injected during the final 1-2 s of the oviposition. The parasitization factor, causing precocious metamorphosis of the host, is injected after the venom, but before the parasite egg. The venom by itself does not cause developmental redirection of the host. Chelonus venom proteins are very stable in the host egg during the first 2 days of egg development. Then, on the last day before hatching, they are rapidly degraded by the proteolytic enzymes appearing in 3-day-old T. ni eggs. Among those that degrade the venom proteins are serine-type proteinases, and at least one seems to be a trypsin-like enzyme.