The ectoparasitic wasp Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) differentially affects cells mediating the immune response of its flesh fly host,Sarcophaga bullata Parker (Diptera: Sarcophagidae)

In this study, we examined cellular immune responses in the flesh fly, Sarcophaga bullata, when parasitized by the ectoparasitoid Nasonia vitripennis. In unparasitized, young pharate adults and third instar, wandering larvae of S. bullata, four main hemocyte types were identified by light microscopy: plasmatocytes, granular cells, oenocytoids, and pro-hemocytes. Parasitism of young pharate adults had a differential effect on host hemocytes; oenocytoids and pro-hemocytes appeared to be unaltered by parasitism, whereas adhesion and spreading behavior were completely inhibited in plasmatocytes and granular cells by 60 min after oviposition. The suppression of spreading behavior in granular cells lasted the duration of parasitism. Plasmatocytes were found to decline significantly during the first hour after parasitism and this drop was attributed to cell death. Melanization and clotting of host hemolymph did not occur in parasitized flies, or the onset of both events was retarded by several hours in comparison to unparasitized pharate adults. Hemocytes from envenomated flies were altered in nearly identical fashion to that observed for natural parasitism; the total number of circulating hemocytes declined sharply by 60 min post-envenomation, the number of plasmatocytes declined but not granular cells, and the ability of plasmatocytes and granular cells to spread when cultured in vitro was abolished within 1 h. As with parasitized hosts, the decrease in plasmatocytes was due to cell death, and inhibition of spreading lasted until the host died. Isolated crude venom also blocked adhesion and spreading of these hemocyte types in vitro. Thus, it appears that maternally derived venom disrupts host immune responses almost immediately following oviposition and the inhibition is permanent. The possibility that this ectoparasite disables host defenses to afford protection to feeding larvae and adult females is discussed.     

Parasitism and venom of ectoparasitoid Scleroderma guani impairs host cellular immunity

Venom is a prominently maternal virulent factor utilized by parasitoids to overcome hosts immune defense. With respect to roles of this toxic mixture involved in manipulating hosts immunity, great interest has been mostly restricted to Ichneumonoidea parasitoids associated with polydnavirus (PDV), of which venom is usually considered as a helper component to enhance the role of PDV, and limited Chalcidoidea species. In contrast, little information is available in other parasitoids, especially ectoparasitic species not carrying PDV. The ectoparasitoid Scleroderma guani injects venom into its host, Tenebrio molitor, implying its venom was involved in suppression of hosts immune response for successful parasitism. Thus, we investigated the effects of parasitism and venom of this parasitoid on counteracting the cellular immunity of its host by examining changes of hemocyte counts, and hemocyte spreading and encapsulation ability. Total hemocyte counts were elevated in parasitized and venom‐injected pupae. The spreading behavior of both granulocytes and plasmatocytes was impaired by parasitization and venom. High concentration of venom led to more severely increased hemocyte counts and suppression of hemocyte spreading. The ability of hemocyte encapsulation was inhibited by venom in vitro. In addition to immediate effects observed, venom showed persistent interference in hosts cellular immunity. These results indicate that venom alone from S. guani plays a pivotal role in blocking hosts cellular immune response, serving as a regulator that guarantees the successful development of its progenies. The findings provide a foundation for further investigation of the underlying mechanisms in immune inhibitory action of S. guani venom.     

腰带长体茧蜂寄生对亚洲玉米螟幼虫体内酚氧化酶活性的影响

通过对被腰带长体茧蜂Macrocentrus cingulum Brischke寄生的5龄亚洲玉米螟Ostrinia furnacalis Guenée幼虫体内不同组织中酚氧化酶活性的测定,采用体外注射腰带长体茧蜂雌性成蜂的萼液成分、毒液成分、萼液与毒液混合物的方法,研究了寄生蜂各种主要生理因子对寄主血清中酚氧化酶活性的影响。结果表明： 寄生蜂寄生可明显抑制寄主体内的酚氧化酶活性,减少黑色素产生;被寄生组FITC标记的血细胞阳性百分率低于未被寄生组,差异极显著( P<0.01）;萼液成分可明显地抑制亚洲玉米螟幼虫血清中酚氧化酶的活性 （P<0.01）;萼液与毒液混合物对酚氧化酶活性也有明显抑制作用（P<0.01）。研究认为寄生蜂产卵时注入的萼液、毒液可对寄主昆虫酚氧化酶活性产生明显的抑制作用,其中萼液是抑制寄主免疫能力的主要因素。     

Parasitism of Lacanobia oleracea (lepidoptera) by the ectoparasitic wasp, Eulophus pennicornis, disrupts the cytoskeleton of host haemocytes and suppresses encapsulation in vivo

Parasitism of Lacanobia oleracea larvae by the ectoparasitic wasp Eulophus pennicornis suppressed host haemocyte-mediated encapsulation of Sephadex DEAE A-25 beads in vivo. Beads dissected out of parasitized larvae had fewer haemocytes associated with them. Moreover, those haemocytes that were associated with the beads tended to retain a rounded configuration and rarely flattened. Similar results were obtained using in vitro encapsulation assays. SDS PAGE indicated that for parasitized and PBS injected larvae, there were some differences in the plasma proteins that bound to Sephadex DEAE A-25 beads, suggesting that parasitism-mediated changes to host plasma proteins might contribute to the differences in the encapsulation response occurring in these larvae. However, in vitro encapsulation assays using beads that had been pre-incubated in plasma from parasitized and unparasitized larvae, demonstrated that major differences in the extent of encapsulation did not occur. These results, plus in vitro haemocyte attachment and spreading assays, suggest that parasitism-mediated suppression of encapsulation is primarily due to reductions in the ability of host haemocytes to attach to (i.e., recognize) and flatten over non-self surfaces and other haemocytes. This proposal is corroborated by staining of actin in the haemocyte cytoskeleton by FITC-labelled phalloidin, which indicated that parasitism disrupts the formation of stress fibers and focal adhesions in plasmatocytes. By contrast, experimental injection of adult female wasp venom into unparasitized L. oleracea larvae had no significant effect on in vivo encapsulation responses or the haemocyte cytoskeleton. Arch. Insect Biochem. Physiol. 49:108-124, 2002. Published 2002 Wiley-Liss, Inc.     

Calyx fluid proteins of two Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) biotypes in Kenya: implications to biological control of the stem borer Busseola fusca (Fuller) (Lepidoptera: Noctuidae)

Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) is an indigenous larval endoparasitoid of Busseola fusca (Fuller) (Lepidoptera: Noctuidae) in sub-Saharan Africa. In Kenya, reports suggest that C. sesamiae occurs as two biotypes. Biotype avirulent to B. fusca gets encapsulated by haemocytes in this host and is unable to complete development. Biotype virulent to B. fusca is able to overcome immune defences. Factors present in the calyx fluid such as the PolyDNAviruses (PDV), venom and calyx fluid proteins have been implicated in the variation of C. sesamiae virulence against B. fusca. In the present study, calyx fluid proteins of the two C. sesamiae biotypes were compared using 2-D gel electrophoresis. More protein spots were observed in the virulent parasitoid calyx fluid, but some proteins were specifically observed in the avirulent parasitoid calyx fluid while others were observed in both. To study changes in proteins due to parasitism of B. fusca larvae by the two strains, SDS-PAGE gel were performed on fat body tissues and the haemolymph at three time points. Differences between the two strains were observed in both the fat body and haemolymph tissues. Parasitism-specific protein bands were detectable in fat body tissues of B. fusca larvae parasitized by the two C. sesamiae strains. These proteins were absent in unparasitized larvae. Implications for using C. sesamiae as a biocontrol agent of B. fusca in Africa are discussed.     

Performance of Microplitis tuberculifer (Hymenoptera: Braconidae) parasitizing Mythimna separata (Lepidoptera: Noctuidae) in different larval instars

The solitary parasitoid Microplitis tuberculifer (Wesmael) is an important biological control agent of various lepidopteran pests in Asia. We examined the preference of M. tuberculifer for different instars of its common host, Mythimna separata (Walker), host instar effects on parasitoid development, and the consequences of parasitism in different stages for growth and consumption of host larvae. The wasp successfully parasitized the first four larval instars of M. separata, but not the fifth, which appeared to be behaviorally resistant. First and second instars were parasitized at higher rates compared to thirds and fourths in no-choice situations, ostensibly due to longer handling times for the latter, but second instars were most preferred in a choice test that presented all stages simultaneously. Although later instar hosts yielded heavier cocoons, the fastest parasitoid development was obtained in second instars. Lower sex ratios were obtained from first instars as females appeared to lay a smaller proportion of fertilized eggs in small hosts. Both weight gain and food consumption of parasitized larvae were reduced significantly within 24 h of parasitism, regardless of the stage parasitized, and final body weights were less than 10% those of unparasitized larvae. Thus, M. tuberculifer has good potential as a biological control agent of M. separata, successfully parasitizing the first four larval instars and dramatically reducing plant consumption by the host in all cases.     

The raspberry Gene Is Involved in the Regulation of the Cellular Immune Response in Drosophila melanogaster

Drosophila is an extremely useful model organism for understanding how innate immune mechanisms defend against microbes and parasitoids. Large foreign objects trigger a potent cellular immune response in Drosophila larva. In the case of endoparasitoid wasp eggs, this response includes hemocyte proliferation, lamellocyte differentiation and eventual encapsulation of the egg. The encapsulation reaction involves the attachment and spreading of hemocytes around the egg, which requires cytoskeletal rearrangements, changes in adhesion properties and cell shape, as well as melanization of the capsule. Guanine nucleotide metabolism has an essential role in the regulation of pathways necessary for this encapsulation response. Here, we show that the Drosophila inosine 5''-monophosphate dehydrogenase (IMPDH), encoded by raspberry (ras), is centrally important for a proper cellular immune response against eggs from the parasitoid wasp Leptopilina boulardi. Notably, hemocyte attachment to the egg and subsequent melanization of the capsule are deficient in hypomorphic ras mutant larvae, which results in a compromised cellular immune response and increased survival of the parasitoid.     

Influence of host plant nitrogen fertilization on hemolymph protein profiles of herbivore Spodoptera exigua and development of its endoparasitoid Cotesia marginiventris

Nitrogen has complex effects on plant–herbivore–parasitoid tritrophic interactions. The negative effects of low nitrogen fertilization in host plants on insect herbivores can be amplified to the higher trophic levels. In the present study, we examined the impact of varying nitrogen fertilization (42, 112, 196, and 280 ppm) of cotton plants (Gossypium hirsutum L.) on the interactions between the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), and the hymenopteran endoparasitoid Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae). We predicted that the development and fitness of C. marginiventris would be adversely affected by low host plant nitrogen fertilization through the herbivore S. exigua. The percentage of C. marginiventris offspring developing to emerge and spin a cocoon, and total mortality of parasitized S. exigua larvae were unaffected by nitrogen level. The developmental time of C. marginiventris larvae in S. exigua larvae feeding on low (42 ppm) nitrogen cotton plants was approximately 30% longer than that of those feeding on higher (112, 196, and 280 ppm) nitrogen plants. Parasitoid size (length of right metathoracic tibia), a proxy for fitness, of C. marginiventris males was positively affected by nitrogen level. Total amounts of S. exigua hemolymph proteins were not affected by nitrogen level, but were reduced by parasitism by C. marginiventris. Two proteins with molecular weights of ca. 84 and 170 kDa dominated the S. exigua larval hemolymph proteins. Concentrations of the 170 kDa hemolymph protein were unaffected by nitrogen treatment, but parasitism reduced concentrations of the 170 kDa protein. Concentrations of the 84 kDa protein, on the other hand, were interactively affected by parasitism and nitrogen treatment: higher nitrogen fertilization (112, 196, and 280 ppm) increased protein concentrations relative to the 42 ppm treatment for unparasitized S. exigua larvae, whereas nitrogen treatment had no effects on parasitized larvae. For S. exigua larvae feeding on 42 ppm nitrogen plants, parasitism increased concentration of the 84 kDa protein, while for those feeding on 112, 196, and 280 ppm nitrogen plants, parasitism decreased concentrations of the protein. Possible mechanisms and ecological consequences for the extended development of C. marginiventris on S. exigua hosts grown on low-nitrogen plants are discussed.     

Interactions between Spathius agrili (Hymenoptera: Braconidae) and Tetrastichus planipennisi (Hymenoptera: Eulophidae), larval parasitoids of Agrilus planipennis (Coleoptera: Buprestidae)

Three hymenopteran parasitoids native to China are being released in the United States as biological control agents for the emerald ash borer (EAB), Agrilus planipennis Fairmaire, an Asian buprestid species responsible for mortality of ash trees (Fraxinus spp.) in North America. Two of these hymenopterans, Spathius agrili Yang (Braconidae), a larval ectoparasitoid, and Tetrastichus planipennisi Yang (Eulophidae), a larval endoparasitoid, prefer late-instar EAB larvae. This overlapping host preference raises concerns that interspecific competition following field releases may compromise establishment of one or both species. In a series of laboratory and field experiments, we found S. agrili and T. planipennisi exhibited similar parasitism rates when presented alone with EAB larvae for 12–14 days. However, S. agrili was more efficient at locating and parasitizing hosts within the first 27 h, possibly explaining why S. agrili excluded T. planipennisi in the laboratory trials and nearly excluded T. planipennisi in field trials when the two species were presented together with EAB larvae. We found that S. agrili parasitized larvae previously parasitized by T. planipennisi but not the reverse. However, S. agrili offspring failed to complete development on hosts that were previously parasitized by T. planipennisi. We recommend releasing these species separately in time or space to avoid the antagonistic interactions observed in this study.     

Haemocytes immunity of rose sawfly,Arge ochropus (Hym.: Argidae) against entomopathogenic nematodes,Steinernema carpocapsae and Heterorhabditis bacteriophora

The rose sawfly, Arge ochropus (Gmelin), is one of the most destructive pests attacking rose bushes in northern Iran. In the present study, the haemocyte reactions of A. ochropus larvae were assessed against two entomopathogenic nematodes, Steinernema carpocapsae (Weiser) and Heterorhabditis bacteriophora Poinar. With injection of infective juveniles of H. bactriophora into A. ochropus larvae, the total haemocyte count showed alternating fluctuations at all time intervals. Encapsulation occurred 22 hours post injection (hpi) of H. bacteriophora infective juveniles into the rose sawfly larvae, while melanization was observed after 24 h. In the case of S. carpocapsae, initial attachment of the haemocytes was detected at 18 hpi and complete encapsulation at 24 hpi; no melanization was observed. In general, findings showed strong immune responses of the rose sawfly larvae against H. bacteriophora, while these reactions were weakened for S. carpocapsae. Therefore, it is concluded that S. carpocapsae has more ability to overcome the host defence system, and this research provides a new window on its potential as a biocontrol agent.     

Parasitism by Cotesia glomerata Induces Immunosuppression of Pieris rapae: Effects of Ovarian Protein and Polydnavirus

A gregarious endoparasitoid wasp, Cotesia glomerata, parasitizes the cabbage butterfly, Pieris rapae. During wandering larval stage for pupal metamorphosis, the parasitoid larvae egress from the parasitized host to form cocoons thus eventually leading to death of the host. This study focused on the effect of C. glomerata parasitization on cellular immune response of P. rapae. For this purpose, an ideal anticoagulant buffer was formulated to procure the hemocytes in native form with morphological, behavioral, and functional characteristics. The hemocytes selectively encapsulated only DEAE beads under in vitro conditions and a quantitative study revealed about 70% of the beads being encapsulated. On the other hand, calyx fluid from C. glomerata injected to P. rapae markedly inhibited the spreading ability of the hemocytes in a dose-dependent manner and also attenuated the in vitro encapsulation response of the hemocytes against the cationic bead. The calyx fluid contained polydnavirus as well as ovarian proteins. The isolated polydnavirus genome consisted of variously sized-segments with their unequal amounts. The P. rapae injected with the calyx fluid expressed several polydnaviral genes within 2 h. These results suggest that the immunosuppression of the parasitized P. rapae may be induced by the polydnaviral gene products as well as ovarian proteins.     

Aspects of the reproductive biology of Pseudaphycus maculipennis (Hym: Encyrtidae), a parasitoid of obscure mealybug,Pseudococcus viburni (Hem: Pseudococcidae)

Laboratory experiments to determine aspects of the reproductive biology of Pseudaphycus maculipennis are described. All experiments were carried out at a constant temperature of 21 ± 2 °C, a 16-h photoperiod and ambient RH. Pseudaphycus maculipennis was shown to be an arrhenotokous, synovigenic, gregarious endoparasitoid of Pseudococcus viburni. Females and males lived for 16 and 11 days, respectively, when fed either honey-agar or mealybug honeydew. Relatively, large instars (third instar or adult females) were preferred for oviposition; mated females parasitized more mealybugs than unmated females, and the progeny sex ratio favored females by 3:1. Egg load increased with age from emergence to day 8, averaging 23 mature eggs/female. Mean realised daily fecundity never exceeded 5, with a mean lifetime fecundity of 46 eggs/female. Parasitised mealybugs remained alive for about 5 days and then mummified. Total development period was 20–21 days (larva 4–5 days, prepupa 3 days, pupa 8–9 days). Development periods of eggs and individual larval instars were not measured. A mean of 3.01 ± 0.1 parasitoids/mealybug were reared after individual parasitism events, increasing through super-parasitism (either self or conspecific) to 9 parasitoids/mealybug when hosts were exposed to competing females. Pseudaphycus maculipennis progeny emerged from the mummies in discrete cohorts over periods ranging from 3 min to 18 h (depending on the number of cohorts).     

Interactions between Phaedrotoma scabriventris Nixon (Hymenoptera: Braconidae) and Diglyphus isaea Walker (Hymenoptera: Eulophidae), parasitoids of Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae)

Liriomyza leafminer flies represent a serious threat to horticultural production in East Africa. Total field parasitism rates recorded in Kenya are below 5%, with the indigenous ectoparasitoid Diglyphus isaea Walker being one of the key parasitoid species. The International Centre of Insect Physiology and Ecology (icipe), in collaboration with the International Potato Centre (CIP), imported into Kenya the endoparasitoid Phaedrotoma scabriventris Nixon to improve natural control of leafminers. The objective of this study was to investigate the interactions between D. isaea and P. scabriventris when used together for the biological control of Liriomyza species. These interactions were studied under laboratory conditions, using treatments that involved single, simultaneous and sequential releases of the different parasitoid species onto plants infested by L. huidobrensis larvae. While used separately, parasitism rates of D. isaea and P. scabriventris were 30.4 ± 10.9% and 63.6 ± 7.7% respectively. However, when used simultaneously, the total parasitism rate increased to 77.0 ± 5.3%. Although P. scabriventris had no effect on D. isaea, the presence of D. isaea reduced the specific parasitism rate of P. scabriventris. In addition, both parasitoids induced leafminer mortality through larval-feeding and stinging. However, feeding and stinging mortality induced by D. isaea (41.9 ± 9.1%) was significantly higher compared to P. scabriventris (11.9 ± 8.7). Similarly, pupal mortality due to feeding and stinging activity was 49.1 ± 6.5% and 21.6 ± 1.9% when exposed to D. isaea and P. scabriventris respectively. The implication for simultaneous use of both parasitoids in East Africa is discussed.     

Host age preference of Microplitis mediator (Hymenoptera: Braconidae), an endoparasitoid of Mythimna separata (Lepidoptera: Noctuidae)

Microplitis mediator (Haliday) is a solitary endoparasitoid of larvae of the cotton bollworm, Helicoverpa armigera (Hübner) and the oriental armyworm, Mythimna = Leucania separata (Walker). The preference and suitability of different instars of M. separata for M. mediator were determined under laboratory conditions at a constant temperature of 26 ± 1 °C, 65 ± 5% RH and L14:D10 photoperiod. The selection coefficient revealed that M. mediator parasitized 1st to 4th instars, but preferred 2nd and 3rd instars. Seventy-one percent of parasitism was achieved within 24 h when the 2nd instars were used as hosts at a density of one parasitoid per 20 Larvae. Parasitoid egression and pupation were dependent on the host instar parasitized and occurred from the 1st through the 4th instar. The mean developmental time from egg to prepupae of M. mediator within 1st to 4th instars of the host was 8.27, 8.30, 8.30 and 9.20 days, respectively. Cocoon weights were lower when 1st and 2nd instars served as hosts rather than 3rd and 4th instars. The percentage of host larva that died before parasitoid egression declined as the age of the host increased, ranging from 26% to 2% for 1st–5th instars, respectively. The results of this study suggest that 2nd and 3rd instars of M. separata would be the best host stages for mass production of M. mediator in the laboratory and the best host instars to target for effective control in field releases.     

Parasitism of Pieris rapae (Lepidoptera: Pieridae) by the endoparasitic wasp Pteromalus puparum (Hymenoptera: Pteromalidae): Effects of parasitism on differential hemocyte counts,micro‐ and ultra‐structures of host hemocytes

Abstract Parasitism by the endoparasitic wasp Pteromalus puparum (Hymenoptera: Pteromalidae) by using only its associated venom, can suppress the immunal responses of Pieris rapae (Lepidoptera: Pieridae). However, up to now, current knowledge of the mechanisms has been limited. The response of host hemocytes to parasitism was investigated using a combination of light and transmission electron microscopy (TEM). Five hemocyte types, prohemocytes (PRs), granulocytes (GRs), plasmatocytes (PLs), oenocytoids (OEs) and coagulocytes (COs), were observed and characterized from both unparasitized and parasitized Pieris rapae pupae. Light microscopy showed that both GRs and PLs became more round and spread abnormally after parasitism, whereas the shape of other types of hemocytes remained unaffected. In addition, the size of PRs and PLs became larger while OEs became smaller. The proportion of PRs significantly increased after parasitism and that of PLs decreased by 43.9%, but there was no significant increase of GRs and OEs. TEM showed that all types of hemocytes except COs were damaged to various degrees after parasitism, especially resulting in electron opaque cytoplasm and nucleus, fewer cell organelles of rough endoplasmic reticulum, mitochondria and vesicles. Our results indicate that parasitism by P. puparum affects differential hemocyte counts and structures of host hemocytes, particularly for GRs and PLs, which may be the main cause of the parasitoid suppressing host cellular immune responses.     

An adjustable action threshold using larval parasitism of Helicoverpa armigera (Lepidoptera: Noctuidae) in IPM for processing tomatoes

An adjustable action threshold that uses estimates of larval parasitism of Helicoverpa armigera (Hübner) in individual fields was assessed over three consecutive years in processing tomatoes in Hawke’s Bay, New Zealand. Tomato fields were monitored weekly for levels of infestation by H. armigera larvae. When infestation levels became of concern, either approaching or exceeding the standard action threshold of one larva per plant, collections of 30+ representative larvae were made. These larvae were measured and reared individually at 30 °C, and after 4 days rates of parasitism were estimated visually. From these data, spray recommendations were made using a formula that adjusted the action threshold to allow for mortality from parasitism. At harvest, damage assessments were made to validate these recommendations. Results showed that estimates of parasitism after 4 days were accurate predictors of final assessments of parasitism. Overall parasitism during the three seasons was 71%, confirming that the original threshold, which relies on about 50% parasitism, needed revision. The dominant parasitoid was Cotesia kazak, reared from 91% of all parasitized larvae over the 3 years. Microplitis croceipes and the self introduced polyphagous parasitoid Meteorus pulchricornis were reared from 4% and 5% of the parasitized larvae respectively. In 16 of 17 fields examined, the adjustable threshold kept fruit damage at harvest below the tolerated level of 5%. The single crop with excessive damage had only 0.5% fruit damage above this level. This adjustable threshold, which varied in this study from 1–8.3 larvae per plant, has been incorporated into an updated IPM programme and contributed to a 95% reduction in insecticide use.     

Effects of the Diadromus pulchellus ascovirus,DpAV-4, on the hemocytic encapsulation response and capsule melanization of the leek-moth pupa,Acrolepiopsis assectella

DpAV-4 is a symbiotic ascovirus found in natural populations of the solitary endoparasitoid wasp Diadromus pulchellus. The female wasp injects this virus into the pupae of the leek-moth Acrolepiopsis assectella during oviposition. The ascovirus replicates in the pupal tissues and the consequent lysis of the cells occurs synchronously with egg hatching and the development of the wasp larva. We show here that encapsulation and capsule melanization were activated when minute nylon monofilaments were implanted into the hemocoel of non parasitized leek-moth pupae and that encapsulation and melanization were inhibited in pupae parasitized by D. pulchellus. When the pupae were infected by DpAV-4, melanization of the nylon monofilaments was abolished, but a capsule was still always formed. These results indicate that DpAV-4 is a free virus able to alter the defence system of the parasitized host so as to improve the development of the parasitoid wasp, D. pulchellus.     

IMPACT OF IMMUNE RESPONSE OF A PARASITIC BEETLE Dastarcus helophoroides ON ITS HOST BEETLE Monochamus alternatus

Dastarcus helophoroides is an ectoparasitoid beetle of Monochamus alternatus, and the parasitism by D. helophoroides larvae remarkably influenced on the immune responses of M. alternatus larvae in many aspects. The hemolymph melanization reactions in the hosts were inhibited 1 h and 24 h postparasitization. The phenoloxidase activities of hemolymph were significantly stimulated 4 h postparasitization and inhibited 12 h postparasitization, and back to control level. The antibacterial activities of hemolymph in the parasitized hosts were significantly lower than that in the unparasitized ones 1 h postparasitization. By 72 h postparasitism, the total hemocyte numbers of the parasitized larvae declined to not more than one‐seconds of the number collected from the unparasitized larvae. All sampled hemolymph held the capability of nodulation, and there were fluctuations in the number of nodules the hemocytes made. However, there were no significant differences between unparasitized and parasitized larvae at each time point in the hemagglutination activity and the ratios of spreading hemocytes. In conclusion, D. helophoroides larvae could regulate M. alternatus immune system and resulted in the changes in host immune responses.     

Retardation of testis development in the armyworm,Pseudaletia separata,parasitized by the braconid wasp,Cotesia kariyai

Summary

In order to complete growth and development, the endoparasitoid wasp, Cotesia (=Apanteles) kariyai, inhibits pupation of its armyworm host, Pseudaletia (=Leucania) separata. In host larvae retardation of testis and spermatocyst development caused by the parasitoid was also observed. The agents causing the retardation were found in the ovaries and venom of the female adult parasitoid. When an unparasitized male host larva was artificially injected with calyx fluid obtained from ovaries together with venom, it showed the same degree of developmental retardation of testes and spermatocysts as in natural parasitization. Testes implanted in isolated abdomens of healthy larvae did not increase in size by ecdysteroid stimulation after exposure to calyx fluid plus venom. It is suggested that both symbiotic polydnavirus existing in calyx fluid and venom in the parasitoid, C. kariyai, are responsible for the parasitic retardation of the male reproductive organs in the host, P. separata.     

Effect of a virus associated with the reproductive system of the parasitoid wasp,Campoletis sonorensis,on host weight gain

The particulate fraction of the calyx fluid of the endoparasitoid, Campoletis sonorensis, reduces host weight gain when manually injected into healthy Heliothis virescens larvae. Reduced weight gain of the host, H. virescens, is normally associated with parasitism by C. sonorensis. Electron microscopy has confirmed that the particulate fraction of the calyx fluid is composed of virus particles and it appears that this virus, injected with the egg at oviposition, actually reduces host weight gain. The effect of the virus is negated when the calyx fluid is exposed to ultraviolet light prior to injection. Furthermore, the calyx fluid is effective only if injected into hosts; there is no effect on host weight gain when hosts are fed or topically treated with the virus-containing calyx fluid.