Is the host or the parasitoid in control?: effects of host age and temperature on pseudoparasitization by Microplitis rufiventris in Spodoptera littoralis

We compared the production of pseudoparasitization by Microplitis rufiventris females in most (third) and less (fourth) preferred instars of Spodoptera littoralis larvae at 20+/-1 and 27+/-1 degrees C. The parasitized hosts were classified into hosts producing parasitoids (type A hosts) and hosts producing no parasitoids, i.e., pseudoparasitized hosts (type B hosts). The latter were further classified into: (a) pseudoparasitized hosts with "well" arrested development (type B1 hosts); (b) pseudoparasitized hosts with partially arrested development (type B2 hosts); and (c) pseudoparasitized hosts that successfully pupated to apparently normal host pupae (type B3 hosts). The present series of experiments showed that parasitization by M. rufiventris was clearly affected by host instar, age within an instar and rearing temperature. Production of type B hosts was less when third instar S. littoralis larvae were exposed to the wasp females than when the host larvae were in fourth instar. The production of type A hosts was much greater when early or mid ages of an instar was stung by the wasp females comparing with stung late age of the same instar. Production of type B hosts may be due to one or overall of the following: (a) dosage dilution of M. rufiventris female's factors in the different age classes of the instar; (b) endocrine system (physiological state) at parasitization time, i.e., early vs late age of the instar; (c) growth rate of host larvae. The lowest production of type B hosts was at highest growth rate; and (d) temperature, larger proportions of type B hosts were produced at 27+/-1 than at 20+/-1degrees C. The three types host development (B1, B2 and B3) are possibly representing three levels of host resistance (host control) resulting in partial or complete failure of parasitoid control. Type A hosts represent complete success of parasitoid control. The results suggest that the impact of parasitoid factor(s) on developmental arrest is affected by host age at the time of parasitism and/or by temperature.     

Host range limitation caused by incomplete host regulation in an aphid parasitoid

Defining host ranges in parasitoid insects is important both from a theoretical and an applied point of view. Based on the literature, some species seem able to use a wide range of hosts, while field studies indicate possible local host specialization. In koinobiont endoparasitoid species, such specialization could involve physiological processes. We tested the ability of two strains of the cosmopolitan and polyphagous parasitoid Diaeretiella rapae, to develop in three of its recorded aphid host species. Both strains produced high parasitism rates on the cabbage aphid Brevicoryne brassicae and the green peach aphid Myzus persicae but almost no progeny on the cherry-oat aphid Rhopalosiphum padi. This last species was less attacked by female parasitoids. Moreover, parasitoid eggs and larvae were smaller than in the two other host aphid species and their development was delayed. This abnormal development appeared to be due to an incomplete host regulation process, probably related to the low number and the size of teratocytes produced by D. rapae in R. padi individuals. Such a failure as far as gaining control of the host's metabolism is concerned could play an important role in shaping the host range of parasitoid insects, leading to local variation of the host spectrum in populations from various geographical areas.     

Effect of entomopoxvirus infection of the smaller tea tortrix, Adoxophyes sp. on the development of the endoparasitoid, Ascogaster reticulatus

Infection of Adoxophyes sp. (Lepidoptera: Tortricidae) larvae by an entomopoxvirus (AsEPV) adversely affected the development of the endoparasitoid, Ascogaster reticulatus Watanabe (Hymenoptera: Braconidae). Parasitoid larvae developing in AsEPV-infected hosts grew more slowly and spent more time in their hosts than did parasitoid larvae developing in noninfected hosts. Percentages of emergence of larval parasitoids that developed in AsEPV-infected hosts were significantly lower than those of parasitoids that developed in noninfected hosts. Parasitoid larvae in AsEPV-infected host perished when their hosts died of AsEPV infection. Significant numbers of parasitized and infected larvae exhibited apolysis to the final instar, whereas noninfected-parasitized larvae died in the penultimate instars due to emergence of parasitoids.     

Nondevelopment ofCotesia kariyai(Hymenoptera: Braconidae) in Entomopoxvirus-Infected Larvae ofPseudaletia separata(Lepidoptera: Noctuidae)

Interaction between an entomopoxvirus (PsEPV) and a gregarious braconid endoparasitoid,Cotesia kariyai,inPseudaletia separatalarvae showed that infection of larvae with PsEPV was deleterious to the development and survival ofC. kariyai.The survival and development ofC. kariyaiin PsEPV-infectedP. separatalarvae depended on the length of time between parasitization and viral infection. No parasitoid larvae emerged from PsEPV-infected hosts when host larvae were exposed simultaneously to parasitization and PsEPV inoculation whereas more than 80% of the hosts produced parasitoids when PsEPV was administered 5 days postparasitization.C. kariyailarvae in PsEPV-infected hosts showed a retarded development, shrank, and died about 8 days after viral exposure. Virion-free plasma from PsEPV-infectedP. separatalarvae was toxic to the parasitoid larvae even up to a dilution level of 32 when it was injected intrahemocoelically into the host larvae. Development of parasitoids in hosts that were simultaneously parasitized and injected with the virion-free plasm never progressed beyond the egg stage. The parasitizedP. separatalarvae injected with the virion-free plasma did not pupate and died within 30 days after injection.     

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.     

Spodoptera litura multicapsid nucleopolyhedrovirus inhibits Microplitis bicoloratus polydnavirus-induced host granulocytes apoptosis

Baculoviruses and parasitoids are critically important biological control agents in integrated pest management (IPM). They have been simultaneously and sequentially used to target insect pests. In this study, we examined the impacts of both baculovirus and polydnavirus (PDV) infection on the host cellular immune response. Larvae of the lepidopteran Spodoptera litura were infected by Spodoptera litura multicapsid nucleopolyhedrovirus (SpltMNPV) and then the animals were parasitized by the braconid wasp Microplitis bicoloratus. The fate of the parasitoids in the dually infected hosts was followed and encapsulation of M. bicoloratus first instar larvae was observed. Hemocytes of S. litura larvae underwent apoptosis in naturally parasitized hosts and in non-parasitized larvae after injection of M. bicoloratus ovarian calyx fluid (containing MbPDV) plus venom (CFPV). However, assessments of the percentages of cells undergoing apoptosis under different treatments indicated that SpltMNPV could inhibit MbPDV-induced apoptosis in hemocytes when hosts were first injected with SpltMNPV budded virus (BV) followed by injection with M. bicoloratus CFPV. As the time of injection with SpltMNPV BV increased, the percentages of apoptosis in hemocytes population declined. Furthermore, in vitro, the percentages of apoptosis showed that SpltMNPV BV could inhibit MbPDV-induced granulocytes apoptosis. The occurrence of MbPDV-induced host granulocytes apoptosis was inhibited in the dually infected hosts. As hemocytes apoptosis causes host immunosuppression, the parasitoids are normally protected from the host immune system. However, in larvae infected with both baculovirus and PDV, the parasitoids underwent encapsulation in the host hemocoel.     

Electroantennogram (EAG) responses of Microplitis croceipes and Cotesia marginiventris and their lepidopteran hosts to a wide array of odor stimuli: Correlation between EAG response and degree of host specificity?

In order to test whether the electroantennogram (EAG) response spectrum of an insect correlates to its degree of host specificity, we recorded EAG responses of two parasitoid species with different degrees of host specificity, Microplitis croceipes (specialist) and Cotesia marginiventris (generalist), to a wide array of odor stimuli including compounds representing green leaf volatiles (GLVs), herbivore-induced plant volatiles (HIPV), ecologically irrelevant (not used by the parasitoid species and their hosts for host location) plant volatiles, and host-specific odor stimuli (host sex pheromones, and extracts of host caterpillar body and frass). We also tested the EAG responses of female moths of the caterpillar hosts of the parasitoids, Heliothis virescens and Spodoptera exigua, to some of the odor stimuli. We hypothesized that the specialist parasitoid will have a narrower EAG response spectrum than the generalist, and that the two lepidopteran species, which are similar in their host plant use, will show similar EAG response spectra to plant volatiles. As predicted, the specialist parasitoid showed greater EAG responses than the generalist to host-specific odor and one HIPV (cis-3-hexenyl butyrate), whereas the generalist showed relatively greater EAG responses to the GLVs and unrelated plant volatiles. We detected no differences in the EAG responses of H. virescens and S. exigua to any of the tested odor.     

The effect of host size on the sex ratio of Syngaster lepidus, a parasitoid of Eucalyptus longhorned borers (Phoracantha spp.)

The solitary larval ectoparasitoid, Syngaster lepidus Brullé, parasitizes the cryptic larvae of two wood-boring beetles, Phoracantha recurva Newman and Phoracantha semipunctata F. The objective of this study was to determine how the female parasitoids allocated the sex of progeny when presented with larval hosts of uniform size classes. Host size was directly correlated with age of the Phoracantha larval hosts. Groups of Phoracantha larvae of a single age class (2-, 3-, 4-, or 5-week-old) were exposed to parasitoids, and sex ratios of the resulting parasitoid progeny from each host age class were determined. A significant relationship was observed among the sizes of P. recurva and P. semipunctata hosts and the sex ratio of emerging parasitoids. Parasitized 2-week-old beetle larvae of both Phoracantha spp. produced only male S. lepidus progeny, whereas older larval hosts produced increasing proportions of female parasitoids (up to 80% females from 5-week-old hosts). Two-week-old Phoracantha larvae of both species produced fewer parasitoids than host larvae 3–5-week-old. The size of parasitoid progeny consistently increased with host larval age (size), and female parasitoids were larger than males across all host size classes. Male S. lepidus developed in approximately 25 days from 2-week-old hosts, and 19–21 days in 3–5-week-old hosts. Female S. lepidus developed in 22–25 days, with developmental time increasing with host size.     

Transient host paralysis as a means of reducing self-superparasitism in koinobiont endoparasitoids

The term ‘idiobiont’ refers to those parasitoid species that permanently paralyse their hosts during parasitism, causing the cessation of host growth and development. This is in contrast to koinobiont parasitoids, which allow their hosts to continue developing after being parasitized. While no koinobiont species induce permanent paralysis in their hosts, a minority of koinobionts induce a temporary paralysis that does not interfere with overall host growth and development. We characterized transient paralysis induction in two koinobiont aphid parasitoids in the genus Binodoxys (Hymenoptera: Aphidiinae). Both Binodoxys species induced transient paralysis in Aphis glycines, with paralysis time ranging between 4.5 and 8 min (depending upon parasitoid species and host instar). In a separate experiment, B. communis was capable of inducing transient paralysis in nine aphid species. We addressed two hypotheses potentially explaining the adaptive value of temporary host paralysis in experiments using A. nerii, which is readily accepted but engages in strong defensive behaviour. The first hypothesis is that paralysis increases oviposition success by interfering with host defences and the second is that it aids in the avoidance of self-superparasitism. Paralysed aphids were more likely to be rejected by B. communis than were aphids that had never been stung or that had recovered from paralysis. This result supports the avoidance-of-self-superparasitism hypothesis and is inconsistent with the hypothesis that transient paralysis increases oviposition success of B. communis.     

寄主大小及寄生顺序对蝇蛹佣小蜂寄生策略的影响

寄主大小模型认为寄生蜂后代性比与寄主大小相关,寄生蜂倾向于在大寄主上产出更多雌性后代,在小寄主上产出更多雄性后代.探讨了以家蝇蛹为寄主时,蝇蛹佣小蜂后代产量和性比变化;单次寄生情况下,寄主大小及寄生顺序对寄生蜂后代性比等影响.结果表明,蝇蛹佣小蜂的产卵期为(8.93±3.34)d,单头雌蜂能产雌性后代(34.11±16.34)头和雄性后代(11.04±8.87)头,且雄性百分比为0.24±0.11.随成蜂日龄的增大,寄生蜂产生雄性后代的比率显著增加.蝇蛹佣小蜂在寄生家蝇蛹时,会优先选择寄生个体较大的蛹;在单次寄生的情况下,蝇蛹佣小蜂倾向于在较大的家蝇蛹内产出更多的雌性后代.     

Effect of nucleopolyhedrovirus infection of Spodoptera litura larvae on host discrimination by Microplitis pallidipes

The behaviour and oviposition of solitary endoparasitoid Microplitis pallidipes Szepligeti (Hymenoptera: Braconidae) were monitored to investigate the ability of the parasitoids to distinguish between nucleopolyhedrovirus (NPV)-infected and noninfected Spodoptera litura Fabricius (Lepidoptera: Noctuidae) larvae. The results indicated that the parasitoid searching time and the time until the first parasitoid attack on infected larvae were greater than those recorded on noninfected larvae; the number of infected larvae attacked by parasitoids, the percent of first attacks and parasitism rate in infected larvae were lower than those on noninfected larvae; and these differences were all significant 3 to 5 days postexposure of the larvae to a dose of 1.6 × 10⁸ occlusion bodies (OB)· ml^?1 and significant 4 and 5 days postexposure of the larvae to a dose of 1.6 × 10⁷ OB·ml^?1. The lowest dosage (1.6 × 10⁶ OB·ml^?1) had no significant effect on the above index values. In a field cage experiment, we found that the percentage of infected larvae parasitized by M. pallidipes gradually decreased as the time after NPV inoculation (1.6 × 10⁸ OB·ml^?1) increased, and that M. pallidipes significantly preferred to oviposit in healthy larvae from day 3 to day 5 after virus inoculation. Our research concluded that this parasitoid's ability to discriminate between healthy and infected hosts increased as virus concentration increased and as the time between exposure of hosts to virus and subsequent exposure to parasitoids increased.     

Factors affecting growth in the koinobiont endoparasitoid Venturia canescens in the flour moth Ephestia kuehniella

With resistance of insect pests to synthetic pesticides on the increase, the role of parasitoid wasps as biological control agents is expanding in pest and resistance management strategies. One of the predictors of reproductive success of endoparasitoids is the relative size of the wasp at host emergence. While in idiobiont parasitoids, where the host stops feeding after parasitism, the wasp size is determined by the host size at the time of parasitism; the size of koinobiont wasps, where the host continues to feed after parasitism, is dependent on additional factors. Here we show that the host mass and temperature are important factors that determine survival and development of the koinobiont endoparasitoid Venturia canescens in late instar larvae of the flour moth Ephestia kuehniella.     

Population dynamics and sex ratio of a parasitoid altered by fungal-infected diet of host butterfly

Variation of host quality affects population dynamics of parasitoids, even at the landscape scale. What causes host quality to vary and the subsequent mechanisms by which parasitoid population dynamics are affected can be complex. Here, we examine the indirect interaction of a plant pathogen with a parasitoid wasp. Under laboratory conditions, parasitoids from hosts fed fungus-infected plants weighed less than those from hosts fed uninfected plants, indicating that the fungus causes the hosts to be of poor quality. However, parasitoids reared from hosts fed fungal-infected diet also tended to be female, a characteristic associated with high host quality. The pathogen, herbivore and parasitoid persist regionally as metapopulations in a shared landscape in Aland, Finland. In an analysis of the metapopulation dynamics of the parasitoid over 6 years, the probability of colonization of a host population increased by more than twofold in patches occupied by the plant pathogen. While we cannot determine that the relationship is causal, a compelling explanation is that the plant pathogen facilitates the establishment by the parasitoid by increasing the fraction of female offspring. This is a novel mechanism of spatial multi-trophic level interactions.     

Effects of an ascovirus (HvAV-3e) on diamondback moth, Plutella xylostella, and evidence for virus transmission by a larval parasitoid

Ascoviruses (AVs) are pathogenic to lepidopteran larvae, and most commonly attack species in the Noctuidae. The unique pathology includes cleavage of host cells into virion-containing vesicles which leads to the milky white colouration of the hemolymph as opposed to the clear hemolymph of healthy larvae. Recently, we showed that a Heliothis virescens AV (HvAV-3e) isolate is able to induce disease in Crocidolomia pavonana F. (Lepidoptera: Crambidae), affecting feeding, growth and survival of infected larvae. In this study, we investigated the effect of different variants of HvAV-3e on diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae) larvae, another non-noctuid host. In hemolymph inoculation bioassays fourth instar larvae showed a significant dose response to each of the HvAV-3e variants and significant differences between the virulence of the three variants were detected. Both second and fourth instars were readily infected with the virus and infected individuals demonstrated significant reductions in food consumption and growth. The majority of infected individuals died at the larval or pupal stage and individuals which developed into adults were usually deformed, less fecund than non-infected controls and died shortly after emergence. In transmission studies, Diadegmasemiclausum (Hymenoptera: Ichneumonidae), a key parasitoid of diamondback moth, infected healthy host larvae during oviposition following previous attack of HvAV-3e infected hosts. In choice tests D. semiclausum did not discriminate between infected individuals but host infection had no detectable impact on the development of immature D. semiclausum or on subsequent adults.     

Effect of entomopoxvirus infection of Pseudaletia separata larvae on the oviposition behavior of Cotesia kariyai

Parasitoid behavior and oviposition were monitored to investigate the ability of Cotesia kariyai (Watanabe) (Hymenoptera: Braconidae) to distinguish between entomopoxvirus-infected and noninfected larvae of Pseudaletia separata Walker (Lepidoptera: Noctuidae). Comparison of individual means revealed that searching time was not significantly different between treatments. Ovipositional time, however, differed significantly after day 8 post virus inoculation. The parasitoid adopted ovipositional posture on infected and noninfected host irrespective of the stage of infection and did not distinguish infected from noninfected larvae up to 4 days post infection. Mean number of larvae stung by the parasitoid was not influenced by the length of time interval between exposure to the virus. However, duration of ovipositor insertion was influenced by the time interval between exposure to the virus and subsequent exposure to parasitoid females. Female parasitoids did not completely reject infected larvae as unsuitable for egg deposition. However, 5 days after virus inoculation they rejected significantly more infected than noninfected larvae. Furthermore, significantly more eggs were laid in noninfected than infected larvae from day 5 following virus administration. These observations suggest that probing by Cotesia kariyai may provide information concerning host suitability.     

Differential host growth regulation by the solitary endoparasitoid, Meteorus pulchricornis in two hosts of greatly differing mass

Solitary koinobiont endoparasitoids generally reduce the growth of their hosts by a significant amount compared with healthy larvae. Here, we compared the development and host usage strategies of the solitary koinobiont endoparasitoid, Meteorus pulchricornis, when developing in larvae of a large host species (Mythimna separata) and a much smaller host species (Plutella xylostella). Caterpillars of M. separata were parasitized as L2 and P. xylostella as L3, when they weighed approximately 2 mg. The growth of parasitized M. separata larvae was reduced by almost 95% compared with controls, whereas parasitized P. xylostella larvae grew some 30% larger than controls. Still, adult wasps emerging from M. separata larvae were almost twice as large as wasps emerging from P. xylostella larvae, had larger egg loads after 5 days and produced more progeny. Survival to eclosion was also higher on M. separata than on P. xylostella, although parasitoids developed significantly faster when developing on P. xylostella. Our results provide evidence that koinobionts are able to differentially regulate the growth of different host species. However, there are clearly also limitations in the ability of parasitoids to regulate phenotypic host traits when size differences between different host species are as extreme as demonstrated here.     

Active suppression of D. melanogaster immune response by long gland products of the parasitic wasp Leptopilina boulardi

To develop inside their insect hosts, endoparasitoid wasps must either evade or overcome the host's immune system. Several ichneumonid and braconid wasps inject polydnaviruses that display well-studied immune suppressive effects. However, little is known about the strategies of immunoevasion used by other parasitoid families, such as figitid wasps. The present study provides experimental evidence, based on superparasitism and injection experiments, that the figitid species Leptopilina boulardi uses an active mechanism to suppress the Drosophila melanogaster host immune response, i.e. the encapsulation of the parasitoid eggs. The immune suppressive factors are localised in the long gland and reservoir of the female genital tractus, where virus-like particles (VLPs) have been observed. Parasitism experiments using a host tumorous strain indicate that these factors do not destroy host lamellocytes but that they impair the melanisation pathway. Interestingly, they are not susceptible to heating and are not depleted with prolonged oviposition experience, in contrast to observations reported for L. heterotoma, another figitid species. The mechanisms that prevent encapsulation of eggs from L. boulardi and L. heterotoma differ in several respects, suggesting that different physiological strategies of immunosuppression might be used by specialised and generalist parasitoids.     

Benefits of self-superparasitism in a polyembryonic parasitoid

Macrocentrus grandii is a polyembryonic parasitoid, with embryos that divide asexually within the host (European corn borer, Ostrinia nubilalis) to produce broods of clonal offspring. From a biological control standpoint, polyembryony seems advantageous because each parasitized host yields multiple parasitoids with minimal time and egg investment. When we observed M. grandii in the field, however, we found that the parasitoid virtually always invested additional time and, if possible, stings into hosts that it had already stung, apparently reducing some of the advantages of polyembryony. We therefore investigated and found support for two potential benefits that can be gained by self-superparasitism in this system. First, multiple stings allowed production of mixed-sex broods: 27% of multiply-stung versus 0% of singly-stung hosts produced mixed-sex broods. Second, multiple stings increased mean parasitoid progeny produced per host, primarily by reducing the chance of complete brood failure. Our results indicate substantial benefit for a second sting, but little benefit for three or more stings, even though M. grandii was sometimes observed to invest more than two stings within a single host. However, we also found that within-host larval competition is prevalent, suggesting that supernumerary stings may pay off in competition against conspecific larvae. Such additional investment within a single host would be particularly beneficial when hosts, rather than eggs, are limiting, but would decrease the overall efficacy of M. grandii as a biological control agent.     

Epizootiology of Hyalinocysta chapmani (Microsporidia: Thelohaniidae) infections in field populations of Culiseta melanura (Diptera: Culicidae) and Orthocyclops modestus (Copepoda: Cyclopidae): a three-year investigation

The epizootiology, transmission dynamics and survival strategies employed by the microsporidium Hyalinocysta chapmani were examined in field populations of its primary mosquito host, Culiseta melanura and its intermediate copepod host, Orthocyclops modestus over a three-year period in an aquatic subterranean habitat. H. chapmani was enzootic and was maintained in a continuous cycle of horizontal transmission between each host. There were three distinct periods during the summer and fall when developing mosquito larvae acquired infections; each was preceded by or coincident with the detection of infected copepods. Results were corroborated in laboratory bioassays, wherein transmission was achieved in mosquito larvae that were reared in water and sediment samples taken from the site during the same time periods. The highest infection rates, ranging from 60% to 48%, were repeatedly observed during the first six weeks of larval development. These were coincident with the most sustained collections of infected copepods obtained during the year and highest levels of infection achieved in the laboratory transmission studies. The high prevalence rates of lethal infection observed in larval populations of C. melanura at this site are among the highest recorded for any mosquito-parasitic microsporidium and clearly suggest that H. chapmani is an important natural enemy of C. melanura. H. chapmani appears to overwinter in diapausing mosquito larvae but may also persist in copepods. The absence of vertical transmission in the life cycle of H. chapmani and the sole reliance on horizontal transmission via an intermediate host are unique survival strategies not seen among other mosquito-parasitic microsporidia. The epizootiological data suggest that this transmission strategy is a function of the biological attributes of the hosts and the comparatively stable environment in which they inhabit. The subterranean habitat is inundated with water throughout the year; copepods are omnipresent and C. melanura has overlapping broods. The spatial and temporal overlap of both hosts affords abundant opportunity for continuous horizontal transmission and increases the likelihood that H. chapmani will find a target host. It is hypothesized that natural selection has favored the production of meiospores in female host mosquitoes rather than congenital transfer of infection to progeny via ovarian infection as a strategy for achieving greater transmission success.     

Nutritional ecology of the interaction between larvae of the gregarious ectoparasitoid, Muscidifurax raptorellus (Hymenoptera: Pteromalidae), and their pupal host, Musca domestica (Diptera: Muscidae)

In this study we examined the relationship between clutch size and parasitoid development of Muscidifurax raptorellus (Hymenoptera: Pteromalidae), a gregarious idiobiont attacking pupae of the housefly, Musca domestica (Diptera: Muscidae). Host quality was controlled in the experiments by presenting female parasitoids with hosts of similar size and age. This is the first study to monitor the development of a gregarious idiobiont parasitoid throughout the course of parasitism. Most female wasps laid clutches of one to four eggs per host, although some hosts contained eight or more parasitoid larvae. In both sexes, parasitoids completed development more rapidly, but emerging adult wasp size decreased as parasitoid load increased. Furthermore, the size variability of eclosing parasitoid siblings of the same sex increased with clutch size. Irrespective of clutch size, parasitoids began feeding and growing rapidly soon after eclosion from the egg and this continued until pupation. However, parasitoids in hosts containing five or more parasitoid larvae pupated one day earlier than hosts containing one to four larvae. The results are discussed in relation to adaptive patterns of host utilization by gregarious idiobiont and koinobiont parasitoids.