Pattern of Egg Management by Trichogramma cacoeciae and T. dendrolimi (Hymenoptera: Trichogrammatidae)

The effect of temporary host deprivation on parasitization rates of Trichogramma cacoeciae Marchal and T. dendrolimi Matsumura was investigated. The study was conducted with females that we allowed to engage in 3 days of oviposition after various periods of host deprivation. It seems that the production and management of eggs by the two species is completely different. During the first day of oviposition, parasitization by T. cacoeciae was almost unaffected after 1 to 5 days of host deprivation. As deprivation time increased, however, the number of parasitized hosts decreased from an average of 28.6 ±2.0 hosts provided at emergence to an average of 12.5 ±2.3 hosts when the waiting time was 10 days. The number of hosts parasitized on the first day of parasitization by T. dendrolimi were not affected whatever the waiting test period. During the second or third days of oviposition, the lack of suitable hosts for T. cacoeciae did not depress egg-laying potentiality, whereas a strong reduction in parasitization rates by T. dendrolimi occurred in the next 2 days of oviposition whatever was the waiting period. This leads to ca. 50% reduction in total activity of 3 days of oviposition. Only in T. cacoeciae was it possible to distinguish between ageing and host deprivation. The data suggest that T. dendrolimi is a typical proovigenic species, while T. cacoeciae is neither definitely proovigenic nor synovigenic. A slight decrease in rate of emergence of offspring of T. cacoeciae females that had waited 8 to 10 days for their hosts was observed. As far as biological control is concerned, the efficiency of T. dendrolimi females may be more sensitive to host deprivation than T. cacoeciae.     

Effect of fertilized,unfertilized, and UV‐irradiated hosts on parasitism and suitability for Trichogramma parasitoids

Trichogramma spp. (Hymenoptera: Trichogrammatidae) parasitoids have been commonly used as biological control agents in insect pest management. Host quality is believed to influence parasitism, host preference, and suitability for parasitoids. To date, limited studies have compared the parasitism of Trichogramma parasitoids on fertilized, unfertilized, and sterilized host eggs. Hence, we studied the performance of three Trichogramma egg parasitoids, Trichogramma japonicum Ashmead, Trichogramma chilonis Ishii, and Trichogramma leucaniae Pang & Chen, on fertilized, unfertilized, and ultraviolet (UV)‐irradiated fertilized (UVF) eggs of rice moth, Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae). In a no‐choice test, T. japonicum and T. leucaniae parasitized significantly more fertilized or UVF than unfertilized hosts, and T. chilonis parasitized significantly more UVF than either fertilized or unfertilized hosts. In a choice test, all three Trichogramma parasitoids parasitized UVF hosts the most, and unfertilized hosts the least. There were similar percentages of adult emergence and female progeny among fertilized, unfertilized, and UVF hosts for all three Trichogramma parasitoids, except that T. japonicum had significantly lower adult emergence on fertilized hosts. We also found that all three Trichogramma parasitoids developed slower on unfertilized hosts. Regardless of host treatments, T. leucaniae had the longest developmental time and T. chilonis had the shortest. We conclude that Trichogramma parasitoids prefer parasitizing UVF eggs of C. cephalonica without negative effects on their emergence and sex allocation.     

Impact of mating on Anagyrus kamali Moursi (Hym., Encyrtidae) lifetime fecundity, reproductive longevity, progeny emergence and sex ratio

Abstract: The solitary endoparasitoid Anagyrus kamali Moursi (Hym., Encyrtidae) and the Hibiscus mealybug Maconellicoccus hirsutus Green (Hom., Pseudococcidae), were used as a parasite/host model to test the effect of mating on several fitness parameters, i.e. longevity, lifetime fecundity, progeny emergence and sex ratio. At 27 ± 2°C, 8 h light : 16 h dark, mating significantly affected the survival of male parasitoids. Virgin males lived longer (32.2 ± 9.51 days) than mated males (23.9 ± 7.52 days). Female longevity (40.7 ± 16.3 days for virgins and 36.2 ± 10.7 days for mated females) was not affected by mating. The lifetime fecundity of female parasitoids and their oviposition period was not significantly affected by mating. However, the number of hosts parasitized was greater for mated wasps (7.54 ± 4.85 hosts parasitized/day) compared with virgin ones (5.12 ± 2.19 hosts parasitized/day). This resulted in greater progeny production from mated A. kamali females. The progeny of virgin females consisted only of males, whereas the mated ones had a more female‐biased sex ratio. The lowest sex ratio (0.41 M/F ± 0.123) was attained when females had free access to males and were multi‐mated.     

Fecundity and Longevity of Green Vegetable Bug,Nezara viridula, Following Parasitism byTrichopoda giacomellii

The effects of parasitism by the ArgentinianTrichopoda giacomellii(Blanchard) on reproduction and longevity of its host,Nezara viridula(L.) are reported. Parasitoid larvae suppress egg maturation, reducing by 70% the fecundity of mature female hosts during the period of larval development. Egg viability was not affected, but mating frequency was reduced by approximately 50%. When parasitized as newly eclosed adults, 84% of females fail to reproduce. In male hosts, fertility and mating frequency were not affected during the period of larval parasitoid development. In male and reproductively immature female hosts, death was coincident with, or occurred shortly after parasitoid emergence (2–4 days); in mature females, death occurred on average 2 weeks after larval parasitoid emergence. Host mortality occurred as a consequence of tissue damage incurred as the parasitoid larvae emerged from the host. Some individuals survived parasitism though no further reproductive activity (mating or oviposition) occurred. The effectiveness ofT. giacomelliias a biological control agent is discussed in relation to its impact on reproduction and survival of its host and contrasted with the action of otherTrichopodaspecies.     

Effect of host density on offspring sex ratios and behavioral interactions between females in the parasitoid waspNasonia vitripennis (Hymenoptera: Pteromalidae)

Pairs of females of the parasitoid waspNasonia vitripennis were videotaped with one or two hosts. The presence of an additional host decreased the number of interactions between females but had no measured effect on the nature of the interactions, i.e., on whether the interaction involved physical contact or occurred while one of the females was parasitizing a host. The number of hosts did not itself affect offspring sex ratios but did influence which other factors were correlated with sex ratio. When there was one host, the proportion of sons was more positively correlated with utilization of previously drilled holes than with female-female interactions, whereas when there were two hosts, the reverse was true. Parasitizing an already parasitized host appeared to affect a female's sex ratio beyond any effects of the physical presence of another female: When two hosts were present, the proportion of sons was greater from hosts parasitized by both females than from hosts parasitized by only one female. The observation that parasitizations in previously drilled holes and female-female interactions are correlated with sex ratios is consistent with previous studies; however, that these relationships are host density dependent is a new result and remains unexplained.     

Survival of the parasitoidEncarsia formosa after treatment of parasitized greenhouse whitefly larvae with fungal spores ofAschersonia aleyrodis

The interaction between the entomopathogenic fungusAschersonia aleyrodis and the parasitoidEncarsia formosa on greenhouse whitefly as a host organism was studied, in particular, the survival of the parasitoid after treatment of parasitized hosts with fungal spores. The mean number of parasitized black pupae per parasitoid produced at 25°C was significantly reduced after spore treatment in the first three days following parasitization. Spore treatment four, seven or ten days after parasitization resulted in a mean number of parasitized pupae not significantly different from the number of black pupae in the control. The rather sudden change from low to high survival of parasitized hosts when treated with spores four days after parasitization in spite of high numbers of infected unparasitized larvae, coincided with the hatching of the parasitoid larva from the egg inside the host. Possible reasons for this decrease in susceptibility to infection after parasitoid egg hatch, such as induced changes in host cuticle or haemolymph, are discussed. Parasitoids emerged from treated hosts did not show differences in reproduction compared with parasitoids emerging from untreated hosts. Both natural enemeies of whitefly are compatible to a great extent.     

Biology of Cotesia ( = Apanteles) telengai (Hymenoptera: Braconidae) on its natural host Agrotis segetum (Lepidoptera: Noctuidae)

The host suitability of Agrotis segetum Denis & Schiff., A. ipsilon Hufn., Spodoptera littoralis Boisd, S. exigua Hub., Mythimna loreyi Duponchel and Mamestra oleracea L. for the gregarious braconid Cotesia ( = Apanteles) telengai Tobias was determined under laboratory conditions. The parasitoid only completed its development in larvae of A. segetum. The percentage of successfully parasitized larvae and the mean duration of C. telengai egg‐larval period were inversely related to the age of the host or host instar at parasitization. The mean number of parasitoids which emerged per parasitized larva was positively correlated with the larval age. The sex ratio was consistently high (ca. eight males to one female), independent of the host instar parasitized, as compared to 1:1 as observed frequently in field populations of this wasp. The females of C. telengai were active and produced offspring at temperatures of 15, 20, 25 and 30° C. However, the mean percentage of parasitized larvae increased from 13.1 to 72% and the mean progeny per parasitoid female increased from 14.7 to 129.4 parasitoids, both significant, when the experimental temperature was raised from 15 to 30°C, while their mean development time decreased from 75.5 to 19.2 days. At 25°C, the virgin and mated females continued oviposition until days 16 and 17, with a lifetime total of progeny of 397.6 (SD ±224.7) and 611.1 (SD± 128.8) parasitoids respectively, reaching a maximum of 64.3 and 99.2 on day 2 respectively.     

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.     

Influence of host age and host deprivation on longevity, egg load dynamics and oviposition rate in Microplitis rufiventris

Adult size, longevity, egg load dynamics and oviposition ofMicroplitis rufiventris Kok. which began their development in the first, second, third （preferred hosts） or fourth （non-preferred hosts） instar larvae of Spodoptera littoralis （Boisd.） were studied. The parasitoid size was largely determined by the initial host size at parasitism. Non-ovipositing females derived from older hosts lived for longer periods than those derived from younger ones. However, the ovipositing females, irrespective of their size, lived for almost the same periods. At emergence, the oviducts of adult females contain a significant amount of mature eggs available for oviposition for a few hours on eclosion day. Egg load increases during the early phase of adult life. The amount of additional mature eggs and rate of egg maturation per hour was greater for wasps derived from preferred hosts compared with those in females derived from non-preferred hosts. The pattern of egg production in M. rufiventris females depended on the availability of hosts for parasitization. Host-deprived females depleted the egg complement with aging; the longer the host deprivation, the lower the oviduct egg load. Marked reduction in both realized or potential fecundity of host-deprived females was observed following host availability. Host privation for more than 3 days induced a marked deficit fecundity pattern through the female＇ s life. The realized fecundity was determined by the interaction among host availability, the number of eggs that are matured over the female＇ s life span, oviposition rate and host size from which the female was derived. These results suggest that： （i） M. rufiventris wasp is a weak synovigenic species; （ii） the maturation of additional eggs is inhibited once the maximum oviduct egg load is reached; （iii） the egg load of the newly emerged female is significantly less than the realized fecundity; and （iv） because M. rufiventris females oviposit fewer eggs when they begin depleting their egg supply at 3 days, augmentative releases will require release immediately following emergence to ensure the highest parasitization rate in the field.     

The effect of host size on quality attributes of the egg parasitoid,Trichogramma pretiosum

In a study of the quality ofTrichogramma pretiosum Riley (Hymenoptera: Trichogrammidae), we compared female wasps emerging from natural hosts, parasitized in the laboratory or the field with those emerging from factitious hosts used for commercial mass production. Females from the natural hosts were larger, more fecund, and longer lived than those from the factitious hosts. Compared to small females, large female wasps are substantially more fecund when honey (carbohydrate) is available but marginally more fecund when honey is unavailable. The size of a femaleT. pretiosum depends on two factors: the size of the host egg from which it emerges even when the wasp was gregarious, and the number of conspecifics that emerge with it. The similarities in the size distribution of female wasps emerging from natural hosts, in conjunction with the mechanism by whichTrichogramma measure host size and allocate eggs accordingly, suggests the hypothesis that size related components of fitness in femaleT. pretiosum are under strong selection in the field.     

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

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

Growth and development of Encarsia formosa (Hymenoptera: Aphelinidae) in the greenhouse whitefly, Trialeurodes vaporariorum (Homoptera: Aleyrodidae): effect of host age

The tiny parasitoid wasp, Encarsia formosa, has been used successfully to control greenhouse whiteflies (GHWFs) in greenhouses in many countries throughout the world. Therefore, there has been considerable interest in developing methods for artificially rearing this wasp. However, little information is available concerning the regulation of its development including the host-parasitoid interactions that are required for the parasitoid to complete its life cycle. Here we confirm that parasitoid developmental rates differ significantly based upon the host instar parasitized. Development was faster when 3rd and 4th instar GHWFs were offered for parasitization than when 1st or 2nd instars were used. Our results show that it is primarily the embryo and the first two parasitoid instars that exhibit prolonged developmental times when 1st and 2nd instar whiteflies are parasitized. Although percent emergence was not affected by host age at the time of parasitization, adult longevity as well as adult emergence pattern varied greatly depending upon the instar parasitized. When 3rd and 4th instar GHWFs were selected for oviposition, adult wasps lived significantly longer than when 1st or 2nd instars were used; also, there was a sharp emergence peak on the 2nd day after emergence was first observed (reduced or absent when 1st or 2nd instar GHWFs were parasitized) and the emergence period was reduced from between 8 and 11 days to 5 days. In general, the younger the host instar parasitized, the less synchronous was parasitoid development. Previous reports that E. formosa will not molt to the 2nd instar until the host has reached its 4th instar were not confirmed. When 1st instar host nymphs were parasitized, 2nd instar parasitoids were detected in 3rd instar hosts. Importantly, however, no matter which instar was parasitized, the parasitoid never molted to its last instar until the host had reached Stage 5 of its last instar, a stage in which host pharate adult formation has been initiated. It appears, then, that a condition(s) associated with host pharate adult formation is required for the parasitoid's final larval molt. Results reported here should facilitate the development of in vitro rearing systems for E. formosa.     

Impact of the Timing of Male Emergence on Mating Capacity of Males in Trichogramma evanescens Westwood

In species with highly structured population, such as Trichogramma spp., mating occurs mostly at emergence on the patch and early emerging males have an advantage, as they are present when the first females emerge. However, early emergence of male could also enable males to mature sexually before the emergence of females or enhance their capacity to induce higher receptivity in females. We measured time of emergence of male and female Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae) from hosts that were parasitized within a 30 min period. We also measured the effect of male age on their capacity to mate, and the ability of inseminated females to produce daughters. To verify if early emerging males induced higher receptivity in females, we observed the females mate choice between males of different ages. Our results indicated that the mean time of emergence between males and females was 29 min for individuals that develop in 9 days and 10 min for individuals that develop in 10 days. The protandry observed in this species could be the result of either a faster development of males or a male first strategy by the ovipositing female. In T. evanescens, protandry does not permit males to mature sexually nor to induce higher receptivity in females. The main advantage of protandry for males thus appears to be early access to females as they emerge.     

Rediscovery of the workerless inquiline antPogonomyrmex colei and additional notes on natural history (Hymenoptera: Formicidae)

Summary Pogonomyrmex colei is a workerless inquiline ant known only from nests ofP. rugosus, its closest relative. Ten of 776 (1.3%) host nests were parasitized at a site in central Arizona, while none of 1499 potential host colonies were parasitized at two other locales. Colonies ofP. colei are perennial, and host alate females in 9 of 10 colonies demonstrates that host queens survive parasitism. Three of 10 colonies died over 19 colony years of observation, while only 1 of 601 colonies became newly parasitized. Mating occurs in morning for up to 2–3 days following summer and fall rains and in afternoon during cool fall days. Mating is intranidal just outside the nest entrance, with males returning to the natal nest. MaleP. colei may be flightless because their wing area is reduced compared to host males. Females fly from the nest and locate potential host colonies by following trunk trails. Workers are the largest barrier to nest establishment, as they removed over 90% ofP. colei females placed in trunk trails or that entered host nests. Males and females ofP. colei andP. anergismus, the only other congeneric inquiline species, are diminutive compared to their hosts, with females 30% lighter than host workers. Fat content is lower and water content is higher inP. colei andP. anergismus females than in their hosts.     

Effects of previous experience and age-related changes on host eggs parasitization by <Emphasis Type="Italic">Trichogramma buesi</Emphasis> Voegele (Hymenoptera,Trichogrammatidae) females

The influence of the previous parasitization experience and age-related endogenous changes on the parasitization of Sitotroga cerealella Oliv. (Lepidoptera, Gelechiidae) eggs by Trichogramma buesi Voegele (Hymenoptera, Trichogrammatidae) females was estimated in the laboratory conditions. The experiment included two exposures separated by a period lasting from 0 to 20 days at 20°C. The first exposure lasted for 4 h and was conducted at a temperature of 25°C which promoted parasitization. The second exposure lasted 48 h and was conducted at a temperature of 15°C which inhibited parasitization. The survival of the control females (deprived of the hosts at the first exposure) was slightly higher than that of the experimental females. The mean number of mature eggs and the mean fecundity during the second exposure were lower in females that parasitized during the first exposure than in the controls and in females that rejected the host during the first exposure. The proportion of T. buesi females that parasitized S. cerealella eggs during the second exposure was much higher among the females that started parasitization during the first exposure than among controls and among those that rejected the host during the first exposure. This effect of the previous parasitization experience on the following parasitization of the same host species persisted for 16 days. However, on day 20 after the first exposure the proportion of the parasitizing individuals among the experienced females was the same as among the controls and those that rejected the host during the first exposure. This sharp decay in the effect of experience coincided with an increase in mortality and with a decrease in the proportion of parasitizing females among the controls. Thus, the experience-induced behavioral changes per se could be considered as practically permanent, since the period of their persistence is close to the female active life span.     

A sex ratio theory of gregarious parasitoids

Summary A mathematical model is constructed to explain a density-dependent increase in the progeny sex ratios of gregarious parasitoids. In the model we considered non-cooperative game between females concerned with their own inclusive fitness. Equilibrium progeny sex ratios of the first and second females ovipositing on the same host are expressed in terms of the probability of double parasitism (p), the ratio of a male to a female in contribution to resource competition (α), the clutch size ratio between the two females (β), the crowding effect on female reproductive success (γ), and the inbreeding coefficient (f). Major predictions from the model are: 1) the progeny sex ratios of both the first and second females increase withp, 2) as β becomes smaller, the progeny sex ratios of the first females decrease, while those of the second females dramatically increases, 3) when a host is attacked by at most two wasps, the sex ratio of the total number of eggs laid on the host does not exceed 0.25. The effects of α and preferential death by female progeny in doubly parasitized hosts are considered as factors responsible for an excess number of males at emergence. Some possible modes of density-dependent increase in the sex ratios of the overall progeny populations is also discussed on the basis of the present model.     

Impact of mating status on egg-laying and superparasitism behaviour in a parasitoid wasp

Most parasitoid female wasps can distinguish between unparasitized and parasitized hosts and use this information to optimize their progeny and sex allocation. In this study, we explored the impact of mating on oviposition behaviour (parasitism and self‐ and conspecific superparasitism) on both unparasitized and already parasitized hosts in the solitary parasitoid wasp Eupelmus vuilleti (Crw.) (Hymenoptera: Eupelmidae). Virgin and mated females had the same oviposition behaviour and laid eggs preferentially on unparasitized hosts. The sex ratio (as the proportion of females) of eggs laid by mated females in parasitism and conspecific superparasitism was 0.67 ± 0.04 and 0.57 ± 0.09, respectively. Likewise, females laid more eggs in conspecific superparasitism than self‐superparasitism under our experimental conditions. These experiments demonstrate that E. vuilleti females can (i) discriminate between unparasitized and parasitized hosts and adapt the number of eggs they lay accordingly, and (ii) probably discriminate self from conspecific superparasitized hosts. Finally, mating does not appear to influence the host discrimination capacity, the ovarian function, or the oviposition behaviour.     

Parasrnzatlon of bemisia argentifolii (Hom.: Aleyrodidae) by encarsia pergandiella (Hym.: Apheunidae)

The biology of the arrhenotokous autoparasitoid,Encarsia pergandiella Howard, was studied in the laboratory on the silverleaf whitefly,Bemisia argentifolii Bellows & Perring. Egg to adult development of parasitoid females averaged ca. 14 days at about 25.3+0.2?C regardless of whether the whitefly host was reared on tomato, eggplant or squash. While all instars ofB. argentifolii were accepted for primary parasitization, a greater percentage of third and fourth instars were parasitized. Mortality of whitefly nymphs in the absence of parasitization did not differ among instars and averaged about 35%. Second instar to pupal parasitoid females were accepted for secondary parasitization although a greater percent of pupal females were parasitized. About 40% of immatureE. pergandiella females more than 4 days old died in the absence of secondary parasitization when exposed to adultE. pergandiella females.     

Development of Meteorus pulchricornis and regulation of its noctuid host, Pseudaletia separata

The solitary endoparasitoid Meteorus pulchricornis can parasitize many lepidopteran host species successfully. In the case of parasitization of Pseudaletia separata, developmental duration of M. pulchricornis was 8-9 days from egg to larval emergence and 6 days from prepupa to adult emergence. Successful parasitism by M. pulchricornis decreased with host age. Following parasitization of day-0 4th host instar, the parasitoid embryo, whilst still enclosed in serosal cell membrane, hatched out of the egg chorion 2 days after oviposition. Subsequently, the 1st instar parasitoid emerged from the surrounding serosal cell membrane. Serosal cells dissociated and developed as teratocytes 3.5 days after oviposition. One embryo of M. pulchricornis gave rise to approximately 1200 teratocytes, a number that remained constant until 6 days after parasitization, but decreased drastically to 200 at 7 days post-oviposition. The teratocytes of M. pulchricornis were round- or oval-shaped and grew from 65 microm at 4 days to 200 microm in the long axis at 6 days post-parasitization. At 4 days post-parasitization, many cells or cell clusters with lipid particles were observed in the hemocoels of parasitized hosts. In addition, paraffin sections of parasitized hosts revealed that many teratocytes were attached to the host's fat body and contributed to disrupting the fat body tissue. Further, examination of the total hemocyte count (THC) during parasitization revealed that THC was maintained at low levels. Surprisingly, a temporal decrease followed by restoration of THC was observed in hosts injected with virus-like particles of M. pulchricornis (MpVLPs) plus venom, which contrasts with the constant THC suppression seen in parasitized hosts. This indicates that MpVLP function is temporal and is involved in regulation of the host during early parasitism. Therefore, teratocytes, a host regulation factor in late parasitism, could be involved in keeping THC at a low level.     

Reproductive strategies under multiparasitism in natural populations of the parasitoid wasp Nasonia (Hymenoptera)

Parasitoid Nasonia wasps adjust their progeny sex ratio to the presence of conspecifics to optimize their fitness. Another trait under female control is the induction of offspring diapause. We analysed progeny sex ratios and the proportion of diapausing offspring of individual Nasonia females in host patches parasitized by two species, Nasonia vitripennis and Nasonia giraulti, in North American field populations using microsatellite fingerprinting. Both Nasonia species produced similar sex ratios on hosts that were co‐parasitized by their own species as by the other species, indicating that females do not distinguish between con‐ and heterospecific clutches. The sex ratios of the diapause and adult fractions of mixed broods from single females were not correlated. We found further indications that N. vitripennis females take the emergence time of the offspring into account in their sex allocation. The reproductive strategies of Nasonia under multiparasitism are largely adaptive, but also partially constrained by information.