The effects of host age and superparasitism by the parasitoid, Microplitis rufiventris on the cellular and humoral immune response of Spodoptera littoralis larvae

To study the dynamics of stage-dependent immune responses in Spodoptera littoralis (Boisd.) larvae (Lepidoptera: Noctuidae), single and superparasitism experiments were carried out using the parasitoid Microplitis rufiventris Kok. (Braconidae: Hymenoptera). Compared to younger (preferred) host larvae, the older (non-preferred) host larvae displayed a vigorous humoral response that often damaged and destroyed the single wasp egg or larva. Superparasitism and host age altered both the cellular and humoral immune responses. Younger host larvae showed a stronger encapsulation response compared to older host larvae. Moreover encapsulation rates in younger hosts (e.g., second instar) decreased with increasing numbers of parasitoid eggs deposited/larvae. In older larvae, the encapsulation rate was low in fourth, less in fifth and absent in sixth instar hosts. Conversely, the order and magnitude of the cellular immune response in S. littoralis hosts were highest in second instar larvae with the first instar larvae being a little lower. The immune response steadily decreased from the third through to the fifth instar and was least obvious in the sixth instar. In contrast, the general humoral immune response was most pronounced in sixth instar larvae and diminished towards younger stages. The results suggest that both cellular and humoral responses are stage-dependent. Wasp offspring in younger superparasitized host larvae fought for host supremacy with only one wasp surviving, while supernumerary wasp larvae generally survived in older superparasitized larvae, but were unable to complete development. Older instars seem to have a method for immobilizing/killing wasp larvae that is not operating in the younger instars.     

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

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

Ovipositional discrimination by Microplitis rufiventris females between healthy and granulosis virus-infected Spodoptera littoralis larvae

Ovipositional choice tests by Microplitis rufiventris females (Hym., Braconidae) between granulosis virus‐infected (GVI) and non‐infected (NI) Spodoptera littoralis larvae (Lep., Noctuidae), were assessed using discriminatory methods for re‐isolating the NI and virus‐infected hosts after removing the female parasitoid. When M. rufiventris females were given a choice between NI and GVI S. littoralis hosts, the adult females exhibited marked preference (P < 0.01) for the NI (i.e. higher quality) hosts. In this case, M. rufiventris females and S. littoralis GV (SlGV) did not significantly compete for the same type of host larvae and are, generally, compatible. However, when the choice was given between two low qualities of S. littoralis hosts, i.e. virus‐free previously parasitized hosts and viral‐infected hosts a significant preference (P < 0.01) of the parasitoid females for the GVI larvae was observed. In this case, the parasitoid would be at a disadvantage when competing with GV for the same host. However, the parasitoid could be used as an additional tool for the dissemination of biocontrol viruses within different pest populations, i.e. hosts other than S. littoralis. Importantly, the results showed different strategies of parasitoid female in egg‐laying management. When M. rufiventris female was given a choice between healthy and SlGVI hosts, the female deposited more eggs than when she was given a choice between two low qualities of host larvae. The results of the study may have implications in pest management strategies using M. rufiventris and SlGV against S. littoralis larvae.     

A possible therapy by juvenile hormone I to Spodoptera littoralis (Boisd.) larvae previously treated by precocene II

An effective constant dose (55 μg) of precocene II (PII) was topically tested against the last three instars of Spodoptera littoralis (Boisd.) larvae. Application of PII induced morphogenetic abnormalities typical of juvenile hormone (JH) excess. The resultant imperfect insects included larval‐pupal mosaic and partial or severe cases of untanned pupae. The sixth‐instar larvae were more sensitive to PII administration than the two preceding instars. However, sensitivity of the last larval instar to PII varied with the timing of dose application relative to the developmental status of the larvae. Whereas the newly ecdysed (0‐day old) larvae were more sensitive, the older larvae of the same sixth‐instar showed sharp decrease in their sensitivity to PII with a concomitant increase of their age. Application of a single dose (5 μg) of JH I to PII pre‐treated larvae significantly (P < 0.001) reduced the production of imperfect insects where many PH‐treated larvae developed successfully to apparent normal pupae. Although a single dose of PII was more effective on S. littoralis larvae than repeated daily doses, the effectiveness of JHI‐therapy to PH pre‐treated larvae by repeated doses was less effective in producing perfect insects than JH‐therapy to PII pre‐treated larvae by single doses. The reversal of any of these by applied JHI is quite interesting but the mechanisms remain to be unraveled.     

Development of a gregarious ectoparasitoid, Euplectrus separatae (Hymenoptera; Hymenoptera: Eulophidae), that parasitizes Pseudaletia separata (Lepidoptera: Noctuidae)

Euplectrus separatae is a gregarious ectoparasitoid that parasitizes Pseudaletia separata during its third to sixth (last) instars. The eggs of the parasitoid are fixed on the integument of the host dorsolaterally with a hard substance like a piling driven into the integument by the female wasp at the time of oviposition. The first instar of the parasitoid, which hatches three days after oviposition is nourished by ingesting the hemolymph of the host, and ecdyses to the second stadium six days after oviposition. Many hemocytes and epidermal cells were found assembled under the piling and places where a parasitoid had attached its mouth, suggesting that the host had repaired the integument destroyed by the parasitoid. Botryoidal tissue, which stained well with hematoxylin, began to develop from four days after oviposition and became gradually larger with development. Botryoidal tissue appears to function as a secretory organ for thread and a storage organ for nutrients. Seven days after oviposition, the parasitoid larvae migrate down from the dorsal surface to the ventral side of the host. Just before descending they ecdyse to the third stadium and kill the host during their migration. If all parasitoid larvae were removed artificially from the host before they migrate, the host did not die. However, removing the parasitoids after they had started to migrate did not prevent the death of the host. Transmission electron microscopic (TEM) observation of salivary glands of a parasitoid larva before migrating revealed that the salivary gland was composed of cells that were rich in rough surfaced endoplasmic reticulum (rough-ER) with many ribosomes and cells that were filled with a lot of vacuoles just before their collapse. After moving from the host body, the parasitoid larvae doubled in weight by ingesting the tissue of the host and then spun a cocoon. Almost all host tissues were consumed for growth of the parasitoid, like an idiobiont parasitoid.     

Effects of juvenile hormone I and precocene I & II on Microplitis rufiventris when administered via its host, Spodoptera littoralis

We investigated the effect of juvenile hormoneI (JHI) and precocene I & II (PI & PII) onthe endo-developmental stages, reproductiveperformance and longevity of Microplitisrufiventris Kok. after topical treatment ofhost larvae of Spodoptera littoralis(Boisd.). Host larvae were treated with each ofthe test compounds by a single dose 2–4 h afterparasitization or 1 day prior to parasitoidemergence, or by repeated daily applications 2–4 h after parasitization to parasitoid emergence.JHI-treatments increased parasitoiddevelopmental time, induced developmentalabnormalities and inhibition of parasitoidegression. Interestingly, one of the causal factorsthat inhibited the parasitoid egression was themoulting of some parasitoid larvae into asupernumerary instar. Applications of PI or PIIto parasitized S. littoralis larvae didnot affect parasitoid developmental time, butsome developmental abnormalities were noted.Melanin formation in host's blood was greaterin PI-treatments than in PII-treatments.PII-treatments arrested development of somefirst instar parasitoid larvae typical of JHIexcess. Adult female wasps that emerged fromJHI-treated hosts lived for significantlylonger periods than control females, but didnot produce more offspring. The longevity andreproductive capacity of females whichdeveloped in hosts treated by precocenes werereduced compared with the females emerged fromcontrol hosts. Even the small number ofadult wasps from PII-treated hosts which livedfor the same period as control wasps, showed asignificant reduction in their reproductiveperformance. Repeated daily applications of thetest compounds reduced wasp fecundity andlongevity to a significantly greater degreethan the single applications, except for a lowdose of JHI (1 µg). The study demonstratesthat growth disrupters, such as JHs andprecocenes have a delayed developmental effect onM. rufiventris and points out the need tobe aware of these effects in implementingcontrol strategies of S. littoralis innatural habitats.     

Interspecific competition between the braconid endoparasitoids Glyptapanteles porthetriae and Glyptapanteles liparidis in Lymantria dispar larvae

The effect of interspecific competition between the solitary endoparasitoid Glyptapanteles porthetriae Muesebeck (Hymenoptera: Braconidae) and the gregarious Glyptapanteles liparidis Bouché (Hymenoptera: Braconidae), was investigated in larvae of Lymantria dispar L. (Lepidoptera: Lymantriidae). Host larvae were parasitized by both wasp species simultaneously in premolt to the 2^nd or the 3^rd host instar or in an additional approach with a 4‐day delay in parasitization by the second wasp species. Host acceptance experiments revealed that both wasp species do not discriminate between unparasitized host larvae and larvae parasitized previously by the same or the other species. In more than 90% female wasps parasitized the larva they encountered first. During the period of endoparasitic development, larvae of the competing parasitoid species never attacked the egg stage of the other species. When host larvae were parasitized simultaneously by both wasp species, the rate of successful development of both species depended on the age of the host larva at the time of its parasitization; G. liparidis emerged successfully from 44% of host larvae parasitized during the premolt to 2^nd instar, G. porthetriae from 28%, and in 20% of the hosts both parasitoid species were able to develop in one gypsy moth larva. However, when host larvae were parasitized simultaneously during premolt to the 3^rd instar, G. liparidis was successful in 90% of the hosts, compared to 8% from which only G. porthetriae emerged. In the experiments with delayed oviposition, generally the species that oviposited first succeeded in completing its larval development. Larvae of the species ovipositing with four days delay were frequently attacked and killed by larvae of the first parasitizing species or suffered reduced growth. As the secondary parasitoid species, G. porthetriae‐larvae were never able to complete their development, whereas G. liparidis developed successfully in at least 12,5% of the multiparasitized host larvae. Thus, multiparasitism of gypsy moth larvae by both Glyptapanteles species corresponds to the contest type; however, G. porthetriae is only able to develop successfully as the primary parasitoid of young host larvae.     

Gregarious development of the solitary endo-parasitoid, Microplitis rufiventris in its habitual host, Spodoptera littoralis

Abstract:  Earlier research has shown that the koinobiont parasitoid, Microplitis rufiventris , attacks and can develop on early instars of Spodoptera littoralis larvae with preference to third instars. However, the present study was carried out using the newly moulted sixth instar larvae at two different temperatures (20 ± 1 and 27 ± 1°C) to study the developmental interaction between the parasitoid and the last instar host larvae. Parasitoid eggs laid in singly parasitized host larvae invariably died. As the number of parasitoid eggs/host larvae increased, the proportion of eggs that hatched and number of viable parasitoid larvae successfully reached to their final instar increased. The effect of superparasitization seems to be dose (no. of eggs + parasitoid factors)-temperature-dependent. The results demonstrate a kind of 'Allee effect' suggesting that superparasitized last instar S. littoralis larvae provide a better host environment than singly parasitized hosts for the parasitoid, M. rufiventris . This may be due to host's hormone and/or low dose of factors injected with parasitoid eggs. The supernumerary individuals of wasp larvae developed normally to the point of emergence but most did not successfully emerge from the host. The improvement of both hatchability and post-embryonic development of parasitoid wasp was significantly (P < 0.01) greater at 20°C than at 27°C. The results of the present study are useful in understanding the evolution of life-history strategies and host range in parasitic hymenoptera.     

Life‐history traits in a parasitoid dipteran species with free‐living and obligate parasitic immature stages

The robber fly Mallophora ruficauda Weidemann (Diptera: Asilidae) is an important pest of apiculture in the Pampas of Argentina. As adults, they prey on honey bees and other insects, whereas the larvae are ectoparasitoids of Scarabaeidae grubs. Females of M. ruficauda lay eggs in grassland where the larvae drop to the ground after being wind‐dispersed and burrow underground searching for their hosts. A temporal asynchrony exists between the appearance of the parasitoid larvae and the host, with the parasitoid appearing earlier than the host. The present study investigates whether a strategy of synchronization with the host exists in M. ruficauda and determines which of the larval instars are responsible for it. Survival patterns and duration of the immature stages of the parasitoid are investigated to determine whether there is a modulation in the development at any time that could reduce the asynchrony. Experiments are carried out to determine the survival and duration of free‐living larval stadia in the absence of cues associated with the host. It is established that the first instar is capable of moulting to the second instar without feeding and in the absence of any cues related to the host, a unique event for parasitoids. Also, the first instar of M. ruficauda moults to the second stage within a narrow temporal window, and the second instar never moults in the absence of the host. After parasitizing a host, the second instar has the longest lifespan and is the most variable with respect to survival compared with the rest of the instars. All larval instars, except for those in the last (fifth) stadium, have a similar rate of mortality to that of second‐instar larvae. Additionally, it is established that the host is killed during the fourth (parasitoid) stadium and that the first‐ and fifth‐larval instars develop independently of the host. Finally, possible mechanisms that could aid in compensating for the asynchrony between the parasitoid and the host, promoting the host–parasitoid encounter, are discussed.     

Interspecific competition between the braconid endoparasitoids Glyptapanteles porthetriae and Glyptapanteles liparidis in Lymantria dispar larvae

The effect of interspecific competition between the solitary endoparasitoid Glyptapanteles porthetriae Muesebeck (Hymenoptera: Braconidae) and the gregarious Glyptapanteles liparidis Bouché (Hymenoptera: Braconidae), was investigated in larvae of Lymantria dispar L. (Lepidoptera: Lymantriidae). Host larvae were parasitized by both wasp species simultaneously in premolt to the 2^nd or the 3^rd host instar or in an additional approach with a 4-day delay in parasitization by the second wasp species. Host acceptance experiments revealed that both wasp species do not discriminate between unparasitized host larvae and larvae parasitized previously by the same or the other species. In more than 90% female wasps parasitized the larva they encountered first. During the period of endoparasitic development, larvae of the competing parasitoid species never attacked the egg stage of the other species. When host larvae were parasitized simultaneously by both wasp species, the rate of successful development of both species depended on the age of the host larva at the time of its parasitization; G. liparidis emerged successfully from 44% of host larvae parasitized during the premolt to 2^nd instar, G. porthetriae from 28%, and in 20% of the hosts both parasitoid species were able to develop in one gypsy moth larva. However, when host larvae were parasitized simultaneously during premolt to the 3^rd instar, G. liparidis was successful in 90% of the hosts, compared to 8% from which only G. porthetriae emerged. In the experiments with delayed oviposition, generally the species that oviposited first succeeded in completing its larval development. Larvae of the species ovipositing with four days delay were frequently attacked and killed by larvae of the first parasitizing species or suffered reduced growth. As the secondary parasitoid species, G. porthetriae-larvae were never able to complete their development, whereas G. liparidis developed successfully in at least 12,5% of the multiparasitized host larvae. Thus, multiparasitism of gypsy moth larvae by both Glyptapanteles species corresponds to the contest type; however, G. porthetriae is only able to develop successfully as the primary parasitoid of young host larvae.     

Developmental status of endo-developmental stages of Microplitis rufiventris kok. in Spodoptera littoralis (boisd.) larvae topically treated by juvenile hormones I and II

The juvenile hormones I and II (JHI and JHII) were topically applied at concentrations of 1 or 5 μg to Spodoptera littoralis larvae containing newly deposited eggs of Microplitis rufiventris. The study demonstrated that both hormones do influence several aspects of the development of the parasitoid after treatment of its host larvae. Of these effects: (1) significant lengthening of periods of eggs and larvae, (2) moulting failure of parasitic larvae, (3) moulting the parasitic larvae into supernumerary instar, (4) arrest of postembryonic development in the first larval instar, (5) reduction in the emergence rate of parasitoid larvae, and (6) influence on embryogenesis. The application of JHI was more effective in disrupting the endo-development of the parasitoid than JHII. In all tests, control hosts produced significantly (P < 0.01) more parasitoids than treated ones. Off-target effects on natural enemies may seriously limit the use of JHs, especially in integrated control programmes.     

The influence of two endoparasitic wasps, <Emphasis Type="Italic">Hyposoter didymator</Emphasis> and <Emphasis Type="Italic">Chelonus inanitus</Emphasis>, on the growth and food consumption of their host larva <Emphasis Type="Italic">Spodoptera littoralis</Emphasis>

The influence of parasitism by Hyposoter didymator (Thunberg; Hymenoptera: Ichneumonidae) and Chelonus inanitus (Linnaeus) (Hymenoptera: Braconidae) on the growth and food consumption of their host Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) was studied in the laboratory. Parasitised larvae consumed significantly less artificial diet than unparasitised ones. Egg parasitisation by C. inanitus affected host larval consumption from the second day after emergence and it was significantly different from that of unparasitised ones. H. didymator, however, started to reduce larval consumption 4 days after parasitisation on the third instar host larvae. The overall reduction achieved by the larval endoparasitoid H. didymator is higher than that caused by the egg-larval endoparasitoid C. inanitus. The final body weight of a parasitised host larva by H. didymator and C. inanitus was only 6.7 and 13.0% of the maximum weight of an unparasitised sixth instar larva respectively. Moreover, parasitised larvae never reached the last instar. Results indicated that parasitised larvae might cause considerable less damage to the host plant than unparasitised ones.     

Egg maturation dynamics of the parasitoid Microplitis rufiventris: starvation speeds maturation in early life

The number of mature eggs carried by a female parasitoid at any given moment (egg load) is a fitness‐related parameter affecting reproductive potential and impacting upon host population dynamics. Microplitis rufiventris Kokujev (Hymenoptera: Braconidae) is a solitary koinobiont endoparasitoid wasp of several noctuid pests, including Spodoptera littoralis. The number of mature eggs carried by females at emergence is approximately 50. The rate of egg maturation is strongly affected both by feeding status and access to host larvae. In early adult life, egg maturation rates are lower for 6–72 h in fed wasps compared with food‐deprived wasps. When given access to hosts, honey‐fed wasps live for approximately 9 days with high lifetime fecundity (226 eggs). By contrast to early adult life, the total realized fecundity is positively affected by feeding status, where water‐fed and starved females have 140 and 107 eggs, respectively. Egg resorption is most pronounced in the later life of females. The results suggest, in addition to confirming the effect of honey‐feeding on total fecundity, that fecundity of starved wasps includes rapid egg maturation early in life, which potentially could improve the performance of the parasitoid as a biological control agent.     

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.     

Microplitis croceipes teratocytes cause developmental arrest of Heliothis virescens larvae

Microplitis croceipes teratocytes placed into nonparasitized Heliothis virescens larvae survived in the absence of a parasitoid larva and caused developmental changes in the host. Expressions of these changes included delayed larval mortality, incomplete larval-pupal ecdysis, or delayed pupation. Two day old 4th stadium H. virescens larvae were more sensitive to injected teratocytes than were 5th stadium larvae. Three day old teratocytes were more effective than were 6 day old teratocytes. The degree of response was related to the number of injected teratocytes. For example, 750 three day old teratocytes (the approximate number from a single parasitoid egg) caused delayed larval mortality in 96% of the treated larvae whereas 175 three day old teratocytes caused delayed larval mortality in only 33% of the treated larvae. Even a dose of 80 teratocytes resulted in 15% incomplete larval-pupal ecdysis compared to 0% for controls. Treatment with hemocyte-and teratocyte-free hemolymph from parasitized larvae, hemocytes from nonparasitized H. virescens, unfertilized M. croceipes eggs, Cotesia congregata teratocytes, or Micrococcus lysodeikticus cells all had very little effect either on larval growth or development time.     

Influence of host size on oviposition behaviour and fitness of Elachertus cacoeciae attacking a low-density population of spruce budworm Choristoneura fumiferana larvae

1. Oviposition behaviour and host size ? fitness relationships of a gregarious, idiobiont ectoparasitoid, Elachertus cacoeciae (Howard) (Hymenoptera: Eulophidae), were studied by implanting one fourth‐, fifth‐, and sixth‐instar spruce budworm Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae) larva per tree in a stand where the density of the wild C. fumiferana population was low. 2. Development time of E. cacoeciae larvae was quickest on fifth‐instar C. fumiferana larvae, which were the preferred hosts for oviposition. 3. Brood sex ratio (proportion of females) was related positively to increasing C. fumiferana instar, indicating that more females were laid on larger hosts. 4. Parasitoid offspring size increased with increasing C. fumiferana instar and decreased with increasing brood size on smaller hosts. Female but not male size was related positively to increasing brood sex ratio (proportion of females). 5. Under laboratory conditions, parasitoid longevity was related positively to parasitoid size and realised lifetime fecundity, and clutch size was related positively to host size. 6. These results suggest that selection of intermediate‐sized C. fumiferana larvae may be adaptive for E. cacoeciae.     

Growth and development of Cardiochiles nigriceps viereck (hymenoptera,braconidae) larvae and their synchronization with some changes of the hemolymph composition of their host,Heliothis virescens (F.) (Lepidoptera,Noctuidae)

Larval development of the parasitoid Cardiochiles nigriceps Viereck occurs in the last instar larva of its host, Heliothis virescens (F.). This allows the parasitoid to exploit the nutritional increase in the biosynthetic activity occurring in the host in preparation for metamorphosis. To understand the biochemical basis of this host parasitoid developmental synchrony, we undertook host ligation studies and analyzed host hemolymph for proteins and glycerol esters. Parasitization affected the biochemical profile of the host. The hemolymph protein concentration of parasitized last instar H. virescens larvae increased through time, whereas unparasitized (control) larvae were characterized by a decrease in the protein titer when they reached the prepupal stage. The effect of parasitism on glyceride titers of host hemolymph was not as pronounced as the effect on proteins. Ligation conducted on 5th instar hosts, which were parasitized as 4th instars, affected parasitoid development in a time-dependent way. The percentage of successfully developing C. nigriceps larvae increased with the increase of the time interval between parasitization and ligation. Ligation performed before day 2 of the 5th larval instar of H. virescens completely inhibited parasitoid development. Ligations that disrupted parasitoid developmentwere associated with a low host hernolymph protein concentration. Parasitoid development was successful when hernolymph protein titer was high, as occurred when ligations were performed after day 3 of the 5th host instar in both control and parasitized larvae. Ligations in both situations resulted in a slight increase in glyceride titers. The results suggest that host proteins and/or some factor(s) associated with them may play a role in parasitoid growth and development. © 1993 Wiley-Liss, Inc.     

Polydnavirus of Microplitis croceipes prolongs the larval period and changes hemolymph protein content of the host,Heliothis virescens

Polydnaviruses from certain parasitoid Hymenoptera have been reported to interfere with both host immunity and host development. Heliothis virescens larvae injected with either calyx fluid or sucrose gradient-purified polydnavirus from Microplitis croceipes (McPDV) gained less weight than saline-injected larvae. The active feeding portion of the fifth stadium larva (time to reach the burrowing-digging stage) was doubled (7.0 vs. 3.4 days) when a 0.25 wasp equivalent (WE) of sucrose gradient-purified McPDV was injected into a newly ecdysed fifth stadium host. Many of the treated larvae were unable to pupate, successfully and died at a point of incomplete larval-pupal ecdysis. Pupae that did result from the treated larvae weighed significantly less than controls, even at 0.025 WE. The rate of weight gain and extent of delay of development were dose-dependent; as little as 0.1 WE extended the time of active feeding by 1.5 days and yielded only 25% adults. A 0.05 WE dose yielded 78% adults compared to 95% for controls. The total protein content of hemolymph from individuals injected with McPDV was significantly less than that of controls at any McPDV dose equal to or greater than 0.1 WE. SDS-PAGE profiles of hemolymph proteins from control and McPDV-injected larvae revealed a marked inhibition of the normal accumulation of storage proteins during the fifth stadium and a lesser reduction of serine protease inhibitor protein. Thus, McPDV-injected larvae exhibited some symptoms (less total hemolymph protein and reduced amounts of storage protein) similar to those shown by both parasitized larvae and by larvae injected with M. croceipes teratocytes. However, McPDV affected development during the active feeding stage of the larva, while teratocytes primarily impacted larvae at the time when larval-pupal transformation processes are initiated. © 1995 Wiley-Liss, Inc.     

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

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

Reproductive biology of the microtype tachinid fly Zenillia dolosa (Meigen) (Diptera: Tachinidae)

Reproductive biology including mating, adult longevity, fecundity and development of the tachinid fly Zenillia dolosa was investigated for optimizing rearing procedures using Mythimna separata as a host in the laboratory. Females lay microtype eggs containing a first instar larva on food plants of the host and then the eggs must be ingested by the host for parasitization. Mating success was 58.5% with mating duration of 80.7 min. Mating was most successful when day 0–1 females were kept with day 2–4 male flies. Female body size was positively correlated with its fecundity but not with longevity. However, females that survived longer produced more eggs during their lifetime. Parasitoids successfully developed in 4th to 6th instar host larvae. Host instars at the time of parasitoid egg ingestion significantly influenced development time of the immature parasitoid, but did not affect body size of the emerging parasitoid. We suggest that pairing newly emerged females with day 2–4 males should result in higher mating success and using the last instar hosts for parasitization should minimize development time of the parasitoid for rearing.