Growth and development of the endoparasitic wasp Apanteles congregatus: dependence on host nutritional status and parasite load

ABSTRACT. Previously we have shown that the number of Apanteles congregatus Say (Hymenoptera, Braconidae) larvae developing in Manduca sexta (L.) (Lepidoptera, Sphingidae) larvae that are parasitized in the first instar determines the timing of emergence of the parasites from the host. Here we show that the first larval ecdysis of the wasps occurs after the host ecdyses to the terminal stage, regardless of whether that stage is the host's fourth, fifth or supernumerary sixth instar. Starvation of newly ecdysed terminal stage host larvae prevents emergence of the parasites. When starvation is begun at progressively later times, then an increasing proportion of the hosts have parasites that emerge, suggesting a period of indispensable host nutrition exists during which the host must feed to satisfy the developmental requirements of the parasites. In hosts fed ad libitum , the weight of the host plus its parasites at the time of emergence is positively correlated with the number of parasites developing in the host. When the weight of the parasites alone is subtracted from the weight of the host—parasite complex, the data show that heavily parasitized hosts have a larger host mass than lightly parasitized larvae. In contrast, the wasp larvae, and the adult males and females that develop from them, have lower individual weights after development in heavily parasitized hosts.     

The ectoparasitic wasp Eulophus pennicornis (Hymenoptera: Eulophidae) uses instar-specific endocrine disruption strategies to suppress the development of its host Lacanobia oleracea (Lepidoptera: Noctuidae)

To successfully complete its development, the gregarious ectoparasitoid Eulophus pennicornis must inhibit the moult of its host, Lacanobia oleracea. In the present study, we examined the possibility that moult- and metamorphosis-associated endocrine events may be disrupted in caterpillars parasitized as newly moulted last (sixth) instars. Juvenile hormone (JH) titres on days 2 and 5 of the final stadium were significantly higher (> 100 fold) in parasitized than in non-parasitized hosts, in which JH was essentially absent. Elevated JH levels were associated with reduced haemolymph JH esterase (JHE) activity (down by 99.8%) and enhanced in vitro JH biosynthesis by the corpora allata (CA) (up to 4.5 fold). Wasp adults and/or larvae, in which we measured high levels of JH III (up to 2.7 ng/g), but little or no JH I or JH II, were not seen as likely sources of JH in parasitized hosts, in which we found mostly JH I and JH II. In addition, removal of parasitoid eggs or larvae after oviposition did not prevent the rise in JH titres seen in parasitoid-laden hosts, suggesting that wasp venom may be responsible for the observed hormonal dysfunction. Host haemolymph 20-hydroxyecdysone (20-E) levels were largely unaffected by parasitism during the final stadium although they were observed to increase earlier and decrease more rapidly in parasitized insects. We compare these results with those reported earlier for L. oleracea larvae parasitized by E. pennicornis as penultimate (fifth) instars, which display significantly depressed 20-E titres relative to control larvae. We conclude that E. pennicornis employs host endocrine-disruption strategies that differ according to whether the host is parasitized as a penultimate or final-stadium larva.     

Dose-dependent influence of Microplitis rufiventris factors on developmental rate and growth of last-instar Spodoptera littoralis larvae

The solitary endoparasitoid, Microplitis rufiventris, attacks and can develop in earlier instars of Spodoptera littoralis larvae with preference to third‐instar larvae. We used the last stadium (sixth instar), a stage which is not naturally parasitized. The newly moulted larvae (0–3 h old) of this stadium were more acceptable for parasitization by the wasp females than the older ones (24 h old). Parasitization by M. rufiventris wasp of last instar S. littoralis larvae leads to dose (no. of eggs + parasitoid factors)‐dependent effects which were more pronounced at 20°C than at 27°C. A single oviposition into a sixth instar host larva resulted in normal development of the host. However, superparasitization increased the proportions of developmentally arrested hosts and number of live wasp larvae. Development of supernumerary individuals of the parasitoid in the host larva leads to dose‐related adverse effects on host growth and development. The present study may provide interesting opportunities for studying the physiological bases of host–parasitoid interactions and parasitoid intra‐specific competition in the biological system considered.     

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.     

Relationships between the parasitoid Hyposoter exiguae and Trichoplusia ni: Parasitoid-induced histo- and cytopathology

The histology and cytology of Trichoplusia ni larvae were studied for evidence of abnormality or pathology induced by the solitary ichneumonid endoparasitoid, Hyposoter exiguae. Sample control and parasitized larvae were fixed every other day, and sections of these larvae were stained with mercuric-bromophenol blue. The fat body of parasitized larvae failed to show many of the changes characteristic of normally developing controls and, on the last day of parasitism, revealed extensive pathological changes. Spermatogenesis continued normally until the end of the association in parasitized hosts even though their development was halted in the fifth larval stadium. Parasitoid larvae seemed to secrete a proteinaceous material from their salivary and rectal glands into the host hemocoel. This material may be responsible for the pathological changes reported here. The parasitoids apparently fed on hemolymph alone until about 24 hr before emergence and pupation.     

Stage-specific effects of Campoletis sonorensis parasitism on Heliothis virescens development and prothoracic glands

Abstract The ichneumonid endoparasitoid Campoletis sonorensis Cameron (Hymenoptera: Ichneumonidae) injects a polydnavirus when it oviposits into a host. We compared the development of Heliothis virescens (F.) (Lepidoptera: Noctuidae) larvae parasitized in the penultimate (fourth) stadium with those parasitized in the last (fifth) stadium by C.sonorensis and show that hosts stung in the fifth stadium exhibited arrested or delayed development compared to the controls. Parasitoids developed normally to the point of emergence in larvae stung in the fifth stadium but most did not successfully emerge from the host. The prothoracic glands in all successfully parasitized fifth stadium hosts and most unsuccessfully parasitized fifth stadium hosts showed some degree of virally-induced degeneration. Larvae stung in the fourth stadium developed more slowly than controls and either did not moult or developed to a fifth and sometimes a supernumerary sixth stadium before parasitoid emergence. Unsuccessfully parasitized hosts were delayed in their development but eventually moulted to the fifth and, in some cases, a supernumerary sixth stadium before pupating. Hosts stung in the fourth stadium showed no signs of prothoracic gland degeneration whether successfully parasitized or not. In addition, calyx fluid injections into early fourth stadium hosts did not cause prothoracic gland degeneration even after these hosts moulted to the fifth stadium, suggesting that degeneration induced by polydnavirus is specific to the last stadium of the host.     

The effect of host age ofLymantria dispar larvae [Lep.: Lymantriidae] on the development ofGlyptapanteles liparidis [Hym.: Braconidae]

The endoparasitic development ofG. liparidis was examined in 3 different host stages of gypsy moth larvae. Hatching ofG. liparidis-larvae occurred 3 to 5 days after oviposition in hosts parasitized during their premoulting period, and after 5 to 7 days in those parasitized in the 3^rd midinstar state. The parasites generally moulted to the 2^nd larval instar between the 11^th and 13^th day in the first group, and between the 13^th and 15^th day in the latter, when they had reached a volume of 0.04–0.05 mm³. The positive correlation between host ecdysis and the ecdysis of 1^st stadium larvae to L₂ suggested that host moulting influenced the development of the parasitoid larvae. Emergence from the host larvae occurred at 20°C after 27 days on average, and coincided with the parasites moulting to the 3^rd instar. Five to 7 days after spinning their cocoons near the developmentally arrested host larva, the male, and 1 to 2 days later the female wasps eclosed. Due to the variation in the number of parasites per host, no difference was observed between the hosts parasitized at various stages; however, a tendency for later parasitized hosts to contain more parasite larvae was evident. The nutritional conditions of the moth parental generation influenced both host and parasite development. On the other hand no influence of host age was observed on emergence dates of larvae and wasps.      

Biology of Microplitis kewleyi (Hymenoptera: Braconidae): A parasite of Agrotis ipsilon (Lepidoptera: Noctuidae) larvae

Microplitis kewleyi Muesebeck is a gregarious internal parasite of larvae of the black cutworm Agrotis ipsilon (Hufnagel). Studies of the biology of the parasite revealed that there was an inverse relationship between host instar and parasite preference. Duration of development from egg to pupa ranged from 18 days at 27°C to 68.7 days at 16°C. Development from egg to pupa took 13.5–21.6 days when fourth and first instar host larvae, respectively, were parasitized. A larger number of parasites emerged from hosts parasitized in the fourth instar (22.4) than the first instar (11.5). Parasite pupation occurred when the host was in the fifth/sixth instar, depending on the instar parasitized. Thirty‐nine per cent of host larvae exposed as first instars to parasites died before parasite emergence. This decreased to 0% for host larvae exposed as fourth instars. The sex ratio was 1:1.2 (M:F). Thirty‐seven per cent of hosts exposed diurnally were stung, compared to 24% exposed nocturnally. Mean daily progeny was highest (12) on the first day, decreasing to zero after 20 days. Percent host parasitism was also highest on the first day (35%) decreasing to nearly 0% after 18 days. There appear to be three parasite larval instars. Host larvae often remained alive after parasite emergence.     

Inhibition of testicular growth and development in Manduca sexta larvae parasitized by the braconid wasp Cotesia congregata

Tobacco hornworm larvae parasitized by the gregarious larval endoparasitoid Cotesia congregata exhibited an inhibition in testicular growth and development, the extent of which was determined by the age and developmental stage of the host at the time of parasitization. The degree of parasitic castration, as assessed by measurements of testicular volume, was correlated with the stadium in which parasitization occurred. A mathematical formula requiring the measurement of testicular length, width and depth was used to calculate testicular volume. The use of the depth parameter revealed a negative correlation between host weight and testicular volume in parasitized larvae. Testicular volumes of fifth instar hosts, which had been parasitized in the first stadium, were significantly smaller than those originally parasitized as fourth or fifth instar larvae and were not correlated with parasitoid load. Effects of natural parasitism were not duplicated by injections of C. congregata polydnavirus and venom, topical treatment with the juvenile hormone analog methoprene, or starvation of nonparasitized larvae. Larvae receiving virus plus venom or methoprene grew larger due to delayed wandering and had larger testes than controls. Deleterious effects on host testes may be due to the effects of nutrient competition between the developing parasitoid progeny and the gonads, combined with the juvenilizing effects believed to be caused by the polydnavirus.     

Infection by the microsporidium Vairimorpha necatrix (Microspora: Microsporidia) elevates juvenile hormone titres in larvae of the tomato moth, Lacanobia oleracea (Lepidoptera: Noctuidae)

The effects of infection by a microsporidium, Vairimorpha necatrix (Kramer), on the endogenous levels of juvenile hormones in tomato moth (Lacanobia oleracea L.) larvae were investigated. Levels of juvenile hormone II (JH II) were 10-fold greater in the infected larvae on day two of the sixth stadium but no significant difference was observed on day seven. Juvenile hormone I (JH I) was also detected in day two and day seven sixth instar infected larvae but was not detected in non-infected larvae. The duration of the fifth and sixth stadia was significantly longer for infected larvae when compared with non-infected larvae. No evidence was found to suggest that supernumerary moults are a feature of infection by V. necatrix in L. oleracea larvae. Experiments were performed to determine whether the elevation in JH levels, which probably prevents pupation, is an adaptive mechanism of the microsporidium for extending the growth phase of the host, thereby allowing increased spore production. A proportion of infected larvae were collected on days 9 and 24 of the sixth stadium and spore extracts prepared from each larva. These days represent the average duration of the sixth stadium required for uninfected larvae to reach pupation, and the average number of days that V. necatrix-infected larvae survive in the sixth stadium before dying from infection. The mean spore yields from infected larvae 24 days into the sixth stadium were significantly higher than the spore yields obtained from day nine sixth instar larvae. The hypothesis that V. necatrix manipulates host endocrinology (i.e. prolong the host larval state to maximise spore yield) is discussed in context with the results obtained.     

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.     

Parasitic castration of Pseudaletia separata by Cotesia kariyai and its association with polydnavirus gene expression

Parasitization by the endoparasitoid Cotesia kariyai caused the inhibition of spermatogenesis of Pseudaletia separata. This phenomenon is called parasitic castration. The degree of castration was dependent on the host stage parasitized. Host parasitized on day 1 of the 4th stadium (the time of primary spermatocyte accumulation), had testicular cells with abnormal chromosomes appearing two days after parasitization, and spermiogenesis was completely inhibited. However, when hosts were parasitized on day 0 of the 6th (final) stadium, the degree of castration was less severe, and elongated cells appeared similar to those found in nonparasitized larvae. Results of this study involving injection of C. kariyai polydnavirus (CkPV) and venom suggested that these wasp components caused the appearance of abnormal chromosomes in specific germ cells, which were in mitotic or meiotic prophases. The amount of CkPV gene expression in host testes increased immediately after parasitization and reached a maximum 12h later. The early-expressed CkPV gene(s) may be related to the parasitic castration phenomenon.     

Venom of ectoparasitoid,Euplectrus sp near plathypenae (Hymenoptera: Eulophidae) regulates the physiological state of Pseudaletia separata (Lepidoptera: Noctuidae) host as a food resource

Euplectrus sp. near plathypenae is an ectoparasitoid that can parasitize from 3rd to day 0-6th instar Pseudaletia separata. The developmental period of the parasitoid from the egg to the pupal stage is about 13 days. Parasitized hosts are developmentally arrested and never molt to the next stadium. The injection of venom fluid results in similar effects on P. separata larvae as does parasitization. The inhibitory effect of the venom on molting was dose dependent. Injection of 0.3 female equivalents of venom into day 0-5th host instar resulted in a similar developmental arrest as seen in parasitized hosts. The amount of total lipid in the hemolymph of the host increased as a function of the amount of venom injected, while the lipid content of the fat body was similar to lipid levels in the fat body of parasitized larvae. The amount of total protein in the hemolymph also increased when venom was injected, whereas the protein level of the fat body did not increase. The lipid concentration within the parasitoid larva was maintained at the same level throughout larval development, but increased before pupation. We conclude that the injected venom increased the hemolymph content of lipid and protein to support the growth and development of the ectoparasitoid larva.     

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.     

拟寄生蜂搜索产卵过程中对寄主的竞争

综述拟寄生蜂搜索产卵过程中对寄主竞争的最新研究进展.这类竞争具有四种方式,即标记寄主、杀卵和杀幼、守护寄主和捕食寄主.（1）标记寄主常涉及寄主标记信息素,这是由雌蜂在产卵前、产卵时或产卵后分泌的化学物质.寄主标记信息素常介导拟寄生蜂对已寄生和健康寄主的辨别、减少过寄生和多寄生、减轻种内和种间竞争压力.（2）雌蜂遇到已寄生寄主时,很多种类杀死前一雌蜂遗留的卵和幼虫,再产下自己的卵.雌蜂使用三种方法杀卵和杀幼,即产卵器穿刺、取食和使用有毒物质.通过杀卵和杀幼,产卵雌蜂清除了前一雌蜂遗留的后代,主动改善了寄主品质,从而有利于自身后代的生存.（3）守护寄主在肿腿蜂科、缘腹细蜂科、金小蜂科、缨小蜂科和茧蜂科中均有报道,守护者驱逐入侵者以保护后代及健康寄主.（4）捕食寄主不仅减少了健康寄主数量,且直接导致已寄生寄主中拟寄生蜂卵和幼虫的死亡.雌蜂一般在体内成熟卵量较少时捕食寄主.讨论了研究拟寄生蜂搜索产卵过程中竞争寄主的理论意义和实际应用价值.     

Protein expression during parasite redirection of host (Trichoplusia ni) biochemistry

Expression of proteins during normal egg and larval development of Trichoplusia ni was compared with that occurring in hosts stung as eggs by the parasitic wasp Chelonus sp. near curvimaculatus. Those stung hosts which produced a parasite (truly parasitized), precociously expressed proteins associated with larval-pupal metamorphosis, as did those stung hosts which did not contain a developing endoparasite (pseudoparasitized). No highly abundant, low-intermediate molecular weight hemolymph proteins were observed in truly or pseudoparasitized larvae which did not also occur at some point in the development of normal larvae. A low abundance, high molecular mass (160,000 Da) protein was observed in the hemolymph of truly parasitized larvae, but not of normal or pseudoparasitized larvae. The protein is glycosylated and very acidic (pI near 4.5). The data show that any parasitization proteins injected or induced by the ovipositing female parasite are in low abundance, in contrast to situations reported for parasitic wasps which sting hosts as larvae.     

白蜡吉丁柄腹茧蜂的寄生和繁殖生物学

白蜡吉丁柄腹茧蜂Spathius agrili Yang是我国天津地区寄生白蜡窄吉丁幼虫的一种重要天敌。本研究通过林间调查并结合室内观察,测定了该寄生蜂在不同营养条件下的存活时间和不同时期的产卵量,调查了不同寄主大小对寄生蜂后代生长发育的影响,以及寄生蜂对不同深度树皮下的寄主利用情况。结果表明：不同营养条件下白蜡吉丁柄腹茧蜂的存活时间差异很大,补充20％蜂蜜水的成蜂存活时间明显延长,最长可达3个月。相同条件下雌蜂的存活时间比雄蜂略长。在补充营养的条件下,茧蜂的产卵时间最长可达8周,产卵的高蜂在羽化后第2周前后,平均每雌每周产卵量在整个产卵期内基本保持在8～12粒上下,没有大的波动。茧蜂低龄幼虫也可能分泌毒素主动攻击寄主,提高了寄生蜂后代的生存能力。寄主个体大,营养量也大,寄生其上的茧蜂幼虫成功完成发育的数量随之增加,表明寄主营养资源的多少直接影响到寄生蜂后代的生长发育和存活。白蜡吉丁柄腹茧蜂对1～6.5 mm树皮深度范围内的适龄寄主幼虫均能够寄生利用,约92％的被寄生白蜡窄吉丁幼虫个体分布于1～4 mm深度的树皮下,在3 mm厚的树皮下分布的数量最多。茧蜂数量与树皮深度大致上呈抛物线关系,理论上在树皮深度为3.97 mm处茧蜂分布数量最多。     

Effects of temporary host deprivation on the reproductive potential of Trichogramma brassicae

The effect of host deprivation on the reproductive potential and parasitization behaviour ofTrichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) was investigated. Upon emergence, females were deprived of hosts for one to four days, and were subsequently provided with an unlimited number of hosts. Regardless of its duration, deprivation did not affect female longevity, overall rate of progeny emergence, or progeny sex-ratio. As deprivation time increased, however, the total number of parasitized host decreased from an average of 81.2 when hosts were provided at emergence, to an average of 34.0 when the waiting time was 4 days. This reduction was mainly due to the reduction in the parasitizations following the first laying peak, which was not affected when deprivation lasted fewer than 4 days.Trichogramma females are able to store ripe eggs (about 35) for 3 days without damage, but resorption occurs after four days of deprivation. Our results suggest that imaginal vitellogenesis occurs in this proovigenic wasp but that it is affected by host deprivation. The behaviour of females, as measured by the average distance between all parasitized hosts, was also modified by host deprivation. When deprivation exceeded one day, parasitizations were more scattered over the host patch. Moreover, increased deprivation times also appeared to delay the initiation of parasitization by a few hours. Host shortage is likely to occur in nature, reducing the efficiency ofTrichogramma as a biocontrol agent. The individual history of females must be taken into account in any study of the reproductive strategies of parasitoid females.     

Parasitism of Lacanobia oleracea (Lepidoptera) by the ectoparasitoid, Eulophus pennicornis, is associated with a reduction in host haemolymph phenoloxidase activity

When haemolymph from fifth instar Lacanobia oleracea was incubated in vitro, rapid melanization occurred. Similar levels of melanization occurred in haemolymph from larvae that had been experimentally injected with venom from the ectoparasitic wasp, Eulophus pennicornis. In contrast, haemolymph from larvae parasitized by this wasp melanized more slowly and less extensively. Phenoloxidase assays indicated that enzyme activity was present in haemocyte lysate supernatants, serum and plasma from L. oleracea and that on day 5 post-parasitization, fractions prepared from parasitized larvae had significantly less phenoloxidase activity than similar fractions from untreated or experimentally envenomated larvae. In addition, no PO activity was detectable in wasp venom, and the venom had no effect on L. oleracea plasma phenoloxidase activity in vitro. These results indicate that parasitism of L. oleracea by E. pennicornis suppresses host haemolymph phenoloxidase activity and that this suppression is not induced by adult wasp venom. The results are discussed with reference to the survival advantages of suppressing the activity of this host enzyme, and to the possible source(s) of putative suppressive factors.     

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.