The parasitoid of a fruit moth caterpillar utilizes fruit components as nutrient source to increase its longevity and fertility

Longevity and fecundity of female wasps are two decisive factors for the effectiveness of parasitoid species as biological control agents. Accessibility and suitability of nutrient sources determine parasitoid survival and reproduction. Host, nectar and honeydew feeding are frequent adult parasitoid behaviors to cover nutritional needs. Here we postulate that especially parasitoid species of endophytic herbivores might use plant tissue as a nutrient source that becomes accessible upon herbivory. We investigated the influence of plant consumption and host feeding on longevity and fecundity of Hyssopus pallidus, a gregarious ecto-parasitoid of caterpillars of the codling moth that feed inside apple fruits. Longevity of unmated and mated ovipositing female parasitoids was highest in treatments with fruit pulp. While longevity in this treatment was not significantly different from that with honey, it was significantly higher than in treatments without food, with water or with a host alone.Reproduction was significantly increased by these sugar-rich nutrient sources compared to the control with a host alone. In contrast, host feeding did not yield any significant contribution to longevity and fecundity in a series of bioassays with different host–parasitoid ratios and with differently aged and sized hosts, compared to controls without food.We conclude that in this synovigenic species host feeding does not contribute to longevity and fecundity, but females can increase survival and reproduction in the field relying solely on the plant tissue damaged by their host caterpillar.     

Lifetime Reproductive Success in the Solitary Endoparasitoid, Venturia canescens

Parasitoid wasps have long been considered excellent organisms in studies examining the evolution of reproductive and life-history strategies. In examining the lifetime reproductive success of parasitoids in the laboratory, most investigations have provided the insects with excess hosts and food, where they exist in a relatively constraint-free environment. Importantly, these conditions may not accurately reflect the true heterogeneity of natural systems, where suitable hosts and food sources are likely to be limiting. This study examines the influence of differences in host and food availability on reproductive and life-history parameters in an asexual strain of the solitary endoparasitoid, Venturia canescens (Hymenoptera: Ichneumonidae). Lifetime reproductive success in V. canescens was measured in response to temporal variations in host and food (honey solution) access. Cohorts of parasitoids were provided with 200 fifth-instar larvae of the Indian meal moth, Plodia interpunctella (Lepidoptera: Pyralidae), and food for variable periods daily after eclosion. V. canescens is synovigenic, and host-deprived wasps continued to mature eggs over the first few days after eclosion until the egg storage capacity was reached in the oviducts. When these wasps were subsequently provided with hosts, oogenesis resumed and continued until later in adult life. Constantly fed wasps lived longer and produced more progeny than wasps from cohorts which were alternately fed and starved or were starved from eclosion. Moreover, wasps with constant host and food access produced most progeny early in life and usually experienced prolonged periods of postreproductive survival. In contrast, the reproductive period of wasps with limited host access was more evenly distributed throughout the adult life. Consequently, the cumulative progeny production by V. canescens with constant food access was fairly uniform irrespective of host availability. Longevity and fecundity in V. canescens were positively correlated with adult size. However, variable host access had little effect on the longevity of wasps which were constantly supplied with honey. Over the first 2 days of adult life, variation in food access also had no effect on progeny production by V. canescens. We argue that manipulating temporal host and food access to parasitoids in the laboratory more closely approximates natural conditions, where these resources are likely to be spatially separated. Moreover, our findings suggest that many highly synovigenic parasitoids like V. canescens, which produce microtype (=hydropic) eggs, have a considerably higher reproductive potential than ovary dissections have revealed. Our findings are discussed in relation to life-history evolution in the parasitic Hymenoptera.     

Comparing and contrasting development and reproductive strategies in the pupal hyperparasitoids Lysibia nana and Gelis agilis (Hymenoptera: Ichneumonidae)

In most animals, the optimal phenotype is determined by trade-offs in life-history traits. Here, I compare development and reproductive strategies in two species of solitary secondary hyperparasitoids, Lysibia nana and Gelis agilis, attacking pre-pupae of their primary parasitoid host, Cotesia glomerata. Parasitoid larvae of both species exploit a given amount of host resources with similar efficiency. However, adults exhibit quite different reproductive strategies. Both species are synovigenic, and female wasps emerge with no mature eggs. However, G. agilis must first host-feed to produce eggs, while L. nana does not host-feed but mobilizes internal resources carried over from larval feeding to initiate oogenesis. Further, G. agilis is wingless, produces large eggs, has a long life-span, and generates only small numbers of progeny per day, whereas these traits are reversed in L. nana. Given unlimited hosts, the fecundity curve in L. nana was “front-loaded,” whereas in G. agilis it was depressed and extended over much of adult life. In L. nana (but not G. agilis), wasps provided with honey but no hosts lived significantly longer than wasps provided with both honey and hosts. Differences in the fecundity curves of the two hyperparasitoids are probably based on differing costs of reproduction between them, with the wingless G. agilis much more constrained in finding hosts than the winged L. nana. Importantly, L. nana is known to be a specialist hyperparasitoid of gregarious Cotesia species that pupate in exposed locations on the food plant, whereas Gelis sp. attack and develop in divergent hosts such as parasitoid cocoons, moth pupae and spider egg sacs. Consequently, there is a strong match between brood size in C. glomerata and egg production in L. nana, but a mismatch between these parameters in G. agilis.     

Adult feeding and lifetime reproductive success in the parasitoid Aphytis melinus

The diet of adult females of the parasitoid Aphytis melinus DeBach (Hymenoptera: Aphelinidae) includes host insects and sugar-rich foods such as nectar and honeydew. We compared the contributions of host feeding to longevity and fecundity in A. melinus females in the presence and in the absence of honey meals. First, we assessed the longevity of females that were not allowed to oviposit. While the longevity of females fed honey was significantly increased by host feeding (median ages were 30.5 days for host-fed females and 17 days for females not allowed to host feed), the lifespan of parasitoids not fed honey did not exceed 3 days for any individual and there was no effect of host feeding on longevity in this group. In the second set of experiments, we assessed the fecundity and longevity of females allowed to oviposit. We conducted two experiments, one in which honey was continuously available, and one in which honey was not available. In both experiments, daily observations were made of females that were either allowed to host feed or manually prevented from host feeding. In the presence of honey, host feeding significantly increased both fecundity and longevity, and in the absence of honey, parasitoids died within 2 days and host feeding had no significant effect on either fecundity or longevity. The lifetime fecundity of females fed honey but not hosts exceeded the initial egg complement by 60% on average. Approximately one host per day was used for host feeding whether honey was supplied or not, and each host-feeding meal contributed approximately 3.9 eggs to the lifetime fecundity of honey-fed females. In the last experiment, we compared the rate of egg resorption over a 36-h period in A. melinus females that were deprived of hosts and either fed honey or starved. While no egg resorption was detected in honey-fed females over this time period, starved females resorbed approximately 9 eggs. Thus, the availability of a sugar-rich food interacts strongly with host feeding in influencing longevity and fecundity and has a strong direct effect on egg resorption.     

Influence of adult diet on fitness and reproductive traits of the egg parasitoid Anagrus virlai (Hymenoptera: Mymaridae), a potential biocontrol agent against the corn leafhopper

Dalbulus maidis is the most important leafhopper pest of maize in the Americas. Anagrus virlai is an egg parasitoid commonly associated with the corn leafhopper. We evaluated whether the performance of A. virlai is dependent on different diets provided during 24 hr or throughout adult female lifetime. Additionally, functional response of A. virlai on D. maidis eggs using maize leaves containing honeydew plus honey was described. A. virlai is a mostly pro-ovigenic autogenic species whose females are able to parasitize eggs immediately after emergence. We found that wasps oviposit the majority of their eggs in the first day of their adult life. Realized lifetime fecundity and lifetime potential fecundity did not differ significantly among treatments, but longevity and egg production increased when honey was added to diet. Data were consistent with an intermediate functional response between type II and III, but closer to type II, indicating a high parasitism rate at low host densities and a decrease in the oviposition rate at high host densities, due to a possible egg limitation. Our results suggest that carbohydrate food sources (honeydew and honey) might not be the factor limiting reproductive success during the first 24 hr. Food supply, however, might influence egg maturation and survivorship of wasps, thus potentially enhancing biological pest control when hosts are scarce in the course of the first few days of adulthood.     

Feeding and survival in parasitic wasps: sugar concentration and timing matter

Sugar consumption can increase the longevity and lifetime fecundity of many species of parasitic wasps. Consequently, for these insects the availability of sugar sources in the field is important for their reproductive success. As sugar sources can be highly variable in quantity, space and time, the chances of finding a sufficient amount of sugar to increase longevity might be very low. Therefore, the reward from a single feeding event can be critical for the forager's fitness. We measured the longevity of the parasitoid Cotesia rubecula after a single honey meal differing in sugar concentration (25, 47, 86% w/w) and timing (day of emergence and 24 h later). Survival was analysed with Cox's Proportional Hazards Model. The risk of starving to death in sugar-fed wasps was reduced by 0–73% in comparison to unfed wasps, depending on sugar concentration and timing. Longevity was significantly increased by sugar concentration and by feeding later in life. Our results suggest that in the field, adult C. rubecula has to locate food at least once per day to avoid starvation.     

Effects of Five Naturally Occurring Sugars on the Longevity,Oogenesis, and Nutrient Accumulation Pattern in Adult Females of the Synovigenic Parasitoid Neochrysocharis formosa (Hymenoptera: Eulophidae)

Neochrysocharis formosa (Westwood) (Hymenoptera: Eulophidae), one of the dominant natural enemies of agromyzid leafminers, is a synovigenic parasitoid. We compared the longevity, oogenesis, and nutrient levels of female wasps provided with 10% solutions of five naturally occurring sugars. All five sugars significantly increased the longevity of female wasps, which was 6.5–9.3-fold higher than that of parasitoids provided with water only. We found no significant difference in longevity of female wasps fed on glucose versus fructose or trehalose versus melezitose, but longevity of wasps fed on glucose or fructose was significantly longer than those fed on trehalose or melezitose. Also, we examined the oosorption capability of wasps fed on the five sugars. Some mature eggs were present in the ovaries of newly emerged females, but these were fully reabsorbed within 72 h when wasps were starved. Once wasps were fed with any of the sugars, the number of mature eggs increased at first and then decreased due to oosorption. The longevity and oogenesis dynamics of female wasps fed on five sugars were related with their function of hydrolysis and digestion. As female wasps have no lipogenesis capability, by acquiring exogenous sugars for oogenesis, they can either maintain or exceed the original level of capital nutrients held on adult emergence because none of the wasps’ glycogen need be metabolized to burn as sugar.     

Adult diet affects the life history and host-killing behavior of a host-feeding parasitoid

Neochrysocharis formosa (Westwood), an important biocontrol agent of agromyzid leafminers worldwide, is a host-feeding, idiobiont parasitoid. Female wasps have three types of host-killing behaviors: reproductive (parasitism), non-reproductive host feeding (host feeding), and host stinging without oviposition or feeding (host stinging). In this study, we compared the life history and host-killing behaviors of female parasitoids under four adult diets: starvation, hosts only, hosts plus honey (10% w/v honey solution), and honey only. Furthermore, we analyzed the host-feeding and oviposition preferences of adult females in the hosts-only and hosts-plus-honey treatments. Female parasitoids feeding on hosts had significantly increased longevity, higher fecundity, more host-stinging events, and caused a higher total host mortality than parasitoids in the starvation treatment. The honey supplement significantly increased longevity, fecundity, host-stinging events, and total host mortality, as well as average daily fecundity, but did not alter host-feeding events, host-stinging events, or daily total host mortality. However, the honey supplement did reduce the number of daily host-feeding events and induced a shift toward oviposition. Finally, we found that the non-reproductive host killing caused by host feeding and host stinging enhanced the control potential of N. formosa. These results should contribute to a better understanding of the biocontrol efficiency of destructive host feeders.     

不同营养源对白蛾周氏啮小蜂主要生物学特性的影响

补充10%果糖水、10%蔗糖水、10%葡萄糖水、10%蜂蜜水后,均显著提高了亲代蜂的寿命,其中10%的果糖水效果最好,比对照长2.13 d;补充10%果糖水和10%葡萄糖水均能显著延长子代蜂的寿命,并显著提高了子代蜂的出蜂量,其中10%的果糖水处理效果最好。发生寄生行为的小蜂,其寿命明显短于未发生寄生行为的小蜂。     

Comparative Development and Performance of Artificially Reared versus Host-RearedDiapetimorpha introita(Cresson) (Hymenoptera: Ichneumonidae) Wasps

Diapetimorpha introita(Cresson) (Hymenoptera: Ichneumonidae), a native ectoparasitoid ofSpodopteraspp. pupae, was reared in the laboratory on an artificial diet devoid of any insect host components. Diet-reared wasps demonstrated a propensity to search for and parasitize natural hosts in a field cage trial. Longevity of the diet-reared wasps was comparable with the longevity of wasps reared on host pupae. Survival rate ofD. introitawas 61.3% when reared on diet and 76.3% when reared on host pupae. Wasps reared on the artificial diet had longer developmental times, reduced fecundity, and reduced adult weights compared to wasps reared on host pupae. These studies suggest that future research efforts should focus on increasing fecundity and weight of diet-reared wasps and decreasing the mortality and developmental time of wasps reared on the artificial diet. The ability to rearD. introitaon an inexpensive, artificial diet significantly enhances the potential of mass rearing this parasitoid for inundative releases againstSpodopteraspp.     

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.     

Divergent life history strategies in congeneric hyperparasitoids

Life histories can reveal important information on the performance of individuals within their environment and how that affects evolutionary change. Major trait changes, such as trait decay or loss, may lead to pronounced differences in life history strategies when tight correlations between traits exist. Here, we show that three congeneric hyperparasitoids (Gelis agilis, Gelis acarorum and Gelis areator) that have diverged in wing development and reproductive mode employ markedly different life history strategies. Potential fecundity of Gelis sp. varied, with the wingless G. acarorum maturing a much higher number of eggs throughout life compared with the other two species. Realized lifetime fecundity, in terms of total offspring number was, however, highest for the winged G. areator. The parthenogenic G. agilis invests its resources solely in females, whilst the sexually reproducing species both invested heavily in males to reduce competitive pressures for their female offspring. Longevity also differed between species, as did the direction of the reproduction-longevity trade-off, where reproduction is heavily traded off against longevity only in the asexual G. agilis. Resting metabolic rates also differed between the winged and wingless species, with the highest metabolic rate observed in the winged G. areator. Overall, these geline hyperparasitoids showed considerable divergence in life history strategies, both in terms of timing and investment patterns. Major trait changes observed between closely related species, such as the loss of wings and sexual reproduction, may contribute to the divergence in key life history traits.     

食物对棉铃虫生长发育及繁殖的影响

用棉花、花生、玉米及人工饲料作为食料,模拟幼虫田间取食习性,同时为雌蛾设立补充和无补充营养两个处理,研究了食物对棉铃虫 Helicoverpa armigera (Hübner) 生长发育及繁殖的影响。4种食料组幼虫历期之间有显著差异;雌、雄蛹重花生组显著小于其余三组。雌蛾腹部干重及其脂肪百分含量与雌蛹体重的排列顺序一样,雌蛾腹部干重人工饲料组显著大于棉花组和花生组。雌蛾寿命和繁殖受幼虫食料和成虫食物的双重影响。喂10%蜂蜜时,雌蛾寿命、交配率和产卵量在四个幼虫食料组之间没有显著差异。但喂以清水时,花生组雌蛾均未交配,寿命和产卵量显著小于其余三组。从同种幼虫食料来看,除人工饲料组外,其余3组雌蛾喂清水时的产卵量和寿命均比喂10%蜂蜜溶液时的显著下降。基于这些结果,作者认为棉花、玉米比花生更适合于棉铃虫的生长发育和繁殖。在田间自然栽培状态下,不同食料植物的糖分含量对棉铃虫生长发育和繁殖影响较大,含氮量的变化影响小。     

Nectar sugars enhance fitness in male Coenonympha pamphilus butterflies by increasing longevity or realized reproduction

The principal components of floral nectar are water and the sugars sucrose, fructose and glucose. Several studies have shown the importance of nectar sugars for female butterfly fecundity, whereas to date little attention has been paid to the effect of nectar sugars on male butterfly reproduction. Clear evidence for an effect of nectar sugars on male realized reproductive success is still missing. In this study, we fed male Coenonympha pamphilus butterflies nectar mimics with low (5%), medium (20%) or high (30%) total sugar concentrations with a sucrose:glucose:fructose ratio of 2.7:1.1:1. Sugar solutions were made mimicking Knautia arvensis, an essential nectar plant for C. pamphilus and many other European butterflies. Realized male reproductive success for each treatment was measured indirectly via nuptial gifts, by recording reproductive parameters and by characterizing time patterns over the oviposition period of their female partner. Male butterflies fed high‐concentrated nectar sugars had a longer lifespan than males fed low‐concentrated nectar sugars. In contrast, offspring of males fed medium‐concentrated nectar sugars had a higher hatching mass than progeny of males fed low‐concentrated nectar sugars, indicating a tradeoff between somatic maintenance and reproduction in the use of nectar sugars. Thus, allocation patterns of nectar sugars differed according to sugar concentrations in adult food. The method used in this experiment took into account the indispensable role of female butterflies in passing male nutrients to offspring. With this comprehensive approach, we can show the general importance of nectar sugars for male butterfly fitness and support previous findings suggesting a coevolutionary process between butterflies and flowers dependent on butterfly pollination.     

Remarkable similarity in body mass of a secondary hyperparasitoid Lysibia nana and its primary parasitoid host Cotesia glomerata emerging from cocoons of comparable size

Lysibia nana is a solitary, secondary idiobiont hyperparasitoid that attacks newly cocooned pre-pupae and pupae of several closely related gregarious endoparasitoids in the genus Cotesia, including C. glomerata. Prior to oviposition, the female wasp injects paralysing venom into the host, thus preventing further development. Here, host fate, emerging hyperparasitoid mass, and egg-to-adult development time was compared in hosts parasitized at different ages over 24-h intervals. Cocoons of C. glomerata were parasitized by L. nana at 12, 36, 60, 84, and 108 h post-egression from the secondary host, Pieris brassicae. Hyperparasitoid survival exceeded 80% in hosts parasitized within the first 60 h after pupation, but dropped thereafter, with no hyperparasitoids emerging in hosts aged 108 h. The mass of hyperparasitoids was positively correlated with the mass of the host cocoon, and this relationship remained consistent in hosts up to 60 h old. Within each host age cohort, the mass of male and female wasps was not significantly different. Development time in L. nana was uniform in hosts up to 60 h old, but increased significantly in 84-h-old hosts, and male wasps completed their development earlier than female wasps. Regulation of host growth varied with the age of the host at parasitism, with the early growth of older hosts reduced much more dramatically than young hosts. Unlike most parasitoids, pupal hyperparasitoids do not make cocoons but instead pupate within the already prepared cocoon of the host parasitoid. Consequently, for a given mass of cocoon, newly emerged L. nana adults were remarkably similar in size with male and female adults of C. glomerata. This reveals that L. nana is extremely efficient at exploiting its primary parasitoid host.     

营养对不同地理种群周氏啮小蜂生物学特性的影响

【目的】研究补充营养对周氏啮小蜂海南本土地理种群和北京地理种群的生物学参数是否有差异。【方法】设置不同的营养(10%蜂蜜、10%蔗糖、10%葡萄糖、水、空白)分别饲喂周氏啮小蜂,统计2个地理种群的寄生率、羽化率、出蜂量、寿命。【结果】2个地理种群的周氏啮小蜂羽化后不久即可进行交配,补充10%蜂蜜、10%蔗糖、10%葡萄糖能显著提高2个地理种群的寄生率、羽化率、出蜂量、雌雄蜂寿命,补充不同的营养对两个地理种群的雌雄比、发育历期的影响差异不显著;饲喂10%蜂蜜的海南地理种群寄生率最高(84.60%),饲喂10%葡萄糖的海南地理种群羽化率最高(97.47%),饲喂10%葡萄糖的海南地理种群出蜂量最高(60.03头),饲喂10%葡萄糖的海南地理种群雌、雄蜂的寿命均为最高,分别为9.13和8.53d。营养和地理种群的交互作用对周氏啮小蜂雄蜂的寄生率、羽化率、出蜂量、雌雄比、雌雄蜂寿命具有显著影响,而对周氏啮小蜂的发育历期无显著影响。【结论】补充营养可不同程度促进周氏啮小蜂生殖力、寿命及寄生率,对寄生蜂繁育和利用其进行生物防治具有一定的意义。     

Effects of a lipid-rich diet on adult parasitoid income resources and survival

Effectiveness of parasitoids as natural enemies in agro-ecosystems depends on key traits such as fecundity and longevity. Energy sources allocated into survival and reproduction can be mobilized from capital stores acquired during larval feeding, or from income resources through adult feeding. Adult parasitoids have a restricted diet consisting solely of carbohydrates and most species do not replenish lipid levels after emergence from their host. Here, we have adopted a novel approach that could improve pest elimination by parasitoids, in which we added different ratios of olive oil to the food of adults to reveal the potential of a lipid-rich diet to increase lipid levels and allocation into survival. Our results show that males of the parasitoid Cotesia glomerata had higher lipid levels when fed a diet containing a ratio of 90:10% honey to olive oil when compared to males at emergence and males fed honey-only. For females, lipid levels at emergence were similar to those of females fed a diet supplemented with a ratio of 75:25% honey to olive oil, yet in both of these treatments lipid levels were significantly higher when compared to females fed honey-only. This suggests that females on a lipid-containing diet economized on their lipid use. In contrast, the survival of males and females was negatively affected by the addition of olive oil and no differences in survival were found when wasps were fed 1 day on various ratios of honey to olive oil compared to honey-only. Our results show that the addition of a lipid source can increase or maintain nutrient availability and further research into lipid supplementation could minimize detrimental effects in order to increase the effectiveness of parasitoids in certain agro-ecosystems.     

Nutritional ecology of a parasitic wasp: food source affects gustatory response, metabolic utilization, and survivorship

The success of biological control is partly mediated by the longevity and reproductive success of beneficial insects. Availability of nectar and honeydew can improve the nutrition of parasitic insects, and thereby increase their longevity and realized fecundity. The egg parasitoid, Anaphes iole, showed strong gustatory perception of trehalulose, a carbohydrate found in homopteran honeydew. Chromatographic analysis demonstrated that enzymatic hydrolysis of sucrose, a common nectar sugar, proceeded at a faster rate than that of melezitose, a sugar common in aphid honeydew. A long-term bioassay showed that longevity was greater at 20 °C than at 27 °C, and at both temperatures survival was generally greatest for wasps provisioned with the three major nectar sugars, sucrose, glucose, and fructose. Patterns of food acceptance and utilization showed that A. iole accepted and utilized a broad range of sugars found in nature, including those found in nectar as well as honeydew. Glucose, fructose, and several oligosaccharides composed of these monosaccharide units appear to be more suitable for A. iole than other sugars tested. Evidence suggests that individual fitness benefits afforded by food sources are important for a time-limited parasitoid, and that continued investigations on the interface between nutrition and biological control are warranted for A. iole.     

The effect of snowdrop lectin (GNA) delivered via artificial diet and transgenic plants on Eulophus pennicornis (Hymenoptera: Eulophidae), a parasitoid of the tomato moth Lacanobia oleracea (Lepidoptera: Noctuidae)

Snowdrop lectin (Galanthus nivalis agglutinin, GNA) has previously been shown to confer significant levels of protection against the lepidopteran pest Lacanobia oleracea when expressed in transgenic potato. The effect of GNA on the parasitism of L. oleracea by the gregarious ectoparasitoid Eulophus pennicornis was investigated. Maize-based, and potato leaf-based diets containing GNA, and excised transgenic potato leaves expressing GNA, were fed to L. oleracea larvae from the beginning of either the third or fourth larval instar. Lacanobia oleracea larvae were individually exposed to single mated adult female E. pennicornis parasitoids from the fifth instar onwards.The success of the wasp was not reduced by the presence of GNA in any of the diets, or by the length of feeding of the host prior to parasitism. However, the mean number of wasps that developed on L. oleracea reared from the third instar on the GNA-containing maize diet was significantly higher than on the controls (20.6 and 9.3 adults/host respectively). In all other cases differences were not significant. Eulophus pennicornis progeny that developed on L. oleracea reared on GNA-containing diets showed little or no alteration in size, longevity, egg load and fecundity when compared with wasps that had developed on hosts fed the respective control diets.The results suggest that expression of GNA in transgenic crops to confer resistance to lepidopteran pests will not adversely affect the ability of the ectoparasitoid E. pennicornis to utilise the pest species as a host.     

Effects of the mixed biocide Bacillus thuringiensis–abamectin on the development of the parasitoid Microplitis mediator and its host Helicoverpa armigera

The effects of the mixed biocide Bacillus thuringiensis Berliner with abamectin (BtA) on the development of the parasitoid Microplitis mediator (Haliday) (Hymenoptera: Braconidae) and its cotton bollworm host, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), were evaluated in the laboratory. Weight gain in larvae of H. armigera was initially delayed, but larval developmental period increased and pupal weight increased when they were fed on a diet containing BtA. Due to increased longevity of the host larvae, the susceptible period to parasitization of H. armigera by M. mediator increased when the host larvae were reared on diets containing BtA at concentrations of 0.5, 1, 2, and 4 μg g^?1. The longevity of female and male parasitoids significantly decreased when newly emerged wasps were fed a honey solution containing 200 μg ml^?1 BtA in comparison with those fed only a honey solution. Mean longevity was significantly prolonged when parasitoids were fed a honey solution and BtA–honey solution in comparison with those fed BtA–distilled water, distilled water, or nothing. There were no significant differences compared with the control in any biological characteristics for the offspring of female parasitoids fed the honey solutions containing BtA at concentrations of 50, 100, and 200 μg ml^?1; characteristics measured include the egg‐larval period, pupal weight, male and female pupal periods, adult fresh weight, and adult longevity. When female parasitoids parasitized host larvae that had been fed the diet containing BtA, their male and female pupal periods were significantly prolonged compared with the control (without BtA).