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.     

Asymmetric effects of adult nutrition on reproductive success of male and female Diaeretiella rapae (Hymenoptera: Aphidiidae)

The role of diet supplements (honey, water or no supplements) on egg maturation, oviposition strategy and longevity of the parasitic wasp Diaeretiella rapae McIntosh (Hymenoptera: Aphidiidae) is investigated. Parasitoids feed as larvae on hosts to acquire nutrition for growth and development, and further gain additional resources during their adult stage by feeding on either host or nonhost resources. The additional resources acquired by adults can help them to increase their reproductive activity or life expectancy, or both. Diaeretiella rapae females emerge with some developed eggs and no additional resources are required for egg maturation or successful oviposition. Females are able to oviposit and produce viable offspring immediately after emergence, and the number of eggs left in the ovaries of females decreases with subsequent oviposition, suggesting that ovigeny index of D. rapae is inclined towards pro‐ovigenic status. When unmated males and females are offered honey solution, females are attracted to it, whereas males display courtship and make mating attempts but then feed on honey after mating. The oviposition efficiency of female D. rapae increases by 30% when they feed on honey compared with when starved. Honey‐fed D. rapae adults live significantly longer (almost twice as long) than starved adults. Honey‐fed females deprived of hosts live longer than those offered hosts regularly. The positive effects of honey‐feeding on longevity are greater in females than in males. Taken together, the results of the present study suggest that the provision of additional resources to adult D. rapae parasitoids could enhance their life expectancy and parasitism efficiency in biological control programmes.     

Importance of host feeding for parasitoids that attack honeydew-producing hosts

Insect parasitoids lay their eggs in arthropods. Some parasitoid species not only use their arthropod host for oviposition but also for feeding. Host feeding provides nutrients to the adult female parasitoid. However, in many species, host feeding destroys an opportunity to oviposit. For parasitoids that attack Homoptera, honeydew is a nutrient‐rich alternative that can be directly imbibed from the host anus without injuring the host. A recent study showed that feeding on host‐derived honeydew can be an advantageous alternative in terms of egg quantity and longevity. Here we explore the conditions under which destructive host feeding can provide an advantage over feeding on honeydew. For 5 days, Encarsia formosa Gahan (Hymenoptera: Aphelinidae) parasitoids were allowed daily up to 3 h to oviposit until host feeding was attempted. Host feedings were either prevented or allowed and parasitoids had ad libitum access to honeydew between foraging bouts. Even in the presence of honeydew, parasitoids allowed to host feed laid more eggs per hour of foraging per host‐feeding attempt than parasitoids that were prevented from host feeding. The higher egg‐laying rate was not compromised by survival or by change in egg volume over time. In conclusion, host feeding can provide an advantage over feeding on honeydew. This applies most likely under conditions of high host density or low extrinsic mortality of adult parasitoids, when alternative food sources cannot supply enough nutrients to prevent egg limitation. We discuss how to integrate ecological and physiological studies on host‐feeding behavior     

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.     

Egg resorption behaviour by the solitary egg parasitoid Anaphes nitens under natural conditions

We investigated under outdoor conditions and inside a climate chamber: (i) whether Anaphes nitens Girault (Hymenoptera: Mymaridae), an egg parasitoid of the Eucalyptus snout beetle, Gonipterus scutellatus Gyllenhal (Coleoptera: Curculionidae), experienced egg resorption, and (ii) how various treatments (location, food, and/or host supply) and body size influenced egg load, egg resorption, fecundity, and longevity. One‐day‐old females were mated and randomly assigned to five groups: (A) honey + hosts, (B) water + hosts, (C) only honey, (D) only water, and (E) control females killed at emergence. We compared the egg load of the newly emerged females, which represent the control group (egg load = ovarian eggs present at emergence), with the lifetime egg load (i.e., ovarian eggs + emerged offspring + not emerged offspring) of the females with various host and diet treatments, by dissection of the ovaries to find evidence of egg resorption. All groups reared outdoors had fewer eggs than the control, while indoors there was no significant difference. Outdoors, starved but host‐provided wasps (B) experienced the highest reduction of the lifetime egg load (51%). Groups without access to food (B + D) resorbed more eggs than groups provided with honey (A + C). Females with honey and hosts (A) had the highest lifetime fecundity, but those with water and hosts (B) showed a higher daily realized fecundity. Host‐deprived females with access to food (C) attained the longest lifespan. Our results suggest that under stress conditions, such as low temperature and food shortage, A. nitens females practice egg resorption, probably to save energy.     

Lifetime gains and patterns of accumulation and mobilization of nutrients in females of the synovigenic parasitoid, Diglyphus isaea Walker (Hymenoptera: Eulophidae), as a function of diet

In nature, adult parasitoids feed to obtain and use nutrients for supplementing and/or replenishing some of their existing array of nutrient reserves. When adults feed on host or non-host food, they can enhance fitness, typically by increasing egg production or longevity. In the present study, ovigeny index (OI) and impact of female fitness, as well as physiological state on the reproductive strategies, were investigated in the synovigenic parasitoid, Diglyphus isaea, fed on host food (2-3rd instars of Liriomyza sativae larvae), non-host foods (10% honey solution) and starved (distilled water, control). The results showed that D. isaea was a strongly synovigenic parasitoid, of which OI value was 0.002. Both types of food enhanced the fecundity and prolonged the longevity of the females. D. isaea females fed on non-host food showed higher levels of gut sugar, body sugar and glycogen than those fed on host food, but the levels of lipid were higher in the host-fed females. D. isaea females seemed to show lipogenesis, with low rates of lipid catabolism sufficient to satisfy the requirement of egg maturation. Females might absorb lipids directly from the haemolymph of paralyzed hosts.     

Host feeding in insect parasitoids: why destructively feed upon a host that excretes an alternative?

Host feeding is the consumption of host tissue by the adult female parasitoid. We studied the function of destructive host feeding and its advantage over non‐destructive feeding on host‐derived honeydew in the whitefly parasitoid Encarsia formosa Gahan (Hymenoptera: Aphelinidae). We allowed parasitoids to oviposit until they attempted to host feed. We either prevented or allowed host feeding. Parasitoids had access to sucrose solution, with or without additional access to honeydew. Parasitoids that were allowed to host feed did not have a higher egg load 20 or 48 h after host feeding than parasitoids prevented from host feeding. Host feeding did not increase the number of eggs matured within these periods, nor did the time spent host feeding positively affect any of these response variables. On the other hand, the presence of honeydew did have a positive effect on egg load 20 and 48 h after host feeding compared with parasitoids deprived of honeydew. Parasitoids with access to honeydew matured more eggs within these periods than honeydew‐deprived parasitoids. Host feeding increased life expectancy, but this effect was nullified when honeydew was supplied after the host‐feeding attempt. In conclusion, feeding on honeydew could be an advantageous alternative to host feeding in terms of egg quantity and longevity. This applies especially to parasitoids exploiting Homoptera, because these parasitoids can obtain honeydew from the host itself. It is possible that destructive host feeding has evolved to enable females to sustain the production of high‐quality anhydropic eggs, which may be important in the parasitoid's natural environment. We argue that future studies should take natural alternative food sources into more consideration.     

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.     

Floral resources impact longevity and oviposition rate of a parasitoid in the field

1. The use of floral resource subsidies to improve herbivore suppression by parasitoids requires certain trophic interactions and physiological changes to occur. While the longevity and fecundity of parasitoids are positively affected by nectar subsidies in laboratory studies, the impacts of floral subsidies on the fecundity and longevity of freely foraging parasitoids have not been studied. 2. We studied the longevity and per capita fecundity of naturally occurring Diadegma insulare foraging in cabbage plots with and without borders of flowering buckwheat, Fagopyrum esculentum, as well as relationships between longevity, fecundity, sugar feeding and parasitism rates on larvae of the diamondback moth, Plutella xylostella. 3. Relative longevity was estimated by counting broken setae on the fringe of the forewing. Floral borders increased the longevity of males and females in adjacent cabbage plots. 4. The egg maturation rate of D. insulare was estimated by comparing egg loads of females collected early in the day with egg loads of females held without hosts in field cages throughout the day. Females in buckwheat cages matured 2.7 eggs per hour while females in control cages resorbed 0.27 eggs over the same time period. 5. The fecundity of females collected in the afternoon was estimated by comparing their actual egg load to the estimated egg load in the absence of oviposition for females in a given plot. Females foraging in buckwheat plots had marginally fewer eggs remaining in their ovaries, and laid marginally more eggs than females in control plots. Females from both treatments carried 30-60 eggs by the afternoon and therefore were time-limited rather than egg-limited. 6. Plots where a greater proportion of females had fed on sugar had longer-lived females. This suggests that feeding enhanced longevity of D. insulare. However, plots with longer-lived and more fecund females did not exhibit higher parasitism rates, although the power of these tests were low.     

The influence of hosts, temperature and food sources on the longevity of Trichogramma platneri

Feeding experiments were conducted with Trichogramma platneri Nagarkatti (Hymenoptera: Trichogrammatidae) reared from the Angoumois grain moth, Sitotroga cerealella (Oliver) (Lepidoptera: Gelechiidae). T. platneri provisioned with host eggs do not live any longer than T. platneri without host eggs. Longevity of T. platneri is inversely related to temperature declining from 53 days at 10 °C to 3 days at 35 °C for honey-fed parasitoids and from 9 days at 10 °C to 1 day at 35 °C for unfed parasitoids. Sugar sources are necessary to prolong longevity of T. platneri, but a source of amino acid did not promote longevity. Honey solutions greater than 10%, and 43% fructose and sucrose solutions increased longevity 10–13 fold to 15–20 days in comparison to water when fed daily to T. platneri. Parasitoids fed only at the onset of the trial had greater longevity than unfed parasitoids but had a shorter longevity than parasitoids fed daily, due to the evaporation of the sugar solutions and consumption of the honey. Aphid honeydew is a suitable field-available sugar source supporting longevity up to 10 days, but is not as good as other sugar sources. Stabilizing additives did not reduce evaporation of a dilute sugar solution nor prolong longevity of T. platneri. Simulating a daily dew fall by misting vials, to redissolve the crystallized food residues left after providing food at the onset of the trial, failed to increase parasitoid longevity.     

Influence of honey and maternal age on egg load of lab-cultured <Emphasis Type="Italic">Cotesia marginiventris</Emphasis>

Laboratory experiments were conducted to determine the impact of feeding status and maternal age on egg load of Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae), a solitary, koinobiont endoparasitoid of noctuid pests. Egg load was defined as the number of mature (i.e., fully-chorionated) eggs found in the ovaries and oviducts. Significantly more mature eggs were stored in honey-fed than starved females. For honey-fed females, egg load increased within several days of isolation from hosts. This study suggests that C. marginiventris is weakly synovigenic because females emerge with a considerable number of mature eggs and are capable of maturing many more eggs. Feeding on a suitable source of carbohydrate should increase the egg load (i.e., potential fecundity) of this insect within 3–4 days in an in vivo rearing system.     

The effect of different dietary sugars and honey on longevity and fecundity in two hyperparasitoid wasps

In nature adult insects, such as parasitic wasps or 'parasitoids' often depend on supplemental nutritional sources, such as sugars and other carbohydrates, to maximize their life-expectancy and reproductive potential. These food resources are commonly obtained from animal secretions or plant exudates, including honeydew, fruit juices and both floral and extra-floral nectar. In addition to exogenous sources of nutrition, adult parasitoids obtain endogenous sources from their hosts through 'host-feeding' behavior, whereby blood is imbibed from the host. Resources obtained from the host contain lipids, proteins and sugars that are assumed to enhance longevity and/or fecundity. Here we conducted an experiment exploring the effects of naturally occurring sugars on longevity and fecundity in the solitary hyperparasitoids, Lysibia nana and Gelis agilis. Although both species are closely related, L. nana does not host-feed whereas G. agilis does. In a separate experiment, we compared reproduction and longevity in G. agilis reared on either honey, a honey-sugar 'mimic', and glucose. Reproductive success and longevity in both hyperparasitoids varied significantly when fed on different sugars. However, only mannose- and water-fed wasps performed significantly more poorly than wasps fed on four other sugar types. G. agilis females fed honey produced twice as many progeny as those reared on the honey-sugar mimic or on glucose, whereas female longevity was only reduced on the mimic mixture. This result shows not only that host feeding influences reproductive success in G. agilis, but also that non-sugar constituents in honey do. The importance of non-sugar nutrients in honey on parasitoid reproduction is discussed.     

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.     

Costs and benefits of host feeding in the parasitoid wasp Trichogramma turkestanica

Females of the parasitoid wasp Trichogramma turkestanica Meyer (Hymenoptera: Trichogrammatidae) generally host feed after ovipositing on the first egg of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) they encounter. We measured the impact of host feeding on the fecundity and longevity of females, in absence of host or food, and on the fitness of their progeny. We also determined if the frequency of host feeding is influenced by the humidity level at which T. turkestanica females developed. Host feeding increased egg production by 70% but decreased female longevity. This impact of host feeding on the longevity of females is probably due to the allocation of carbohydrates to egg production at the expense of somatic maintenance. Humidity did not influence the occurrence or duration of host feeding. The size of individuals developing in eggs on which females host fed was smaller, indicating that their fitness was affected.     

Intraspecific variability in egg maturation patterns and associated life‐history trade‐offs in a polyembryonic parasitoid wasp

1. Life‐history theory predicts a trade‐off between the resources allocated to reproduction and those allocated to survival. Early maturation of eggs (pro‐ovigeny) is correlated with small body size and low adult longevity in interspecific comparisons among parasitoids, demonstrating this trade‐off. The handful of studies that have tested for similar correlations within species produced conflicting results. 2. Egg maturation patterns and related life‐history traits were studied in the polyembryonic parasitoid wasp, Copidosoma koehleri (Hymenoptera: Encyrtidae). Although the genus Copidosoma was previously reported to be fully pro‐ovigenic, mean egg loads of host‐deprived females almost doubled within their first 6 days of adulthood. 3. The initial egg‐loads of newly emerged females were determined and age‐specific realised fecundity curves were constructed for their clone‐mate twins. The females' initial egg loads increased with body size, but neither body size nor initial egg load was correlated with longevity and fecundity. 4. The variation in initial egg loads was lowest among clone‐mates, intermediate among non‐clone sisters and highest among non‐sister females. The within‐clone variability indicates environmental influences on egg maturation, while the between‐clone variation may be genetically based. 5. Ovaries of host‐deprived females contained fewer eggs at death (at ～29 days) than on day 6. Their egg loads at death were negatively correlated with life span, consistent with reduced egg production and/or egg resorption. Host deprivation prolonged the wasps' life span, suggesting a survival cost to egg maturation and oviposition. 6. It is concluded that adult fecundity and longevity were not traded off with pre‐adult egg maturation.     

Pollen as a source of food for egg parasitoids of the genus Trichogramma (Hymenoptera: Trichogrammatidae)

The value of corn pollen as a food source for Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) was assessed in the laboratory by testing the effect of different pollen diets on the longevity, capacity of parasitism and other life-table parameters. T. brassicae females that fed on corn pollen and water (wet filter paper dusted with pollen) lived significantly longer (4.97 days) than females that fed on water alone (2.67 days), but significantly shorter than those feeding on honey alone (8.37 days) or corn pollen and honey (8.23 days), respectively, in the absence of host eggs. The presence of European corn borer eggs (Ostrinia nubilalis Huebner, Lepidoptera: Pyralidae) significantly increased longevity. With host eggs available, female T. brassicae that fed on corn pollen and water lived significantly longer (4.9 days) than on water alone (2.60 days), but significantly shorter than on honey alone (12.33 days) or corn pollen and honey (12.17 days), respectively. The cumulative lifetime fecundity was 82.53 offspring pupae when fed on pollen and water, which was significantly higher than 61.70 for water alone but lower than feeding on honey alone (95.70) or corn pollen and honey (99.97), respectively. Compared to water alone, corn pollen and water increased the net reproduction rate (R₀), intrinsic rate of increase (r_m), and finite rate of increase (λ), and reduced the doubling time (T₂), but had no effects on the emergence rate, sex ratio, and mean generation time (T_c). In another set of experiments, 13 out of 30 females reduced the number of pollen grains offered to them. The average number of pollen grains utilized per female in this 48-h test 2.46±0.40 (mean±SE). Hence, T. brassicae used corn pollen as food that significantly increased longevity and fecundity of the tested females. Pollen and honey supplied a complete diet for T. brassicae, compared to pollen and water or water alone.     

Lifetime gains of host-feeding in a synovigenic parasitic wasp

Abstract. Understanding behavioural decisions relative to host use for feeding or reproduction by foraging parasitoids requires not only the study of metabolic pathways followed by nutrients, but also the quantification of lifetime fitness gains of each alternative behaviour. By using a combination of observational and manipulative approaches, the lifetime host‐feeding gains are measured both in terms of fecundity and longevity in the parasitoid Eupelmus vuilletti. Host‐feeding increases both egg production and longevity. The increase in fecundity is mainly determined by the amount of lipids obtained whereas the lifespan extension is mainly determined by carbohydrates. Proteins obtained through host‐feeding have been implicated previously in egg production by parasitoids but protein intake has no effect on fecundity and longevity in E. vuilletti. The amount of nutrients gained through host‐feeding and invested in eggs is variable and changes over the lifetime of the animal. Therefore, lifetime feeding gains are best understood through the construction of dynamical budgets running over the entire lifespan of an insect.     

Dynamic host-feeding and oviposition behavior of an aphid parasitoid <Emphasis Type="Italic">Aphelinus asychis</Emphasis>

In order to maximize the lifetime reproductive success of parasitoids, they should be induced to dynamically accept individual hosts that have different suitability for oviposition. Parasitoids tend to exhibit higher host-selective behavior when their egg load is limited, and are less selective if they are facing time constraints. Here, we evaluated the effects of parasitoid age on egg load, fecundity and host instar preference of a honey-fed aphid parasitoid, Aphelinus asychis Walker (Hymenoptera: Aphelinidae). Host selective experiment was conducted to measure host-preference of honey-fed A. asychis females at different ages, using the second and fourth instars of the green peach aphid Myzus persicae as their hosts. The results showed that the choice of host-instar for oviposition was significantly influenced by the parasitoid age. Honey-fed parasitoids in the age groups of 1, 5, 10 and 20 days tended to parasitize predominantly second-instar aphids, whereas 15-days old parasitoids showed no significant preference of host instars. On the other hand, host-feeding preference was not affected by parasitoid age. Parasitoid females of all ages preferred younger aphids to older aphids. This result could help evaluate the effectiveness of A. asychis for biological control of M. persicae when they encountered mixed-instar aphids in the field. In addition, the results might be helpful in assessing the host killing effects of other host-feeding parasitoids.     

Longevity and fecundity of Eulophus pennicornis, an ectoparasitoid of the tomato moth Lacanobia oleracea, is affected by nutritional state and diet quality

• 1 Adult female Eulophus pennicornis require a source of nutrition, provided by sources such as pollen, nectar and honeydew or by host feeding, to promote longevity and facilitate egg production. There is potential for parasitoids to be exposed directly to contaminants, including gene products in transgenic crops, through feeding on plant materials, honeydew or hosts. Among such potential contaminants are lectins such as Galanthus nivalis agglutinin (GNA) and concanavalin agglutinin (Con A).
• 2 The effect of direct exposure to honey diets containing GNA and Con A on the longevity and fecundity of E. pennicornis was examined. These lectins have been expressed in a number of plant species for the control for various insect pests. Both GNA and Con A significantly reduced longevity and fecundity at the highest concentration used (0.5% w/v). The effect on fecundity was shown to be related to a reduction in longevity.
• 3 Examination of the gustatory response of adult female E. pennicornis to honey diet containing 1% w/v GNA or Con A revealed no significant differences in consumption rate on first exposure. A significant reduction in the time spent feeding on diet containing 1% Con A was found on the second exposure to the diet. This could have been the result of either a conditioned aversion response or the intoxication of the insect. The effect of Con A on longevity and fecundity could have been, in part, a result of reduced food intake.
• 4 Studies on nutrition and egg resorption demonstrated that the availability of honey solution prolongs the longevity of E. pennicornis and the lack of a source of nutrition promotes oosorption.
• 5 A greater understanding of feeding behaviour and ovigeny is required to understand fully the potential ecological consequence of transgenic crops on parasitoid species through routes of direct exposure to transgene products.

     

Life history of Aptesis nigrocincta (Hymenoptera: Ichneumonidae) a cocoon parasitoid of the apple sawfly, Hoplocampa testudinea (Hymenoptera: Tenthredinidae)

Aptesis nigrocincta: Gravenhorst is a bivoltine ectoparasitoid of apple sawfly cocoons, hosts that must be found and parasitized by females at a depth of 10-25 cm in the soil. Females are significantly smaller than males and nearly wingless. After encountering a host, females needed 29.3 min at 20 degrees C and 19. 9 min at 25 degrees C to deposit an egg on the host. Development from egg to adult took 39.6 days for females and 38.0 days for males at 20 degrees C. This small difference was significant. At 20 degrees C, the longevity of females that had no opportunity to oviposit was on average 72.5 days, significantly higher than male longevity (50.6 days). The longevity of females given access to hosts throughout their lifetime averaged 58.6 days. Females were able to mate immediately after emergence and copulation lasted on average 21.7 s. After a pre-oviposition period averaging 5.8 days, females laid 20.2 eggs during their lifetime, thus less than one egg per day. Neither the fecundity nor longevity of individual females was correlated with body size. If females were deprived of food, longevity as well as lifetime fecundity were drastically reduced. Field studies were carried out in one organically managed apple orchard in Switzerland. Aptesis nigrocincta showed parasitism rates ranging from 12.1 to 39.7 % within single parasitoid generations, thereby constituting the most important mortality factor of apple sawfly cocoons.