Lifetime reproductive success in the solitary endoparasitoid, Venturia canescens

Parasitoid wasps have long been considered excellent organisms in studies e xamining the evolution of reproductive and life-history strategies. In exam ining the lifetime reproductive success of parasitoids in the laboratory, m ost investigations have provided the insects with excess hosts and food, wh ere they exist in a relatively constraint-free environment. Importantly, th ese 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 availabil ity 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 t emporal variations in host and food (honey solution) access. Cohorts of par asitoids were provided with 200 fifth-instar larvae of the Indian meal moth , Plodia interpunctella (Lepidoptera: Pyralidae), and food for variable per iods daily after eclosion. V. canescens is synovigenic, and host-deprived w asps 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 la ter in adult life. Constantly fed wasps lived longer and produced more prog eny than wasps from cohorts which were alternately fed and starved or were starved from eclosion. Moreover, wasps with constant host and food access p roduced most progeny early in life and usually experienced prolonged period s of postreproductive survival. In contrast, the reproductive period of was ps with limited host access was more evenly distributed throughout the adul t life. Consequently, the cumulative progeny production by V. canescens wit h constant food access was fairly uniform irrespective of host availability . Longevity and fecundity in V canescens were positively correlated with ad ult size. However, variable host access had little effect on the longevity of wasps which were constantly supplied with honey. Over the first 2 days o f adult life, variation in food access also had no effect on progeny produc tion by V canescens. We argue that manipulating temporal host and food acce ss to parasitoids in the laboratory more closely approximates natural condi tions, where these resources are likely to be spatially separated. Moreover , our findings suggest that many highly synovigenic parasitoids like V. can escens, which produce microtype (=hydropic) eggs, have a considerably highe r reproductive potential than ovary dissections have revealed. Our findings are discussed in relation to life-history evolution in the parasitic Hymen optera.