Life‐history strategies in parasitoid wasps: a comparative analysis of ‘ovigeny’

Abstract

Summary: Ecologists concerned with life‐history strategies of parasitoid wasps have recently focused on interspecific variation in the fraction of the maximum potential lifetime egg complement that is mature when the female emerges into the environment. Species that have all of this complement mature upon emergence are termed ‘pro‐ovigenic’, while those that do not are termed ‘synovigenic’. We document and quantify the diversity of egg maturation patterns among 638 species of parasitoid wasps from 28 families. We test a series of hypotheses concerning variation in ‘ovigeny’ and likely life‐history correlates by devising a quantitative index – the proportion of the maximum potential lifetime complement that is mature upon female emergence. Synovigeny, which we define as emerging with at least some immature eggs, was found to be by far the predominant egg maturation pattern (98·12% of species). Even allowing for some taxonomic bias in our sample of species, pro‐ovigeny is rare among parasitoid wasps. There is strong evidence for a predicted continuum in ovigeny index among parasitoid wasps, from pro‐ovigenic (ovigeny index = 1) to extremely synovigenic species (ovigeny index = 0). As predicted, synovigenic species are longer‐lived than pro‐ovigenic ones, and ovigeny index and life span are negatively correlated across parasitoid taxa, suggesting a life span cost of concentrating reproductive effort early in adult life. There is equivocal evidence that host feeding (i.e. consumption of host haemolymph and/or tissues by adult wasps) is confined to synovigenic parasitoid wasps. It is also not certain from our analyses whether host feeding is associated with a relatively low ovigeny index. As predicted, egg resorption capability is concentrated among producers of yolk‐rich eggs. Also, the hypothesis that it is associated with a tendency towards a low ovigeny index is supported. Parasitoid species that produce yolk‐rich eggs also exhibit a lower ovigeny index than species that produce yolk‐deficient eggs. Ovigeny index appears to be linked to parasitoid development mode (koinobiosis–idiobiosis). We conclude that ‘ovigeny’ is a concept applicable to insects generally.