BROOD SEX-RATIO VARIANCE, DEVELOPMENTAL MORTALITY AND VIRGINITY IN A GREGARIOUS PARASITOID WASP

Females of the parasitoid wasp Goniozus nephantidis paralyse host cate rpillars and lay a clutch of up to 18 eggs onto the host integument. T he known biology of G. nephantidis suggests that matings occur exclusi vely between siblings from the same brood. This leads to the predictio n that brood sex ratios should be highly female-biased and have low va riance. Sex ratios are indeed female-biased, with the mean proportion of males equal to 0.093. However, while sex ratio variance is signific antly less than binomial, many broods contain no males at emergence. D uring development 28% of C. nephantidis offspring die. Male mortality offers a potential explanation for all-female (= virgin) broods. For t he clutch sizes and mortality observed, theory predicts that <10% of f emales will emerge from all-female broods but the empirical value is m uch higher. The prediction that the prevalence of virginity decreases with increasing clutch size is, however, supported. We consider altern ative explanations for the observed proportion of all-female broods, b ut this appears to be neither an artefact of the laboratory environmen t nor due to incorrect assumptions about G. nephantidis life history. Although its reproductive biology has been much investigated and its s ex ratio matches some theoretical predictions, we conclude that a full er understanding of C. nephantidis sex ratio requires a deeper knowled ge of its field biology.