Sex Ratios Within the Quasi‐Social Parasitoid Genus Sclerodermus

Sex ratios are an important component of parasitoid wasps' reproductive strategies and seem to be generally well described by evolutionary ecological theory, such as local mate competition (LMC). The sex ratios of several Sclerodermus species do not fit the predictions of standard LMC models, as their sex ratios remain strongly female biased irrespective of the number of foundress females contributing offspring to locally mating groups. Unusually among parasitoids, Sclerodermus are quasi-social: co-foundresses remaining in association with each other for long periods while communally producing and tending large broods of offspring on a single host. Modified LMC theory, considering that some co-foundresses may actively alter the sex ratios produced by other co-foundresses via physiological suppression or post-ovipositional infanticide, predicts that brood sex ratios at maturity will be relatively insensitive to foundress number, as observed within species. Here, we explore whether the within-species and with-study sex ratio patterns are also observed across studies and species, using data from 38 prior studies in a comparative analysis of the relationship between sex ratio and foundress number. We find that, like within-species observations, sex ratios increase very only mildly, or not at all, as foundress numbers increase, and are only slightly affected by host species and by wasp species identity: Sclerodermus brood sex ratios essentially remain at around 9% males. Current theory and current evidence are broadly akin but do not match exactly: This may be due to methodological constraints in our comparative analyses or to unexplored or unmodelled aspects of the biology of Sclerodermus.