Sib‐mating and sex ratio strategies in scelionid wasps

Abstract

Abstract. 1. Theoretical models by Hamilton and others predict that the optimal sex ratio (proportion males) for a species should decrease with increasing levels of sib‐mating. A test of this hypothesis is made for members of the parasitoid family Scelionidae. 2. Scelionid wasps differ in levels of sib‐mating as a consequence of differences in host egg mass size, male—male aggression and female—female aggression. 3. Sex ratios for thirty‐one species vary with inferred changes in sib‐mating as predicted by the models. 4. Interspecific differences in sex ratio may represent different fvted strategies or different manifestations of a single variable strategy (sex ratio game) in response to parasitoid‐produced stimuli. 5. Males and females are assigned non‐randomly to egg masses in a manner which ensures mixed broods in the proper proportions for a particular species.