Local mate competition,sex ratio and clutch size in bethylid wasps

Summary Parasitoid wasps of the family Bethylidae lay groups of eggs on the larvae of beetles and moths. The larvae develop together and pupate in the vicinity of the host. On hatching, the majority of copulations are between siblings leading to a high degree of local mate competition. Sex ratio theory predicts that as the number of individuals developing on a host increases, the population sex ratio will become progressively more female biassed. A comparative study of sex ratios across the family supports this prediction.