Combined effects of host quality and local mate competition on sex allocation inLariophagus distinguendus

Summary Many parasitoid wasps are known to adjust sex ratio in response to either local mate competition (LMC) or host quality. Nevertheless, few studies have investigated the combined effects of these two factors on sex allocation. The sex allocation pattern inLariophagus distinguendus, a parasitoid of granary weevil larvae, is contrasted to the expectations of Werren's (1984) model combining LMC and host quality. Several predictions of the model are confirmed, but others are not. Sex ratio on both large and small hosts declines with proportion of small hosts attacked in a manner consistent with the model. However, when only one host size is parasitized, sex ratio is not independent of that host size, as predicted by the model. Various possibilities for the deviation between expected and observed are discussed. A partial LMC/host quality model is developed which allows for some matings outside the natal patch, and predictions of this model conform more closely to the pattern observed inL. distinguendus. Finally, the application of parasitoid studies to basic questions in evolutionary ecology is briefly discussed.