Evolution and behavioral ecology of heteronomous aphelinid parasitoids

In almost all species of parasitic wasps in the Coccophaginae, a sub-family of Aphelinidae, males have host relationships different from females. In these "heteronomous" species, females are generally endoparasitoids of sternorrhynchous Hemiptera, such as scale insects, mealybugs, and whiteflies. In contrast, males may be hyperparasitoids, developing in or on conspecific females or other primary parasitoids. In other species, females are endoparasitoids of whiteflies, and males are primary endoparasitoids of eggs of Lepidoptera. Males and females may both be primary parasitoids on the same species of scale insect hosts, but females develop as endoparasitoids, whereas males are ectoparasitoids. Here we review these life histories, focusing on examples of sexually dimorphic host relationships, development, and morphology. Coccophagine species may be sexual or parthenogenetic; we discuss reproductive modes and the interaction of sex ratio distorters with sex-specific host relationships. Sex allocation in the species in which males are hyperparasitoids involves choices of not what sex egg to lay, but whether to accept or reject a host of a given type; study in this area is reviewed as well as research in kin discrimination and ovicide. Last, we present the current understanding of phylogenetic relationships within this lineage and discuss hypotheses for the evolutionary origin of heteronomy in the Aphelinidae.