Sociality in Polyembryonic Parasitoids

Abstract

Some polyembryonic parasitoid species produce two morphologically different types of larvae from a single egg. The specialized larval morph that forms in addition to the reproductive larvae has been variously described as asexual (Silvestri 1906), teratoid (Parker and Thompson 1928), and precocious (Doutt 1947, 1952) larvae and is characterized by its slender body and developed mandibles. In Copidosoma floridanum, many reproductive larvae appear at the final-instar stage of the host and eventually develop into adults, whereas a small number of precocious larvae first appear at the early-instar stage of the host and then die without undergoing metamorphosis (Fig. 4.1). Thus, the precocious larvae represent a sterile caste. There are two hypotheses for why precocious larvae are produced: (1) to act as soldier larvae that defend sibling embryos against competitors invading the same host and (2) to adjust the sex ratio in mixed-sex broods. Therefore, the function and evolution of precocious larvae have mostly been examined from the viewpoint of sociobiology.