Parasitoids and Polydnaviruses

Abstract

E ndoparasitic wasps develop within other insects and, invariably, kill their hosts. Because they cause host death, they are unlike other parasites that debilitate but do not kill their hosts; endoparasitic wasps are therefore designated as parasitoids (Godfray 1994). Parasitoid wasps in the hymenopteran families Braconidae and Ichneumonidae carry virus particles that are injected into the host insect in large numbers at the same time that eggs are deposited into the host. In 1965 George Salt, an entomologist at Cambridge University, noted that wasp eggs that were washed free of material from the ovary of the adult female wasp were rapidly encapsulated and killed by blood cells of the caterpillar host; by contrast, eggs that retained the material escaped this fate (Salt 1965). Later, that material was shown to consist of viruslike particles on the surface of the parasitoid egg (Rotheram 1973). Subsequent research efforts have focused on illuminating the role of these particles in regulating the host's physiology during parasitism-particularly their effects on the host's immune system. Only wasp species that develop as internal parasites of other insects, typically flies and moths, harbor these viruslike particles, and flies and moths usually serve as hosts of these virus-carrying parasitoids. The