Viruses and parasitism in insects

This chapter focuses on viruses and parasitism in insects. In recent years, virus-like particles have been observed in the reproductive tracts of a large number of endoparasitic hymenoptera (i.e., wasps whose larvae develop inside host larvae), belonging to the families of braconidae and ichneumonidae. Some of these agents have now been characterized to the extent that one does not hesitate in referring to them as viruses, in which context they are discussed in the chapter; indeed, the most prevalent type of particle observed in braconid wasps appears to represent a highly unusual form of baculovirus. A unique feature of all parasitoid viruses, thus far discovered, is that they replicate only in the ovary (of wasps), from which they are transmitted to host larvae or eggs during oviposition. In affected species, large concentrations of virions can always be observed in either cell nuclei of the calyx, an epithelium situated between the ovarioles and oviduct, or within the lumen of calyces and oviducts. It is now apparent that the presence of virus particles in the ovaries of parasitoid wasps is not an isolatcd phenomenon. Indeed, it may represent the rule rather than the exception among certain groups of endoparasitic hymenoptera. The invariable presence of particulate calyx fluids in some parasitoid species suggests that these particles represent an integral component of the parasitoid life cycle.