Chapter 5 - Evolution and Origin of Polydnavirus Virulence Genes

Abstract

This chapter discusses the evolution and origins of polydnavirus (PDV) virulence genes. Parasitoid wasps and their associated PDVs are likely to be under strong selection pressure to maintain efficient virulence genes in order to develop in caterpillar hosts. PDV genomes packaged in the particles harbor collectively hundreds of genes, many of which appear to be involved in lepidopteran host regulation. PDVs have a unique life-cycle, comprised of a mutualistic lifestyle with their associated parasitoid wasps and a parasitic interaction with the lepidopteran wasp hosts. They are present as proviruses in the parasitoid wasps that harbor them. The female wasps produce particles that contain circular double-stranded DNA versions of the viruses that are injected into the wasps' lepidopteran hosts. This “injected circular form” is replication deficient but is absolutely essential for the physiological regulation of caterpillars that leads to parasitoid survival. PDVs are divided into two genera, bracoviruses (BVs) and ichnoviruses (IVs) associated with tens of thousands of endoparasitoid braconid and ichneumonid wasps, respectively, belonging to the Ichneumonoidea superfamily.