10 - Parasitoid Polydnaviruses and Insect Immunity

Abstract

This chapter reviews the mechanisms whereby polydnavirus (PDV) gene products interface with the host insect immune system and exert potent effects on its cellular and humoral functions. The PDVs are associated with braconid, and ichneumonid parasitoid wasps are unique viruses with very large segmented genomes (200 kb), which are integrated within the wasp's chromosomal DNA, representing genetic symbionts of the parasitoid. Parasitoids are insect parasites of other insect species that ultimately kill their host, either by physiological manipulation and induction of host developmental arrest or by physical consumption of host tissues. PDVs affect both the cellular and humoral arms of the insect host's immune system, and the induced changes in host immune function may be either transient, thus suppressing host immunity temporarily until the parasitoid egg hatches, or permanent and lasting for the duration of parasitism, once parasitization occurs. PDV genome sequencing projects have revealed a wealth of information about potentially significant viral genes that are critical to regulating the host's immunocompetence, endocrine physiology, and development. PDVs have also been linked to reprogramming of host development and induction of developmental arrest before the wasps emerge from the host. They also act as endocrine regulators of developmental reprogramming in addition to serving as potent host immunosuppressors during parasitism. Aside from their immunological role, PDV genes and their expression products have many regulatory roles. PDV genomic analysis for braco- and ichnoviruses has demonstrated major differences in these two taxonomic groups and offers exciting potential for development of new insect pest control technologies based upon PDV gene action on host immunity as well as on host endocrine function and development.