Keynote Presentation #1 POLYDNAVIRUSES AS MUTUALISTS AND IMMUNOSUPPRESSIVE AGENTS OF INSECT
Michael Strand, University of Georgia
Insects rely upon a well-coordinated innate immune system for protection against foreign invaders. Pathogens and parasites have reciprocally evolved a diversity of counterstrategies for suppressing host insect defenses. Among the most important
mortality agents of insects are thousands of parasitoid wasp species that carry polydnaviruses (PDVs). PDVs persist asproviruses in wasps and replicate asymptomatically in the reproductive tract of females. Wasps reproduce by laying eggs into hosts that progeny consume. During egg laying females also inject PDV particles into hosts. PDVs do not replicate in the hosts of wasps but expression of PDV-encoded genes causes physiological alterations that are essential for survival of wasp offspring. Thus, a mutualism exists between PDVs and wasps as viral transmission depends on parasitoid survival and parasitoid survival depends on infection of hosts by the virus. Genome analysis indicates that PDVs in the genus Bracovirus evolved from a group of viruses that are virulent insect pathogens. Novel alterations in genome organization and function underlie why bracoviruses persist and cause no disease in wasps, yet produce virulence gene products in the hosts of wasps. Functional studies indicate that several of these virulence genes target immune pathways, which disables defenses that otherwise would kill wasp offspring.