The Viruses 1998, pp 105-139

Polydnavirus Biology, Genome Structure, and Evolution

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Polydnaviruses are an unusual group of insect viruses that have an obligate mutualistic association with certain parasitic wasps. Polydnaviruses are unique both in terms of their association with parasitic Hymenoptera and because of their profusely segmented DNA genomes. These viruses are named on the basis of their unique polydisperse DNA genomes (i.e., poly -DNA-viruses), but their life cycles are equally distinctive (Stoltz et al., 1995). In this chapter, a general overview of polydnaviruses is provided but is biased by the preponderance of molecular studies performed in a single species, the Campoletis sonorensis polydnavirus (CsPDV). CsPDV is the type species member of the ichnoviruses, one of the two major polydnavirus groups. Bracoviruses, which comprise the other major group, have distinctive morphologies and appear to be evolutionarily unrelated to the ichnoviruses (Whitfield, 1997), making it likely that significant differences will continue to be found in the organization and function of the two polydnavirus genera. While attempting to provide comprehensive coverage of the field, I have deliberately focused on more recent work. For more comprehensive consideration of earlier developments, the reader should consult reviews by Stoltz and Vinson (1979a), Fleming (1992), Stoltz and Whitfield (1992), Beckage (1993), Fleming and Krell (1993), Strand and Pech (1995a), and Lavine and Beckage (1996).