A simple technique for the preliminary screening of parasitic wasps for polydnavirus-like particles

Abstract

Certain hymenopteran parasitoid species in the families Ichneumonidae and Braconidae contain symbiotic viruses known as polydnaviruses (PDVs; Polydnaviridae) (Stoltz et al. 1984; Beckage 1998; Pennacchio & Strand 2006). PDVs have double-stranded DNA (dsDNA) genomes that are segmented, with up to 30 circular dsDNAs reported (Espagne et al. 2004; Kroemer & Webb 2004; Pennacchio & Strand 2006). The PDVs of both ichneumonids (ichnoviruses) and braconids (bracoviruses) occur as proviruses integrated in the wasp genome, with replication and virus particle production occurring only in the wasp ovaries in a region called the calyx (Fleming 1992; Albrecht et al. 1994; Strand & Pech 1995). A very high number of virus particles (containing circular episomal forms of the integrated DNA genome) are released (by cell rupture in braconids) or secreted (by ichneumonids) from the calyx cells into the oviducts and during oviposition the PDVs are injected with the eggs and ovarian fluid into the host larvae (Stoltz & Vinson 1979; Fleming 1992; Dupuy et al. 2006). Although there is no PDV replication in the wasp's host, PDV gene expression in the host disrupts the host's development and cellular defence systems thus allowing the wasp's progeny to survive and complete their development (Strand & Pech 1995; Webb 1998; Pennacchio & Strand 2006; Webb et al. 2006).