Textbooks define viruses as infectious agents with nucleic acid genomes (RNA or DNA), which replicate inside living host cells to produce particles (virions) that can transfer the genome to other cells. The Polydnaviridae was recognized as a family of viruses in 1995, and is currently divided into two genera named the Bracovirus and Ichnovirus.
Polydnavirus (PDV) virions consist of enveloped nucleocapsids and package multiple circular, double-stranded (ds) DNAs with aggregate sizes that range from 190 to more than 500 kbp. PDVs are also strictly associated with insects called parasitoid wasps (Hymenoptera), which are free living nectar feeders as adults but which develop during their immature stages by feeding inside the body of another insect (the host). Recent studies indicate that PDVs differ from all other known viruses in ways that challenge traditional views of what viruses are and how they function.