The parasitic wasp, Chelonus inanitus, relies on viruses to successfully colonize its hosts. When the wasp injects eggs into its host, the eggs are accompanied by viruses. The viruses selectively colonize the cells of the host immune system and destroy them. This allows the developing wasp to avoid attack by immune cells. The viruses also arrest the development of the caterpillar host.
The Chelonus inanitus ichnovirus is fully integrated into the wasp life cycle. The virus only replicates in the nucleus of the calyx cells in the female reproductive system. Both double stranded virus DNA and protein capsule are produced and assembled in the nucleus of the calyx cells. The virus particles are released from the cells by budding, in which the viruses are surrounded by the outer cell membrane which is pinched off, releasing the virus in to the oviduct of the wasp.
The viruses evolved from ancestors that lived independently, but are now integrated into the wasp such that neither the wasp nor the virus would survive without the other.
U. Albrecht, T. Wyler, R. Pfister-Wilhelm, A. Gruber, P. Stettler, P. Heiniger, E. Kurt, D. Schiimperli and B. Lanzrein. Polydnavirus of the parasitic wasp Chelonus inanitus (Braconidae): characterization, genome organization and time point of replication. Journal of General Virology (1994) 75: 3353-3363.