Correlating the initiation of virus replication with a specific pupal developmental phase of an ichneumonid parasitoid.

The morphogenesis of virus particles associated with the calyx region of the lateral oviduct of the ichneumonid parasitoid Campoletis sonorensis is initiated during a specific phase of pupal development. The extent of body pigmentation proved to be the most reliable visual marker for correlation of induction of virus replication with particular phases of pupal development. Parasitoids removed from their pupal cases at 15 and 16 days after egg deposition were categorized into one of four developmental groups based on the degree of pigmentation. Viruses were not evident in the calyx cells of pupae representing the initial developmental stage, however, in all subsequent stages the concentration of particles gradually increased as development progressed. Observations of freeze-fractured tissue support previous suppositions that the viruses bud through the nuclear envelope following synthesis de novo within the nucleus.