Characterization of a polydnavirus (PDV) and virus-like filamentous particle (VLFP) in the braconid wasp Cotesia congregata (Hymenoptera: Braconidae)

Two morphologically distinct virions were found to replicate in the female reproductive tract of wasps belonging to the species Cotesia congregata. Polydnaviruses (PDV) replicate in the ovaries of braconid and ichneumonid endoparasitic wasps and are injected into host insects during oviposition. Ultrastructural studies showed that in females of C. congregata, the polydnavirus initiated replication in specialized cells of the lower calyx following pupation, during the final phases of adult development, and replication and virus assembly continued throughout adult life. Viral envelopes initially were synthesized de novo at the periphery of the virogenic stroma, then multiple nucleocapsids were encapsidated; the maximum number seen per sectioned virion was 14. The extracellular virions in the calyx lumen measured >150 nm in diameter and had a tail. The PDVs did not replicate in cells composing the calyx wall. Replication also did not occur in a small subset of cells containing cytoplasmic PDVs, which appeared to be encased in whorls of endoplasmic reticulum. A virus-like filamentous particle (VLFP) was seen in the nucleus and cytoplasm of a few upper calyx cells that did not support PDV replication. This virus replicated significantly later than the PDV and contained only a single nucleocapsid per envelope. Only a few extracellular filamentous virions were seen in the calyx fluid. Those present had a double envelope and measured ca. 60 nm in diameter; their length was variable and sometimes exceeded 1 μm. Two viruses replicate in the reproductive system of C. congregata, as reported for other Cotesia species.