38th Annual Meeting of the Society for Invertebrate Pathology

Cotesia congregata is an endoparasitic wasp that develops in the tobacco hornworm, Manduca sexta. Parasitization occurs when the female Cotesia wasp injects her eggs mixed with venom and polydnavirus (PDV) into the host caterpillar. PDV-encoded proteins are expressed beginning immediately after parasitization, which triggers apoptosis (programmed cell death) of host hemocytes and host immunosuppression. Expression of the PDV protein, CrV1, which was first isolated in Cotesia rubecula, appears to accompany host immune suppression necessary for parasitoid survival. Morphological changes such as rounding up and nuclear compaction in hemocytes from a parasitized M. sexta larva were observed using fluorescence microscopy, to follow the temporal progression of events leading to apoptosis. Antibody staining correlated the presence of the CrV1 homolog protein (CcV1) in these apoptotic hemocytes. We further compared the number of apoptotic hemocytes from a parasitized M. sexta using a TUNEL assay with healthy M. sexta hemocytes. Hemocyte viability was determined through BrdU-labeling to investigate differences between parasitized and non-parasitized hemocytes. We have identified a viral-encoded protein from the C. congregata polydnavirus (CcV1) that participates in immunosuppression of M. sexta. Our research will clarify the importance of CcV1 protein expression in mediating cell death of insect immune cells, which weakens the immune system of M. sexta.