Anti-aggregation and cytolytic behaviour of venomous saliva of Rhynocoris fuscipes (Fab.) (Hemiptera: Reduviidae) in response to its prey hemocytes.

Venomous saliva (VS) from Rhynocoris fuscipes (Fab.) was analyzed for immunosuppressive activity toward two prey species, Spodoptera litura (Fab.) and Helicoverpa armigera (Hubner). Immunosuppression was assessed by examining changes in total hemocyte counts and hemocyte behaviors (aggregation and spreading). Newly ecdysed fifth stadium larvae displayed total hemocyte counts of 1.285x10 7 cells/ml and 1.397x10 7 cells/ml for S. litura and H. armigera , respectively. When isolated hemocytes were exposed to saliva from R. fuscipes , a concentration and time dependent decline in hemocyte numbers was observed for both prey species. The decrease was attributed to cell death presumed to involve both cytolytic and apoptotic pathways. Saliva also altered the behavior of hemocytes from both lepidopteron species. Plasmatocytes and granular cells incubated with saline (PBS) or untreated formed aggregations within a few minutes after introduction into 96-well plates, and also attached and then spread over the plastic surfaces. By contrast, aggregation by both cell types, as well as the ability to spread were reduced following exposure to reduviid saliva, and these events were both concentration and time dependent. The possible significance of inducing prey immunosuppression during feeding by R. fuscipes is discussed.