High temperature-induced Cscaspase-8 disrupts the developmental relationship between Chilo suppressalis and its endoparasitoid.

Host hemolymph is an important place of growth and development for most endoparasitoids. Immunofluorescence assay showed that parasitism induced Chilo suppressalis larvae to produce large numbers of granulocytes, but high temperatures led to granulocytes apoptosis and loss of phagocytosis. In addition, high temperatures activated the endoplasmic reticulum apoptotic pathway, leading to apoptosis of prohemocytes. In the present study, the initiator Cscaspase-8 was obtained from the rice pest C. suppressalis. The results of real-time PCR showed that Cscaspase-8 expression was highest in hemocytes; furthermore, transcription was most highly in female adults. Cscaspase-8 was significantly induced when larvae were exposed to 39 °C for a 2-h period. Cscaspase-8 expression was significantly elevated after 2 d of parasitism. Results of the interference test showed that the survival rate of C. suppressalis larvae is not affected by Cscaspase-8 gene silencing under high temperature and parasitism stress. However, developmental delays were observed in Cotesia chilonis larvae when the host Cscaspase-8 gene was knocked down. These results contribute to the current knowledge on the regulatory mechanisms of apoptosis in insects subjected to high temperature and parasitism stress.