Abstract: To explore cellular defense against thermal stress in Chilo suppressalis larva, we investigated the effect of thermal stress on the generation of reactive oxygen species （ROS）, heat shock protein 90（HSP90）and apoptosis in haemocytes of C. suppressalis larvae by flow cytometry. The results indicated that thermal stress significantly elevated the level of ROS in the 5th instar larva of C. suppressalis. The ROS level in larvae exposed to 33, 36, and 39℃ for 2 h reached 1.71-, 1.69- and 1.38- fold of the control （28℃）, respectively, while there was no significant difference in the level of ROS in larvae exposed to 33-39℃. Real-time quantitative PCR showed that HSP90 gene expression could be induced by heat stress. Flow cytometric results revealed that the expression profile of HSP90 at the protein level is highly in agreement with at the mRNA level. The exposure to target temperatures did not lead to any significant apoptotic differences in the larval haemocytes. The study further suggests that ROS can modulate HSP90 gene expression, and increased HSP90 protein synthesis may determine their greater resistance to stressor that elicits the formation of ROS-induced cellular damage, and this inhibits haemocyte apoptosis in the exposed organism.

Key words: Chilo suppressalis, haemocytes, heat stress, ROS, HSP90, apoptosis