Abstract: 【Aim】 The ghost moth, Thitarodes xiaojinensis (Lepidoptera: Hepialidae), is a host insect of Chinese caterpillar fungus (Ophiocordyceps sinensis). Living at high altitude area, T. xiaojinensis is well adapted to the cold environment, while fails to survive under room temperature (RT, 25-27℃). To elucidate the physiological mechanism of death under RT, the effects of heat stress (27℃) on the digestive enzymes and antioxidant system of larval T. xiaojinensis were investigated. 【Methods】 The 8th instar larvae of T. xiaojinensis were treated in two groups: the high temperature group maintained at 27℃ and the control group maintained at 16℃. At 24 h after treatment, the living state of larvae was observed, and midguts and hemolymph were obtained through dissection. The relative contents of malondialdehyde (MDA) in the hemolymph were measured. The mitochondria structures of the midgut cells were observed under transmission electron microscope (TEM). The activities of enzymes including the total proteases and glycosyl hydrolase in the midgut, superoxide dismutase enzyme (SOD), catalase (CAT), and peroxidase (POD) in the hemolymph were tested. 【Results】 The activities of the total protease and glycosyl hydrolase in both groups increased with the reaction temperature (16-37℃). Covariance analysis indicated that the enzyme activities of the high temperature group were significantly lower than that of the control group (P<0.01). However, both protease and glycosyl hydrolase activities in the heat treated larvae tested at 27℃ reaction temperature were not significantly different from that in the control larvae tested at 16℃ reaction temperature (P<0.05). The MDA content in the hemolymph increased significantly after heat stress, indicating that oxidative damage occurred. The TEM analysis of mitochondria showed that mitochondrial structure was damaged with cristae disarranged and mitochondrial membrane broken. Among the protective enzymes, only the POD activity increased significantly upon heat stress (P<0.05), while the SOD and CAT activities did not significantly change (P>0.05). 【Conclusion】 The change of digestive enzyme activities may not be the important factor for the intolerance of T. xiaojinensis larvae under RT. Oxidative damage is one of the most important causes of larval death of the moth under heat stress.

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