氧化损伤是热胁迫下小金蝠蛾幼虫不能存活的重要原因

【目的】小金蝠蛾Thitarodes xiaojinensis是冬虫夏草菌Ophiocordyceps sinensis的寄主昆虫,生活于高海拔、高寒地区,低温适应性强,但在室温下（25~27℃）不能正常存活。本研究检测了热胁迫（27℃）对小金蝠蛾幼虫消化酶及抗氧化系统的影响,以期揭示小金蝠蛾室温不耐受的生理机制。【方法】小金蝠蛾8龄幼虫分两组进行处理：高温组于27℃下饲养,对照组于16℃下饲养。处理24 h后观察虫体状态,并解剖,取中肠及血淋巴。透射电镜观察中肠细胞线粒体结构,分别测定中肠总蛋白酶和糖基水解酶活性,血淋巴丙二醛（MDA）含量,以及血淋巴保护酶系中超氧化物歧化酶（SOD）、过氧化氢酶（CAT）和过氧化物酶（POD）的活性。【结果】两组幼虫中肠总蛋白酶及糖基水解酶活性均随反应温度（16~37℃）升高而增强。协方差分析显示,高温组幼虫酶活性极显著低于对照组（P<0.01）。然而,高温组幼虫在27℃下的酶活性与对照组幼虫在16℃下的酶活性无显著差异（P<0.05）。热胁迫下虫体血淋巴中丙二醛含量显著升高（P<0.05）,提示出现了氧化损伤。透射电镜结果显示,高温组中肠细胞线粒体肿胀,膜受损,嵴排列混乱,结构破坏。对活性氧起清除作用的3种保护酶中,仅POD活性显著升高（P<0.05）,SOD和CAT活性均无显著变化（P>0.05）。【结论】消化酶活性的变化可能不是小金蝠蛾室温不耐受的重要因素;氧化损伤是其热胁迫下不能正常存活的一个重要原因。

Oxidative damage is one of the most important causes of death of Thitarodes xiaojinensis (Lepidoptera: Hepialidae) larvae under heat stress

【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.