Oxidative Damage Of The Ghost Moth Larvae Thitarodes Xiaojinensis.(lepidoptera: Hepialidae) Under Heat Stress

Thitarodes xiaojinensis (Lepidoptera: Hepialidae) is the host insect of Chinesecaterpillar fungus (a famous precious Chinese medicine), which distribute in TibetanPlateau and the cold, high altitude area nearby. It could survive in low temperature ratherthan room temperature (RT,25-27℃). Due to rising price and excessive excavation, thesupply of cordyceps sinensis resource is less and less. In addition, the supply is alsoaffected by the change of living environment’s temperature because of global warming.This paper studied the physiological, biochemistry, and molecular mechanism in order toknow whether can Thitarodes xiaojinensis survive at room temperature.Firstly, the relative content of malonaldehyde in hemolymph was measured, which isthe marker of the oxidative damage. The result showed that the content of malonaldehydestressed was twice of the contrast group, which indicated that there were serious oxidativedamage and significant peroxidation of membrane lipids. The structures, stressed at27℃were observed by Transmission Electron Microscopy (TEM), shows that swollenmitochondria of the midgut cell with broken membrane, vesicles and disarranged cristae.It indicated that there was an oxidative damage in the mitochondria stressed by27℃.What’s more, the protective enzymes including superoxide dismutase (SOD), catalase(CAT), peroxidase (POD) were measured and the conclusion that no significant changeson the SOD and CAT except POD between stressed and contrast was got. SOD has animportant status in clearing the excessive reactive oxygen species (ROS), and it couldcatalyze O2.-to H2O2; while CAT and POD could catalyze H2O2to H2O and Q2. Thus, thelarvae failed to clear the excessive ROS, because of the low total activity of protectiveenzymes, and suffered oxidative damage.GC-MS was utilized to analyze the metabonomics of the hemolymph and fatbody.The result was that the contents of the reducing matters reduced significantly inhemoplymph and fatbody, such as the reducing sugar, amino acid, and so on; while theproportion of cholesterol increased in hemolymph. Some studies have shown that there aresome associations between cholesterin and the generation of induction ROS. The changeof Pentose Phosphate Pathway (HMP) was obtained by the analysis of the metabolites inthe pathway. The level of HMP increased in hemolymph indicated that HMP offer a mass of NADPH to the larvae to resist oxidative damage in hemolymph. Besides that, thecontent of cholesterol reduced, the enzyme activity of NADPH oxidase increased, and amass of ROS could be produced instantaneously by NADPH oxidase induced bycholesterol. At the same time, the level of HMP reduced in fatbody, which indicated thatthere was a low level of NADPH in the fatbody. The reducing meters in the larvae reduced,even though the level of the HMP rised to provide more NADPH in hemolymph, sincemore ROS was produced along with increasement of NADPH oxidase activity. In theprocess, the metabolic balance of ROS could not be maintained and oxidative damageoccurred.