| Alligatorweeds, Alternanthera philoxeroides (Mart.) Griseb is one of the invasive species in China in year. As the host-specific natural enemy, a flea beetle, Agasicles hygrophila Sehnan&Vogt (Coleoptera: Chrysomelidae) successfully controlled against Alternanthera philoxeroides. However, the geographical distributions of the flea beetle are larger than those of Agasicles hygrophila. Our results revealed that temperature is mainly responsible for distributions of A. hygophila. The free radical that would damage the insect body, and therefore temperature may be one of the important environment stresses factors to the survival of A. hygophila. For insect species, three kinds of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), constitute the protective enzyme system. This system can remove the excess reactive oxygen and thus protect organisms from the damage of environmental stresses. The researches on effect of three kinds of protective enzymes activity of A. hygophila under different temperature were conducted. The main results were as following.Temperature stress had some effects on the activity of SOD of A. hygophila. The trend appeared increased and then reduced with the increase of temperature. For the low temperature, the activity of SOD slowly rise from less than7.5℃of temperature when exposure to1h and6h, and the peak occured at0℃. The activity of SOD rise significantly at15℃of temperature when the exposure to24h, and the peak occurred at5℃of temperature. Under5℃, the activity of SOD was significantly decreased with extension of time. The activity of SOD in male and female Agasicles hygrophila was reduced to21.61U/mg and24.39U/mg after1h under-7.5℃, respectively. SOD in the high temperature was more sensitive than in the low temperature stress. The activity of SOD slowly rised in more than30℃of temperature, and the peak occurred at37.5℃of temperature when exposure to1h and6h. When exposed to12h and18h, the peak occurred at35℃and32.5℃of temperature, respectively. When exposure to40℃·2h and42℃·1h, they were far lower than the control.The activity of POD increased and then decreased with the increase of temperature. for the low temperature, the activity of SOD slowly rised from less than7.5℃of temperature with the decrease of temperature. The peak occurred at0℃of temperature when exposure to1h and6h. In the treatment of1h, the activity of POD in male and female was2.2and3.1times more than the control. When exposed to6h, the activity of POD in male and female was1.5and2.2times more than the control. The activity of POD increased and then decreased with prolonged time at-2.5℃of temperature. For the high temperature, the peak occurred at37.5℃of temperature when exposure to1h, and the activity of POD in male and female was2.1and3.0times more than the control, thus revealing that there was a significant difference between male and female. When exposure to40℃·2h and42℃·1h, they were far lower than the control. At more than32.5℃of temperature, the activity of POD increasingly decreased and finally was lower than the control as the extension of time. Therefore, the temperature of above32.5℃would do harm to A. hygophila with the prolonged time.3. The activity of CAT increased and then decreased with the increasing temperature. For the low temperature, the activity of CAT was higher than the other two enzymes. The peak occurred at2.5℃of temperature and10℃of temperature when exposure to1h, and was2.0times and1.5times higher than the control, respectively. The activity of CAT decreased significantly after exposure to12hours with the temperature of lower than0℃. At-2.5℃of temperature, the activity of CAT decreased and then rised and finally decreased, thus indicating that CAT could be adapted at-2.5℃of temperature in short time. For the high temperature, the activity of CAT was characterized by "upside down N" type, and the peak occurred at37.5℃of temperature when exposure to12hours. When exposure to40℃·6h and42℃·1h, the activity of CAT in male and female was less than the control. At the temperature of higher than32.5℃, the activity of CAT increasingly decreased and finally was lower than the control as the extension of time.Three protective enzymes in A. hygophila adult differently change under the same stresses. The activity of SOD and POD in female was higher than those for male, whereas the activity of CAT was lower than those for male. As regard as temperature stress, the ascensional range of the three protective enzymes of female was higher than male.In this study, we revealed the physiological mechanism of A. hygophila thermal adaptation, and clarified the importance of cold resistant and heat resistant of A. hygophila. |
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