高温对田间小菜蛾种群及抗性水平的抑制

田间调查结果表明，6月期间，田间小菜蛾种群密度处于相对较高水平，但在7月初至8月初期间急剧下降，8月下旬开始逐渐升高，9月～11月期间，小菜蛾种群密度显著高于春季的6月及夏季的8月下旬。总体上看，与25°C处理相比，40°C预处理田间小菜蛾8h后，氰戊菊酯、甲胺磷和阿维菌素对田间小菜蛾的24h和48h毒力均显著增高。与25℃处理相比，33．5°C预处理24h、36°C预处理8h和36℃预处理24h均显著抑制田间小菜蛾多功能氧化酶活性，且随着高温处理时间延长，抑制率明显增大。上述结果表明，夏季高温可导致田间小菜蛾种群密度急剧下降，并会显著抑制田间小菜蛾对杀虫剂的抗性水平及多功能氧化酶活性。

Inhibition of the dynamics of population density and insecticide resistance affected by high temperatures in field Plutella xylostella

The results indicated that the population density of field Plutella xylostella was high in June but declined sharply from early July to early August. The population density of P. xylostella increased after the end of August and was higher than it was in June and at the end of August. In general, pretreatment at 40°C for 8 h resulted in a significant increase in susceptibility to fenvalerate, methamidophos and avermectin in field P. xylosteUa compared to insects that were pretreated at 25 °C for 8 h. Compared to an 8 - h 25°C treatment, the treatments at 33.5°C for 24 h, 36°C for 8 h or 36°C for 24 h resulted in a significant inhibition of the mixed function oxidase activity in both larval and adult P. xylostella. Also, the inhibition increased with an increase in the high - temperature treatment period. The results indicated that high temperatures during the summer could result in significant declines in population densitv and inhibition of both insecticide resistance and detoxification enzyme ae.tivitv in field P. xylostella.