合理施用选择性杀虫剂促进瓜绢螟天敌的控害作用

田间小区药效试验表明，乐斯本、氰戊菊酯、抑太保、Bt对葫芦科作物主要害虫瓜绢螟低龄幼虫都有很高的毒杀效果，其中抑太保、Bt效果较为缓慢。室内生测表明，乐斯本对寄生于瓜绢螟卵的赤眼蜂高毒，Bt则无毒。在秋黄瓜作物生长前中期连续施用乐斯本或Bt防治瓜绢螟，施药期间瓜绢螟均可得到较好的控制；但随着季节推移，在施用乐斯本的地块，瓜绢螟卵被寄生率很低，而在使用Bt的地块持续上升，高达70％以上；在停止使用杀虫剂12d后，施用乐斯本的地块瓜绢螟为害严重，而使用Bt的地块虫害被有效控制。结果表明，合理使用选择性农药可对天敌起到显著的保护和促增作用，并使瓜绢螟得到有效控制。

Enhancing Efficacy of Natural Enemies of the Melon Worm Through Strategic Application of Selective Insecticides

The melon worm,Diaphania indica,is an important insect pest of cucurbit crops.Small plot field tests of insecticides indicated that chlorpyrifos,fenvalerate,chlorfluazuron and Bt all had high toxicity to young instar larvae of the melon worm,but the effects of chlorfluazuron and Bt were relatively slow. Laboratory bioassay showed that chlorpyrifos was highly toxic to the Trichogramma wasp egg parasitoid of the melon worm,while Bt was non-toxic to the wasp. Repeated applications of chlorpyrifos or Bt for control of the melon worm in different plots of autumn cucumber demonstrated that in the early stage of the crop,the melon worm was under effective control in all plots.As the season progressed,egg parasitism by parasitoids were low in plots treated with chlorpyrifos,while those in plots treated with Bt were steadily increasing,reaching over (70%.) Twelve days after the cease of insecticide application,the melon worm caused significant damage in plots which had been treated with chlorpyrifos,while the pest inflicted little damage in plots treated with Bt.These results indicate that strategic application of selective insecticides can effectively conserve and enhance natural enemies,and thereby help to bring the melon worm under effective control.