印楝素对不同龄期茄二十八星瓢虫的毒力及田间防效

室内毒力测定结果表明:印楝素对茄二十八星瓢虫的毒力随着龄期的增加而减弱。施药后24 h和48 h，0.3 %印楝素乳油（EC）对1～2龄期幼虫的LC50都小于0.2 mg·L^-1，对3～4龄期幼虫的LC₅₀都小于1.0 mg·L^-1，成虫对印楝素的敏感性明显降低,施药后24 h LC₅₀为2.122 7 mg·L^-1。田间试验结果显示:0.3 %印楝素EC 400～800倍液对茄二十八星瓢虫幼虫药后7 d的防效达91.17 %以上，400～600倍液对茄二十八星瓢虫成虫药后7 d的防效达81.20 %以上，在生产上防治幼虫时建议使用浓度为600～800倍液，防治成虫时建议使用浓度为400～600倍液。

Laboratory Toxicity and Field Efficacy of Azadirachtin to Henosepilachna vigintioctopunctata(Fabricius)in Different Instars

Testing result in laboratory showed that the toxicity of azadirachtin to Henosepilachna vigintioctopunctata was deducted with the increase of instars.The larva in 1-2 instar was the most sensitive,both of LC₅₀ values were less than 0.2 mg·L^-1. LC₅₀ of azadirachtin to the 3-4 instar larva was less than 1.0 mg·L-1.The toxicity to the adult was decreased obviously,it’s LC₅₀ was 2.122 7 mg·L^-1 in 24 h.In the field,the effect of azadirachtin against larva was over 91.17 % at the 7th day at 400-800 times,it suggested the insecticide could be applied at 600-800 times in farming practice,the effect of azadirachtin against adult was over 81.20 % at the 7th day at 400-600 times,it suggested the insecticide could be applied at 400-600 times.