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.