Acute Toxicity of Four New Types of Insecticides to the Fourth Instar Larvae of Chironomus flaviplumus Tokunage(Diptera:Chironomidae)

Acute toxicity of four new types of insecticide(15% monosultap-triazophos EC,20.2% avermectin-triazophos EC,1.8% avermectin-imidacloprid EC and 2.4% beta-cypermethrin-avermectin EC) was evaluated by using fourth instar larvae of dipteran Chironomus flaviplumus Tokunage of the Chironomidae family.Results show that 48 h acute toxicity of 1.8% avermectin-imidacloprid EC was the highest(LC₅₀=0.001 5 mg·L^-1) among the four insecticides.Concentration had significant effects on survival rates of Chironomus flaviplumus Tokunage larvae except for 15% monosultap-triazophos EC(24 h toxicity).For each insecticide,the differences in survival rates of chironomid larvae between 24,48,72 and 96 h were significant.For each day,the effects of the four insecticides on larvae were also significant.In conclusion,survival of chironomid larvae was severely affected by these insecticides.The patterns of action of the four insecticides were different,too.Larvae exposed to 15% monosultap-triazophos EC died slowly within four days but died much quicker when exposed to the other three insecticides.The serious impacts of insecticides on chironomid larvae in this study may help promote monitoring and assessing water quality in China.