Toxicity Variation of Five Pyrethroid Pesticides to Bombyx mori at Different Temperatures

Temperature has an effect on the toxicity of pyrethroid pesticides to insects.The acute toxicities of five commonly used pyrethroid pesticides to silkworm(Bombyx mori) at 35 ℃,30 ℃,25 ℃ and 20 ℃ were evaluated in laboratory by using the feed intake method.The acute toxicities of pyrethroid pesticides to silkworm reduced with the increase of temperature.The LD50 of Deltamethrin,Fenvalerate,Bifenthrin,Beta-cypermethrin and Beta-cyfluthrin to the 2nd instar silkworm larvae at 35 ℃ was 7.63,12.27,8.49,2.76 and 1.75 times to that at 20 ℃,respectively.The results indicated that the acute toxicity of five commonly used pyrethroid pesticides to silkworm behaved as a negative temperature effect,among which the effect of temperature on acute toxicity of Fenvalerate to Bombyx mori is the most obvious,that on Deltamethrin and Bifenthrin is relatively obvious,and that on Beta-cypermethrin and Beta-cyfluthrin is very little.