Fumigating Toxicity of Insecticides Commonly Used in Rice Fields to Silkworm,Bombyx mori

Fumigating toxicities of 7 insecticides commonly used in rice fields were tested by the method of airtight fumigation against silkworm,Bombyx mori so as to reduce the risk of poor cocoon production due to the improper spray of insecticides in grain-mulborry mix-growing areas.Results showed that the LC50s of these insecticides against second instar sillkwrom larvae were 0.186 0 mg/m3(dichlorvos),1.324 1 mg/m3(10% chlorpyrifos+ 25% dichlorvos),48.411 1 mg/m3(chlorpyrifos),139.881 8 mg/m3(1%fipronil+30%triazophos),161.151 4 mg/m3(triazophos),and 208.33 mg/m 3(fipronil),respectively, but no toxic symptom appeared even when the concentration was up to 333.33 mg/m3 of imidacloprid under 30 ℃ for 24 h.However,the LC50s were 0.202 0 mg/m3(dichlorvos),3.728 2 mg/m3(10% chlorpyrifos+ 25% dichlorvos) and 91.366 9 mg/m3(chlorpyrifos) respectively under 25 ℃ for 24 h.Resultes indicated the fumigating toxicities of the tested insecticides were enhanced as the temperature increased.Dichlorvos and 10% chlorpyrifos + 25% dichlorvos showed the highest fumigating toxicity to silkworm,Bombyx mori,chlorpyrifos showed media toxicity while 1% fipronil + 30% triazophos,triazophos,fipronil,and imidacloprid extremely low.