Toxicity evaluation of chlorpyrifos and dimethoate to silkworm variety (Bombyx mori L. 9·Fu) in south China

As the main silkworm variety in south China,Bombyx mori L.9.Fu was used as the testing organism to evaluate the toxicities of the widely used organophosphorus pesticides: chlorpyrifos and dimethoate.Firstly,the acute toxicity effects of 97% chlorpyrifos and 80.7% dimethoate on Bombyx mori L.9.Fu(the second instar larvae) were evaluated by using the leaf dipping method.The grade was compartmentalized according as toxicity scope and the toxic symptoms of silkworms were systematically observed after treatment with these two pesticides.According to the Experimental Criterion for Environmental Safety Assessment of Chemical Pesticide,the 96h median lethal concentration(LC50) of chlorpyrifos to Bombyx mori L.9.Fu was 2.0 mg.L-1,belonging to high toxicity grade,while the 96 h-LC50of dimethoate was greater than 400 mg.L-1,belonging to low toxicity grade.The sensitivities of Bombyx mori L.9.Fu to chlorpyrifos and dimethoate were consistent with those of other local silkworm varieties reported in different studies.Typical symptoms of organphosphorus pesticide poisoning were observed in these tests,and more quick responses were detected when chlorpyrifos was used.These results suggest that Bombyx mori L.9.Fu can serve as the testing organism for the environmental safety assessment of pesticide in our country.Chlorpyrifos might have high risk to Bombyx mori L.9.Fu and strict controls should be taken on its application way and period.Although dimethoate belongs to low toxicity grade,it can still cause the toxic effects on Bombyx mori L.9.Fu and should be treated cautiously.