Acute Toxicity Evaluation of Neonicotinoid Insecticides to Bombyx mori and Observation of Toxic Symptoms

In order to identify the toxicity of neonicotinoid insecticides to non-target organism silkworm(Bombyx mori) and their impact on the security of ecological environment,we determined and compared the acute toxicity of 6 neonicotinoid insecticides and 3 other insecticides to silkworm with leaf dipping method.The differences in symptoms of acute toxicity caused by treatment with various kinds of insecticides were observed and recorded.The results indicated that,among the 6 neonicotinoid insecticides,LC50 of clothianidin,imidacloprid,thiacloprid and nitenpyram to the 2nd instar silkworm larvae at 96 h was 0.065 1,0.174,0.258 and 0.445 mg/L respectively,being pesticides of virulent toxicity grade.That of thiamethoxam and acetamiprid was 1.31 and 2.73 mg/L respectively,being pesticides of high toxicity grade.They all had great security risk on silkworm.The major poisoning symptoms on silkworm after treatment with neonicotinoid insecticides included antifeeding,body twisting into C or S shape,and head tumidity etc.In the other 3 insecticides,the antibiotic insecticide abamectin belonged to virulent toxicity grade and had the highest toxicity among all tested pesticides.Its main poisoning symptoms on silkworm were vomiting,head or tail bending upwards,and antifeeding etc.The organophosphate insecticide chlorpyrifos belonged to high toxicity grade and its poisoning sym-ptoms on silkworm were similar to neonicotinoid insecticides.The pyrroles insecticide chlorfenapyr belonged to middle toxicity grade.In consideration of their virulent toxicity on silkworm,it is suggested that neonicotinoid insecticides should be used far away from mulberry field to avoid damage on sericultural production.