An Evaluation on Toxicity of Pesticide Methomyl in Different Product Formulations to Bombyx mori

In order to validly evaluate the impact of methomyl in different product formulations on the security of silkworm(Bombyx mori) during pest control in mulberry field,its acute toxicity of three product formulations,namely 20% EC,24% soluble liquid formulation and 40% EC,to Bombyx mori was determined through feeding the 3rd instar silkworm larvae with mulberry leaves soaked in methomyl of various mass concentrations.The results showed that LC50 at 24 h of the three product formulations to the 3rd instar larvae ranged from 14.626 4 to 17.617 9 mg/L,with no significant difference(P0.05).LC50 at 48 h was about 10.760 3~11.498 7 mg/L,with no significant difference(P0.05),either.And LC50 at 72 h ranged from 9.450 2 to 10.213 7 mg/L,also with no significant difference(P0.05).However,LC50 at 24 h and at 72 h were significantly different(P0.05).Moreover,toxicity regression equations of the three pesticide formulations to the 3rd instar larvae all had the highest slopes(b-values) at 48 h,indicating that the maximized toxicity of methomyl to Bombyx mori emerged 48 h after pesticide ingestion by the larvae.Three kinds of methomyl pesticide products were diluted to mass concentrations of 66.67,133.33 and 266.67 mg/L respectively,and sprayed onto mulberry trees for determining the residue toxicity.As was brought to light that their residue toxicity to silkworm was slightly different.The 3 600 times diluted solution of 24% methomyl soluble liquid had the shortest residue toxicity(8 d).Combining to toxicity determination,it is suggested that the safety time interval of the three pesticide formulations is 8~12 d to silkworm.