Evaluation Criteria And Ancillary Biochemical Indexe Of Chronic Toxicity Of Six Different Pesticides To Silkworm

Silkworm(Bombyx mori L.), an economically important insect in China, is very sensitive to pesticides. As the unique food of silkworm, the leaves of mulberry tree was vulnerable to be polluted by pesticides during silkworm rearing seasons, whether drift or direct application. Exposure of silkworm larvae to pesticides may cause acute toxicity or chronic toxicity effects, both of which could seriously affect the productivity of the silk industry. At present, the test methods and the evaluation criteria in research about chronic toxicity of pesticide to silkworm have not yet been established. With the support of national science and technology support project, our laboratory has completed chronic toxicity of five insecticides to silkworm and preliminary propose the assay method and evaluation criteria about chronic toxicity of pesticides to silkworm. In order to validate the applicability of previous research results, we carried out a systematic investigation using six different types of representative pesticides, namely chlorpyrifos, chlorantraniliprole, azoxystrobin, tebuconazole, carbendazim and nicosulfuron. Furthermore, we determined the changes of enzyme activity in the body of silkworm after treated with pesticide, which aimed to choose anancillary biochemical indexe to evaluate chronic toxicity of pesticide to silkworm. The main results were as follow:96 h-LC50 of insecticides chlorantraniliprole and chlorpyrifos to the 2nd instar silkworm larvae by quantitative spraying method was 0.00232 and 0.232 mg/kg respectively, exhibiting special high toxicity. 96 h-LC50 of fungicides tebuconazole and azoxystrobin was 116.560 and 159.113 mg/kg, belonging to moderate toxicity. 96 h-LC50 of herbicide nicosulfuron and fungicide carbendazim to the 2nd instar silkworm larvae was 253.213 and 585.553 mg/kg, all of which were of low toxicity.In the study, the silkworm was fed with mulberry leaves treated by quantitative spraying method from second to third instar, and with nontoxic mulberry leaves from fourth instar to cocooning. During the larval, we observated and recorded developmental duration weight of molting silkworm. Eight days after cocooning, we collected and chopped cocoon, and weighed cocoon weight, cocoon shell weight and pupa weight. The results showed that larvae fed with different concentrations of pesticide showed prolonged larval duration, lighter larval weight at ecdysis, lower cocoon weight, lower cocoon shell weight, lower cocoon shell percentage, and lower cocooning percentage. Especially, the cocooning percentage lowered remarkably had significant difference among different concentrations, this suggested that the relationship of the cocooning percentage and administration dose is better. In addition, we used 1/20, 1/50, 1/100, 1/200, 1/400 of 96 h-LC50 as administration dose and found that the influence of 1/20 and 1/50 to growth and economic characteristics had no significant difference. To our point view, it may be due to 1/20 caused a large number of silkworm death in the process of test. The assay method and evaluation criteria about chronic toxicity of pesticides to silkworm in this research was consistent with previous research conclusion in our laboratory. In a word, the method is that in chronic toxicity test of pesticide to silkworm, the appropriate administration ways should be quantitative spraying method, the appropriate administration phase should be silkworm from second to third instar larvae, the appropriate administration dose should be 1/50, 1/100, 1/200, 1/400, 1/800 of the 96 h-LC50 value, and the main evaluation index should be cocooning rate of silkworm.According to the evaluation criteria about chronic toxicity of pesticides to silkworm proposed by our laboratory, the chronic toxicity of chlorantraniliprole and chlorpyrifos to silkworm is special high risk, and the chronic toxicity of tebuconazole, azoxystrobin, nicosulfuron and carbendazim is low risk.We explicated that CarE could be used as a referential evaluation indexe to indicate the chronic influence of pesticide to silkworm through determining the relationship of CarE, GSTs and administration dose, sampling time.