Toxicity Of Pesticides To Silkworm (Bombyx Mori)and Detoxification Method

Silkworm (Bombyx mori) is very sensitive to pesticides. Toxicity level of pesticides toBombyx mori is divided into hypertoxic grade with LC50value lower than0.1μg/mL, hightoxicity grade with LC50value between0.1μg/mL and10μg/mL, moderate toxicity gradewith LC50value between10μg/mL and l000μg/mL, the last is low toxicity grade with LC50value more than l000μg/mL. In recent years, silkworm poisoning events occurredfrequently. Evaluating toxicity level of pesticides to silkworm is more and more popular.Pesticides are various, so the study of many pesticides toxicity to silkworm is still blank.Therefore, increasing research on the toxicity of pesticides to silkworm is increasinglyimportant to reduce losses caused by pesticide pollution. There were plenty of research haddemonstrated that Pyrethrin, Nereistoxin and Organophosphorpus Pesticides was virulent toBombyx mori, while plant growth regulator was less. The toxicity to silkworm depends onnot only molecular structure of pesticide effected the receptor, but also humidity,temperature and light. Temperature is one of the most important influence factors.Temperature has an effect on the toxicity of pesticide to insects，which is diversity.In our study, the acute toxicities of five commonly used pyrethroid pesticides tosilkworm at different temperature were evaluated in laboratory. The acute toxicities ofpyrethroid pesticides to silkworm reduced with the increase of temperature. The ratios ofLD50of Deltamethrin, Fenvalerate, Bifenthrin, Beta-cypermethrin and Beta-cyfluthrin to2nd instar larvae at35℃was7.63,12.27,8.49,2.76and1.75times to that at20℃,respectively. The results showed that toxicity of five commonly used pyrethroid pesticidesto silkworm behaved as a negative temperature effect, among which the effect oftemperatures on acute toxicity of Fenvalerate to Bombyx mori was most obvious, that onDeltamethrin and Bifenthrin was relatively obvious, and that on Beta-cypermethrin andBeta-cyfluthrin was very little.Brassinolide was a new type of plant growth regulator, which has an effect on growthand development of Bombyx mori. The ratios of LD50of Brassinolide to2nd instar larvaewas2.9907μg/larva. Brassinolide had obvious harmful effect to growth, development andcocoons characters of Bombyx mori, which showed dependent of intaking Brassinolide dose.Brassinolide delayed the growth and development of silkworm larvae. After intaking0.001μg/mL,0.010μg/mL and0.100μg/mL Brassinolide, larvae were prolonged to2d18h，4d 6and5d12h, respectively. Cocoon weight, cocoon layer ratio and cocoon shell weight oftested group was decreased, and cocoon layer ratio was more decreased significantly tomale cocoon.This paper preliminary studied on screening Dimehypo-resistance strain and removingand detoxification of pesticide. Resistance of silkworm directed screening by Dimehypowas enhanced. The ratios of LC50of HaoYue F7was1.2074μg/mL that was higher thanhybrid of HaoYue×JingSong, and JingSong F6was1.0101μg/mL, the two was increased1.37and1.20times, respectively. The ozone water had obvious effect on the digestion ofDimehypo and Acephate. Lethality of mulberry leaves sprayed with10μg/mL Dimehypo toBombyx mori was70.00%, which was53.33%after poisonous mulberry leaves treated bywater, reduced24.29%, while ozonization was46.67%, reduced33.33%. Lethality of500μg/mL Acephate sprayed on mulberry leaves was66.67%, group with water immersion was60.00%, no obvious difference. While ozonization was40.00%, reduces40.00%, thedifference was significant. Cocooning and pupation rate of Group with ozonization wasincreasing. Dimehypo poisoning4instar silkworm, Lethality was significantly decreasedand4molting silkworm weight had obvious unchanged after intaking5μg/mL P-toluic acidand5,5’-Dithio bis（-2-Nitrobenzoic acid）. And cocooning and pupation rate was increasing,the difference was significant, while weight of cocoon was reduced, and Cocoon layer ratiohad no obvious changed compared with the control group. The result showed that P-toluicacid and5,5’-Dithio bis-（2-Nitrobenzoic acid） had detoxification effect on poisoningsilkworm of Dimehypo, while Acetylcholine was opposite.