Chronic Toxicity Method And Chronic Toxicity Of Imidacloprid To Silkworm (Bombyx Mori L.)

Silkworm (Bombyx mori L.) are very sensitive to pesticides, for mulberry fields and farmland connects each together, the mulberry leaves can be polluted easily by the drift of pesticide, and the silkworm could be caused poisoning. This research used dimethoate to establish the method of chronic toxicity, aims at exploring how the non-lethal-dose pesticide effected the biological parameters and economic indicators, evaluating its chronic toxicity to silkworm, detecting the detoxification activity, and discussing its feasibility as a chronic toxicity evaluation. This research will be a larger significance to improve the environmental toxicity risk assessment system of pesticide, guide of control the mulberry pest and security sericulture to China. Acute toxicity of5kinds of representative pesticide to silkworm were determined through3kinds of methods, such as food poisoning method, leaf-dipping method and. The results were as follows:compared by the LC50, quantitative spraying method was the biggest of3methods, doubled than the other methods. Showed that the toxicity of2methods were unrealistically high than1time. Quantitative spraying method was quantitatively accurate, suitable for silkworm chronic toxicity experiment.This research used dimethoate to establish the method of chronic toxicity. Quantitative spraying method was used to spraying pesticide on the back of mulberry leaves. The original volume was2or4mL(decide by the mulberry weight), pressure was7psi, waiting time was20sec. Put the petiole into a centrifuge tube(1.5mL) filled with agar after the leaves were dry, then transferred them to the ventilated insect toxicity experiment culture device. According to the silkworm growth and development characteristics, design feeding pesticides at2nd and5th instar. Dimethoate diluted to5-6concentrations, silkworm of2nd or5th instar was used, each handling contained10silkworm,3repeats. The economic indicators were measured8th day after mounting. The results showed that:after dealing silkworm larvae with pesticide of non-lethal dose, the biological parameters and economic indicators of silkworm was observed, high concentrations groups were lower than others. The highest toxic mulberry leaves of40.0mg/kg fed to2nd instar, compared with the control, the developmental period of2nd instar,3rd instar,4th instar,5th instar were extended by1.92%,3.81%,3.93%,4.22%; The weight of2nd dormancy,3rd dormancy,4th dormancy, matured silkworm were reduced by7.57%, 8.10%,3.64%,5.32%; Cocoon weight, cocoon shell weight were reduced by13.7%,10.9%. When toxic mulberry leaves fed at5th instar, its developmental period was extended by5.79%, matured silkworm quality reduced by7.88%, cocoon weight and cocoon shell weight were reduced by16.2%and17.3%. Compared with5th instar and2nd instar, cocoon weight and cocoon shell weight were reduced by3.05%and1.80%, showed that economic indicators were more impact when toxic mulberry leaves were fed at5th instar, the results were more accurate and reliable. The chronic toxicity of the silkworm LOED of dimethoate was16.0mg/kg, LC50value of2nd instar silkworm was824mg/kg, and suitable chronic toxicity dose for the treatment is about1/51.5of the LC50value.The established method was used to determination the chronic toxicity of imidacloprid to silkworm. The results showed that:The biological parameters and economic indicators became lower when the non-lethal-dose razing. The highest toxic mulberry leaves of40.0mg/kg fed to2nd instar, compared with the control, the developmental period of2nd instar,3rd instar,4th instar,5th instar were extended by1.68%、5.36%、6.01%、7.41%; The weight of2nd dormancy,3rd dormancy,4th dormancy, matured silkworm were reduced by8.92%、10.5%、5.58%、7.83%; Cocoon weight, cocoon shell weight were reduced by14.8%、16.8%. When toxic mulberry leaves fed at5th instar, its developmental period was extended by9.63%, matured silkworm quality reduced by11.3%, cocoon weight and cocoon shell weight were reduced by16.4%、19.8%. Compared with5th instar and2nd instar, cocoon weight and cocoon shell weight were reduced by9.99%and3.70%, showed that economic indicators were more impact when toxic mulberry leaves were fed at5th instar, the results were more accurate and reliable. The chronic toxicity of the silkworm LOED of dimethoate was0.0200mg/kg, LC50value of2nd instar silkworm was0.905mg/kg, and suitable chronic toxicity dose for the treatment is about1/45.5of the LC50value.The instar silkworm detoxification enzyme activity was measured. Studies have shown that carboxylesterase activity of silkworm becoming higher when the age increased; the glutathione-S-transferase enzyme was just of the opposite. Non-lethal doses of imidacloprid was used on the young silkworm, CarE activities increased in a short term, and the higher concentration was, the lager the increase was, But there was no significant difference with the control. The GST activities were detected after feeding toxic mulberries at2nd instar. Compared the concentration of0.0200mg/kg with control, these activity was significant difference at the first time, but the difference disappeared as the growing of the age. The GST activities were detected after feeding toxic mulberries at5th instar. Compared the concentration of0.0200mg/kg with control, these activity was significant difference, but the2concentrations wasn’t significant difference. Therefore, the variation of the detoxifying enzymes could not become the evaluation of detecting chronic toxicity to silkworm.