[Effects of sub-lethal dosages abamectin on food intake and digestive enzyme activities of silkworm Bombyx mori L].

Mulberry leaves treated with sub-lethal dosages (LC5, LC10 and LC20) abameetin were fed to the 5th instar larvae of silkworm (Bombyx mori L.), and the food intake and digestive enzyme activities of the larvae were studied by using gravimetric method and measuring enzyme activities. The results showed that sub-lethal dosages abameetin significantly inhibited the growth and food intake of the larvae, with their body mass and its increase rate as well as their relative growth rate being significantly lower than the control, and accompanied with the decreases of food intake, its relative consumption rate, and feces amount. The efficiency of the conversion of ingested food (ECI) and that of the conversion of digested food (EDI) also reduced, but the approximate digestibility (AD) increased significantly. The amylase and sucrase activities in the midgut of the larvae treated with abameetin decreased significantly for a longer time at the beginning, and then recovered to the same as or a higher level than the control, whereas the trehalase activity decreased significantly for a shorter time at the beginning, then increased significantly, and finally recovered to the normal. It was suggested that sub-lethal dosages abameetin had definite toxicity to the silkworm, and the toxic effect was increased with increasing dosage, which could result in the turbulence of silkworm's digestive system, and further, affect its food intake and its growth and development.

[Biodegradation of acetochlor in soil and its persistence against Echinochloa crusgalli].

Gas chromatograph and bioassay were used to study biodegradation of acetochlor and its influence on the persistence against Echinochloa crusgalli in soil. The results showed that half-life of degradation of acetochlor was significantly shorter in unsterilized soil than that in sterilized soil under the same experimental conditions of concentrations, water content and temperature, when acetochlor was added to the soil with concentrations of 1.25, 2.5 and 5.0 mg x kg(-1) respectively, which demonstrated that microorganisms could evidently degrade acetochlor in soil. The experiment on degradation of three main kinds of microorganism cultivated in liquid culture medium gave same results above. The bioassay' s result showed that the period of acetochlor persistence against Echinochloa crusgalli was shorter in unsterilized soil than that in sterilized soil, which indicated that existence of microorganism could accelerate the degradation of acetochlor and shorten remaining time of the herbicide in soil, consequently reduce its persistence against the weed.