Studies On The Resurgence Of Rice Leaf Folder (Cnaphalocrocis Medinalis Güenée) Induced By Selective Insecticides And The Resistance To Rice Leaf Folder Derived From Different Rice

The present study was conducted during 2004²006. And the effect of two selective insecticides buprofezin and imidacloprid on fecundity and hormone level of the rice leaf folder, Cnaphalocrocis medinalis Guenee, and on soluble sugar, soluble protein and free amino acid of rice plants were investigated. Main results were as follows:The number of laid egg by female adults developed from the second instar larvae fed on rice plants treated with the two insecticides depended on study years. Buprofezin showed suppressed fecundity of the insect during 2004 study, but buprofezin and imidacloprid stimulated the fecundity of the insect during 2005-2006 study. Therefore, We considered the two insecticides stimulated fecundity of C. medinalis.The investigation on effect of insecticides on pupae weight of C. medinalis showed that there were no significant differences on the weight of pupae developed from larvar fed on rice plants treated with buprofezin and imidacloprid during 2004 experiment compared with that on control plants. There were no significant differences between the weight of larvae fed on rice plants treated with buprofezin and imidacloprid and that on control plants according to 2005 experiment. The weight of pupae that developed from the second instar larvae fed on rice plants sprayed with 37.5 g.a.i. ha^-1 imidacloprid in field was significantly higher than that on control plants, and there were no significant differences on the weight between the other treatments and control. On the contrary to pupae weight in field experiment, the weight of pupae developed from larvae fed on control plants in cement experiment was significantly higher than that on treated plants. The weight of pupae developed from larvae fed on rice plants treated with 180.g.a.i. buprofezin did not show significant difference compared with that on control plants. There were no significant differences on pupae weight between treatments and control. JH level in larvae developed from larvae fed on insecticide-treated plants was significant lower than that on control plants, but MH level did not show significant difference between treatment and control.Effect of insecticides on biochemical substances indicated that, at the tillering stage, soluble sugar content in plants after 80g.a.i.ha^-1 imidacloprid treatment was significantly higher than that in control plants, and soluble protein content in plants after 60g.a.i.ha^-1 imidacloprid treatment was significantly higher than that in control plants. At the late tillering stage, soluble sugar content in rice plants after 60g.a.i.ha^-1 imidacloprid treatment was significantly higher than that in control plants. In addition, at the tillering stage and late tillering stage, free amino acid content in rice plants after 300g.a.i.buprofezin treatment was significantly higher than that in control plants.Fourthermore, damage index and damage rate of rice leaves by C. medinalis larvae on Yangfujing 8, Yangjing9538, Xieyou63, Yangdao9 and Huidao9 were investigated in this paper, and resistance of the above-variety to C. medinalis was also measured.The results showed that varietal resistance has obvious difference, and Huidao9 and Yangfujing8 were susceptibility. Biochemical measurement demonstrated that variety with high content of free amono acid was favor to the occurrence of C. medinalis and that with high soluble protein content was unfavor to the occurrence of the insect.