Toxicity and feeding inhibition effect of three insecticides on rice leaf folder larvae(Cnaphalocrocis medinalis Guenee) and rice borer larvae(Chilo suppressalis Walker)

【Objective 】The study aimed at assessing the management of three presently used pesticides chlo-rantraniliprole, flubendiamide and chlorantraniliprole thiamethoxam, against leaf folder larvae(Cnaphalocrocis medinalis Guenee) and striped rice borer larvae(Chilo suppressalis Walker) to provide scientific basis for the rational use. 【Method 】Potter Tower Method was used to estimate the susceptibility and inhibited feeding of 1-4-day-old C. medinalis and C. uppressalis against these commonly used insecticides. 【 Result 】 The order of the toxicities against rice leaf folder(Instar I and II) was: flubendiamide chlorantraniliprole chlorantraniliprole thiamethoxam, varying in the multiple of 1.55-1.83. The toxicities of chlorantraniliprole thiamethoxam and chlorantraniliprole against C. medinalis(InstarⅣ) were 2.04-2.32 times as high as that of flubendiamide. The toxicity differences among the three pesticides against rice borer larvae were not significant. There were obvious differences in three pesticides against different stages of the two pests. The toxicity of Instar I and Instar Ⅳ differed by a factor of 3.20-13.62. All the three pesticides inhibited larval feeding when treated by concentrated LC50 where the onset time of C. medinalis was 1-4 h and while for C. suppressalis was 4-16 h. The onset time of three pesticides was prolonged with increased instar age. 【Conclusion 】These three pesticides are relatively efficient against C. medinalis and C. uppressalis in their young larva stage.Flubendiamide is preferred in the management of young larva, while chlorantraniliprole thiamethoxam is preferred in the old larva management.