Resistance Risk Analysis And Biochemical Mechanism Of Spodoptera Litura To Indoxacarb

The common cutworm, Spodoptera litura (Fabricius), was a worl- dwide distributed agricultural pest. Frequent application of chemical insecticides against S.litura had led to the development of insecticide resistance. Indoxacarb was a novel insecticide belonging to the oxadiazine class with unique action mechanism, excellent insecti- cidal activity and low toxicity to no target organisms; it was therefore an ideal candidate to substitute organophosphate and pyrethroid insect- icides. In this paper, the toxicological characteristics of indoxacarb against S.litura had been studied, which including toxicity, resistance risk and biochemical mechanism of resistance.(1) Toxicity of indoxacarb to 3rd instars larvae of a susceptible and a Tai'an field population of S. litura was determined by artificial diet dipping method. The results showed that the LC50 values of the susceptible and field populations were 0.5816 and 3.3189 mg·L^-1, respectively. The toxicity of Tai'an field population was lower 5.71 times than that of the susceptible population, which demonstrated that Tai'an field population had low resistance to indoxacarb.(2) Based on the bioassay results, 0.3 mg·L^-1 of indoxacarb as initial concentration was used to select 3rd instars larvae of the susceptible population of S. litura by artificial diet dipping method. After 11 times of selection with indoxacarb during 13continuous generations, the selection population obtained 69.58 folds of resistance compared with its unselected parents. So we can infer from above results that S.litura have high capability to develop resistance to indoxacarb in relative short time. When realized heritability was 0.697 and killing rate was 80% 90%, resistance of S.litura reached l00 folds in just 8 to 10 generations.(3) Activity of carboxy lesterase, glutathioneS-transferase and multi- function oxidase of selected F₁₂ generation was determined. The results showed that the activity of carboxy lesterase and multi-function oxidase in selected F₁₂ generation were 3.70 and 2.53 times high than that of unselected parents.But the activity of glutathione S-transferase in the same selection genenration was really close to the unselected parents with no significant difference. Above results demonstrated that resistance of S.litura to indoxacarb had close relation with carboxy lesterase and multi-function oxidase.