Resistance Risk Analysis And Biochemical Mechanism Of Spodoptera Litura To Avermectin

The common cutworm, Spodoptera litura (Fabricius), is a worldwide distributed agricultural pest occuring intermittently. Frequent use of chemical insecticides controlling S. litura had led to the development of insecticide resistance. Avermectin is an environmental friendly and human-animal harmless neurotoxin with special toxicious action. In this paper, the insecticide resistance levels of a field population of S. litura, resisntance risk to avermectin and detoxification enzyme activities were studied. The main results are as follows:1. Resistance levels of a Tai'an field population of S. litura to 8 insecticiedes were determined using leaf-dipping method. The results showed that the resistance levels of the field population were: Deltamethrin (138-fold)> Cypermethrin (97-fold)> Chlorpyrifos (15-fold)> Fipronil (4.5-fold)> Chioefenapyr (3.2-fold)> Chlorfluazuron (3-fold)> Mimic (1.9-fold)> Abamectin (1.4-fold).2. Based on the bioassay results, 5.0 mg/L of avermectin as initial concentration was used to select first instar larvae of a susceptible population of S. litura by artificial diet dipping method. After 10 times of selection with avermectin during 13 continuous generations, the selection population obtained 4.54 folds of resistance compared with its unselected population. So we may infer from the above results that S. litura have low capability to develop resistance to avermectin. When realized heritability was 0.0505 and killing rate was 80% 90%, S. litura developing l0 folds of resistance to avermectin will need 14 to 18 continuous generations.3. Activities of carboxylesterase (CarE), glutathione S-transferase (GSTs) and multi-function oxidase (MFO) of three different populations of S. litura were determined. The results showed that the CarE activities of Tai'an field population and the avermectin-selected population were 2.2 and 2.5 times high than that of unselected susceptible population. P₄₅₀ contents and MFO O-demethylase activities.of the field and selected populations were 1.7, 1.43 times and 2.26, 1.76 times high than that of unselected susceptible population, respectively. GSTs activities of the field and selected population were 1.26 and 1.08 folds of the susceptible population. Activities of CarE and MFO O-demethylase of three populations also were significantly increased by abamectin treatments while GSTs activities were almost not affected. Above results demonstrated that low level of resistance of S. litura to avermectin was related to carboxylesterase and multi- function oxidase, and had no relation with glutathione S-transferase.