Abstract: To determine the relationship between the resistance to lambda-cyhalothrin and the detoxification enzymes of the common cutworm, Spodoptera litura (Fabricius), we investigated the resistance levels and activities of detoxification enzymes in lambda-cyhalothrin selected and non-selected populations based on a field population collected from Tai’an suburb with 543.7-fold resistance to lambda-cyhalothrin by topical application. The results indicated that the resistance of the original population decreased to 102.3-fold at F30- generation without exposure to any insecticide and increased to 3 049.3-fold at F30 generation after selection with lambda-cyhalothrin for 28 generations. When selection stopped from F15 generation, the resistance decreased again from 2 593.8-fold at F14 to 786.3-fold at F30 generation. Compared with the susceptible strain, the activities of esterase and glutathione S-transferase in midguts of the 5th instar larvae of the original field generation were significantly higher, while the activity of microsomal O-demethylase showed no significant difference. For the selected generations, the activities of esterase, glutathione S-transferase and microsomal O-demethylase were significantly increased. After selection stopped, the activities of three detoxification enzymes deceased significantly. For non-selected generations, the activities of esterase and glutathione S-transferase also decreased gradually, but were still significantly higher at F30 generation than those of the susceptible strain. The results suggest that the enhancement in activities of esterase, glutathione S-transferase and microsomal O-demethylase is an important mechanism for the resistance increase of S. litura to lambda-cyhalothrin

Key words: Spodoptera litura, lambda-cyhalothrin, insecticide resistance, resistance selection, detoxification enzymes