Abstract: Malathion resistance of brown planthopper (Nilaparvata lugens Stal) was selected in laboratory and the successive changes in carboxylesterase (CarE) and AChE were also analyzed. The results showed that the speed of resistance selection varied with generations. The biggest change of LD₅₀ occurred between the 3rd－5th generations. The rise of carboxylesterase activity was correlated with the change in malathion resistance for the first 5 generations, while change in AChE sensitivity between 6th－8th generations had a higher correlation with the resistance development. Therefore, it was concluded that carboxylesterase activity increase play important role in the early stage of the resistance development and the AChE insensitivity at the late stage.

Key words: malathion, brown planthopper, carboxylesterase, acetylcholinesterase