Abstract: The resistance selection of diamondback moth (DBM), Plutella xylostella (L.), to avermectins (AVMs) and its effect on activities of detoxification enzymes in AVMsselected DBM were investigated during 1996～1999. After 27 generations of continuous selection pressure, resistance to AVMs was over 812-folds in this strain compared with the unselected parents. Resistance selection by AVMs has no effect on activity of acetylcholinesterase (AChE). The activities of carboxylesterase (CarE) and glutathione S-transferases (GST) in DBM larvae of F₂₇ generation increased 1.5 and 2.2-folds respectively, compared with the unselected parents (F₀). Piperonyl butoxide (Pb) can moderately increase the toxicity of AVMs to the selected strain for about 6-folds. It suggests that the resistant mechanisms of DBM to AVMs were probably associated with microsomal mixed function oxidases (MFO), GST and CarE.

Key words: Plutella xylostella, avermectins, resistance selection, detoxification, acetylcholinesterase