The Stability of Resistance and the Strategies for Management of Insecticide Resistance in Plutella xylostella (L.)

High resistances to organophosphates(OPs), carbamates and pyrethroids were found in the field strain of diamondback moth(DBM), P. xylostella (L.),in Fuzhou,Fu jian Province. The resistance quickly decreased after DBM were released from selection pressure for only 3 generations，and significant synergism to OPs i n R strain was found after 24 h pretreatment with Bt. The activities of AchE were strongly depressed by Bt pretreatment in R Strain. The higher values of Ki were detected in R Strain with Bt pretreatment, but no significant changes in S strain. The results showed that the resistance management of insecticides with different toxicity mechanism, in volving alternating and mixing insecticide , should be adopted in IPM strategies.