Abstract: An investigation was made on the aldrin epoxidationase activity and cytochrome P-450 level in the larvae of the diamond-back moth Plutella xylostella which were collected from different regions and distinguished as strains susceptible and resistant to DDVP and pyrethroids. The results of our further study indicated that there existed significant difference in quality and quantity of aldrin epoxidationase and cytochrome P-450 between the resistant and susceptible diamond-back moth larvae. The K _m,and V_max, values of aldrin epoxidationase from the resistant strain were 6.5 and 5.4 times higher when compared with that from the susceptible strain. Based on this finding, we presume that the difference of aldrin epoxidationase in quaility and quantity as well as the increase in cytochrome P-450 level are important factors for the development of insecticide resistance in the diamondback moth larvae and the qua litative difference in the enzyme systems may be more important.

Key words: Plutella xylostella L.——inseeticide resistance——aldrin epoxi- dationase——cytochrome P-450