Abstract: The mechanisms of chlorfluazuron resistance in diamondback moth (DBM) (PluteUa xylostella L. ) were investigated in a chlorfluazuron-selected strain (CH-R) and a field population collected from Shanghai (SH-R) in October 1996, with 9.16-folds resistance to chlorfluazuron.The results showed that: (1)' The activities of MFO in O-demethylation increased 2.00 and 1.08-folds in CH-R and SH-R strains, respectively, compared with the SZ-S strain. (2) There were differences in quality and quantity of Care between CH-R and SZ-S strains. The K_m value of CH-R strain was 20.46 times lower than that of the SZ-S strain, suggesting that the property of Care inCH-R strain was altered. But there was no significant difference between SH-R and SZ-S strains in K_m and Vmax values. (3) Difference of phosphatase activities between SZ-S and CH-R or SH-Rstrains was not significant. (4) The activities of cuticle chitinase and phenol oxidase were decreasedby 48% and 60%, respectively, compared with the SZ-S strain.

Key words: Plutella xylostella, chlorfluazuron, resistance mechanism