Abstract: The properties of carboxylesterase and insecticide resistance were investigated in diamondback moth (DBM), Plutella scylostella collected from Wuhan, Hubei Province and Zhangjiakou, Hebei Province during 1995 to 1997. The resistant levels of Zhangjiakou population to avermectin, malathion, hexafiumuron and deltamethrin were 1.8, 2.9, 0.5 and 1.7-folds and that of Wuhan population were 4.3, 2.2, 3.2 and 2.4-folds respectively, compared with the susceptible strain. There was significant difference in carboxylesterase (CarE) activity among larvae of the above two field populations and one susceptible strain and no difference in Care activity among the adults of the above three populations, when a-naphthyl acetate (a-NA) or β-naphthyl acetate (β-NA) was used as substrate. The affinity of Care toward a-NA was almost same as that toward β-NA in larvae of the two field populations, but the affinity of Care was much higher toward a-NA than toward β-NA in susceptible strain. Inhibition on Care by SV1 and paraoxon was much stronger in susceptible strain than in Wuhan population.

Key words: Plutella xylostella, arboxylesterase , insecticide resistance