Abstract: The acetylcholinesterase (AChE) sensitivity and insecticide resistance of Plutella xylostella and its parasitoid, Apanteles plutellae Kurd.collected from Fuzhou, Fujian Province, were detected and monitored by bioassays and biochemical analyses. The results show that the AChE sensitivity of P.xylostella to six kinds of organophosphorus and carbamate insecticides increased gradually from September 1998 to April 1999, and that sensitivity of A. plutellae(collected from the corresponding hosts) showed the same trend. AChE sensitivity was higher in A.plutellae than in P. xylostella. After release from the selective pressure of the insecticides, both P. xylostella and A. plutellae displayed a rapid recovery in susceptibility to these insecticides and a significant increase in the K_i value of AChE. Insecticide resistance was associated with insensitivity to AChE in P. Xylostella and A. plutellae based on the kinetic parameters, K_m, V_max and the bimolecular rate constant K_i. This paper also profiles the K_i activity of AChE at different developmental stages of susceptible and resistant P. xylostella, and discusses the possible mechanism of AChE sensitivity in natural populations of both P.xylostella and A. plutellae.

Key words: Plutella xylostella, Apanteles plutellae, acetylcholinesterase sensitivity, insecticide