Abstract: The dry vial film method was adopted in the bioassay of Apanteles plutellae, a larval parasitoid of Plutella xylostella by treating with the insecticides for 1 h and recording the mortality 8 h after treatment. Compared with the conventional control dosage to P. xylostella, dichlorvos,methomyl and bisultap were high toxic to A. plutellae, but acephate,fenvalerate, cypermethrin,fipronil,abamectin, chlorfluazuron and Bt were not. The apparent michaelis-menten constant (Km) and maximal velocity (Vmax) in A.plutellae were 0.22 and 2.08 times as high as those in its host P.xylostella, and bimolecular rate constant (Ki) to dichlorvos in A.plutellae were 10.37 times as high as those in P. xylostella, respectively. There were obviously synergistic effects on fenvalerate by combined with 100 mg/L piperonyl butoxide (PB) or triphenyl phosphate (TPP) in A.plutellae, and the synergisms of PB to the insecticides were higher. PB and TPP showed very weak inhibition on the activity of acetylcholinesterase(AChE), in vivo. Low concentration of PB (100 mg/L) showed strong inhibition on CarE activity, while only at high concentration(1 000 mg/L) could TPP exhibited significant inhibition on CarE activity. It were speculated that the high susceptibilities to organophosphates and carbamates in A.plutellae were related to its high sensitivity of AChE to the insecticides. In addition, the oxidative metabolism might be more effective in the tolerance to the insecticides than non-oxidative metabolism in A.plutellae.