Abstract: The susceptibilities to dichlorvos and the bimolecular rate constants (Ki) values of acetylcholinesterase (AChE) to dichlorvos in three parasitoids, Cotesia plutellae, Diadromus collaris, Diaeretiella rapae, were far higher than those in their host insects Plutella xylostella and Lipaphis erysimi. Comparing with those incubated at 25℃, significant increase of Ki values of AChE to dichlorvos were found in five species of insects when AChE and dichlorvos were incubated at high temperature (37℃), but no obvious changes of Ki values of AChE incubated at 5℃. Higher inhibitions of AChE activity were found in C. plutellae, D. collaris and D. rapae than those in P. xylostella, L. erysimi when AChE and dichlorvos were incubated at 37℃, and these facts would be not avail to parasitoids in their evolutions of insecticide resistance in the field.