Abstract: The induced activities of the mixed-function oxidases(MFOs) and juvenile hormone esterase(JHE) in vivo of Plutella xylostella treated with different concentrations of(spinosad),were investigated.The results show that the dynamics of target enzymes activities depended on the treated concentrations of spinosad.The juvenile hormone(JH) titers induced by LC50 were similar to the control.The JH titer peaks,induced by LC80,were appeared ahead and maintained a lower level as compared with control.The dynamics of O-demethylation activities,induced by all tested concentrations,were fluctuated with treating time.The increasing inflexion of dynamic curves induced by LC20 and LC50 occurred(at 24) h and(12) h,respectively.All treatments,except LC80 at(36) h,could restrain the N-demethylation activities. JH titers and the activities of O-demethylation and N-demethylation,induced by higher concentrations of spinosad(LC50 and LC80),could be interactional.