Abstract: 【Aim】 To clarify the resistance mechanisms of Tetranychus truncatus Ehara to pyridaben by detecting the change of detoxification enzyme activities and the synergism of synergists to pyridaben. 【Methods】 The experiment was carried out in laboratory by biological assay. The specific activity, the Michaelis constant (K_m) and the maximum reaction velocity (V_max) of several detoxification enzymes in pyridabenresistant strain (Py-R) and susceptible strain (SS) were detected by microplate reader. Then the synergistic effects of piperonyl butoxide (PBO), diethyl maleate (DEM) and icresyl phosphate (TPP) to pyridaben were detected in Py-R and SS.【Results】 The resistance of Py-R at the 49th generation selected with pyridaben increased to 955.25-fold as high as that of SS. The piperonyl butoxide(PBO), triphenyl phosphate (TPP) and diethylmaleate (DEM) enhanced the toxicity of pyridaben, and the relative synergistic coefficients of 3 synergists to pyridaben were 95.97%, 85.14% and 97.37%, respectively. The activities of carboxylesterases (CarE), glutathione-Stransferase (GSTs) and mixed function oxidase (MFO) in Py-R significantly increased compared with those in SS (P<0.05), while the activities of acid phosphatase (ACP) and alkaline phosphatase (ALP) had no significant difference between Py-R and SS (P>0.05). The Km values of CarE, GSTs and MFO in Py-R were lower than those in SS, while their V_max values in Py-R were higher than those in SS. 【Conclusion】 The increased activity of CarE, GSTs and MFO, and higher affinity with substrate might be the main resistance mechanisms to Py-R of T. truncatus. When 3 synergists (PBO, TPP and DEM) and pyridaben are mixed, a higher level of virulence to T. truncatus would be exhibited.

Key words: Tetranychus truncatus, pyridaben, resistant strain, susceptible strain, detoxification enzyme, resistance, synergist, Michaelis constant