Abstract:  In order to clarify the mechanisms of deltamethrin resistance in Tetranchus urticae Koch. Pyrethroid acaricide fenpropathrin was used to select the resistance in T. urticae in the laboratory. Selected with fenpropathrin for 38 generations, T. urticae developed 247.35-fold resistance to fenpropathrin. The activities of detoxification enzymes were measured and compared between the susceptible strain (S) and the fenpropathrin-resistant strain (Fe-R) of T. urticae. The results showed that the activities of carboxylesterase (CarE), acid phosphatase (ACP), alkaline phosphatase (ALP), glutathione S-transferases (GSTs) and mixed function oxidase (MFO) in Fe-R₃₈ were significantly higher than those in S strain, increased by 1.822-, 13.941-, 3.789-, 4.262- and 17.386-fold, respectively. However, except that the activity of MFOs in Fe-R₂₅ and Fe-R₃₂ showed significant difference from that in S strain (P< 0.05), the activities of other detoxification enzymes (CarE, ACP, ALP, GSTs) in the resistant strain selected for 9, 19, 25, and 32 generations were significantly different with those in S strain. The activities of all the detoxification enzymes in the resistant strain selected for 38 generations were significantly different with those in S strain (P<0.05). These results suggest that with the increasing of selection generations (after the 25th generation) with fenpropathrin, the increased activity of MFO may the main factors responsible for the resistance of T. urticae to fenpropathrin.

Key words: Tetranychus urticae, fenpropathrin, resistant selection, detoxification enzyme, mixed function oxidase, resistance mechanism