Abstract: After the susceptible strains of Tetranychus urticae were sprayed with omethoate, fenpropathrin, clofentezine for 15 times, their resistance to these insecticides increased 38.5, 479.8 and 67.3-fold respectively. Cross and backcross breeding between the resistant and the susceptible strains showed that the dominance coefficient (D) of the R-omethoate strain was RS=0.4700 and SR=0.4797; D of the R-fenpropathrin strain was RS=0.5155 and SR=0.5237; D of the R-clofentezine strain was RS=0.2466 and SR=0.3134. It was inferred that their resistance to the insecticides was controlled by a single and incomplete dominant gene. The resistance of three strains significantly declined when spraying was suspended for 10 months, and following spraying for fifteen successive times with the 3 insecticides respectively resulted in recovery of their resistance to the corresponding insecticide to different extents.

Key words: Tetranychus urticae Koch, fenpropathrin, omethoate, clofentezine, resistance, genetic analysis