Abstract: 【Objective】The objectives of this study are to survey the sensitivity of different populations of Tetranychus urticae Koch to the acaricides in Beijing area, as well as the relationship between their sensitivity to the acaracides and the activity of resitance-related enzymes. 【Method】 Bioassays of four frequently used acaricides of bifenazate, abamectin, spirodiclofen and pyridaben to five field populations of the T. urticae, i.e. Fangshan, Huairou, Changping, Yanqing and Pinggu of Beijing area, were conducted by using modified slide-dip method. Bifenazate resistance-related mutations were detected by PCR amplification and sequencing of the CYTB gene from individual specimens. Additionally, the activities of four resistance-related enzymes of cytochrome P450 monooxygenases, acetylcholinesterase (AChE), carboxylesterase (CarE) and glutathione S-transferase (GST) were tested by microplate assay in microplate reader for the five populations.【Result】All of the five field populations of Fangshan, Huairou, Changping, Yanqing and Pinggu were sensitive to bifenazate, with LC50 of 2.4880, 6.4693, 6.2398, 0.7882 and 14.7783 mg•L-1, respectively, followed by the abamectin, with LC50 of 22.4712, 35.4431, 14.5260, 15.4904 and 14.0023 mg•L-1, respectively. T. urticae showed low sensitivity to the spirodiclofen and pyridaben in the five tested populations. In populations of Fangshan, Huairou, Changping, Yanqing and Pinggu, the LC50 of spirodiclofen was 49.6833, 81.8826, 72.9609, 204.4609 and 1 433.5137 mg•L-1, respectively, whereas that of pyridaben was 202.6902, 806.8324, 375.3518, 188.3234 and 2 310.9040 mg•L-1, respectively. The sensitivity of the AChE, CarE and GST of Yanqing population was higher than that of other populations, with a value of 14.9508 U/(mg protein), 0.2271 μmol?mg-1 protein?30 min-1 and 58.2962 U/(mg protein), respectively. The cytochrome P450 monooxygenases of Huairou population was significantly lower than that of other populations with a value of 1.4272 μmol?mg-1 protein?30 min-1. There was no linear relationship between the toxicity of bifenazate, abamectin, spirodiclofen and pyridaben and the activities of cytochrome P450 monooxygenases, AChE, CarE and GST. One individual from Huairou population with one site mutation on the CYTB gene (the first codon position of the 126th amino acid was changed from G to A) was detected in 288 individuals of five populations, which lead the amino acid Gly mutated into Ser. The low level of resistance-related mutation in the detected populations of the T. urticae was consistent with their high sensitivity to the bifenazate. 【Conclusion】 T. urticae in Beijing area showed highest sensitivity to the bifenazate, followed by the abamectin, and lastly to spirodiclofen and pyridaben. The sensitivity of T. urticae to the four tested acaricides is not linearly related to the activity of cytochrome P450 monooxygenases, AChE, CarE and GST. The PCR detection of resistance-related mutation indicated that the Huairou population has high risk to generate resistant individuals to the bifenazate. PCR method could fastly and accurately detect the development of acaracide resistance than the bioassay method. In the controlling practice, the pyridaben should not be used, the spirodiclofen should be avoided, and abamectin and bifenazate could be used alternatively.

Key words: Tetranychus urticae Koch , bioassay , enzyme activity , bifenazate