Establishment of base line values for susceptibility of Tetranychus urticae Koch to major acaricidesover successive generations

The susceptible culture of two spotted spider mite, T. urticae Koch was successfully maintained on mulberry leaves under laboratory condition without exposing to any acaricides for two years designated as the susceptible reference population. The susceptibility of the spider mite to selected acaricides viz., fenazaquin, propargite, chlorfenapyr, dicofol, diafenthiuron, spiromesifen and abamectin was determined after every five generations starting from 118th to 128th generation. The LC50 values of different acaricides in 128th generation were 0.18 ppm for fenazaquin, 0.20 ppm for propargite, 0.29 ppm for spiromesifen, 0.32 ppm for abamectin, 0.42 ppm for chlorfenapyr and 0.30 ppm for diafenthiuron and dicofol. This laboratory population was the reference population and the dose-mortality values estimated for laboratory population during 128th generation was considered as base-line susceptibility of spider mite for corresponding acaricide and was further used to estimate the level of resistance in different field population.