Resistance of Tetranychus urticae (Koch) to acaricides applied on strawberries in Zamora, Michoacan, Mexico
The Valley of Zamora, Michoacán, is the major strawberry (Fragaria x ananassa Duchesne) growing region of México. In this valley as in many other regions of México, the red spider mite Tetranychus urticae Koch is the main pest of this crop; although its control is mainly based on the use of acaricides and its level of resistance to these compounds is unknown. Therefore, the response of a spider population to abamectine, endosulfan, phenpropatrin, oxidemeton methyl and propargite, was evaluated. The red spider mite field population exhibited resistance to abamectine, endosulfan and oxidemeton methyl, whose LC95 values were 4986, 211389, and 390675 mg L-1, which correspond to RR95 values of 224.6, 110.2 and 26.2-fold. In contrast, the population was susceptible to propargite (RR95=0.4-fold) and phenpropatrin (RR95=11.0-fold). These results coincide with the frequency of acaricide use in the field. In the cases where resistance was detected, growers apply acaricides at an average of 30 times per crop season every crop cycle and perceive that their field effectiveness is lower than it was originally.