Spider Mite Species (Acari: Tetranychidae) Response to Propargite: Basis for an Acaricide Resistance Management Program

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Abstract
Spider mites were collected from cotton at 36 locations in the San Joaquin Valley of California, both before propargite had been applied and again late in the season. All populations of Tetranychus turkestani Ugarov & Nikolski, the dominant early season spider mite, were susceptible to propargite. Populations of Tetranychus urticae Koch and Tetranychus pacificus McGregor exhibited a variety of responses from highly susceptible to highly resistant. These levels of resistance were defined by the range and homogeneity of response. Early season T. urticae populations were predominantly susceptible. Late-season collections of T. urticae from the same locations exhibited lower, equal, or increased tolerance to propargite, suggesting instability of resistance. Early and late-season collections of T. pacificus exhibited a consistently higher and narrower range of response to propargite than T. urticae , suggesting a possible natural tolerance to propargite. Field plots demonstrated lack of control with propargite when populations were composed of resistant T. pacificus alone. Cases of multiple resistance to propargite and dicofol were found for both T. urticae and T. pacificus.