Characterization of Resistance to Dicofol in Spider Mites (Acari: Tetranychidae) from New York Apple Orchards

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Abstract
Susceptibility to dicofol of populations of Panonychus ulmi (Koch) and Tetranychus urticae Koch from New York apple orchards was estimated in 1985-1986 with a whole-plant residual bioassay. Nine of 14 P. ulmi populations collected from throughout the state in 1985 had 1,000-fold resistance to dicofol residues. Whereas susceptible mites were approximately equally affected by residual or topical exposure to dicofol, resistant mites (possessing a > 1,000-fold resistance to residual exposure) were < 15-fold resistant to topical contact with dicofol. Field trials conducted at orchard locations with P. ulmi resistant or susceptible to dicofol (as shown by bioassay results) illustrated that the resistance resulted in reduced efficacy of dicofol treatments. Advantages of the dicofol-spider mite system for evaluating resistance dynamics and resistance management strategies are described.