Cyhexatin and Propargite Resistance in Populations of Spider Mites (Acari: Tetranychidae) from California Almonds

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Abstract
Cyhexatin (Plictran 600 Flowable) or propargite (Omite 30 Wettable Powder) resistances or both were detected using a residual-bioassay procedure in spider mite (Tetranychus spp.) colonies collected from California almonds. Cyhexatin-susceptible Tetranychus urticae Koch and Tetranychus pacificus McGregor responded with identical probit lines. Significant cyhexatin resistance was only detected in T. pacificus. Propargite-susceptible T. urticae were 8-fold more susceptible to propargite than the most susceptible T. pacificus colony collected. Propargite-resistant individuals of both T. urticae and T. pacificus were found. Colonies collected in the field were heterogeneous in their response to cyhexatin and propargite and contained varying frequencies of susceptible types.