Monitoring Dicofol-resistant Spider Mites (Acari: Tetranychidae) in California Cotton

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Abstract
A sampling and bioassay procedure for estimating the frequency of dicofolresistant spider mites (Tetranychus (spp.) in San Joaquin Valley (SJV), California, cotton fields was developed and used to evaluate within-field variability in dicofol susceptibility estimates and to assess dicofol susceptibility in cotton fields throughout the SJV. Criteria were established for describing the severity of dicofol resistance at specific locations; an action threshold was designated based on the observed reliability of susceptibility estimates obtained with the described sampling and bioassay procedure. Monitoring of dicofol resistance throughout the SJV in June, July, and August 1982 detected no dicofol-resistant spider mites for a large percentage of the locations sampled. However, locations with low to very high frequencies of resistant types were detected, and the proportion of locations with detectable levels of resistant types increased late in the season. Dicofol continues to be used successfully for integrated management of spider mites throughout most of the SJV, and a project to monitor and manage dicofol resistance is underway.