Laboratory and Field Investigations of Spider Mite (Acari: Tetranychidae) Resistance to the Selective Acaricide Propargite

Abstract

Evaluations of spider mite, Tetranychus spp., susceptibility to propargite, initiated in response to grower concerns about potential resistance in the field, revealed 0- to 42-fold resistance in Tetranychus urticae Koch in a whole-plant residual bioassay. Surveys of spider mites collected from throughout the San Joaquin Valley in June and August 1984 indicated that propargite-resistant phenotypes exist throughout the San Joaquin Valley; 22 of 32 sites sampled in August contained individuals that survived 1,000 ppm in residual bioassays. However, resistant phenotypes were much less common in June than August; only 3 of 23 sites sampled in June had survivors of 1,000 ppm. The shift in susceptibility of populations during the season was shown to result from intraspecific increases in frequency of resistant phenotypes or interspecific shifts in spider mite species abundance, or both. Although resistant phenotypes of T. urticae and Tetranychus pacificus McGregor were discovered, no propargite-resistant Tetranychus turkestani Ugarov and Nikolski were found. Widely differing susceptibilities to propargite exist both within and between T. urticae and T. pacificus populations. A dicofol-resistant laboratory culture of T. urticae originating from the San Joaquin Valley and maintained under pressure for 2 yr possessed a 26-fold resistance to propargite. Although resistance to propargite was discovered in the laboratory, we did not observe diminished performance of propargite in field trials at a location possessing spider mites with up to 45% survivorship of the discriminating concentration of 1,000 ppm propargite.