Variability in Toxicity of Propargite to Spider Mites (Acari: Tetranychidae) from California Almonds

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Abstract
Variability in propargite (Omite) toxicity in spider mites (Tetranychus spp.) from California almonds was determined using a residual-bioassay procedure. T. pacificus McGregor collected from the Bakersfield area in September 1983 had an LC50 of 484 ppm (95% CL, 315–678) propargite. Spider mites from this culture which were selected twice using propargite-treated leaves (10,000 ppm) had an LC50 of 11,466 ppm (95% CL, 9,159-15,284) propargite (cotton seedlings) and an LC50 of 14,861 ppm (95% CL, 12,720-18,651) (almond foliage). In a topical bioassay, an average of 32.5% (SD 13.9%) of the selected T. pacificus were killed by 1,621 ppm propargite, the highest registered tank-mix rate for California almonds. T. pacificus collected in a June 1984 survey of California almond growing regions were found primarily in the southern part of the Central Valley. These T. pacificus were more tolerant of propargite (when tested using the residual bioassay) than T. unticae Koch collected in the survey. Substantial differences in propargite susceptibility were found between cultures of both species. These results suggest that propargite resistance may pose a problem in almonds, especially with T. pacificus.