CONTROL OF LESSER GRAIN BORER (COLEOPTERA, BOSTRICHIDAE) WITH CHLORPYRIFOS-METHYL, BIORESMETHRIN, AND RESMETHRIN - EFFECT OF CHLORPYRIFOS-METHYL RESISTANCE AND ENVIRONMENTAL DEGRADATION

Soft red winter wheat treated with 6 ppm chlorpyrifos-methyl, 2 and 5 ppm resmethrin, and 2 and 5 ppm bioresmethrin was stored under ambient conditions for 10 mo. Six field strains of lesser grain borer, Rhyzopertha dominica (F.), with chlorpyrifosmethyl resistance frequencies of 21-100% and a susceptible laboratory strain were confined on the treated wheat at regular intervals during storage. Three highly resistant strains were not controlled by the chlorpyrifos-methyl residues. Survival in the remaining three field strains and the laboratory strain increased as the storage interval increased. Chlorpyrifos-methyl resistance frequencies were correlated with residual mortality only immediately after insecticide application. Residues from the bioresmethrin and resmethrin applications controlled all six field strains for 10 mo.