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Variation in susceptibility of field three stored grain insect species to spinosad and chlorpyrifos-methyl plus deltamethrin on hard red winter wheat

Blossom Sehgal, Bhadriraju Subramanyam, Frank H. Arthur, Bikram S. Gill
Journal of economic entomology 2013 v.106 no.4 pp. 1911-1919
Oryzaephilus surinamensis, Rhyzopertha dominica, Tribolium castaneum, adults, chlorpyrifos-methyl, defense mechanisms, deltamethrin, dose response, hard red winter wheat, lethal dose, monitoring, mortality, progeny, spinosad, storage insects, stored grain, Kansas
Spinosad and chlorpyrifos-methyl plus deltamethrin efficacy at labeled rates on hard red winter wheat was evaluated against 11 strains of the red flour beetle, Tribolium castaneum (Herbst); six strains of the sawtoothed grain beetle, Oryzaephilus surinamensis (L.); and two strains of the lesser grain borer, Rhyzopertha dominica (F.), collected mostly from farm-stored grain in Kansas. Adults of each species were exposed to wheat treated with spinosad at 1 mg(AI)/kg or chlorpyrifos-methyl plus deltamethrin at 3 plus 0.5 mg (AI)/kg, respectively. Adult mortality was assessed after 7 and 14 d and progeny production after 42 d. Spinosad did not provide complete mortality or progeny suppression of T. castaneum and O. surinamensis field strains, but was effective against field strains of R. dominica. Chlorpyrifos-methyl plus deltamethrin produced complete mortality and progeny suppression of field strains of all three species. The two least susceptible T. castaneum and O. surinamensis field strains and the two R. dominica strains were selected for dose-response tests with spinosad. The LD99 values for T. castaneum and R. dominica field strains were similar to that of the corresponding laboratory strains. Corresponding values for the two O. surinamensis field strains were significantly greater (≈6 times) than the laboratory strain. The effective dose for progeny reduction (ED99) of only one R. dominica field strain was significantly greater (≈2 times) than the laboratory strain. Baseline data on the susceptibility of field strains of the three insect species to spinosad will be useful for monitoring resistance development when this product is commercially released as a grain protectant.