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

item SEHGAL, BLOSSOM - Kansas State University
item SUBRAMANYAM, BHADRIRAJU - Kansas State University
item Arthur, Franklin
item GILL, BIKRAM - Kansas State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2013
Publication Date: 8/1/2013
Publication URL:
Citation: Sehgal, B., Subramanyam, B., Arthur, F.H., Gill, B.S. 2013. Variation in susceptibility of field strains of three stored grain insect species to spinosad and chlorpyrifos-methyl plus deltamethrin on hard red winter wheat. Journal of Economic Entomology. 106(4):1911-1919. DOI:

Interpretive Summary: Grain protectants are insecticides that are applied as the grain is being loaded into a grain bin or elevator silo. In the United States, there is one grain protectant called Storicide II that has only been sold for several years, and another one called spinosad that is registered but not yet sold, but there are no studies evaluating different field strains of stored-grain insects for susceptibility to these new products. We exposed different field strains of several insect species on wheat treated with these two new insecticides. The Storicide II insecticide killed adults of all the various field strains of the insect species and prevented reproduction. The spinosad insecticide was more effective on some species than others, and field strains of some species were harder to kill than the laboratory strains. Results show that field strains of insect species may not be as susceptible to certain insecticides as laboratory strains, and this factor should be taken into account when introducing new grain protectants into management programs.

Technical Abstract: 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 days and progeny production after 42 days. 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 (approx. 6 times) than the laboratory strain. The effective dose for progeny reduction (ED99) of only one R. dominica field strain was significantly greater (approx. 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.