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Title: Effects of Short Exposures to Spinosad-Treated Wheat or Maize on Four Stored-Grain Insects

item Arthur, Franklin
item Throne, James

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2009
Publication Date: 2/19/2010
Citation: Athanassiou, C.G., Arthur, F.H., Throne, J.E. 2010. Effects of Short Exposures to Spinosad-Treated Wheat or Maize on Four Stored-Grain Insects. Journal of Economic Entomology. 103: 197-202.

Interpretive Summary: Insecticides are one tool for controlling insect pests of stored grain, but we are losing many stored-grain insecticides because of insect resistance and registration issues. We evaluated control of four insect pests of stored wheat and corn after short exposures to a new insecticide, spinosad, which has low mammalian toxicity. Short exposures may occur because a grain bulk may not be completely treated with insecticide. The lesser grain borer was very susceptible to spinosad and no progeny were produced after eight hours exposure. There was moderate mortality of adult rice weevils, but progeny production was not impacted by spinosad. Spinosad had little effect on red flour beetles or the psocid Lepinotus reticulatus. This information will help grain storage managers select protectant insecticides for control of stored-grain insects.

Technical Abstract: The effect of short exposures to spinosad-treated wheat and maize was evaluated against adults of four stored-product insects: the lesser grain borer, Rhyzopertha dominica (F.), the rice weevil, Sitophilus oryzae (L.), the red flour beetle, Tribolium castaneum (Herbst), and the psocid Lepinotus reticulatus (Enderlein). Adult mortality was recorded after 0, 2, 4, 8, 16, and 40 h on commodities treated with 1 ppm of spinosad (immediate mortality). Surviving individuals were removed and placed on untreated wheat or maize, and mortality was recorded again 7 d later (delayed mortality). Progeny production was determined 65 and 35 d later for the beetles and psocids, respectively. Rhyzopertha dominica was most susceptible, and immediate mortality after 40 h reached 78 and 72% on wheat and maize, respectively. Seven days later, all adults that had been exposed for >2 h were dead on both commodities. Progeny production was reduced, and no progeny were found when parental adults had been exposed for >8 or >4 h on wheat and maize, respectively. For S. oryzae, 40-h exposures increased delayed mortality on both wheat and maize, but progeny production still was high. Generally, no effect of short exposures was observed for T. castaneum. Lepinotus reticulatus progeny production was not avoided despite increased parental mortality on maize. More progeny were found on wheat than on maize, except for T. castaneum. The results indicate that R. dominica is very susceptible after short exposures to spinosad-treated substrate, but the other species can survive and reproduce at the exposure range examined.