Spinosad, a reduced-risk pesticide derived from a bacterial fermentation product, is effective on stored hard red winter wheat against the lesser grain borer, but not against the red flour beetle. We hypothesize that the method of exposure and insect feeding habits contribute to the differences in susceptibility to the pesticide. In order to verify this hypothesis, adults and first instars were exposed to wheat and glass (petri) dishes treated with spinosad at 0.1 and 1 mg/ml. Time mortality curves were generated to estimate LT50s. In addition, adults and first instars were placed on clean whole wheat, cracked wheat, and wheat flour treated with 0.1 and 1 mg/ml of spinosad and checked after 7 and 14 days to determine mortality. The impacts of exposure method and grain condition on susceptibility were assessed based on LT50 comparisons and mortality after 7 and 14 days.
Species 1: Coleoptera Bostrichidae Rhyzopertha dominica (lesser grain borer)
Species 2: Coleoptera Tenebrionidae Tribolium castaneum (red flour beetle)
Keywords: stored wheat, pesticide
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