Field strains of the Indianmeal moth, Plodia interpunctella (H¨ıbner); red flour beetle, Tribolium castaneum (Herbst); rusty grain beetle, Cryptolestes ferrugineus (Stephens); and lesser grain borer, Rhyzopertha dominica (Fabricius) were collected from hard red winter wheat stored on farms at two locations in northeast Kansas. Twenty-five adult beetles or 50 eggs of Indianmeal moth were exposed to 100 g of untreated or spinosad treated wheat to examine the susceptibility of these four species to the insecticide. Field strains of Indianmeal moth, red flour beetle, and rusty grain beetle were relatively more tolerant to spinosad than the insecticide-susceptible lab strains. The LC50 and LC95 values for the field strains of the three species were 1.4 ¨C 5.8 and 1.2 ¨C 2.5 times greater than the corresponding values for the laboratory strains. Spinosad treated wheat at 0.5 or 1 mg/kg resulted in 100% mortality against the laboratory strains of Indianmeal moth, rusty grain beetle, and lesser grain borer but not against the field strains. However, LC50 and LC95 values were similar among the three strains of lesser grain borer. Results from this study could be used as baseline data to monitor insecticide resistance among the common stored grain insects in Kansas following future registration and use of spinosad as a stored grain protectant.
Species 1: (red flour beetle, rusty grain beetle)
Species 2: (lesser grain borer)
Species 3: Lepidoptera Pyralidae Plodia interpunctella (Indian meal moth)
Keywords: Stored product insects, Spinosad
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