Insecticidal effect of spinosad dust against four stored product insect species in different grain commodities

Spinosad is a new bacterial-based insecticide, which is registered for used in several crops. However, most available experimental data are for liquid formulations, while very little is know about applying spinosad as a dust. The effectiveness of spinosad dust formulation (0.125% a.i.) against stored-product insects was assessed on different commodities. The insects were the red flour beetle, Tribolium castaneum (Herbst), the lesser grain-borer, Rhyzopertha dominica (F.), the rice weevil, Sitophilus oryzae (L.) and the saw-toothed weevil, Oryzaephilus surinamensis (L.). The spinosad dust was tested at the label rate of 1 mg (a.i.)/kg. The 7-day adult mortality of R. dominica, S. oryzae, and O. surinamensis, exposed to spinosad, was >= 90% on maize, wheat, and sorghum. Rhyzopertha dominica was the most susceptible of the three species tested. Progeny production of all three species was significantly lower on spinosad-treated grains than on untreated grains. Mortality of T. castaneum adults was < 13% on spinosad-treated maize and sorghum, and 65% on treated wheat, but progeny production was significantly lower on all three grains in comparison with the untreated ones. Based on these results, spinosad dust could be used as an effective alternative to traditional grain protectants, but its insecticidal effect is influenced by several factors.