Laboratory trials were conducted to determine the effectiveness of diatomaceous earth (DE) applied to stored rough rice. The rice was treated with the label rates of two commercial formulations of DE, and adult lesser grain borers, Rhyzopertha dominica, were exposed on the treated rice for 1, 2, 3, 5, and 7 days at 27 and 32 oC, 57 and 75% relative humidity. Upon completion of the exposure interval, the insects were removed and mortality was assessed. The rice was held at the same exposure conditions for an additional 8 weeks to record F1 progeny production. Mortality increased with exposure interval but did not exceed 68% for any treatment combination. The number of F1 adults also increased with exposure interval, and more F1 adults were produced on rice stored at 32 than at 27 oC. In addition, there were more F1 adults in rice held at 75 than at 57% relative humidity. DE alone failed to give complete suppression of R. dominica, and F1 progeny were produced on rice treated with the label rates of both commercial formulations of DE. Results show a decrease in efficacy compared with previous studies in which R. dominica was exposed on wheat treated with DE. It may be necessary to apply DE in combination with other reduced-risk insecticides to control R. dominica on rough rice.
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