Efficacy of stored grain insecticides against 2 pest beetles in rough rice

Insecticidal grain protectants can provide control of pest insects during grain storage, but studies which directly compare the efficacy of insecticides in rough rice are few. We examined methoprene, deltamethrin, commercial formulations of methoprene + deltamethrin, β-cyfluthrin, and diatomaceous earth applied to rough rice over a 6-month period for control of lesser grain borers, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), and rice weevils, Sitophilus oryzae (L.) (Coleoptera: Curculionidae). We found that methoprene, deltamethrin, or a combination of the 2 were the most effective controls of both beetles in 22.7-liter metal containers. Damage mass and beetle mass in methoprene-treated rice were reduced by 38% and 55%, respectively, when compared to the nontreated control. Similarly, the mixture of deltamethrin and methoprene reduced damage mass by 32% and total beetle mass by 45% below that of the nontreated control. Deltamethrin reduced total beetle mass by 38% relative to the nontreated rice. In vial assays, only the combination of deltamethrin and methoprene provided control of R. dominica. Diatomaceous earth had the greatest impact upon S. oryzae, but it did not affect R. dominica. Based on these results, a commercial formulation of deltamethrin and methoprene is likely to provide the best overall control of stored grain beetles, though diatomaceous earth may be effective when use of chemical insecticides is undesirable or when S. oryzae is the sole pest present.