The residual efficacy of the enhanced diatomaceous earth (DE) formulation DEBBM alone and in combination with Beauveria bassiana (Hypocreales: Cordycipitaceae) or with the neonicotinoid insecticide imidacloprid against Tribolium castaneum (Coleoptera: Tenebrionidae), Rhyzopertha dominica (Coleoptera: Bostrychidae), Cryptolestes ferrugineus (Coleoptera: Laemophloeidae), and Liposcelis paeta (Psocoptera: Liposcelididae) was investigated in the laboratory. The combination treatments were more effective compared to the single treatments against all examined species. The combinations of DEBBM and imidacloprid and imidacloprid with the highest dose rate of B. bassiana provided the highest mortality values against all tested species for 90 days of storage period. The combination of DEBBM plus B. bassiana resulted to the highest mortalities and to the lowest offspring production of all combinations tested after 180 days of storage. Mortality of adults for each test insect species was decreased over the storage period of 6 months, and the progeny production was increased with the extended storage period. Among the tested insect species, L. paeta was the most susceptible to all three grain protectants followed by C. ferrugineus, R. domina, and T. castaneum. The findings of the current study suggest that the use of DEBBM, imidacloprid, and B. bassiana as grain protectants may provide elevated control of major stored-grain insect species during a prolonged period of storage.

The effectiveness of Grain-Guard, an improved form of diatomaceous earth (DE), with low risk to the environment, was evaluated against the storage pests Liposcelis paeta, Cryptolestes ferrugineus, Rhyzopertha dominica, and Tribolium castaneum on four grain commodities, wheat, rice, maize and sorghum. The overall mortality of stored grain pests increased with the rise of application rate and exposure intervals of diatomaceous earth and decreased over 120 days of post-treatment period. Our results revealed that mortality of adults 14 days post-disclosure was > 80% on wheat at the start of post-treatment than rice, maize, and sorghum, respectively. During the first 60 days of post-treatment, adult mortality increased, whereas later on, a steady decrease in adult mortality was observed. Considerable differences in dose rates were observed on mortality levels along with grain commodities. Following 14 days of exposure, all adults of four species were dead on wheat at 100 ppm and on rice at 150 ppm except maize and sorghum. The suppression of progeny was noticeably higher at the beginning of post-treatment duration while after 60-days of post-treatment, progeny numbers started to increase with the rise in post-treatment durations. This new improved DE formulation was found to be effective at dose rates that are extensively lower than required with previous DE formulations and will contribute to lower the risk of health and environment.