Residual Toxicity of Iranian Diatomaceous Earth against Rhyzopertha dominica and Tribolium confusum on Concrete, Galvanized Steel, and Mosaic Surfaces

Diatomaceous Earths (DEs) have a long history for on-farm and commercial grain storage, hygiene, and structural treatment. Structural treatments by DEs have shown to be useful for eradication of residual insect infestations in storage facilities. In this study, the residual toxicity of different DE formulations was examined against adults of Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae) on different surfaces including concrete, galvanized steel, and mosaic. The surfaces were treated with 0.2 mg cm-2 concentration of DE formulations that included SilicoSec®, Protect-It, and an Iranian DE formulated from a Mamaghan Mine, Iran, supplemented with an amorphous silica gel product to enhance efficacy. The residual toxicity of DEs was assessed at 7, 15, 30, 45, and 60 days post-treatment. The mortality was determined after 1, 3, 5, and 7 days of insects’ exposure to each surface. According to the results, the most effective product proved to be SilicoSec® when compared to Protect-It and the Iranian Mamaghan DE. The toxicity and persistence of DE formulations were higher on the galvanized steel compared to that achieved on the concrete and mosaic surfaces. Nevertheless, the results demonstrated that an Iranian DE containing 10% locally available amorphous silica is capable of controlling R. dominica and T. confusum in warehouses and other storage facilities. However, additional studies are needed to confirm these findings.