Effect of particle size of two Iranian diatomaceous earth deposits and a commercial product on Sitophilus granarius (Col.: Dryophthoridae)

Laboratory bioassays were carried out to study the insecticidal efficacy of two Iranian diatomaceous earths (DEs) and SilicoSec® formulation against Sitophilus granarius (L.). Four different particle sizes of DEs were applied at five concentrations. The mortality was counted 2, 5 and 7 days after exposure. The experiment was carried out at 27 ± 1°C and 55 ± 5% relative humidity in continuous darkness. For SilicoSec® and Mamaghan with less than 37 µm particle size, 500 ppm was sufficient to cause 100% mortality after 5 days of exposure. While in case of Maragheh deposit with the same particle size, complete mortality was recorded at 1000 ppm after 5 days. LC50 values indicated that SilicoSec® and Mamaghan with < 37 µm particle size were the most efficient DE samples against S. granarius. In most cases, the efficacy of DEs increased with decreasing particle size. The visual observation of scanning electron microscopy (SEM) images showed that SilicoSec® has more attachment to insectsâ body. However, the adhesiveness of DE particles cannot be the main indicative of their insecticidal effectiveness