Insecticidal efficacy of two candidate diatomaceous earth powders against the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae)

Abstract

The insecticidal efficacy of amorphous silica powders 1 and 2 with different physical and elemental compositions were evaluated against the lesser grain borer, Rhyzopertha dominica (F.) using concrete arenas. The particle diameter and shape characterization (circularity, elongation, aspect ratio, and convexity) of the two silica powders were performed using Morphology G3 instrument. The particle diameter and shape characteristics (circularity and elongation) of silica powder 1 were significantly higher compared to silica powder 2. However, these factors did not influence the efficacy of silica powders against R. dominica. Silica powder 2 showed higher mortality at lower application rates and shorter exposure times compared to silica powder 1. The efficacy of silica powder 2 was due to its higher oil adsorption capability, low pH, and high silicon dioxide content compared to silica powder 1. Adult progeny production was inversely related to the powder application rate. Silica powder 2 was more effective on R. dominica in inhibiting adult progeny production at 0.25 g/m2. Lower percentages of insect-damaged kernels and grain weight loss were observed at lower application rates (0.10–0.20 g/m2) following exposure to silica powder 2 compared to silica powder 1, which required higher application rates (2.0–3.5 g/m2). Overall, silica powder 2 demonstrated superior efficacy against R. dominica in terms of mortality, progeny production, insect-damaged kernels, and grain weight loss.