Efficacy of two amorphous silica powders applied to soft red winter wheat against the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae)

Abstract

The increased demand for residue-free grains and development of insect resistance to insecticides has led to a surge in the utilization of diatomaceous earths as grain protectants. Diatomaceous earth formulations, effective at lower application rates, are crucial for managing stored product insects without compromising grain quality. In this study, the efficacy of two different amorphous silica powders applied to soft red winter wheat was tested against the lesser grain borer, Rhyzopertha dominica (F.). Twenty adults of R. dominica were exposed to 100 g of organic soft red winter wheat admixed with varying application rates (0 for the untreated control, 0.05, 0.1, 0.15, and 0.20 g/kg) of silica powders 1 and 2. Mortality assessments were made after 14 d of exposure, and data on adult progeny production, insect-damaged kernels, and grain weight loss were determined at 42 d. Exposing R. dominica adults to wheat treated with 0.20 g/kg of silica powder 1 resulted in a mean ± SE of 94.5 ± 5.5% mortality and 1.3 ± 1.3 adult progeny production. Insect-damaged kernels and grain weight loss caused by R. dominica exposed to 0.20 g/kg of silica powder 1 were 0.19 ± 0.19 and 0.1 ± 0.1%, respectively. Exposure of R. dominica adults exposed to wheat mixed with 0.20 g/kg of silica powder 2 resulted in complete mortality, with no observed adult progeny production, insect-damaged kernels, or grain weight loss. Overall, silica powder 2 exhibited greater efficacy than silica powder 1, and this superior performance can be attributed to its higher oil adsorption capability and low pH (<8.5) value.