Efficacy of two amorphous silica powders applied to hard red spring wheat against the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

Silica-based inert dusts, such as diatomaceous earth formulations, have emerged as potential alternatives to chemical insecticides in stored product protection against insect pests. In this study, we evaluated the efficacy of two amorphous silica powders, silica powder 1 and silica powder 2, applied to hard red spring wheat against the rice weevil, Sitophilus oryzae (L.). Laboratory experiments were performed using a 2 x 5 factorial design by exposing 25 adults of S. oryzae to 100 g of wheat in glass jars admixed with five different application rates, 0 (untreated control), 0.05, 0.15, 0.25, and 0.30 g/kg of silica powders 1 and 2. Untreated and treated wheat in jars were held inside a growth chamber at 28 degrees C and 65% r.h. with a light:dark photoperiod of 14:10 h. Each powder and application rate combination was replicated five times. Mortality assessments were made after 14 d, and the data on adult progeny production, insect-damaged kernels and grain weight loss were recorded at 42 d. Complete mortality of S. oryzae occurred after 14 d at an application rate of 0.25 g/kg of silica powder 2. No adult progeny production, insect-damaged kernels and grain weight loss were observed when adults were exposed to 0.30 g/kg of silica powder 1 and 0.25 g/kg of silica powder 2. Silica powder 2, characterized by high oil absorption capability and low pH (<8.5), proved effective against S. oryzae than silica powder 1. The findings underscore the potential of both powders, particularly silica powder 2, in effectively managing S. oryzae infestations in stored wheat.