Protection of Stored Common Bean and Maize Grains Using Optimally Synthesized Biosilica from Rice Husk Ash

Losses provoked by insect pests on stored cereals and legumes contribute immensely to reduce food security, especially in rural communities in Sub-Saharan Africa. The application of integrated control strategies, involving the use of synthetic pesticides, is often expensive and hazardous to humans and the environment. This study was conducted to optimize the production and use of biosilica from rice husk ashes, for the control of Sitophilus zeamais and Acanthoscelides obtectus, major insect pests of stored maize and common bean grains. The amorphous nature of the derived silica molecules coupled with the silanol and siloxane groups on their surfaces seemed to account for silica’s insecticidal effects on the pests, which were more on A. obtectus on common beans than S. zeamais on maize grains, with full mortalities obtained at doses of about 1.25 g per 50 g bean seeds and about 2.25 g per 50 g maize seeds, within 3 and 12 days, respectively. Similarly, the daily lethal dose (LD₅₀) of silica powder required to obtain the mortality of half of the insects was lower on common beans than on maize seeds. The reduced phytotoxic activity of the biosilica on the stored common bean and maize grains indicates therefore that it could make an ecofriendly alternative to conventional protectants for small quantities of stored grains. However, large-scale studies are needed in order to evaluate its potential use in grain storage systems.