Use of essential and vegetable oil-impregnated rice husk silica to control Sitophilus zeamais (Motschulsky) on stored maize (Zea Mays L.) seeds

Abstract Although neem ( Azadirachta indica ) and rosemary ( Rosmarinus officinalis ) oils have repellent properties against stored grain insects, their effectiveness is limited due to their volatility and sensitivity to heat and light, which causes them to be released from grains quickly. In this study, a bioinsecticide was formulated by impregnating optimally silica, derived from rice husk ash, with mechanically extracted oil from neem and hydro-distilled rosemary. The resulting formulation was tested for its ability to control Sitophilus zeamais (Motschulsky) during storage of maize grain. The silica, which had some surface functional groups, controlled the populations of S. zeamais in stored maize grains within 12 days of exposure. Compounding the silica with neem and rosemary oils further maintained these functional groups and produced a synergistic effect in controlling the pests in stored maize grains. These results were only comparable to those obtained with the use of synthetic pesticides after 5 days of application. The results indicate that the inert surface functional groups caused the cuticles of the insect pests to dehydrate, ultimately leading to their death. Overall, silica derived from rice husk ash and impregnated with neem and rosemary oils could be a promising alternative to synthetic pesticides for storing maize grains, as it retained more than 85% of their germinative capacity even after prolonged storage.