Efficacy of Acanthus montanus Extracts as Protectants of Maize Grains against Maize Weevil, Sitophilus zeamais (Motschulsky 1855) [Coleoptera: Curculionidae]

The insecticidal activity of Acanthus montanus leaf extracts against maize weevil, Sitophilus zeamais, was examined using different extraction solvents, including methanol, ethanol, water, acetone, petroleum ether, and n-hexane. The extracts were evaluated for their effects on weevil mortality, oviposition, and adult emergence, as well as their capacity to protect maize grains during prolonged storage. The results showed that weevil mortality increased with longer exposure to the extracts. The ethanol extract was the most effective, causing 100% mortality at eight day after treatment, a value significantly higher than those recorded for n-hexane (83.20%), petroleum ether (84.25%), acetone (80.15%), steam distillate (94.25%), and methanol (88.50%) extracts. All A. montanus extracts significantly reduced oviposition and adult emergence of S. zeamais. In terms of grain protection, all solvent extracts provided more than 100% protection to treated maize grains, except for the n-hexane and steam distillate treatments, which recorded grain damage levels of 6.40% and 5.50%, respectively. The treatments did not adversely affect seed viability, as high germination rates were recorded in all treated grains. Maize grains treated with n-hexane extract showed 100% germination, followed by methanol (95.75%), petroleum ether (90.50%), ethanol (90.0%), and steam distillate (80.15%). Overall, the findings indicate that A. montanus leaf extracts are highly effective in managing S. zeamais infestations in stored maize and could serve as an environmentally friendly alternative to synthetic insecticides.