Synergistic efficacy of three botanical powders against Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) in maize grain storage

Abstract Sitophilus zeamais Motschulsky infestation causes severe post-harvest losses of grains in Ghana leading to a major reduction in the quality and economic value. The synergistic efficacy of three botanical powders against adult S. zeamais was assessed. The botanical powders of Aframomum melegueta, Pipper nigrum, and Zingiber officinale in unmixed forms as positive controls, and admixed forms and the synergy were evaluated against the adult Sitophilus zeamais in stored maize grains at different dosage rates. The botanical powders in admixed and unmixed forms were used to treat 100g of maize grains infested with 40 adult S. zeamais at dosage rates of 0g, 10g, 20g, and 30g. The treatments were kept in glass jars covered with muslin cloth for 28 days post-exposure. The experiment was laid out in a completely randomized design. The highest mean adult mortality was recorded from admixed alligator pepper + black pepper at 20g and 30g at day 21, followed by the admixed alligator pepper + black pepper at 30g at day 28. The lowest mean maize grain damage in the admixed botanicals was recorded from alligator pepper + black pepper at 30g exposure at day 28. From the results, we found that the admixed powders demonstrated anti-feedant properties. The study found synergy between the admixed botanical powders in affecting adult S. zeamais mortality and the prevention of grain damage. Their effectiveness in affecting adult S. zeamais mortality and maize grain damage is dose dependent. Farmers could apply the botanical powders in admixed forms to exert stronger efficacy against S. zeamais.