Laboratory Evaluation of Spice Powders and Extracts for Biocontrol of Maize Weevil (Sitophilus zeamais) in Stored Maize Seeds

Background and Objective: Maize (Zea mays) is a versatile grain with high genetic yield potential, originally domesticated in Central America. It thrives across diverse seasons and ecological zones, making it a globally significant crop. The study investigated the toxicity of seed powders and extracts derived from Curcuma longa (turmeric) and Piper guineense (African black pepper) for their potential to control maize weevils (Sitophilus zeamais) in stored maize grains under laboratory conditions. Materials and Methods: Powders were applied at doses of 0.2, 0.4, 0.6, 0.8, and 1.0 g/20 g of maize, while extracts were evaluated at concentrations of 0.2, 0.4, 0.6, 0.8, and 1.0 mL/20 g of maize. Key parameters assessed included insect mortality, oviposition rates, adult emergence, weight loss, seed damage, and the weevil perforation index (WPI). The laboratory experimental data were analyzed using Analysis of Variance (ANOVA) with a significance level of 5%. Results: The results revealed that P. guineense powder was the most effective, causing 81.7% adult mortality at 1.0 g/20 g within 24 hrs. This was followed by C. longa powder, which achieved 70% mortality at the same dose. Remarkably, the extracts were more toxic than the powders, with P. guineense extract achieving 96.7% mortality at 1.0 mL/20 g within 24 hrs. Similarly, C. longa extract induced 80% mortality under comparable conditions. Additionally, powders and extracts from the two botanicals completely inhibited oviposition, adult emergence, weight loss, and seed damage, demonstrating their effectiveness in suppressing the reproductive and developmental processes of the weevils. Conclusion: These findings underscore the potential of C. longa and P. guineense as viable alternatives to synthetic pesticides in managing S. zeamais infestations in stored maize grains. Their use as botanical insecticides offers an eco-friendly, cost-effective, and sustainable approach to reducing post-harvest losses and preserving seed quality. This could significantly enhance food security in developing countries, where maize is a staple food crop and post-harvest pest infestations often lead to substantial losses.