Solanum incanum Leaf Powder Exhibits High Insecticidal Efficacy Against Sitophilus zeamais in Stored Maize Seeds: Implications for Sustainable Pest Management

Introduction The maize weevil, Sitophilus zeamais Motschulsky, represents one of the most economically devastating storage pests affecting cereal seeds in tropical regions. However, dependence on synthetic insecticides poses environmental, health, and economic constraints that limit their sustainable use in smallholder farming systems. This study evaluated the insecticidal efficacy of 10 botanical powders against S. zeamais in stored maize seeds over 56 days, examining mortality rates, dose-response relationships, temporal efficacy dynamics, and seed protection capacity. Methods Laboratory bioassays conducted at Sokoine University of Agriculture employed a completely randomised design with botanical treatments (Cajanus cajan, Azadirachta indica, Eucalyptus globulus, Cymbopogon citratus, Lantana camara, Ricinus communis, Ocimum basilicum, Hyptis suaveolens, and Solanum incanum leaves and fruits) at four concentrations (5, 10, 15, and 20 g per 200 g maize seeds) compared against Actellic Super Dust® (pirimiphos-methyl 16 g/kg + permethrin 3 g/kg) and untreated controls. Results Two-way factorial analysis of variance (ANOVA ) revealed significant main effects for botanical type (p < 0.001) and concentration (p < 0.001), with a significant interaction (p = 0.019) indicating differential dose-response patterns among species. Solanum incanum leaf powder exhibited the strongest efficacy, achieving 62.52-84.09% mortality across concentrations compared with 100% for the synthetic standard. Two-way repeated-measures ANOVA with Greenhouse-Geisser correction demonstrated significant effects for treatment (p < 0.001), storage interval (p < 0.001), and their interaction (p < 0.001), confirming that temporal dynamics varied among botanical classes. Solanum incanum retained 61% of its initial 14-day efficacy at 56 days, demonstrating superior temporal stability attributed to the environmental persistence of glycoalkaloid compounds. In contrast, terpenoid-based E. globulus lost 84% of initial efficacy over the same period, reflecting volatile compound dissipation. Solanum incanum leaf powder provided seed protection statistically equivalent to synthetic standards at 56 days (0.25% versus 3.55% weight loss in untreated controls). The significant treatment × storage interval interaction for weight loss (p < 0.001) indicates that protective capacity varies differentially across time. Conclusion These findings establish S. incanum as a promising candidate for botanical insecticide development, offering smallholder farmers an accessible, locally available alternative for integrated pest management in stored maize seed systems. The widespread distribution of this species throughout tropical Africa, combined with simple processing requirements aligned with traditional practices, positions S. incanum as a practical solution for resource-constrained households where synthetic insecticides remain economically prohibitive.