Entomocidal Properties of Some Spices as Protectants of Paddy Rice against Rice Weevil, Sitophilus oryzae (Coleoptera: Curculionidae) during Storage

Background and Objective: The toxicity effects of seed powders and extracts of Piper guineense, Aframomum melegueta, and Syzygium aromaticum were evaluated for their insecticidal properties against the rice weevil, Sitophilus oryzae. The study aimed to assess the potential of these spices as eco-friendly protectants of stored paddy rice by determining their efficacy in controlling S. oryzae under laboratory conditions. Materials and Methods: Experiments were conducted at an ambient temperature of 28±2°C and 75±5% relative humidity. The seed powders were tested at doses of 0.2, 0.4, 0.6, 0.8, and 1.0 g/20 g of paddy, while the extracts were tested at concentrations of 0.2, 0.3, 0.4, and 0.5 mL/20 g of paddy. The parameters evaluated included adult mortality, weight loss, adult emergence, seed damage, and the weevil perforation index (WPI). Data were analyzed using ANOVA in SPSS 25.0, with Tukey’s test for mean separation at p≤0.05. Results: The results indicated that P. guineense powder was the most potent, causing 60% adult mortality at 1.0 g/20 g after 24 hrs, followed by A. melegueta powder (50% mortality) and S. aromaticum powder (40% mortality). Extracts were more toxic than powders, with P. guineense extract causing 100% mortality at 0.4 and 0.5 mL/20 g of paddy after 24 hrs, followed by A. melegueta (90%) and S. aromaticum (80%). Extracts of P. guineense and A. melegueta completely prevented adult emergence, seed damage, and weight loss. The lethal dose (LD₅₀) and lethal concentration (LD₉₀) values confirmed the highest toxicity of P. guineense, with its effect continuing to increase over time. Conclusion: The study demonstrates the potential of P. guineense, A. melegueta, and S. aromaticum as effective biopesticides for controlling S. oryzae in stored paddy rice. Their application can enhance food security by preventing seed damage, reducing post-harvest losses, and ensuring viable seed storage.