Phytochemical Screening and the Efficacy of Leaf Extract and Powder of Ageratum conyzoides against Callosobrochus maculatus Fabricius (Coleptera: Chrysomelidae) on Stored Cowpea Seeds

Cowpea weevil is a major pest of stored grains worldwide. This study evaluated the insecticidal efficacy of leaf powder and ethanol leaf extract of Ageratum conyzoides against Callosobruchus maculatus. Efficacy of A. conyzoides was assessed based on adult mortality, oviposition, adult emergence, long-term storage protection, and seed viability. Fresh leaves of Ageratum conyzoides were air-dried and ground into fine powder using an electric Binatone 1.5 Liters (Model BLG-401) Blender. A portion of the powder (50 g) was extracted in 250 mL of ethanol and heated at 60 °C for 30 minutes. Phytochemical screening of the leaf powder was conducted using standard procedures. The extract was filtered through Whatman No. 1 filter paper, and the filtrate was concentrated using a rotary evaporator. Extract concentrations of 2, 4, 6, and 8% (v/w) were prepared from the stock solution, while the effects of powder at dosages of 1, 2, 3, and 4 g (w/w) were also tested. The results showed that weevil mortality increased with increasing extract concentration, powder dosage, and exposure time. Cowpea seeds treated with A. conyzoides powder at 8 g (w/w) recorded 92.25% mortality within 96 hours, while 100% mortality was achieved with 8.0% (v/w) ethanol extract within the same period. No oviposition occurred on seeds treated with 8.0% (v/w) extract, and no adult emergence was observed in seeds treated with 4 g (w/w) powder. Extract concentrations of 4, 6, and 8% (v/w) completely prevented seed damage for three months of storage. Germination tests conducted after seven days showed 100% germinability for all treated seeds. Phytochemical analysis revealed the presence of alkaloids, glycosides, saponins, anthraquinones, tannins, terpenes, and flavonoids. The study concludes that leaf extract and powder of A. conyzoides are effective in controlling C. maculatus and can serve as a viable alternative to synthetic insecticides, which are costly and environmentally hazardous.