Abstract

A laboratory study was carried out on the chemical composition and evaluation of Annona muricata leaf extract on Callosobruchus maculatus infesting Vigna unguiculata seeds in the store. Air dried leaves of Annona muricata were pulverized into fine powder using an electric grinder (Model: Binatone electric grinder BL 400). The leaves were extracted with soxhlet extractor at 60^oC in the laboratory, using ethanol as the solvent. The effects of the extract was investigated on adult mortality, ovipostion, emergence of F1 progeny, germinability and seed damage under ambient laboratory conditions of 28 ^oC and 70% Relative Humidity. The results obtained showed that, adult mortality generally increased with increased in dosages applied and the length of time the weevils were exposed to the extracts. There was 100% mortality of C. maculatus in the cowpea seed treated with 0.9 mL/20 g and 1.2 mL/20 g of the extract within 96 h and 72 h respectively. Oviposition and adult emergence decreased with increased in the amount of dosages used. Oviposition and adult emergence were significantly lowered (p≤ 0.05) in the cowpea seeds treated with the extract than the untreated seeds (control). Oviposition was significantly low (9.20) and adult emergence were totally prevented in cowpea seeds with 0.9 mL/20g of A. muricata leaf extract, while oviposition and adult emergence were totally prevented in cowpea seeds treated with 1.2 mL/20g extract. Almost all the treated seeds germinated regardless of the dosages of the leaf extracts. The untreated cowpea seeds had the highest germination of 100%, followed by seed Treated with 0.3, 0.6 and 0.9 mL which are not significantly different (p ≤ 0.05). A. muricata leaf extract at dosages of 0.6, 0.9, and 1.2 mL, completely prevented, seed damage and weight loss of the treated cowpea seeds. The qualitative phytochemical screening of A. muricata showed the presence of glycoside, flavonoids, saponins and steroids, while alkaloid, phenols and tannins were not detected. The results obtained from this study revealed that the extracts of A. muricata are effective in managing C. maculatus and could serve as an alternative to synthetic insecticides for the protection of stored cowpeas against weevils.