Phytochemical Composition and Repellent Activities of Selected Botanical Extracts Against Cowpea Weevil for Natural Preservation of Cowpea Seeds

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Phytochemical Composition and Repellent Activities of Selected Botanical Extracts Against Cowpea Weevil for Natural Preservation of Cowpea Seeds

ABSTRACT

Callosobruchus maculatus (Fab.) is a significant field-to-store pest that causes quantitative and qualitative losses in stored cowpea. Management of this pest has primarily relied on synthetic pesticides, which are associated with severe health risks, including fatalities. In view of the recent increased interest in developing biopesticides as an alternative to synthetic pesticides, this study evaluated the synergistic repellent activities of botanical extracts against C. maculatus. Fresh leaves of Vernonia amygdalina, Ocimum grattisimum, and Gongronema latifolium were harvested, washed, dried, pulverized, and soaked in distilled water (1:10) and hexane (1: 10) for 24 hours. The bioactive components of the extracts were analyzed using Gas Chromatography-Flame Ionization Detector (GC-FID). Stock solutions (200mg/ml) were prepared and reconstituted in distilled water, acetone, and Tween80 to produce lower concentrations (20, 50, 100, and 150 mg/ml). The repellency effects of these reconstituted extracts against C. maculatus adult were assessed using a filter paper repellency method with three replicates, three negative controls, and one standard (2.5 μl/ml Deltamethrin synthetic insecticide). The analysis identified Apigenin (31.36%) as the dominant compound in the aqueous extract of V. amygdalina, while Artemetin (80.94%) was predominant in its hexane extract. O. grattisimum aqueous extract was dominated by Sinapinic acid (72.04%), and its hexane extract by Syringic acid (56.91%). G. latifolium aqueous extract contained Kaempferol (47.22%) as its major compound, while Luteolin (22.15%) was dominant in its hexane extract. The repellency of all extracts increased with concentration, with 200mg/ml demonstrating the highest repellency (up to 100%) over 96hours. The aqueous extract showed repellency ranging from 16.7% to 100%, acetone reconstituted hexane extract ranged from 11.1% to 100%, and Tween80 reconstituted hexane extract ranges from 6.7% to 100%. Statistical analysis revealed that differences in repellency were not statistically significant (p>0.05) across most concentrations, except for 50mg/ml of Tween80 reconstituted hexane extract. In descending order of effectiveness, the repellency trend was: aqueous extract > acetone reconstituted hexane extract > Tween80 reconstituted hexane extract. This finding suggest that botanical extracts, particularly aqueous formulations, are promising natural repellents for C. maculatus and offer a safer alternative to conventional synthetic pesticides.

 

Keywords: Callosobruchus maculatus, Botanical extracts, Repellency, Biopesticides, Cowpea protection

 

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