Insecticidal Efficacy of Onion and Garlic Peel Extracts for Sweet Potato Preservation. Nigerian Journal of Post-Harvest Research, 3(6), 8-16

This study examined the insecticidal activity of onion and garlic peel extracts as a control method for sweet potato beetles, Cylas formicarius, infesting sweet potatoes after harvest. The primary objective of this study was to extract bioactive compounds from onion and garlic peels using a column chromatographic technique. The extracts were bioassayed against five C.formicarius adults in various concentrations: 0.01 g/0.25 kg, 0.02 g/0.25 kg, and 0.04 g/0.25 kg. Methanolic extract of onion peel being the most effective was subjected to isolation using column chromatography packed with silica gel of 60-120 mesh, employing a gradient elution technique. The elution started from 100% hexane and gradually incorporated 10% ethyl acetate until a 10% methanol in ethyl acetate solution. TLC was used to monitor similar fractions collected, and the combined fractions were then subjected to Prep-TLC until a pure compound, known as OM-15, was obtained. The results revealed that onion peel methanolic extract (OMH) caused 93.3% mortality 96 h postexposure. In contrast, garlic peel methanolic extract (GMH) caused 73.3% mortality, but hexane garlic peel extract caused 80% mortality 96 h postexposure, and the pure compound showed mortality of 60% on Cylas formicarius 96 h postexposure. It can be concluded that the methanolic extract of onion peels was more effective than the ethyl acetate and hexane extracts, and is not statistically different from the standard insecticide (cypermethrin) at P < 0.05 significant level. The extracts are eco-friendly and potent against Cylas formicarius, providing a scientific rationale for incorporating their development into biopesticides.