BIOACTIVITIES OF PLANT EXTRACTS AGAINST POST–FLOWERING INSECT PESTS OF COWPEA (Vigna unguiculata L. Walp, AND THEIR EFFECTS ON FATTY ACID

Abstract

This study was carried out during the 2020/2021 planting seasons to evaluate the effect of Petiveria alliacea (Lin.), Annona squamosa (Lin.), and their combinations on insect pests of cowpea, as well as their influence on the fatty acid profile. Synthetic insecticides (Lambda-cyhalothrin and Dichlorvos) were used as a synthetic check and a control was set up in which there was no treatment. The treatments were arranged in a Randomized Complete Block Design with three replications. Data were collected on insect populations, pod damage, grain yield, and the fatty acid composition of harvested grains. The findings revealed that the plant extracts were effective in managing insect pests, though their efficacy varied among different species. For example, a single application of P. alliacea exhibited the lowest insecticidal effect (12%) against Mylabris spp. (Fab.), whereas higher control was observed against Nezara viridula and Megalurothrips sjostedti (74% and 45%, respectively) compared to A. squamosa. The mixture of P. alliacea + A. squamosa and Dichlorvos were statistical effective as individual plant extracts in controlling insect pests and reducing pod damage, but none of the other treatments was effective as Lambda-cyhalothrin. However, grain yield of cowpea plants treated with plant extracts compared favourably with those treated with Dichlorvos. The fatty acid composition of grains from Lambda-cyhalothrin-treated plants contained only one compound (methyl palmitate), whereas those treated with plant extracts had a higher diversity of fatty acids than both synthetic insecticide-check and untreated grains. These results suggest that plant extracts can serve as an effective alternative for insect pest control while also enhancing the fatty acid content of cowpea grains.