This experiment was carried out at Ladoke Akintola University of Technology, Teaching and Research farm during the late and early planting seasons of 2016 and 2017 to determine the efficacy of Tephrosia vogelii F. and Annona squamosal L. extracts on major insect pests of watermelon (Citrullus lanatus Thumb.) and their effects on nutritional content and fatty acid compounds of watermelon. This experiment was arranged in a randomized complete block design and each treatment was replicated three times. Each of the plant extracts was applied at three different concentrations (5, 10 and 20%). Gas chromatography was used to determine the level of fatty acid composition. The results clearly showed that the applied plant extracts exhibited insecticidal action against the Phyllotreta cruciferea (Weise) and Dacus cucurbitae (Coquillet) pests. T. vogelii proved to be more effective than A. squamosa extracts in the control of the observed insects. Although, none of these plant extracts significantly(p<0.05) performed better than synthetic insecticide (Lambdacyhalothrin) against the studied insects during the rainy season but plant extracts treated fruits had higher number of fatty acid compounds than that of synthetic insecticide. However, the tested plant extracts had positive effect on the proximate composition of the target crop. Therefore, the use of plant extracts in the management of insect pests of watermelon in organic farming not only controlled the observed insects but improved the nutritional contents of watermelon fruit.

Keywords: Annona squamosa, Dacus cucubitae, Lambdacyhalothrin, Phyllotreta cruciferea, Tephrosia vogelii, Watermelon