author(s)
Sherifat A Aboaba, Funmilayo E Mobilawon and Mobolade D Akinbuluma

abstract
Essential oils have been found to possess numerous biological activities which include pesticidal activities against various pests and mosquitoes. Essential oils were obtained from the flower, leaves, stem-bark, epicarp and seed of Thevetia neriifolia using hydro-distillation and analysed by Gas Chromatography coupled with Mass Spectroscopy (GC-MS). The insecticidal activity of the oils was evaluated on Callosobruchus maculatus (F.) using cultured cowpea seeds under laboratory conditions of 27 ± 2 ⁰C ambient temperature and 78 ± 5% relative humidity. Parameters including mortality, repellent effects and viability of seeds were assessed and all data were analysed using Analysis of Variance (ANOVA). The percentage yield of essential oils from the flower, stem bark, leaves, epicarp and seed of oils were 0.55%, 0.39%, 0.35%, 0.30% and 0.40% respectively. A total of 11, 15, 17, 7 and 5 compounds were identified in the flower, stem-bark, seed, epicarp and leaf with E-5-Octadecene (25.01%), humulene (62.80%), methyl-11-octadecanoate (24.63%), methyl stearate (36.14%) and hexa-hydrofarnesylacetone (24.88%) being the predominant compounds in the essential oils respectively. The highest percentage mortality (36.11%) of adult C. maculatus to the oils was observed with 80% (v/v) concentration at 12, 18 and 24 hour post-treatment from the stem bark which was relatively better than other parts studied. The essential oil from the flower showed the highest pest repellent effect (88.43%) on adult C. maculatus at 80% (v/v) treatment when compared to the control. There was no significant difference in the percentage germination of treated and untreated cowpea seeds although the flower and seed oil were most effective at 80% (v/v). Therefore, it can be concluded that the essential oils of T. neriifolia were effective as protectant against C. maculatus on stored cowpea.