Phytochemical Profile and Bioactivity of Essential Oil from Pimenta Dioica Leaves on Cowpea Beetle, Callosobruchus Maculatus (F.) (Coleoptera: Bruchidae): A Farmer Friendly Solution for Postharvest Pest Management

Pimenta dioica (Allspice) leaf essential oil was isolated using hydro-distillation and insecticidal properties were evaluated for their ability to suppress post-harvest insect pest Callosobruchus maculatus in storage legumes and pulses. Four concentrations of leaf oil (0.5, 0.6, 0.8 and 1.0 v/v% ) were tested to evaluate their contact and fumigation repellency as well as insecticidal activities. Volatile organic compounds of leaf oil were analyzed by headspace solid-phase micro extraction coupled with gas chromatography and mass spectrometry (HS-SPME/GCMS) using polar and medium polar fibers. All concentrations elicited significantly higher repellent effects on insects after 2 hour exposure when compared with those of the control with the highest concentration producing 98.0% and 92.0% contact and fumigation repellency effects. Contact and fumigation toxicity tests exhibited 100% mortality for the highest concentration after 6 and 12 hour exposure respectively giving low LC50 values of 0.3 (v/v%). Volatile oil analysis indicated that the leaf essential oil comprised of high amount of Eugenol (89.8%), Methyl eugenol (2.3%) and caryophyllene (4.1%) for the polar fiber. Eugenol (42.6%), Caryophyllene (27.9%), Humulene (6.8%) and 1,8 Cineol (8.1%) were obtained for the medium polar fiber. Results indicate that the leaf essential oil of P.dioica would be a safe, eco-friendly alternative botanical insecticide in managing C.maculatus during storage.