Toxicity and repellant activity of Cymbopogon citratus (D.C.) Stapf.. and Murraya koenigii Sprang, against Callosobruchus maculatus (F.) (Coieoptera; Bruchidae)

Abstract

Essential oils of Cymbopogon citratus (Lemongrass) and Murraya koenigii (Curry leaf) were tested for their toxicity and repellant activity against Callosobruchus maculatus (F.) in stored cowpea. In the contact toxicity ihioassay, lemongrass oil at a concentration of 0.15 g/1 caused 100 % mortality and the number of eggs Said was zero. Curry leaf oil also showed similar activity at a concentration of 0.75 g/1. In fumigant toxicity bioassays lemongrass oil at 1.5-g/f concentration and curry leaf oil at 7.5-g/l concentration caused 100 % bruchid mortality and reduced their opposition and F, adult emergence. In contact toxicity bioassay, the lowest LC^ value off 0.026 g/1 was observed for lemongrass and the LC* value of curry leaf was 0.240g/1. The results indicated that lemongrass oil was more effective as a contact toxicant on bruchids than curry leaf oil. In olfactometer and choice chamber bioassays, the % responses of bruchid decreased with increasing doses of both oils. Only 7.0 % bruchids settled in at the dosage of 160 mg in choice chamber for both lemongrass and curry leaf oils. These results suggested that the essential oils of lemongrass and curry leaf could be used as alternatives to develop less toxic treatment system to protect stored cowpea.