Phenolic and Monoterpenoid Mosquito Repellent Constituents of Headspace Vapors of Conyza newii

Abstract

The plant Conyza newii has been reported to posses, mosquito repellent and fumigant toxicity properties. In this study headspace vapors emitted by the plant were obtained by adsorption on porapak Q® through headspace trapping under field conditions in West Pokot (35oE, 1oN) and Kericho (35oE, 0o) and analyzed using Gas Chromatography-Mass Spectrometry and co-injection with authentic standards. Mosquito repellency bioassays of volatiles and their synthetic blend were carried out according to the World Health Organization protocol for evaluation of repellents. Five major compounds identified in the volatiles were trans-limonene oxide, cislimonene oxide, cis-dihyrocarvone, 4-methoxyphenol and 3-ethoxy-2-methyl phenol (2:2:2:2:1). Authentic standards of the compounds were bioassayed against Anopheles gambiae s.s and the three of them, trans-limonene oxide, cis-dihyrocarvone and 4-methoxyphenol exhibited repellency of RD50 = 9.2 × 10-5 mg cm,-2, 95% CL, RD50 = 5.4 × 10-4 mg cm,-2, 95% CL and RD50 = 6.7 × 10-4 mg cm,-2, 95% CL respectively.Synthetic blend of the three compounds in their natural ratio (1:1:1) exhibited higher repellency (6.2 × 10-5 mg cm-2) than the individual compounds and even the oil of the plant obtained through steam distillation.