Chemical composition and mosquito repellency of essential oil of Conyza newii propagated in different geographical locations of Kenya

Abstract

Previously, essential oil of Conyza newii (Asterale: Asteracea, Oliv. & Hiern) growing in the northern part of West Pokot (35◦E, 1◦N) of Kenya was shown to be highly repellent [RD50 =8.9×10−5 mg/cm2, 95% confidence interval (CL)] to Anopheles gambiae s.s. Fumigant toxicity of the oil to the mosquito was also demonstrated. The major constituents of the oil were found to be monoterpenoids, including (S )-(-)-perillyl alcohol, (S )-(-)-perillaldehyde, geraniol, (R)-(+)-limonene, trans-β-ocimene and 1,8-cineol. In this study, the chemical composition and repellency of essential oils of the plant seedlings collected from West Pokot (35◦E, 1◦N) and propagated in seven different geographical regions of Kenya [West Pokot (35◦E, 1◦N), Kilome (37◦E, 1◦S), Naivasha (36◦E, 0◦), Webuye (34◦E, 1◦N), Nyakach (34◦E, 0◦), Kericho (35◦E, 0◦) and Nairobi (36◦E, 1◦S)] were compared. There were significant variations (P <0.01, 95% CL) in the relative proportions of the six constituents and this was reflected in the repellency of the essential oils (P <0.01, 95% CL). Higher repellency of the oil was associated with greater proportions of (S )-(-) perillyl alcohol, (S )-(-)-perillaldehyde and geraniol, and lower repellency was associated with an increased proportion of (R)-(+)-limonene. The results suggest significant epigenetic (chemotypic) variations in the repellency and composition of C. newii essential oils growing in different regions of Kenya.