Browsing by Author "Ahmed, Hassanali"

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    Chemical composition and mosquito repellency of essential oil of Conyza newii propagated in different geographical locations of Kenya
    (John Wiley & Sons, 2014) Mayeku, Philip Wafula; Omollo, N. I.; Odalo, O. J.; Ahmed, Hassanali
    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.
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    Phenolic and Monoterpenoid Mosquito Repellent Constituents of Headspace Vapors of Conyza newii
    (2013-01) Mayeku, Philip Wafula; Sauda, Swaleh; Ahmed, Hassanali
    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.