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Volatility and Mosquito Repellency of Hemizygia welwitschii Rolfe Oil and Its Formulations

Published online by Cambridge University Press:  19 September 2011

A. O. Oyedele ,
Lara O. Orafidiya ,
A. Lamikanra  and
J. I. Olaifa
A. O. Oyedele
Affiliation:
Department of Pharmaceutics, Obafemi Awolowo University, Ile-Ife, Nigeria
Lara O. Orafidiya
Affiliation:
Department of Pharmaceutics, Obafemi Awolowo University, Ile-Ife, Nigeria
A. Lamikanra
Affiliation:
Department of Pharmaceutics, Obafemi Awolowo University, Ile-Ife, Nigeria
J. I. Olaifa
Affiliation:
Department of Plant Science, Ladoke Akintola University of Technology, Ogbomosho, Nigeria
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Abstract

The volatility and mosquito repellency of the essential oil of Hemizygia welwitschii Rolfe (Laminaceae) and its prototype pharmaceutical formulations were examined and compared with those of a commercial mosquito repellent. At ambient temperature (28°C), neat Hemizygia oil had a volatility of 4.47±1.02 mg/cm2/ h for 15 hours, after which the rate declined. The oil evaporated at 200 μg/ cm2/ h from 10% w/w liquid paraffin solutions, and at 60 μg/ cm2/ h from soft paraffin during the first 20 hours, after which the decline in evaporation rate was generally bi-phasic. The oil demonstrated concentration-dependent repellency against the mosquito Aedes aegypti. Its liquid paraffin solutions (5% to 15% concentration) prevented up to 50% of starved mosquitoes from feeding on a blood meal for 6 hours. Lower concentrations were less effective and inhibited feeding for only 1 hour. A 15% w/w oil-in-water emulsion formulation of Hemizygia oil produced 55% feeding deterrence in the mosquitoes for 2 hours. Neither the solution nor the emulsion formulations of the oil provoked any adverse reaction on human skin.

Résumé

La volatilité et le pouvoir répulsif de l'huile essentielle de Hemizygia welwitschii Rolfe (Laminaceae) et ses prototypes de formulations pharmaceutiques ont été examinés et comparés avec des répulsifs commerciaux utilisés contre les moustiques. A la température ambiante (28°C), l'huile pure de Hemizygia avait une volatilité de 4,47±1,02 mg/cm2/h, au cours de 15 heures, après quoi le taux d'évaporation diminuait. Pour les solutions de 10% d'huile de Hemizygia dans de la paraffine liquide ou semi liquide, l'évaporation respective était de 200 μg/ cm2/ h et de 60 μg/ cm2/h pendant 20 heures après quoi, la courbe baissante d'évaporation de l'huile montrait une tendance généralement biphasée. L'huile a également montré une relation dépendante entre sa concentration et la répulsion de Aedes aegypti. Des solutions de 5% à 15% de cette huile dans de la paraffine liquide empêchaient, pendant six heures, jusqu'à 50% de moustiques à jeun de prendre un repas sanguin. Les basses concentrations du produit étaient moins efficaces et déclenchaient un effect anorexique pendant une heure seulement. Des émulsions aqueuses à 15% d'huile de Hemizygia provoquaient 55% d'effet anorexique chez les moustiques, pendant deux heures. Ni les solutions ou émulsions de Hemizygia ne provoquaient des réactions néfastes sur la peau humaine.

Keywords

Hemizygia welwitschiiAedes aegyptivolatile oilevaporation ratemosquito repellencyformulationHemizygia welwitschiiAedes aegyptihuile volatiletaux d'évaporationrépulsion de moustiqueformulation
Type
Research Articles
Information
International Journal of Tropical Insect Science , Volume 20 , Issue 2 , June 2000 , pp. 123 - 128
Copyright
Copyright © ICIPE 2000

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