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Effects of a biologically active fraction from Melia volkensii on Culex quinquefasciatus

Published online by Cambridge University Press:  19 September 2011

L. W. Irungu
Affiliation:
Department of Zoology, University of Nairobi, P.O. Box 30197, Nairobi, Kenya
R. W. Mwangi
Affiliation:
Department of Zoology, University of Nairobi, P.O. Box 30197, Nairobi, Kenya
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Abstract

A chromatographically enriched fraction designated Fraction B from dry fruits of the plant Melia volkensii (family Meliaceae) was evaluated with the objective of determining its toxic and growth inhibiting effects on the larvae and adults of Culex quinquefasciatus mosquitoes. The fraction was purified from a crude methanolic extract by cold precipitation and elution of the precipitate dissolved in a hexane-ethyl acetate solvent system through a silica gel column. Larval treatments involved rearing the larval stages in water containing the fraction at concentrations of between 5 and 200 ppm. The LC50 for this fraction was found to be 34.72 μg/ml in 48 h. Second instar larvae were found to be more susceptible to fraction B when compared to fourth instar larvae. All fourth instar larvae that survived the treatment moulted into larval-pupal intermediates that were short-lived. The extract was also found to be an oviposition deterrent at a concentration of 20 ppm and above. It is concluded that M. volkensii extract has potential in the control of Culex quinquefasciatus.

Résumé

Une fraction enrichie chromatographiquement et designée Fraction B des fruits secs de la plante Melia volkensii (famille Meliaceae) a été évaluée pour déterminer sa toxicité et ses effets inhibiteurs de croissance sur les larves et adultes de Culex quinquefasciatus. La fraction a été purifiée à partir de l'extrait méthanolé brut par précipitation à froid et elution du précipité dissoit dans un mélange de solvent hexane-ethyl acetate à travers une colonne de silica gel. Des traitements destinés aux larves impliquaient l'élevage des stades larvaires dans le l'eau contenant la fraction aux concentrations comprises entre 5 et 200 ppm. La DL50 pour cette fraction a été de 34.72 μg/ml en 48 heures. On a trouvé que les larves du 2nd instar ont été les plus susceptibles à la fraction B, comparées aux larves du 4ème instar. Toutes les larves du 4ème instar qui ont survécu au traitement ont mué en intermédiares larve-pupe dont la durée de vie a été écourtée. L'extrait s'est aussi révélé un dissuadant de l'oviposition à la concentration de 20 ppm et au dessus. On en a conclu que l'extrait de M. volkensii offre un moyen potentiel de lutte contre Culex quinquefasciatus.

Type
Research Articles
Copyright
Copyright © ICIPE 1995

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