Browsing by Author "Ndoile, Mwanaidi Mbaraka"

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    Larvicidal and mosquitocidal flavonoids from a neorautanenia species occurring in Tanzania
    (2001) Ndoile, Mwanaidi Mbaraka
    The investigations reported in this Thesis were aimed at carrying out phytochemical studies of plant species used locally for pest control in order to unveil pesticidal natural products that may be present in the studied plant species. The research focused on the search for compounds that are active against mosquito larvae and adult Anopheles mosquitoes, which are vectors of malaria parasites. Chemical analysis of a tuber of a Neorautanenia species which was collected from Iringa region, Tanzania yielded five isoflavonoid derivatives; neotenone, ficinin (4-methoxyneoduline), neorautanone, mitisin and neoduline, as well as the substituted coumarin pachyrrhizine. Structural determination was achieved by extensive spectroscopic analysis of each of the compounds, all of which displaying strong larvicidal and mosquitocidal activities in the present investigations. All the crude extracts from the tuber displayed larvicidal and mosquitocidal activities at different levels, the pet ether extract being the most active, followed by the dichloromethane extract. The ethanol extract that was obtained in a sequential extraction involving pet ether, dichloromethane and ethanol respectively, had the least activity. Petether extract desplayed an activity against larvae of Anopheles gambiae and Culex quinquefacitttus, with LC5p values of 0.068 mg/L and 0.16 mg/L respectively and 0.3 mglL against adult A. gambiae mosquitoes. The dichloromethane extract exhibited activity with LC5p values of 0.13 mglL and 0.2 mg/L against A. gambiae and C. quinquefaciatus larvae and 1.29 mg/L against adult A. gambiae mosquitoes. Among the isolated pure compounds, mitisin was the most active, displaying an LC5p value of 0.003 mg/ml against A. gambiae adult mosquitoes, followed by neoduline (LC5p = 0.005 mglml). In general, the compounds exhibited activity that was nearly of the same magnitude, the crude extracts being slightly more active than the pure compounds, while some mixtures of two of the compounds displayed an enhanced activity as compared to the individual compounds, which may indicate a synergistic effect occurring between the mixed compounds.