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Larvicidal and Adulticidal Effects of Extracts from Some Indigenous Plants against the Malaria Vector, Anopheles arabiensis (Diptera: Culicidae) in Ethiopia

Damtew Bekele, Beyene Petros, Habte Tekie and Zemede Asfaw 

The mosquito Anopheles not only cause nuisance by their bites but also transmit deadly diseases like malaria in Sub-Saharan Africa, where most of the malaria deaths occur in the world. In Ethiopia, despite the use of native plants in traditional combat against mosquitoes, use in a modern way has remained scanty. The present study, being based on an initial ethno botanical survey, carried out screening experiments on five indigenous ethno botanical species (Aloe pirottae Berger, Aloaceae; Acokanthera schimperi (A.DC) Schweinf, Appocynaceae; Brassica nigra L. Koch, Brassicaceae; Oreosyce africana Hook.f., Cucurbitaceae and Piper capense L.f., Piperaceae). The larvicidal activity of 80% methanol extracts of the first two plant species against the fourth instars of Anopheles arabiensis Patton, and adulticidal activity with the same solvent extracts of the latter four species against Anopheles arabiensis adults, gave positive results upon evaluation under laboratory condition. The 80% methanol extract of the gel of A. pirottae had more activity within 24 hours on the larvae than the leaf extract of Acokanthera schimperi. The highest (100%) mortality in the fourth instars occurred on treatment with 160 ppm extract of Aloe pirottae and 480 ppm extract of Acokanthera schimperi. The maximum adult mortality was detected in the leaf extract of Oreosyce africana (LC50 18.74 and LC90 39.66 ppm) followed by fruit extract of Piper capense (LC50 24.30 and LC90 46.32 ppm), while no mortality was noticed in the control groups. Phytochemical screening of the methanol extracts of the leaves of Oreosyce africana and the fruits of Piper capense had key secondary metabolites (alkaloids, saponins, flavonoids, cardiac glycosides), further corroborating their adulticidal properties. These findings announce the first evidence that Aloe pirottae is a promising mosquito larvicide while Oreosyce africana and Piper capense carry huge potentials as mosquito adulticides contributing to integrated malaria control through proper mosquito management.