Abstract:
Harrisonia abyssinica (Simaroubaceae) is widely distributed and used in traditional medicine in
Tanzania. Phytochemical studies of the plant report the presence of steroid and limonoid compounds while
much of its biological studies were concentrated on its pharmacological activity on human pathogens. In the
present study, eight extracts from plant materials collected from the Moist forest mosaic (Zone I) and the
Coastal forest and thicket zone (Zone II) were tested against Culex quinquefascintus Say larvae. Detailed
analysis of mosquito larvicidal activity of the eight extracts showed a dose dependent (p>0.05) trend with the
dichloromethane and ethanol extracts of the root bark plant materials collected from Zone I having higher
effectiveness. In 24 h, the dichloromethane and ethanol extracts of the root bark from Zone I achieved
mortality of 90% and 100%, respectively, at 50 ppm. Likewise, at 5 ppm the two extracts were having 60% and
58% mortality, both been not significant different (p>0.05) but significantly different (p<0.05) to the rest of the
extracts and the control. Follow-up isolation of the ethanol extract of the root bark from Zone I yielded two
known limonoids, harrissonin (1) and pedonin (2) which were also present in the dichloromethane extract from
the same Zone. Similarly, the toxicity of the ethanol extract of the root bark from Zone I (LC50 = 6.75 mg/ml)
had high activity compared to other extracts. The variations of activity and chemical compounds in Harrisonia
abyssinica suggest the importance of keeping pharmacopoeias of importance medicinal plants in our regions.
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