Variations of anti-mosquito larvicidal constituents in the Harrisonia abyssinica species of Tanzania

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.