Aloe plant extracts as alternative larvicides for mosquito control

The larvicidal activity of extracts from Aloe turkanensis, Aloe ngongensis and Aloe fibrosa against the common malaria vector, Anopheles gambie, was determined. Ground Aloe leaves from the three plants were sequentially extracted with hexane, ethyl acetate, chloroform, acetone and methanol. Only the ethyl acetate extract of A. turkanensis, hexane, ethyl acetate, acetone, chloroform and methanolextracts of A. ngongensis and the hexane, acetone and methanol extracts of A. fibrosa showed activity. A series of concentrations of the extracts ranging from 0.05-2 mg/ml (0.005-0.2% w/v) were testedagainst third instar larvae and their percentage mortalities, LC50 values determined. The ethyl acetate soluble extract of A. turkanensis showed very high larvicidal activity where 100% mortality wasachieved at a concentration of 0.2 mg/ml and it had an LC50 of 0.11 mg/ml. All the extracts of A. ngongensis showed larvicidal activity to A. gambie larvae, but at higher concentration showing LC50´sof 0.84 (0.55 – 1.27), 1.14 (0.72 – 2.28), 0.98 (0.78 – 1.27), 1.08 (0.90 – 1.28), 2.0 (1.85 – 2.36) for the hexane, ethyl acetate, chloroform, acetone and methanol, respectively. The three active fractions of A. fibrosa had very close LC50´s ranging from 1.76 – 1.90 mg/ml. Thin layer chromatographic analysis (TLC) showed the presence of chromones and anthrones in the chloroform and ethyl acetate extracts. Application of these extracts to larval habitats may lead to promising results in malaria and mosquito management programmes