Phytochemical screening and larvicidal activity of extracts of Ocimum basilicum (Lamiaceae) leaves against Aedes aegypti

Abstract

The leaves of Ocimum basilicum were washed, air dried, ground and soaked in ethanol. The ethanol extract obtained was labeled (OB1) and macerated sequentially using petroleum ether, chloroform and water. The resulting fractions obtained were labeled OB2, OB3 and OB4 respectively. Each fraction was screened for the presence of secondary metabolites using standard procedures. Terpenoids, phenols, flavonoids, steroids, saponins, tannins and volatile oils were detected. All the fractions of O. basilicum were found to be active against fourth instars larvae of Aedes aegypti at 500, 1000, 2000 and 5000μg/ml. The activity was highest with chloroform fraction (OB3) which showed percentage mortality of 67, 77, 80, 97 (LC₅₀ of 241.99μg/ml) and 83, 90, 97, 100 (LC₅₀ of 75.15μg/ml) after 24hrs and 48hrs respectively, followed by ethanol (OB1), aqueous (OB4) and petroleum ether (OB2) with the least activity. The results could encourage the search for bioactive compounds that will provide an alternative to synthetic larvicides.