Larvicidal Activities of N-Hexane Fraction of Ocimum gratissimum Leaf against Mosquito Larvae and Its GC-Ms Analysis of Phytoconstituents

Abstract

Aim: To evaluate the larvicidal efficacy and identify the active phytochemical of Ocimum gratissimum n-hexane leaf extract on mosquito larvae. Study Design: Reflux extraction, standard qualitative phytochemical tests, Column and Thin layer chromatographic methods and GC- MS analysis. Place and Duration of Study: Department of Biochemistry, STEP-B (Genetic Engineering) Laboratory, Federal University of Technology, Minna between August, 2013 and July 2014. Methodology: The plant leaves was extracted with 70% methanol, crude extract was partitioned into fractions and healthy mosquito larvae subjected to Standard WHO insecticide susceptibility protocol for the extract efficacy. Column and Thin layer Chromatographic methods were used for phyto-constituent separation of plant extract. The most effective larvicidal column chromatography fraction was subjected to GC-MS analysis for further quantitative and identification of the most effective phytochemical isolates. The phytochemical constituents were determined qualitatively. Results: Maximum larvae mortality (100%) was observed in 2, 4 and 8% w/v concentrations of leaf extract of O. gratissimum 24 h post exposure. Column chromatographic fraction F42 gave 100% larvicidal activity at 0.5% concentration. The predominant phytochemical constituents detected in the leaf extract of this plant were terpenes, saponins and tannins. Steroids and phenols were detected in all extracts but absent in the ethanolic leaf extracts. Flavonoids were not detected in any extracts of the plant. The GC-MS analysis of fraction F42 from O. gratissimum reflected thymol, caryophyllene and terpenoids were present. Conclusion: The study clearly indicates that O. gratissimum possesses chemical compounds that are active against mosquito larvae. Therefore these chemicals can be formulated into mosquito larvicides to prevent mosquito borne diseases.