Larvicidal Potential of Leaf Extracts and Purified Fraction Ocimum Gratissimum against Culex Quinquefasciatus Mosquito Larva

Purification and structural identificationof the mosquito larvicidal compounds present in Ocimum gratissimum leaf extracts against Culex quinquefasciatus mosquito larvae. The larvicidal potential of the aqueous, ethanol, ethtylacetate, n-hexane and purified fractions of O. gratissimum were tested against the early fourth and third instars larvae of C. quinquefasciatus Mosquito species. Larvicidal toxicity assay were performed using different concentrations and larval mortality was observed after 12 hr, 24 hr and 48 hr of treatment respectively. Thin layer and Column chromatography were used to purify the fraction with the highest larvicidal activity while FTIR and GC-MS were used for structural identification of the phytoconstituents. The result of phytochemical studies revealed the presence of sterols, flavonoids, alkaloids and saponins in O. gratissimum n-Hexane extract. The effective larvicidal activity was observed in O. gratissimum n-hexane extract against C. quinquefasciatus mosquito larvae with percentage mortality of 96 % at 25ppm after 24hr whereas LC50 and LC90 2.57 and 2.52ppm respectively. Following the bioactivity-guided fractionation, the active constituent was found in Fraction three of O. gratissimum n-Hexane extract (F3) with percentage mortality of 100 % at 100ppm after 24hr whereas LC50 and LC90 of (1.28 and 4.28ppm) respectively. Isolated from O. gratissimum n-Hexane fraction (F3) was characterized as caryophylleneoxide in band C by spectroscopic analyses. The Lethal concentration LC50 of the isolated caryophylleneoxide was 2.21ppm and with percentage mortality of 100 %. These work showed that Caryophyllene oxides might be a potent larvicidal agent for mosquito control.