Larvicidal Potential of Persea americana Seed Extract against Aedes vittatus Mosquito

Aims: To investigate larvicidal activity of solvents (Ethanol, Ethyl Acetate, n-Hexane) extracts of Persea americana seed against Aedes vittatus and partially purify the most potent solvent extract and characterise most effective fraction isolated.

Place and Duration of Study: Entomology Research Laboratory and Department of Biochemistry, Ahmadu Bello University, Zaria, Kaduna State, Nigeria. Between August-October, 2013 and June-August, 2014.

Methodology: The mosquito larvae (15 per replicate) were exposed to test concentrations. The number of dead larvae was recorded after six hours interval for 24 hours and the percentage mortality was calculated. The most potent solvent (n-hexane) extract was fractionated using column chromatography and most effective fraction isolated, was identified using gc/ms and ftir techniques.

Results: N-hexane extract is the most potent solvent extract, with an lc50 value of 0.827 ppm showing 100% mortality at 50 ppm, six hours post exposure. While ethanol and ethyl acetate extracts with an lc50 values of 1.79 ppm and 2.732 ppm, show 100% mortality at 200 ppm and 600 ppm twelve hours post exposure, respectively. The n-hexane chromatographic fractions of P. americana (nhp) tested on the larvae, showed increased activity of some fractions, nhp6 and nhp7 with lc¬50 values of 0.486 ppm and 0.727 ppm, having 100% mortality at 50 ppm and 25 ppm, at 24 and 12 hours post exposure respectively. The gc/ms s identification of the most effective fraction, nhp6, revealed eighteen peaks, dominant four of which include fatty acid and fatty acid methyl esters, which correspond to oleic acid (22%), 3-hydroxy-2,2,4-trimethyl pentyl ester of isobutanoic acid (12.26%), methyl-2-(acetyloxy) hexadecanoate (10.28%) and 3,4-dimethyl-1-decene (10.02%). The ftir analysis identified functional groups present which include; alkane, alkene, alkyl halide, aldehyde, carboxylic acid and carbonyl ester.

Conclusion: Based on these findings of all the solvents used, the n-hexane, ethylacetate and ethanol extracts of Persea americana seed have shown good larvicidal activity. The oleic acid content of this plant should be explored and optimised to serve as source of larvicide that is effective and environmentally friendly.