Efficacy of the Seed Oil, Leaf Extract and Fractions of Annona muricata as Repellent and Larvicide against Anopheles gambiae

Vector control has proved to be a successful strategy for reducing incidences of mosquito borne-diseases. This study evaluated the repellent and larvicidal efficacy of A. muricata against An. gambiae. Oil was extracted from the seeds using the solvent extraction method. For the repellency test the oil (0.38 ml) was topically applied on the right arms of 10 human volunteers to evaluate its effect against adult female An. gambiae. The left arms of the volunteers were treated with 1 ml of 20% acetone (control). Ethanol leaf extract was used for phytochemical screening and preparation of n-hexane, ethyl acetate and aqueous fractions. These were used for larvicidal assays. From the stock solution (5 g each in 100 ml of water), 0.15, 0.30, 0.45, 0.60 and 0.75%w/v concentrations were obtained. In the control experiment, larvae were exposed to 100 ml tap water and nutrients only. Test concentrations and controls had 5 replicates each. Each larvicidal experiment consisted of 20 third instar larvae of Anopheles gambiae. Repellency and larvicidal experiments were carried out at the Malaria Vector Research Laboratory and Insectary, University of Uyo and National Arbovirus and Vectors Research Centre, Enugu, Nigeria, respectively. Repellency of the oil reduced with increased exposure time, in each case. The number of mosquito landings on the control arms was higher than landings on the treated arms. Mosquitoes that landed on the treated arms could not bite, suggesting that A. muricata oil could possess feeding deterrent property. Phytochemical screening revealed the presence of some plant metabolites. The ethanol leaf extract and aqueous fractions had no larvicidal activity at the highest concentration. However, n-hexane and ethyl acetate fractions were larvicidal. N-hexane fraction was the most potent with 48hLC50 value of 0.41%w/v, while ethyl acetate fraction had 48hLC50 value of 0.79% w/v. Results suggest that A. muricata has promising repellent and larvicidal potentials against An. gambiae.