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.
Annona muricata L. is a plant commonly used in Southern Nigeria, for nutritional and medicinal purposes. This study wascarried out to determine the larvicidal potentials of ethanol extract and fractions of the leaf of A. muricata. The ethanol leafextract was subjected to phytochemical screening using standard protocol. The leaf crude extract and fractions (i.e., ethylacetate and n-hexane) were used for larvicidal assay. The stock solution (5g each in 100ml of water) was prepared. From thestock solution 0.15, 0.30, 0.45, 0.60 and 0.75_ %w/v concentrations of extract and fractions were prepared and eachconcentration of the extract and fractions had 5 replicates. The control (100ml water and larval nutrient only) was alsoreplicated . Twenty (20), third instar, larvae of Aedes aegypti were exposed to each extract concentration and fractions andtheir controls. Larval nutrient was added to each experimental set up. Observations were made after 24 and 48 hours exposureperiod. Phytochemical screening revealed the presence of some plant metabolites (alkaloids, saponins, tannins etc).Mortality of larvae exposed to the extract and fractions increased with increased in extract concentration and exposure time.This study revealed a differential potency of the extract and fractions used and a difference in susceptibility of larvae to theextract and fractions as evident by the 48hLC values obtained. Exposure of larvae to 0.75_ %w/v of ethanol extract and ethyl 50acetate fraction resulted in 100 _% mortality after 48 hours exposure period. Probit analysis gave 48hr_LC50 values of 0.33and 0.24_ %w/v for ethanol extract and ethyl acetate fraction, respectively. The n-hexane fraction was the least potent with48h_LC50 value of 0.5461%w/v. Results obtained from this study suggest that the leaf extract and fractions of A. muricatahold potential as larvicides against Ae. aegypti. Its active ingredient should be isolated, characterized and formulated for usein larval habitats. Keywords: Potency, Extract, Fractions, Annona muricata, Aedes aegypti
Plant products have been tested as insecticides against mosquitoes as they are promising candidates to replace conventional insecticides. This study was carried out to evaluate the larvicidal potential of ethanol extract of the aerial parts of Diplazium esculentum against Anopheles gambiae and Culex quinquefasciatus. Ethanol extract of the aerial parts of D. esculentum was screened for its phytochemical constituents and used for larvicidal assay. A stock solution of the extract (5 g in 100 ml of water) was prepared. From the stock solution, 0.45, 0.60, 0.75, 0.90 and 1.05% w/v concentrations of the extract were obtained for the study. Each concentration of the extract had 3 replicates. The control was also replicated. Twenty (20) third instar larvae each of Anopheles gambiae and Culex quinquefasciatus were separately exposed to each extract concentration for a duration of 48 hours. Larval nutrient was added to each experimental set up. Observations were made after 24 and 48 hours exposure period. Phytochemical screening revealed the presence of some plant metabolites. Mortality of larvae exposed to the extract increased with increased concentration and exposure time. This study revealed a differential susceptibility of larvae of the two mosquito species to the extract as evident by the 24 h LC50 values obtained which were 0.355 and 2.468% w/v for An. gambiae and Cx. quinquefasciatus respectively. Exposure of An. gambiae larvae to the extract resulted in 100% mortality even with the least concentration of 0.45% w/v after 48 hours exposure period while the highest concentration of extract (1.05% w/v) resulted in 53.33% mortality of Cx. quinquefasciatus larvae, after an exposure period of 48 hours. Results obtained from this study suggest that the aerial parts of D. esculentum if further explored would be useful in the control of An. gambiae and Cx. quinquefasciatus.
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