|Online ISSN : 2349-8080
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This study determined the bio active substances in the physic nut plant, Jatropha curcas and further examined the larvicidal potentials of its hexane, methanol and aqueous leaf and stem extracts on locally reared larvae of the malaria vector, Anopheles gambiae in accordance with the World Health Organization’s guidelines for laboratory and field testing of mosquito larvicides. Various concentrations (25mg/mL, 50 mg/mL 100mg/mL and 200 mg/mL) of the plant extracts were tested against third instar larvae of Anopheles gambiae. Qualitative phytochemical analysis of the different portions of J. curcas leaf and stem extracts revealed the presence of active toxic compounds including alkaloids, saponins, flavonoids, glycoside and tannins. Methanolic extracts were found to be richer in phytochemicals than hexane and aqueous extracts. All plant extracts at the various concentrations showed significant larvicidal activity against Anopheles gambiae mosquito larvae between 30 minutes to 24 hours of exposure. Methanol leaf extract of J. curcas was most effective as it showed larval mortality of 75 to 100% on the test larvae after 30 minutes to 24 hours of exposure while the methanol stem extract showed 60 to 100% larval mortality. Hexane leaf extract showed larval mortality of 65 to 100% after 30 minutes to 24 hours of exposure whereas hexane stem extract had larval mortality of 60 to 100%. However, the aqueous leaf extract had 40 to 100% mortality as the aqueous stem extract showed 35 to 100% mortality after 30 minutes to 24 hours respectively. The methanol leaf extract showed highest toxicity against the test larvae with LC₅₀ value of 2.52 mg/ml; and LC₉₀ value of 218.15 mg/ml while the least toxicity was observed on aqueous stem extract with LC₅₀ value of 70.71 mg/ml; and LC₉₀ value of 1635.76 mg/ml after 30 minutes of exposure respectively. All the test larvae treated with various extracts exhibited 100% mortality after 24 hours of exposure with less concentrations of the extract required to kill the larvae as time of exposure increased. The toxicity of the various leaf extracts on the mosquito larvae were relatively greater than those of the stem. This is supported by the abundance of secondary metabolites. The findings suggest that the hexane, methanol and aqueous leaf and stem extracts of J. curcas have the potential to be used as an effective botanical larvicide.