Phytochemical screening and larvicidal activities of Cymbopogon citratus and Annona senegalensis against Culex quinquefasciatus

The alteration of mosquito life cycle using larvicides is key in the control of diseases transmitted by mosquitoes. The residual and environmental effect of some of these synthetic larvicides has given an opportunity to search for a potent larvicide as an alternate control measure against mosquitoes. Aqueous and ethanol extracts of Cymbopogon citratus and Annona senegalensis were tested against the 3rd and 4th instar larvae of Culex quinquefasciatus using a conventional method described by World Health Organization. Analysis of the ethanol extract for phytochemicals revealed that alkaloids, flavonoids, saponins, steroids, tannins, terpenoids and glycosides were present in both species. Toxicity activities of these extracts were observed on the Cx. quinquefasciatus larvae with the ethanol extract more potent than the aqueous extract. Ethanol extract of A. senegalensis exhibited potent larvicidal activity than C. citratus where 100% mortality was recorded after 24 h in all the treatment concentrations. This therefore, revealed that ethanol extract is more toxic than the aqueous extract on Cx. quinquefasciatus larvae. This is further evident in the result obtained from LC50 and LC95, where ethanol extract had recorded lower concentrations (-2.7E+07 and 0.891 ppm) for C. citratus and A. senegalensis, respectively as compared to 2.669 and 6.656 ppm of aqueous extracts for C. citratus and A. senegalensis, respectively. Therefore, it is imperative for more researches to be conducted on isolation and purification of compounds that enable the plants confers larvicidal properties on insect pests. Also, sustainable use of such bio-pesticides should be encouraged in mosquito control practices.