Bioactivity of Essential Oils of Laggera pterodonta and Laggera aurita against Larvae of Anopheles gambiae, Malaria Vector.

The role of plants as sources of biologically active entities cannot be overemphasized. Plants belonging to different families having mosquitocidal activity have been discovered from an established ethnobotanical and laboratory-based studies. Biological control of mosquitoes using botanicals remains the safest and environmentally sound alternative to chemical control. The essential oil of two Nigerian Laggera species, L. pterodonta and L. aurita, were investigated against the fourth instar larvae of the malaria vector, Anopheles gambiae. WHO protocol was adopted for the larvicidal bioassay. Three replicates comprising of 20 larvae each were exposed to various concentrations of the essential oil. Larval mortality was observed after 24 and 48 hours. The results showed that mortality increased with increase in concentration and period of exposure. The essential oil of L. pterodonta was found most effective with LC₅₀ values of 418 and 404 mg/L after 24 and 48 hours, respectively while the essential oil of L. aurita recorded LC₅₀ value of 688 and 642 mg/L after 24 and 48 hours, respectively.The GC-MS results revealed the essential oil of L. pterodonta comprises 50.83% of compounds that have been reported to have larvicidal activity while the essential oil of L. aurita comprises of 43.69% compounds with larvicidal activity. The better activity of L. pterodonta essential oil could be attributed to it having higher percentage of compounds like ɤ-Terpinene and 4-Carvomenthenol with larvicidal activity. The results suggest that the essential oil of the plants have the potential to be used as eco-friendly approach for the control of mosquitoes.