Bio-efficacy of essential oils of Eryngium foetidum L. and Plectranthus amboinicus (Lour.) Spreng against Anopheles gambiae Giles

  Malaria and lymphatic filariasis transmitted by female Anopheles mosquitoes remain health challenges in tropical Africa. Resistance by vectors to synthetic insecticides limits control efforts. This study evaluated efficacy of essential oils of Eryngium foetidum and Plectranthus amboinicus against Anopheles gambiae. Test oils were obtained by hydro-distillation using Clevenger apparatus. From 1 mL stock solution, 31.25, 62.50, 125 and 250 and 500 μL/mL concentrations of E. foetidum and P. amboinicus oils were prepared using serial-dilution with tween 80 as diluent. Each concentration had eighty adult mosquitoes exposed. Results of knockdown and insecticidal tests after 30 and 60 minutes respectively revealed higher susceptibility of An. gambiae to E. foetidum. Eryngium foetidum (250μL/mL) elicited 100% knockdown after 20 minutes. In the insecticidal test, the same concentration resulted in 100% mortality at 40 minutes. Same effect was observed for 500 μL/mL of P. amboinicus oil at 25 and 60 minutes. From Probit analysis, KD50 values were 66.793 and 251.350 μL/mL for E. foetidum and P. amboinicus respectively. Values for LC50 were 85.818 and 428.663 μL/mL for E. foetidum and P. amboinicus respectively. Results demonstrate that E. foetidum oil holds promise as control agent against An. gambiae. Plectranthus amboinicus oil did not demonstrate appreciable efficacy.