Repellent activity of essential oil of the stem of <i>Kleinia squarrosa</i> against mosquitoes

Abstract

Most commercially available repellents of mosquitoes and other biting arthropods are synthetic and  have a severe toxic effect to human. Moreover, these chemicals cause an irreversible damage to the ecosystem as some of them are non-degradable in nature. Therefore, there is a need to develop safe and effective alternatives to the currently available chemicals used to control vectors. In southern Ethiopia, the smoke obtained from burning the stem of Kleinia squarrosa Cufod. is used as a fumigant to ward off mosquitoes. In the present study hydrodistillation of the powdered stem of K. squarrosa gave a pale yellow oil (0.04%; w/w) with a characteristic pungent odor. A total of twenty-seven compounds have been identified by GC-MS analysis, accounting 48.71% of the total oil. The main constituents of the oil were (E)-iso-γ-bisabolene (9%), α-pinene (5.74%), caryophyllene (5.36%) and sabinene (5.55%). The powdered stem of K. squarrosa was also burned, and the smoke extracted to yield a trace amount brownish oil. Analysis of the oil by GC-MS afforded 36 compounds comprising 94.56% of the total peak area. Terpene-4-ol (18.09%), (E)-iso-γ-bisabolene (14.07%), 5-epi-7-epi-α-eudesmol (12.45%), and caryophyllene (8.35%) figured as major compounds. Mosquito repellent activity of the essential oil was tested on guinea pigs against Anopheles gambiae by a modified Kunming mice technique under laboratory testing conditions. The essential oil exhibited a dose-dependent repellent action in the dose range tested (0.03 - 5%; v/v) with ED₅₀ and ED_99.9 values of 1.49% and 4.74% (v/v), respectively. The study further revealed that that the essential oil possesses a 3 h complete protection time. The similarity in the chemical profiles of the essential oil and the oil extracted from the smoke obtained by burning K. squarrosa stem supports the traditional use of the plant as a fumigant to kill mosquitoes.

Keywords: Kleinia squarrosa; fumigant; essential oil; mosquito repellent; Anopheles gambiae