Acaricidal effect of essential oil of Clausena anisata (Rutaceae) on larvae of three tick species: Amblyomma variegatum, Rhipicephalus (Boophilus) decoloratus and Rhipicephalus (Boophilus) microplus

Abstract

Control measures of livestock ticks based on chemicals has become worrisome because of the development of resistance, especially in the case of Rhipicephalus (Boophilus) microplus. It has become imperative to search for alternative tick control methods. Thus, the toxicity of the essential oil of Clausena anisata was evaluated on larvae of Amblyomma variegatum, Rhipicephalus (Boophilus) microplus and Rhipicephalus (Boophilus) decoloratus in the laboratory in comparison with flumethrin, a reference chemical acaricide. Tests were carried out with Whatman paper circles impregnated with 200 µL of the essential oil of C. anisata either pure or diluted with palm kernel oil (v/v) at concentrations of 0.0625, 0.05, 0.042, 0.03125, 0.025, 0.020, 0.0156, 0.0125 and 0.01. A total of 100 larvae aged 15 to 21 days were tested with the respective doses on filter paper in Petri dishes. The Petri dishes were incubated at 28 ± 1°C, 85-95% RH and mortalities were recorded after 24 h. Chemical composition of leaf essential oil of C. anisata major compounds were estragol (57.06%) and trans-anethole (29.88%), constituting 86.94% of the crude extract. Dilution of 0.0625 caused 100% larval mortality in the three species. The mortalities were similar for A. variegatum and Rh. (B.) decoloratus at the LD 50 (0.021). The LD 99 of R. (B.) decoloratus was the lowest (0.075). Flumethrin was very toxic with 100% mortality for A. variegatum even at the lowest dose (0.01), unlike species of the genus, Rhipicephalus (B.) which were less sensitive. These results on the use of C. anasata as bio-acaricide and further studies will provide a perspective in response to the resistance of ticks to chemical acaricides.