Chemical Composition and Acaricidal Activity of the Essential Oils of Some Plant Species of Lamiaceae and Myrtaceae against the Vector of Tropical Bovine Theileriosis: Hyalomma scupense (syn. Hyalomma detritum).

The present study aimed to investigate the acaricidal properties of six essential oils. They were extracted from some plant species (Lamiaceae and Myrtaceae) using the technique of hydrodistillation with the Clevenger apparatus. The chemical compositions of the essential oils under study were determined by gas chromatography-mass spectrometer (GC-MS). An Adult Immersion Test (AIT) and a Larval Immersion Test (LIT) were used to evaluate the acaricidal activity of these essential oils against the adults and larvae of Hyalomma scupense. GC-MS analysis showed the major constituents of each essential oil: 25.49% of α-thujone (lavender); 46.82% of carvacrol (oregano); 78.78% of carvacrol (thyme); 40.27% of 1,8-cineole (blue gum); 17.45% of p-cymene (river red gum); and 26.96% of 1,8-cineole (rosemary). The biotests on the essential oils revealed that they inhibit the reproduction of H. scupense engorged females at a rate of 100 % with doses of 0.781 μl/ml of rosemary, 1.562 μl/ml of thyme, 3.125 μl/ml of lavender and oregano, and 6.250 μl/ml of blue gum and river red gum. After a treatment that lasted for 24 hours, essential oils showed a larvicidal activity with respective values of lethal concentrations (LC): LC₅₀, LC₉₀, and LC₉₅ (0.058, 0.358, and 0.600 μl/ml for thyme; 0.108, 0.495, and 0.761 μl/ml for rosemary; 0.131, 0.982, and 1.740 μl/ml for oregano; 0.155, 2.387, and 5.183 μl/ml for blue gum; 0.207, 1.653, and 2.978 μl/ml for river red gum; and 0.253, 2.212, and 4.092 μl/ml for lavender). This is the first report on the acaricidal activity of these essential oils against H. scupense. The results obtained showed that the essential oils with chemotype carvacrol, 1,8-cineole, α-thujone, and p-cymene are highly acaricidal, and they can be used for ticks control. However, further studies on their toxicity in nontarget organisms are required.