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

Abstract

The present study aimed to investigate the acaricidal properties of six essential oils. They were extracted from some plant species (<i>Lamiaceae</i> and <i>Myrtaceae</i>) 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 <i>Hyalomma scupense</i>. GC-MS analysis showed the major constituents of each essential oil: 25.49% of <i>α</i>-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 <i>H. scupense</i> engorged females at a rate of 100 % with doses of 0.781 <i>μ</i>l/ml of rosemary, 1.562 <i>μ</i>l/ml of thyme, 3.125 <i>μ</i>l/ml of lavender and oregano, and 6.250 <i>μ</i>l/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 <i>μ</i>l/ml for thyme; 0.108, 0.495, and 0.761 <i>μ</i>l/ml for rosemary; 0.131, 0.982, and 1.740 <i>μ</i>l/ml for oregano; 0.155, 2.387, and 5.183 <i>μ</i>l/ml for blue gum; 0.207, 1.653, and 2.978 <i>μ</i>l/ml for river red gum; and 0.253, 2.212, and 4.092 <i>μ</i>l/ml for lavender). This is the first report on the acaricidal activity of these essential oils against <i>H. scupense.</i> The results obtained showed that the essential oils with chemotype carvacrol, 1,8-cineole, <i>α</i>-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.