Enhancing the acaricide effect of thymol on larvae of the cattle tick Rhipicephalus microplus (Acari: Ixodidae) by solubilization in ethanol.

The aim of the present work was to propose a new method of solubilizing thymol for use as an acaricide and to evaluate the resulting product's efficacy on Rhipicephalus microplus larvae. Two experiments were performed, both employing the larval packet test to evaluate the potential of the solutions formulated. In the first experiment, R. microplus larvae were exposed to three new formulations: formulation 1-distilled water (70%) + ethanol (30%) + thymol (10.0 mg/ml); formulation 2-distilled water (50%) + ethanol (50%) + thymol (10.0 mg/ml); and formulation 3-distilled water (55%) + ethanol (40%) + DMSO (5%) + thymol (10.0 mg/ml). A control was prepared for each formulation (same formulations except thymol), and another control group was formed where the larvae did not receive any treatment. From the results obtained in the first experiment, the formulation with the best performance and cost-benefit relation was chosen and was tested at concentrations of 2.5, 5.0 and 10.0 mg/ml on larvae of this tick. In the first experiment, the mortality of the groups treated with thymol was greater than 95% for all three formulations, with significant differences (p < 0.05) in comparison with the control groups, where the mortality was under 1%. In the second experiment, formulation 2 was selected because of its better cost-benefit relation, and the mortality rates were 94.0%, 96.5% and 99.9% for the concentrations of 2.5, 5.0 and 10.0 mg/ml, respectively, demonstrating that thymol dissolved in ethanol has high acaricide activity on cattle tick larvae.