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

Abstract

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.

Acaricidal activity of thymol against larvae of Rhipicephalus microplus (Acari: Ixodidae) under semi-natural conditions

“…However, this article reports the first experiment of the application of thymol in semi-natural conditions. The mortality observed here was above 95 % starting at a thymol concentration of 10 mg/mL, while in the in vitro study by Scoralik et al (2012), the same mortality percentage was observed starting at a concentration of 2.5 mg/mL. These differences can be related to the method used and the greater dissipation of thymol in open environments.…”

“…The acaricidal activity of thymol, a monoterpene found in essential oil of plants of the families Lamiaceae and Verbenaceae (Pengelly 2004), has already been demonstrated in vitro studies on larvae (Novelino et al 2007;Scoralik et al 2012) and engorged ). However, this article reports the first experiment of the application of thymol in semi-natural conditions.…”

“…These differences can be related to the method used and the greater dissipation of thymol in open environments. The experiments of Scoralik et al (2012) were conducted in controlled laboratory conditions, using the larval packet test, that assures continuous contact of the test organisms with the active ingredient, and the groups were all kept in a climatecontrolled chamber, in contrast to the conditions in this study.…”

“…Thymol was tested at concentrations of 2.5, 5.0, 10.0, 15.0, and 20.0 mg/mL. The dilution of substances was made according to Scoralik et al (2012), using ethanol 50 % (50 % ethanol and 50 % distilled water).…”

“…Its efficiency on ticks has been demonstrated in vitro against larvae and adult females of R. microplus (Novelino et al 2007;Monteiro et al 2010;Scoralik et al 2012); larvae and nymphs of Amblyomma cajennense s.l. (Fabricius, 1787) (Mendes et al 2011;Senra et al 2013); larvae, nymphs, and females of Rhipicephalus sanguineus s.l.…”