ORIGINAL PAPER Enhancing the acaricide effect of thymol on larvae of the cattle tick Rhipicephalus microplus (Acari: Ixodidae) by solubilization in ethanol Márcio Goldner Scoralik & Erik Daemon & Caio Márcio de Oliveira Monteiro & Ralph Maturano Received: 14 June 2011 /Accepted: 28 June 2011 /Published online: 16 July 2011 # Springer-Verlag 2011 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); formula- tion 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 formu- lations 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. Introduction Thymol, or thymic acid (2-isopropyl-5-methylphenol), is a monoterpene derived from the plants of the Lamiaceae family (Meshkatalsadat et al. 2007), can be found in the form of colorless crystals with irritating odor and is slightly soluble in water (Farmacopéia Portuguesa VIII 2005). Various articles have described this monoterpene’ s potential as a bactericide, fungicide, nematicide, molluscicide, insecticide and acaricide against different target species and with different formulations (Imdorf et al. 1995; Mansour et al. 2000; Tsao and Zhou 2000; Ferreira et al. 2009; Pandey et al. 2009; Baggio et al. 2004). Tests under laboratory conditions have revealed that thymol has an acaricide activity against unengorged larvae and engorged females of Rhipicephalus microplus (Canestrini, 1888) (Acari: Ixodidae) (Novelino et al. 2007a; Monteiro et al. 2010), engorged larvae and nimphs of Rhipicephalus sanguineus (Latreille, 1808) (Daemon et al. 2009; Monteiro et al. 2009) and engorged and unengorged larvae and engorged nymphs of Amblyomma cajennense (Fabricius, 1787) (Acari: Ixodidae) (Silva 2011). Novelino et al. (2007b) also showed that thymol acts as a repellant against larvae of the cattle tick. These results indicate that thymol can be a promising alternative for integrated tick management. However, in these studies, the thymol tested was dissolved under heating in water M. G. Scoralik : E. Daemon : R. Maturano Programa de Pós-graduação em Comportamento e Biologia Animal, Universidade Federal de Juiz de Fora, Juiz de Fora, Minas Gerais, Brazil E. Daemon e-mail: erik@acessa.com C. M. de Oliveira Monteiro (*) Programa de Pós-graduação em Ciências Veterinárias, Universidade Federal Rural do Rio de Janeiro, Seropédica, Rio de Janeiro, Brazil e-mail: caiosat@gmail.com Parasitol Res (2012) 110:645–648 DOI 10.1007/s00436-011-2539-5