ORIGINAL PAPER Acaricidal efficacy of thymol on engorged nymphs and females of Rhipicephalus sanguineus (Latreille, 1808) (Acari: Ixodidae) Caio Márcio de Oliveira Monteiro & Erik Daemon & Mateus Aparecido Clemente & Leonardo dos Santos Rosa & Ralph Maturano Received: 25 May 2009 / Accepted: 8 June 2009 / Published online: 27 June 2009 # Springer-Verlag 2009 Abstract The present work was aimed at evaluating the “in vitro” efficacy of different concentrations of thymol on engorged nymphs and females of Rhipicephalus sanguineus. The nymphs were separated in seven groups and immersed in different concentrations of thymol (0.25%, 0.5%, 1.0%, 1.5%, and 2.0%) for 5 min. A control group was established (water+dimethylsulfoxide) together with a positive control group (Amitraz*), and mortality was evaluated after 15 days. In order to perform the experiment with females, the same methodology was used, and the following concentrations were tested: 1.0%, 1.5% and 2.0%. After 5 min of immersion, the engorged females were fixed on Petri dishes with the aid of a double-sided adhesive tape and kept in a climatized room regulated at 27±1°C and UR >80±10%, and different parameters referring to the biology of the non- parasitary phase were evaluated daily. The values found for thymol efficacy on nymphs were 0.0%, 100%, 100%, 100%, and 100% in concentrations of 0.25%, 0.5%, 1.0%, 1.5%, and 2.0%, respectively. In the experiment with engorged females, thymol did not induce any significant alterations (p <0.05) in the parameters of weight alteration, egg mass weight, pre-oviposition period, hatching percentage, egg production index and nutritional index; however, it affected the engorged females final weight in all treatments (p >0.05). The concentration of thymol 2% was the one that showed a better efficacy (41%). It was concluded that thymol had a more accentuated deleterious effect on engorged nymphs, and it might be a promising supporting agent for the control of this ixodid. Introduction Rhipicephalus sanguineus (Latreille 1808) (Acari: Ixodidae), more commonly known as “the brown dog tick,” is an ixodid that has a broad geographic distribution, whose medical– veterinary importance is characterized by direct (host spoliation) and indirect (transmission of pathogens) damages in dogs (Labruna 2004; Dantas-Torres 2008). This tick also assumes importance in the transmission of diseases to humans. In the Mediterranean region, it was incriminated as a vector of Rickettsia conori, etiologic agent of Boutonneuse Fever (Sousa and Bacelar 2004; Matsumoto et al. 2005), and recently, it was also incrim- inated in the USA as a vector of R. rickettsii, etiologic agent of Rocky Mountain spotted fever (Demma et al. 2005). In Brazil, this ixodid is considered a potential vector of this latter agent (Rozental et al. 2002), a fact that has been reinforced by recent reports on human parasitism by this tick (Dantas-Torres et al. 2006; Louly et al. 2006; Guglielmone et al. 2006). The use of synthetic acaricides is the traditional method for the control of this arthropod; yet, currently, there are reports related to R. sanguineus populations resistant to different chemical bases commercially available (Miller et al. 2001; Martins et al. 2006; Borges et al. 2007). Besides the aspect of the resistance, the demand in the search for new pest-control alternatives is increasing, aiming to minimize the use of chemicals, in order to reduce the quantity of residues in the environment (Baladrin et al. 1985; Chagas 2004). Therefore, the search for products of vegetable origin has been gaining more and more ground, as they present lower risk of environment contamination and slower resistance develop- ment rate (Chagas 2004). Thymol (=5meil-2-isopropil-1- fenol) is a volatile, refringent monoterpenoid found in plants Parasitol Res (2009) 105:1093–1097 DOI 10.1007/s00436-009-1530-x C. M. de Oliveira Monteiro (*) : E. Daemon : M. Aparecido Clemente : L. dos Santos Rosa : R. Maturano Universidade Federal de Juiz de Fora (UFJF), Juiz de Fora, Brazil e-mail: -caiosat@gmail.com