Acaricidal efficacy of thymol on engorged nymphs and females of Rhipicephalus sanguineus (Latreille, 1808) (Acari: Ixodidae)

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 degrees 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.