Evaluation of the acaricide activity of thymol on engorged and unengorged larvae of Rhipicephalus sanguineus (Latreille, 1808) (Acari: Ixodidae)

The present work was aimed at evaluating the in vitro efficacy of thymol on engorged and unengorged larvae of Rhipicephalus sanguineus. In order to perform the study, unengorged larvae were interleaved on filter paper (2 × 2 cm) recently sprayed with thymol in the following concentrations: 0.25%, 0.5%, 1.0%, 1.5%, and 2.0%. For each concentration, ten repetitions of 50 larvae each were performed. A control group was established (water + DMSO) together with a positive control group (Amitraz), with ten repetitions each. Mortality was evaluated after 24 h. For the test with engorged larvae, the same thymol concentrations were used with the larvae being immersed for 5 min and mortality evaluated after 15 days. The values found for thymol efficacy for unengorged larvae were of 21.3%, 17.4%, 19.1%, 32.1%, 37.7% and for engorged larvae 3.0%, 0.0%, 3.0%, 97.0%, and 100.0% in concentrations of 0.25%, 0.5%, 1.0%, 1.5%, and 2.0% respectively. We have concluded that thymol had a deleterious effect on larvae of R. sanguineus, especially on engorged larvae for which 100% mortality was found in higher concentration.