Acaricide and ovicide activities of thymol on engorged females and eggs of Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

Abstract

The present work had the objective of evaluating the influence of different concentrations of thymol on the biological parameters of engorged females of Rhipicephalus (Boophilus) microplus and also its ovicide activity on eggs of this tick. In order to carry out the work, four groups were formed, each containing 20 engorged females, which were immersed for 5 min in different concentrations of thymol (1.0%, 1.5%, and 2.0%) and a control group (water + dimethylsulfoxide). The following biological parameters were observed: initial weight (mg); egg mass weight (mg); pre-oviposition, oviposition, and survival period (days); hatching percentage (%HP); egg production (%EPI) and nutritional (%NI) indexes; and the percentage of control (%C). In order to perform the second stage, thymol solutions were sprayed on the egg masses (50 mg). The parameters' initial weight and pre-oviposition did not present significant differences (p>0.05) among the groups. Thymol caused alterations in the parameters egg mass weight, oviposition, survival period, hatching percentage, EPI, and NI, presenting highly significant differences between the treatments and the control group (p<0.01). The control efficacy was higher than 95% in all the treatments, reaching 99% in the concentration of 2.0%. In the ovicide test, the hatching percentage was not affected in any of the treatments (p>0.05). In the second experiment, when eggs were treated directly, the thymol did not affect significantly this parameter. These results demonstrate that thymol showed deleterious action on most of the analyzed parameters; thus, it is possible to conclude that, in laboratorial conditions, this monoterpene was efficient in the control of engorged females of R. (B.) microplus.