Effects of carvacrol and thymol on the antioxidant and detoxifying enzymes of Rhipicephalus microplus (Acari: Ixodidae).

The present study was conducted to evaluate the effects of carvacrol and thymol on the antioxidant and detoxifying enzymes of larvae from two populations of R. microplus: Jaguar (tick population resistant to six classes of acaricides) and Porto Alegre (susceptible tick population). Carvacrol and thymol were tested at concentrations ranging from 0.14 to 5.0 mg mL-1 in both populations to determine the LC50. In addition, the LC1, LC25, and LC75 were estimated using the LC50 and HillSlope of each compound. Larvae of both populations of R. microplus were then treated with the LC1, LC25, LC50, and LC75 of each monoterpene, and those that survived were processed to evaluate the effects of the compounds on the antioxidant and detoxifying systems of larvae; these effects were assessed by determining the activity of the enzymes, glutathione-S-transferase (GST), catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPX). Larvae from the Jaguar population treated with different lethal concentrations of carvacrol and thymol displayed a dose-dependent increase in CAT, GPX, SOD, and GST after treatment with LC25. Further, larvae treated with the LC75 had the highest levels of enzyme activity for carvacrol (1.76 mg mL-1) and thymol (1.32 mg mL-1). CAT, GPX, SOD, and GST activity in Porto Alegre population larvae treated with carvacrol and thymol also increased significantly up to the LC50 of each monoterpene. However, at the LC75 of carvacrol and thymol, a decrease in the activity of all enzymes was observed for this tick population. These findings indicate that carvacrol and thymol induced increased activity of all evaluated enzymes at different lethal concentrations in R. microplus larvae from two populations. Such findings unveil the possible mechanisms of action of these natural acaricides.