Atividade do timol, carvacrol e eugenol sobre larvas de Rhipicephalus microplus (Acari: Ixodidae) e Rhipicephalus sanguineus s.l. (Acari: Ixodidae) em condições laboratoriais e semi-naturais

Abstract

Substances of plant origin, such as essential oils and their components have demonstrated the potential to be used to control different pests, including ticks. Among these substances stand out monoterpenes thymol and carvacrol and the phenylpropanoid eugenol, molecules that already had their activity demonstrated against ticks Rhipicephalus microplus and Rhipicephalus sanguineus s.l., species of great economic importance. Despite the isolated action of these substances on ticks has been demonstrated in vitro in different papers, until now there are no studies on the effect of the combination of this substances and report of possible synergistic action on ticks. Also there are few studies that evaluate the activity of these substances in natural and semi-natural environments in order to control ticks with targeted actions on the non-parasitic phase. Therefore, this study aimed to evaluate the effects of combinations of monoterpenes thymol and carvacrol and phenylpropanoid eugenol on larvae of Rhipicephalus microplus and Rhipicephalus sanguineus s.l. and evaluate the insecticidal activity of thymol on larvae of R. microplus in semi-natural conditions. The first chapter presents the results of the effects of combinations of substances on the larvae of these ticks. For R. microplus larvae were observed LC50 values for the thymol, carvacrol and eugenol of 1.53; 1.76 and 4.67 mg/ml, respectively, and synergism between all combinations tested. The LC50 values of thymol, carvacrol and eugenol observed for larvae of R. sanguineus s.l., were 2.98; 3.29 and 5.19 mg/ml, respectively. This is the first work reporting the LC50 values of these three substances against R. sanguineus s.l. For this species, eight combinations showed synergistic effect and only the combination of carvacrol+thymol in the concentration of LC50, showed moderate synergism. In this study it was observed that the larvae of R. microplus were more sensitive to the tested substances and their combinations. In the second chapter it was observed for the first time that thymol when applied in Brachiaria decumbens seedlings artificially infested with larvae of R. microplus was able to significantly reduce the infestation by this tick. The highest concentrations (10, 15, 20, 25 and 30.0 mg/ml) resulted efficiencies above 95% and the values found for the LC50 and LC90 were 3.45 and 9.25

mg/ml, respectively. It is concluded that associations between thymol, eugenol and carvacrol at sublethal concentrations have a synergistic effect on larvae of R. microplus and Rhipicephalus sanguineus s.l. and thymol has the potential for reducing R. microplus larvae in semi-natural conditions.