Eficácia do composto semi-sintético acetilcarvacrol no carrapato Rhipicephalus sanguineus lato sensu (Latreille, 1806) (Acari: Ixodidae)

Abstract

Rhipicephalus sanguineus sensu lato (s.l.), also known as the brown dog tick, is among the major tick species involved in the transmission of pathogens to animals and humans. Therefore, it is subject to different control methods, such as the use of synthetic acaricides, for example. Synthetic compounds, however, are responsible for toxic effects on hosts and the environment and induce resistance because of their continuous and indiscriminate use. This has led to the search for alternative methods of control, such as the use of extracts, oils and active ingredients from plants. Acetylcarvacrol can be obtained from the acetylation of carvacrol, an aromatic monoterpene extracted from plants with recognized acaricidal action. This process provides an improved pharmacological profile and greater efficacy to the compound. In this context, this work aimed to evaluate the acaricidal potential of acetylcarvacrol in unfed R. sanguineus female ticks, as well as to determine their efficiency in sublethal doses in the control of engorged females of the brown dog tick. The susceptibility of R. sanguineus to acetylcarvacrol, diluted in 3,00% dimethylsulfoxide solution (3,00% DMSO), was evaluated by determining the lethal concentration for 50,00 and 90,00% of ticks after Adult Immersion Test. The efficacy of acetilcarvacrol, in turn, was determined from the analysis of the reproductive performance of engorged females exposed to different concentrations of the product. For this, engorged females were divided into nine groups: two controls (distilled water and 3,00% DMSO) and seven treatments (1,40; 2,10; 2,80; 3,50; 5,00; 6,50 and 8,00 μL/mL). The following parameters were then evaluated for each group: egg production index (EPI), hatching rate (HR), fecundity rate (FR), pre-oviposition period, incubation period, estimated reproduction rate (ER), oviposition and hatch reduction percentage, and product efficacy or percentage of control (PE). The lethal concentrations obtained for 50 and 90% of the animals were, respectively, 2.83 μL/mL and 7.16 μL/mL. Regarding reproductive performance, the animals exposed to 8.00 μL/mL of the product showed the lowest values of EPI, HR, FR and ER. The PE at the highest concentration (8,00 μL/mL) was 90.90%, with reduction of 51.73% and 83.27% in oviposition and hatching, respectively. Thus, the results showed that acetylcarvacrol has acaricidal activity on R. sanguineus s.l., and affects its reproduction when applied in sublethal concentrations.