Acaricidal activity and effects of acetylcarvacrol on Rhipicephalus (Boophilus) microplus (Canestrini, 1888) engorged female ticks (Acari: Ixodidae)

Abstract

This study aimed to verify the acaricidal potential of acetylcarvacrol (5-isopropyl-2-methylphenol acetate) in Rhipicephalus (Boophilus) microplus engorged female ticks, by determining the lethal concentration for 50, 90 and 99% of the ticks (LC50, LC90 and LC99, respectively). The acetylated derivative of carvacrol was obtained from the reaction with acetic anhydride. The final product was identified from its melting point and by infrared spectroscopy. In order to evaluate the acaricidal potential and the lethal concentrations, engorged females were exposed to the adult immersion test at the following concentrations of acetylcarvacrol diluted in 3% DMSO: 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5 and 8.0 μL/mL. This experiment was performed in triplicate. The LC50, LC90 and LC99 (with 95% confidence intervals) for R. microplus females were 4.62 μL/mL (4.45–4.78), 7.97 μL/mL (7.68–8.26) and 8.73 μL/mL (8.39–9.07), respectively. Tegumentary alterations and dorsal circular deformation were observed in some ticks. Moreover, many individuals were considered in a knockdown state, with no ability to move, although still alive. The present study demonstrated that the acetylation of carvacrol enhances its activity on the southern cattle-tick, causing higher mortality rates even at low concentrations, besides numerous physiological and morphological alterations, opening new paths for tick control.