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.

GRAPHICAL ABSTRACT

KEYWORDS:

• Semisynthetic
• cattle
• carvacrol acetate
• control

Highlights

• The LC₅₀ of acetylcarvacrol for Rhipicephalus microplus ticks is 4.62 μL/mL.

• From 4 μL/mL the mean mortality rates were greater than 50%.

• Acetylcarvacrol did not show a dose-dependent effect.

• Knockdown state was observed in a significant percentage of treated ticks.

• Tegumentary changes were observed in ticks treated with acetylcarvacrol.

Acknowledgments

This research was financially supported by CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior), CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) and FAPEMIG (Fundação de Amparo à Pesquisa de Minas Gerais).

Disclosure statement

No conflicts of interest to declare.

Additional information

Funding

Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Brazil) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil).