Terpenes on Rhipicephalus (Boophilus) microplus: Acaricidal activity and acetylcholinesterase inhibition

Authors: DOS SANTOS, CARDOSO AL - Universidade Estadual Do Maranhao; GUIMARAES, DOS SANTOS - Universidade Estadual Do Maranhao; DA SILVA, LIMA ALDILENE - Universidade Estadual Do Maranhao; Temeyer, Kevin; Perez De Leon, Adalberto - Beto; COSTA-JUNIOR, LIVIO - Universidade Estadual Do Maranhao; DOS SANTOS, SOARES ALE - Universidade Estadual Do Maranhao

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2020
Publication Date: 4/1/2020
Citation: Dos Santos, C., Guimaraes, D., Da Silva, L., Temeyer, K.B., Perez De Leon, A.A., Costa-Junior, L.M., Dos Santos, S. 2020. Terpenes on Rhipicephalus (Boophilus) microplus: Acaricidal activity and acetylcholinesterase inhibition. Veterinary Parasitology. 280. https://doi.org/10.1016/j.vetpar.2020.109090.
DOI: https://doi.org/10.1016/j.vetpar.2020.109090

Interpretive Summary: The Rhipicephalus (Boophilus) microplus tick is the principal ectoparasite of cattle in tropical and subtropical regions worldwide, responsible for transmission of bovine babesiosis and anaplasmosis. Resistance to chemical acaricides has become widespread affirming the need for new methods of tick control. Terpene chemicals, derived from plants, are a promising alternative to synthetic chemical pesticides for cattle tick control, however the mechanism of action of these compounds is still controversial. Inhibition of acetylcholinesterase (AChE), an enzyme essential to nervous system function, is a well established mechanism of action of organophosphate (OP) and carbamate acaricides, but little is known regarding action of terpenes on tick AChEs. The aim of the present study was to evaluate terpene inhibition of AChE from OP-resistant and sensitive strains of R. microplus in comparison to their acaricidal activity. In the present study, p-cymene, thymol, carvacrol, and citral displayed acaricidal activity with LC50 of 1.75, 1.54, 1.41, and 0.38 mg mL-1 for the susceptible strain, and LC50 of 1.40, 1.81, 1.10, and 1.13 mg mL-1 for the resistant strain. Thymol and carvacrol exhibited relatively strong inhibiion of the AChE activity from the susceptible strain larvae, with IC50 of 0.93 and 0.04 mg mL-1, respectively. The IC50 exhibited by eucalyptol, carvacrol and thymol for AChE of the resistant strain larvae were 0.36, 0.28, and 0.13 mg mL-1, respectively. This was the first study to investigate the action of terpenes on AChE from OP-susceptible and resistant strains of R. microplus. Because some terpenes with acaridical activity showed AChE inhibition and others did not, the participation of AChE in the acaricidal activity of terpenes needs further investigation.

Technical Abstract: The Rhipicephalus (Boophilus) microplus tick is the main ectoparasite of cattle in tropical and subtropical regions worldwide. Resistance to chemical acaricides has become widespread a'rming the need for new drugs to tick control. Terpenes have become a promising alternative for cattle tick control, however the mechanism of action of these compounds is still controversial. Inhibition of acetylcholinesterase (AChE) is a well established mechanism of action of organophosphate and carbamate acaricides, but the possible action of terpenes on tick AChEs has seldom been studied in resistant and sensitive strains of R. (B.) microplus. The aim of the present study was to evaluate terpene inhibition of AChE from resistant and sensitive strains of R. (B.) microplus in correlation with their acaricidal activity. Among the terpenes used in the present study, p-cymene, thymol, carvacrol, and citral displayed acaricidal activity with LC50 of 1.75, 1.54, 1.41, and 0.38 mg.mL-1 for the susceptible strain, and LC50 of 1.40, 1.81, 1.10, and 1.13 mg.mL-1 for the resistant strain. Thymol and carvacrol inhibited the AChE of the susceptible strain larvae with IC50 of 0.93 and 0.04 mg.mL-1, respectively. The IC50 exhibited by eucalyptol, carvacrol and thymol for AChE of the resistant strain larvae were 0.36, 0.28, and 0.13 mg.mL-1, respectively. This was the 'rst study to investigate the action of terpenes on AChE from susceptible and resistant R. (B.) microplus. As not all terpenes with acaridical activity showed AChE inhibition, the participation of AChE in the acaricidal activity of terpenes needs further investigation.