Laboratory of Plant Biochemistry, Federal University of Maranhão, Sao Luís, MA, Brazil.
Laboratory of Parasite Control, Federal University of Maranhão, Sao Luís, MA, Brazil.
Vet Parasitol. 2020 Apr;280:109090. doi: 10.1016/j.vetpar.2020.109090. Epub 2020 Mar 19.
The Rhipicephalus (Boophilus) microplus tick is the main ectoparasite of cattle in tropical and subtropical regions worldwide. Resistance to chemical acaricides has become widespread affirming 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 LC of 1.75, 1.54, 1.41, and 0.38 mg.mL for the susceptible strain, and LC of 1.40, 1.81, 1.10, and 1.13 mg.mL for the resistant strain. Thymol and carvacrol inhibited the AChE of the susceptible strain larvae with IC of 0.93 and 0.04 mg.mL, respectively. The IC exhibited by eucalyptol, carvacrol and thymol for AChE of the resistant strain larvae were 0.36, 0.28, and 0.13 mg.mL, respectively. This was the first 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.
微小牛蜱（Boophilus）是世界热带和亚热带地区牛的主要外寄生虫。对化学杀蜱剂的抗药性已广泛存在，这证实了需要新的药物来控制蜱虫。萜类化合物已成为牛蜱控制的一种有前途的替代品，然而，这些化合物的作用机制仍存在争议。乙酰胆碱酯酶（AChE）的抑制是有机磷和氨基甲酸酯杀蜱剂的一种既定作用机制，但萜类化合物对蜱虫 AChE 的可能作用在抗性和敏感株微小牛蜱中很少被研究。本研究旨在评估萜类化合物对抗性和敏感株微小牛蜱 AChE 的抑制作用与它们的杀蜱活性相关。在本研究中使用的萜类化合物中，对伞花烃、百里酚、香芹酚和柠檬醛对敏感株的 LC 分别为 1.75、1.54、1.41 和 0.38mg.mL，对抗性株的 LC 分别为 1.40、1.81、1.10 和 1.13mg.mL。百里酚和香芹酚抑制敏感株幼虫 AChE 的 IC 分别为 0.93 和 0.04mg.mL。桉叶油醇、香芹酚和百里酚对抗性株幼虫 AChE 的 IC 分别为 0.36、0.28 和 0.13mg.mL。这是首次研究萜类化合物对敏感和抗性微小牛蜱 AChE 的作用。由于并非所有具有杀蜱活性的萜类化合物都显示出 AChE 抑制作用，因此需要进一步研究 AChE 参与萜类化合物的杀蜱活性。
