Chemical composition, acaricidal activity, and acetylcholinesterase inhibitory activity of two chemotypes of Eugenia stictopetala essential oil against Rhipicephalus (Boophilus) microplus.

Rhipicephalus (Boophilus) microplus, an ectoparasite affecting livestock in tropical and subtropical regions, causes significant economic losses worldwide. In this context, effective control alternatives based on natural products are essential. This study evaluated the chemical composition, acaricidal activity, acute toxicity, and acetylcholinesterase (AChe) inhibition of essential oils (EO) from two chemotypes of Eugenia stictopetala (EOEs-1 and EOEs-2). Gas Chromatography-Mass Spectrometry (GC-MS) analysis revealed that both chemotypes were rich in monoterpene hydrocarbons (64.6 %). EOEs-1 was characterized mainly by myrcene (60.4 %) and citral (neral: 11.0 %; geranial: 15.1 %), whereas EOEs-2 contained myrcene (59.3 %), geraniol (20.0 %), and linalool (14.1 %) as its major constituents. Acaricidal activity was assessed by Larval Immersion Test (LIT) against R. microplus larvae, including the isolade compounds citral, myrcene, geraniol, and linalool. EOEs-1 exhibited the strongest acaricidal activity (LC₅₀ of 1.798 mg/mL), with citral exhibiting similar potency (LC50=1.639 mg/mL), while EOEs-2 showed an LC₅₀ of 2.376 mg/mL. Additionally, both essential oils were capable of inhibiting the native acetylcholinesterase (AChE) of R. microplus, with EOEs-1 showing the strongest activity and emerging as a promising candidate for the control of this ectoparasite.