Acaricidal activity of Myrcia splendens essential oils on Rhipicephalus microplus larvae

Rhipicephalus microplus is a major pest in Brazilian livestock, causing significant economic losses. Current control methods have drawbacks such as high costs, the need for specialized professionals and variable product effectiveness. Myrcia splendens extracts and essential oils are known for their antimicrobial properties, but there is no research on their acaricidal activity. This study aimed to investigate the chemical composition, acaricidal, anticholinesterase and cytotoxic activities of essential oils from two chemotypes (A and B) of M. splendens. Chemical composition was analyzed by Gas Chromatography coupled with Flame Ionization Detection (GC/FID) and Mass Spectrometry (GC/MS). The analysis revealed that the essential oils were rich in sesquiterpenes, with carotol (18.08 %) being predominant in chemotype A, while (2E,6E)-methyl farnesoate (42.64 %) was predominant in chemotype B. The oils exhibited acaricidal activity against R. microplus larvae in a concentration-dependent manner, with chemotype A showing the highest potency (LC₅₀ = 4.06 mg/mL). The oils also inhibited acetylcholinesterase activity (p < 0.05), a potential target for acaricides, with chemotype B showing greater activity (IC₅₀ = 0.14 mg/mL), suggesting this as a mechanism for their acaricidal effect. Cytotoxicity testing in Vero cell cultures showed that only chemotype A reduced cell viability by 19 % at the highest concentration (2 mg/mL). In conclusion, M. splendens essential oils exhibit in vitro anti-tick activity with low toxicity, with chemotype A being more effective.