Acaricidal activity of Myrcia splendens essential oils on Rhipicephalus microplus larvae

Area of Science:

• Veterinary Entomology
• Natural Product Chemistry
• Toxicology

Background:

• Rhipicephalus microplus poses a significant economic threat to Brazilian livestock.
• Existing tick control methods face challenges including cost, specialized labor, and variable efficacy.
• Myrcia splendens essential oils, known for antimicrobial effects, have not been studied for acaricidal properties.

Purpose of the Study:

• To evaluate the acaricidal, anticholinesterase, and cytotoxic activities of Myrcia splendens essential oils from two chemotypes.
• To determine the chemical composition of these essential oils.
• To explore potential mechanisms of action for tick control.

Main Methods:

• Essential oils from two M. splendens chemotypes (A and B) were analyzed using Gas Chromatography coupled with Flame Ionization Detection (GC/FID) and Mass Spectrometry (GC/MS).
• Acaricidal activity against R. microplus larvae was assessed in a concentration-dependent manner.
• Anticholinesterase activity was measured, and cytotoxicity was evaluated in Vero cell cultures.

Main Results:

• Both chemotypes were rich in sesquiterpenes; carotol predominated in chemotype A, and (2E,6E)-methyl farnesoate in chemotype B.
• Essential oils exhibited concentration-dependent acaricidal activity, with chemotype A being more potent (LC50 = 4.06 mg/mL).
• Significant acetylcholinesterase inhibition was observed (p < 0.05), particularly for chemotype B (IC50 = 0.14 mg/mL), and chemotype A showed low cytotoxicity.

Conclusions:

• Myrcia splendens essential oils possess in vitro anti-tick properties.
• Chemotype A demonstrated superior acaricidal efficacy with minimal toxicity.
• These findings suggest M. splendens essential oils as a potential eco-friendly agent for Rhipicephalus microplus control.