Repellent Effect on Rhipicephalus sanguineus and Inhibition of Acetylcholinesterase by Volatile Oils

The brown dog tick, Rhipicephalus sanguineus, is one of the principal tick species of medical-veterinary interest because of its large capacity for transmitting pathogens. This study sought to evaluate the potential for inhibition of acetylcholinesterase and the repellent activity of volatile oils of Satureja montana L., Lamiaceae; Myristica fragrans Houtt., Myristicaceae; and Cymbopogon flexuosus (Nees ex Steud.) W.Watson, Poaceae. The inhibition of AChE was evaluated by spectrophotometry, and the repellent effect was determined by a test of choice in assays with unfed R. sanguineus adults. The principal components found were borneol, γ-terpineol, carvacrol, and p-cymene in the oils of S. montana; sabinene, α-pinene, and β-pinene in the volatile oil of M. fragrans; and geranial in C. flexuosus. The greatest inhibition of acetylcholinesterase was observed with the oils of S. montana and M. fragrans, with an average inhibitory concentration (IC50) of 0.024 and 0.023 µg/ml, respectively. The greatest repellent action against the tick was observed for the oil of S. montana, which exhibited a percentage of repellency (%R) greater than 80% at 14 µl/ml. This activity remained effective for up to 3 h at the highest concentration tested (56 µl/ml), with a %R higher than 60% at these conditions.