Acaricidal efficacy of the monoterpene linalool against the cattle tick Rhipicephalus microplus and its synergistic potential with cypermethrin.

This study evaluated the acaricidal activity of the natural terpene linalool against Rhipicephalus microplus larvae. Four tick populations from different cattle farms with a history of acaricide resistance were selected. The Larval Packet Test (LPT) was used to determine the lethal concentrations (LC50 and LC90) of linalool, cypermethrin, and the combination of LC50 linalool and cypermethrin. Linalool was tested at concentrations ranging from 0.0975 to 50%, while cypermethrin was tested between 0.01% and 3%. The results demonstrated that linalool alone had LC50 values varying across the populations, ranging from 0.5 to 4.33%, and LC90 values ranging from 2.57 to 7.61%. When linalool was combined with cypermethrin, the required concentrations of cypermethrin to achieve LC50 and LC90 were significantly reduced (p ≤ 0.05). This reduction in cypermethrin dosage was observed across all tested populations, indicating that linalool can enhance the acaricidal efficacy of cypermethrin. Integrating linalool with cypermethrin could therefore be valuable for tick management strategies, particularly in reducing reliance on high doses of these acaricides.