Combination of essential oils from Ocimum americanum L., Ocimum gratissimum L., and Lippia multiflora Mold.: a potential solution for controlling the cattle tick Rhipicephalus microplus (Acari: Ixodidae).

The cattle tick Rhipicephalus microplus is one of the most significant ectoparasites affecting livestock in tropical and subtropical regions worldwide. This tick causes substantial economic losses in cattle production by reducing weight gain and milk yield and by transmitting pathogens responsible for diseases such as babesiosis and anaplasmosis. Conventional control strategies rely largely on synthetic acaricides; however, their use poses risks to human health and the environment and has contributed to the rapid emergence of resistant tick populations. Under these circumstances, the search for natural acaricidal alternatives has become essential, with essential oils emerging as a promising solution. The present study aimed to evaluate the acaricidal activity of a combination of Ocimum americanum (1:6), Ocimum gratissimum (2:3), and Lippia multiflora (1:6) essential oils against adult R. microplus using the adult immersion test (AIT). Combination indices and dose reduction indices were calculated to assess the interaction effects between the essential oils. The combination completely inhibited oviposition and larval hatching of R. microplus at concentrations of 100 and 80 mg/mL, respectively. Synergistic effects were observed at all tested concentrations, with achieving 93% efficiency starting at 80 mg/mL. These findings highlight the potential of this essential oil combination for developing natural acaricidal formulations to effectively control R. microplus.