Background: Resistance of ticks to conventional acaricides supports the evaluation of plant-based alternatives. Objective: This study assessed the in vitro acaricidal and repellent activities of Azadirachta indica vegetable oil, Lippia multiflora essential oil and their mixture, together with their effects on the reproduction of Rhipicephalus microplus and Amblyomma variegatum. Methods: The products were tested at 1, 5 and 9 mg/mL and undiluted. Monopropylene glycol and alphacypermethrin at 0.05 mg/mL served as negative and positive controls, respectively. Mortality was assessed at 24, 48 and 72 h after immersion. Oviposition and egg hatch were monitored in surviving engorged females, whereas repellency was evaluated in independent batches of unengorged females at 30, 45 and 60 min. Results: Mortality increased with concentration and time, with A. variegatum being more susceptible than R. microplus. At 9 mg/mL, the plant-based formulations caused very high, often complete mortality after 48–72 h. In R. microplus, no oviposition was observed from 5 mg/mL onward among the few surviving females, and no offspring were observed. Repellency increased with concentration and was more pronounced with L. multiflora. Concentration and tick species significantly affected repellency, whereas observation time and collection site did not. Conclusions: The formulations showed complementary acaricidal and repellent effects and potential for integrated tick management, subject to chemical characterisation, safety studies and in vivo validation.
