In vitro evaluation of the acaricidal activity of Syzygium aromaticum (L.) essential oil and eugenol against non-fed larvae of Rhipicephalus sanguineus

Plant extracts and essential oils have been showing potential for use as acaricides. Rhipicephalus sanguineus, the brown tick, mainly parasitizes dogs and is responsible for pathogens transmission. The insecticidal and acaricidal activity of the essential oil (EO) of Syzygium aromaticum and eugenol have already been reported, however the activity against R. sanguineus is lacked. To evaluate the acaricidal activity of S. aromaticum EO and eugenol against larvae of R. sanguineus, in vitro assays were performed using the larval immersion test. Bioassays were performed in duplicate, within the concentration range of 0.078 to 40 mg.mL-1. Mortality assessment was performed after 24 hours. Mortality above 90% was achieved through using the EO and eugenol at concentrations greater than 5 and 10 mg.mL-1, respectively. The LC50 values of 1.4 and 3.3 mg.mL-1 for eugenol and S. aromaticum EO, respectively, while the LC90 values found for eugenol and S. aromaticum EO were, respectively, 6.4 and 6.7 mg.mL-1 were calculated. These compounds present activity against R. sanguineus larvae and demonstrate potential for use as acaricides.