The indiscriminate use of acaricides is a problem worldwide and has increased the selection of acaricide-resistant tick populations. The goal of this study was to evaluate the acaricide effects of two essential oils (from Schinus molle and Bulnesia sarmientoi) using the larval immersion test on three Rhipicephalus tick species. Rhipicephalus evertsi, Rhipicephalus appendiculatus and Rhipicephalus pulchelus ticks collected in Kenya, without history of acaricide exposure, were tested, as well as individuals from two populations of Rhipicephalus microplus (with or without history of acaricide exposure), for comparison. The sample most resistant to the treatments was a population of R. microplus with previous acaricide exposure, whereas the least tolerant sample was a strain of the same species that never had contact with acaricides (Porto Alegre strain). Interestingly, the field tick samples without previous acaricide exposure responded to essential oils with a mortality profile resembling that observed in the acaricide-resistant R. microplus field population, and not the susceptible Porto Alegre strain. The essential oil of B. sarmientoi and its two components tested (guaiol and bulnesol) caused the highest mortality rates in the tested species and are potential molecules for future studies on control methods against these species.

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Commercial synthetic acaricides have selected resistant populations of Rhipicephalus microplus, and generate residues in the environment or in milk/cattle products. In this study, aqueous extracts (AE) from Melia azedarach (Maz), Allium sativum, Capsicum chinense, Nicotiana tabacum (Nta) and Dysphania ambrosioides were evaluated for the bioactivity against the cattle tick. The treatment using Nta or Maz AE resulted in the lowest egg hatching rate (34.0 ± 11% and 25.0 ± 19%), and in the values of reproduction inhibition ranging from 89.0% to 85.3%. Phytochemical screening associated to RP-HPLC/DAD analysis suggested the presence of alkaloids for Nta, and of flavonoids, other than gallic acid derivatives or catechins, for Maz.Such results highlighted that the use of Nta and Maz AE can be a promising source for the control of infections caused by the cattle tick.