Óleos essenciais de Leptospermum scoparium, Origanum vulgare e Litsea cubeba sobre Rhipicephalus microplus: atividade acaricida, influência dos solventes e busca por frações com maior bioatividade

Abstract

The use of natural products in the research of tick control for Rhipicephalus microplus has increased every year and with promising results. In this sense, the present study performed the phytochemical characterization of the essential oils (EOs) of Leptospermum scoparium, Origanum vulgare and Litsea cubeba, and evaluated the acaricidal activity of these EOs in solutions prepared using ethanol, dimethylsulfoxide (DMSO) and Tween 80 on larvae and females of R. microplus. In addition, the isolation of three L. scoparium fractions was also performed and their acaricidal activity was tested in the same stages already mentioned. The results of Gas Chromatography and Mass Spectrometry showed that cis-calamenene (29.82%), carvacrol (64.85%) and geranial (42.44%) were the majority compounds of L. scoparium, O. vulgare and L. cubeba, respectively. The isolated L. scoparium fractions were: A1, rich in sesquiterpene hydrocarbon, A2 and A3 rich in β-tricetones. Bioassays with unfed larvae were performed by immersion test of larvae with all EOs at concentrations from 2.5 to 10.0 mg/mL and at concentrations from 0.625 to 10 mg/mL for the three fractions obtained from L. scoparium EO. We observed 100% mortality of larvae in all concentrations treated with L. scoparium EO when diluted in DMSO and ethanol, as well as in treatments with O. vulgare EO when diluted in DMSO, while L. cubeba EO obtained over 99% mortality only in concentrations of 10 mg/mL using the same solvents. For engorged females, the immersion test was performed in concentrations from 2.5 to 10.0 mg/mL. A control percentage above 90% was observed only in the highest concentrations of L. scoparium and O. vulgare EOs diluted in DMSO and ethanol, while L. cubeba EO did not reach 90% control in any of the treatments. In tests with L. scoparium fractions, larval mortality in the fractions rich in β-trichetones (A2 and A3) was above 97% at a concentration of 2.5 mg/mL, while in A1 fraction, rich in sesquiterpene hydrocarbons, at the same concentration (2.5 mg/mL), it did not reach 22%. In the Adult Immersion Test, the percentage of control was higher than 98% in the lowest concentration (2.5 mg/mL) of A1 fraction, while in the treatments with fractions A2 and A3, the controls were 16 and 50%, respectively. Thus, we can conclude that the EOs of L. scoparium, O. vulgare and L. cubeba have acaricidal activity on R. microplus, as well as the fractions derived from the L. scoparium EO