Efeito acaricida e repelente dos óleos essenciais de Backhousia citriodora, Callistemon viminalis e Cinnamodendron dinisii em carrapatos do gênero Rhipicephalus (Acari: Ixodidae)

Abstract

The Rhipicephalus microplus and R. sanguineus sensu latu ticks are of great importance in livestock, veterinary medicine and public health, whether for economic reasons or for the transmission of pathogens to their hosts. Due to the problems associated with the toxicity of synthetic substances commonly used tick control, substances of natural origin have been explored for this purpose. In this context, essential oils, constituted by plant secondary metabolites belonging mainly to the classes of terpenes and phenylpropanoids, have been shown as a promising alternative to the use of synthetic products. In the present study, the essential oils of the plant species Backhousia citriodora, Callistemon viminalis and Cinnamodendron dinisii were extracted by hydrodistillation, chemically characterized by Gas Chromatography Coupled to Mass Spectrometry and Gas Chromatography with Flame Ionization Detector and evaluated biologically for their acaricidal action in R. microplus, through Adult Immersion Test, and repellent on R. sanguineus s. l, through a choice test. Additionally, in order to infer a possible mechanism of action of these essential oils, their ability to reduce the enzymatic activity of acetylcholinesterase was evaluated using Ellman's colorimetric method. The extraction yields of essential oils of the species B. citriodora, C. viminalis and C. dinisii were 2.20, 0.94 and 1.50%, respectively. The chemical characterization revealed that the essential oil of B. citriodora is mainly constituted by citral (98.9%), while the essential oil of C. viminalis is rich in 1.8-cineol (78.1%), α- pinene (12.5%) and limonene (3.36%) and that of C. dinisii showed α-pinene (30.8%), β-pinene (12.5%) and sabinene (11.3%) in higher proportions. All the essential oils evaluated showed an acaricidal effect, with B. citriodora being the one that showed the best results, with the lowest concentration value capable of causing 50% lethality of individuals, which was 3,276 μL mL-1), followed by C. viminalis (8,936 μL mL-1) and C. dinisii (8.195 μL mL-1), which presented similar values. Towards the repellency test, B. citriodora essential oil was also the most effective, showing a repellency index of 0.33 even after one hour of application. The C. viminalis and C. dinissi essential oils showed significant repellency only at the highest concentration and in the shortest evaluation time, with repellency indexes of 0.40 and 0.43, respectively. The C. viminalis essential oil was the only one capable of causing a significant reduction in the activity of acetylcholinesterase, which at a concentration of 0.33 μg mL-1 was able to reduce the enzymatic activity by 50%, indicating that this is the only one, among the essential oils studied, which can present their toxic effects to ticks through this mechanism of action. The essential oils evaluated, especially those obtained from B. citriodora, can be considered as sources of bioactive compounds in tick control.