In Vitro Activity of Ethanolic Extract and Essential Oil of Achyrocline satureioides Against Larvae of the Tick Rhipicephalus sanguineus

The tick Rhipicephalus sanguineus is the most prevalent ectoparasite in dogs, causing discomfort to the animals and acting as a vector for several pathogens, including the bacterium Ehrlichia canis and the protozoa Babesia canis, Babesia gibsoni, and Hepatozoon canis. Control of this parasite is traditionally carried out with synthetic chemical acaricides. However, due to the increasing number of cases of resistance, phytotherapy has been increasingly investigated as a promising alternative. In this study, the larvicidal activity of the crude ethanolic extract and essential oil obtained from the inflorescences of Achyrocline satureioides was evaluated, whose constituents were identified through phytochemical analyses and gas chromatography. The analyses revealed that the extract is rich in flavonoids, tannins, and saponins, while the essential oil is composed mainly of terpenes. In contact tests with impregnated paper, the extract at 100 mg/mL showed a mortality rate of 32.2% in R. sanguineus larvae with LC50 calculated at 249.62 mg/mL, while the essential oil, at the same concentration, resulted in 56.55% mortality, and the LC50 and LC90 were 119.73 mg/mL and 185.53 mg/mL, respectively. These results indicate that the essential oil of A. satureioides has significant larvicidal activity and has potential for use as an alternative, alone or in combination with other extracts or synthetic acaricides.