Acaricidal activity of Acmella oleracea (Asteraceae) extract against Rhipicephalus microplus: What is the influence of spilanthol?

Abstract

The present study was carried out to evaluate and compare the acaricidal activity of different fractions of Acmella oleracea methanolic extract, containing 0.0 % (F1), 24.5 % (F2), 48.0 % (F3) and 100 % (F4) of spilanthol, on unfed larvae and engorged females from the same Rhipicephalus microplus population. To obtain these fractions, the crude extract was subjected to different extraction procedures using increasingly polarized solvents to isolate the spilanthol compound. The Larval Packet Test was used to evaluate acaricidal activity in unfed larvae at concentrations ranging from 0.2 to 25.0 mg/mL, while for engorged females, the Adult Immersion Test was performed at concentrations from 3.1 to 25.0 mg/mL. The F1 fraction showed no activity on unfed larvae, while a control percentage of 44.6 % was observed at a concentration of 25.0 mg/mL for engorged females. For unfed larvae, the F2 fraction resulted in 95.7 % mortality at a concentration of 1.6 mg/mL, with a control percentage of 92.7 % for engorged females at a concentration of 12.5 mg/mL. Fractions F3 and F4 had similar activity against unfed larvae, with mortality >84.0 % from the concentration of 0.8 mg/mL. This similarity between the fractions was also observed for engorged females from a concentration of 12.5 mg/mL, resulting a control percentage >94.0 %. These results demonstrate that the presence of spilanthol is an important factor for the acaricidal activity of A. oleracea extract. Fraction extracts with 24.5, 48 and 100 % of spilanthol have similar acaricidal activity on R. microplus.