Use of encapsulated carvacrol with yeast cell walls to control resistant strains of Rhipicephalus microplus (Acari: Ixodidae)

Abstract

The tick Rhipicephalus microplus is typically controlled with synthetic acaricides, but indiscriminate use has selected for ticks that are resistant. The phenol compound carvacrol can serve as an alternative method for controlling R. microplus; however, environmental factors can increase its volatility. A microencapsulation technique using yeast cell walls can prolong the acaricide action of carvacrol, acting as a physical barrier against such environmental action. The aim of the present study was to investigate the encapsulation of carvacrol with yeast cell walls and its activity against resistant R. microplus larvae. Carvacrol was encapsulated with Saccharomyces cerevisiae cell walls; acaricide activity and volatility were measured using a larval immersion test with resistant strains of R. microplus. The efficacy of the encapsulation was confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy. Fourier transform spectroscopy revealed similar vibrational peaks between the analyzed samples, supporting the scanning electron microscopy results that encapsulation occurred. The size difference between the yeast cell walls (diameter 2.5±0.2μm) and the encapsulated carvacrol (diameter de 4.5±0.5μm) was statistically significant (P>0.001). The encapsulated carvacrol showed the highest larvicidal activity against R. microplus, exhibiting a lethal concentration 50 (LC50) of 0.71mg/mL; the LC50 of carvacrol alone was 1.82mg/mL. The yeast cell walls promoted low volatility of carvacrol, maintaining high acaricidal activity for up to 60h, and the reduced efficiency of carvacrol (18%) during 10h following the test was significantly different (P>0.001). The high acaricidal activity and lower volatilization of carvacrol encapsulated with yeast cell walls show that this technique is appropriate for the development of a delivery system and for protecting an active compound to control R. microplus.