Evaluation of the effects of Satureja montana and Callistemon viminalis essential oils on the ovary morphology of Rhipicephalus microplus female ticks (Acari: Ixodidae)

Abstract

Rhipicephalus microplus ticks cause damage to agriculture due to the transmission of pathogens to cattle as well as reduction in products of animal origin. Due to their medical-veterinary importance and problems associated with resistance, these ectoparasites are targets of several control methods. The essential oil of Satureja montana is, in general, rich in carvacrol and borneol, with proven pesticidal activity. Callistemon viminalis, in turn, has an essential oil composed of 1,8-cineole and α-pinene, also with proven acaricidal and repelent activities. Based on this information, this study aimed to evaluate the effects of different concentrations of S. montana and C. viminalis essential oils diluted in 10% dimethyl sulfoxide (DMSO) on the ovary morphology of engorged R. microplus females. For this, the ticks were submitted to the Adult Immersion Test. After seven days, the ticks were dissected to collect the ovaries. The samples were processed and embedded in historesin, sectioned, stained and analyzed through morphometric and semiquantitative analyses. Similar morphological changes were observed for the two essential oils, including: cytoplasmic vacuolization, irregularity and thickening of the chorion, irregularity in the shape of the oocytes, nucleolar vacuolization, cellular changes in the epithelial wall of the oviduct and pedicel, and changes in the content of proteins and carbohydrates. For the essential oil of C. viminalis, it was also possible to observe a decrease in the size of the nucleus and an increase in vacuolization. Thus,

the results demonstrated the potential of essential oils as promising phytopesticides in the long- term control of these ectoparasites, as they impact ticks reproductive system.