Sublethal concentrations of acetylcarvacrol strongly impact oocyte development of engorged female cattle ticks Rhipicephalus microplus (Canestrini, 1888) (Acari: Ixodidae).

•Actetylcarvacrol impairs R. microplus reproduction due to morphological alterations in oocytes.•The main alterations were found in the chorion, cytoplasm and nucleolus.•The semiquantitative analysis used facilitates comparisons between chemicals.