Alpha- and beta-pinene alter the morphology of oocytes in Rhipicephalus microplus ticks (Acari: Ixodidae).

Pinenes are bicyclic monoterpenes that contain two constitutional isomers, alpha- and beta-pinene. Both exhibit a wide range of biological activities, including fungicidal, insecticidal, antimicrobial and antibacterial effects, and are found in the essential oil of numerous plant species with acaricidal properties. Thus, the objective of this research was to evaluate the effect of sublethal concentrations of alpha- and beta-pinene, diluted in 2 % Tween 80, on the morphology of the ovary of semi-engorged Rhipicephalus microplus female ticks. For this, the ticks were immersed in different concentrations of each product for five minutes. After seven days, the animals were dissected to collect the ovaries. The material was processed and included in historesin, sectioned, stained and analyzed using histopathological and semiquantitative analysis. The main morphological changes observed in the oocytes of individuals treated with both compounds were: cytoplasmic vacuolization and disorganization, irregular shape of the oocytes, ring-shaped nucleolus, fusion of granules, irregular basal lamina, basophilic granules in the cytoplasm, and irregular, thick and fragmented chorion. The semi-quantitative analysis showed significant differences between the control group and the groups treated with the highest concentrations of alpha-pinene and all concentrations of beta-pinene. Therefore, the results point to the potential of both isomers as possible compounds to be used in future acaricide formulations.