Metarhizium spp. extracts alter the morphology of the integument and ovary of deltamethrin-resistant Rhipicephalus microplus.

The indiscriminate use of synthetic acaricides in the control of Rhipicephalus microplus ticks results in the accumulation of residues in animal products and the environment, and favors the emergence of resistant strains, making it necessary to develop new control alternatives. Extracts of Metarhizium anisopliae (MA) and M. robertsii (MR) represent a promising strategy, as they contain biodegradable and specific compounds, such as enzymes. This study evaluated the effects of active and denatured extracts of MA and MR, isolated or combined with deltamethrin, on the mortality and morphology of the tegument and ovary of deltamethrin-resistant R. microplus. Ticks were immersed in the solutions and observed for seven days to assess mortality. Histological slides were prepared and evaluated with morphometric and semi-quantitative analyses. The results showed that the fungal extracts induced mortality, while the combination with deltamethrin presented variable results. Changes in the integument included morphological changes in the cuticle, disappearance of cuticular subdivisions, partial absence of the subcuticle, epithelial stratification and disorganization, and pyknotic nuclei. All treatments with MA extracts and the treatment with only the denatured MR extract caused significant changes in the organ. In the ovary, irregular oocytes, cytoplasmic and nucleolar vacuolization, and chorionic thickening were observed. All treated groups showed significant changes in the ovary. These results indicate that Metarhizium spp. extracts negatively affect resistant ticks, although the association with deltamethrin did not potentiate the effects. To our knowledge, this is the first study to report the effects of Metarhizium spp. extracts in the control of R. microplus.