Avaliação dos efeitos dos extratos de Metarhizium spp. e da deltametrina na morfologia do integumento e do ovário de Rhipicephalus microplus (Acari:Ixodidae)

Abstract

Rhipicephalus microplus ticks are responsible for significant losses in livestock production. Among the damage caused to their preferred hosts, cattle, are the transmission of pathogens, reduced productivity, and skin damage. The primary method of controlling these ectoparasites is the use of synthetic acaricides. However, these substances, especially when misused, can lead to adverse effects such as the accumulation of residues in animal-derived products and the environment, as well as the selection of resistant tick strains. In this context, it is necessary to develop new control alternatives. The use of fungal extracts, which can be obtained from the fermentation of Metarhizium anisopliae (MA) and Metarhizium robertsii (MR), for example, represents a promising alternative, as they contain biodegradable and highly specific substances. Therefore, this study aimed to evaluate the effects of active and denatured extracts of MA IP119 and MR IP146, applied either alone or in combination with the synthetic acaricide deltamethrin, on the mortality of ticks and morphology of the integument and ovaries of R. microplus. To achieve this, ticks were immersed in different treatment solutions and observed daily for seven days to assess mortality and to collect integument and ovary samples. Histological slides were prepared using standard techniques, and the organs were evaluated through morphometric and semiquantitative analyses. The results showed tick mortality in groups exposed to fungal extracts, while the addition of deltamethrin led to distinct effects among the groups. The main morphological changes observed in the integument included altered cuticle morphology, disappearance of cuticular subdivisions, partial absence of the subcuticle, epithelial stratification and disorganization, and pyknotic nuclei. In the semiquantitative analysis, treatments with both M. anisopliae extracts, applied alone or in association with the synthetic acaricide, as well as the group exposed to the denatured extract of M. robertsii, showed higher individual index averages compared to the control group. Among the alterations observed in the ovaries were oocytes with irregular shapes, cytoplasmic and nucleolar vacuolization, and irregularities and thickening of the chorion. In the semiquantitative analysis, all treatment groups exhibited higher individual index averages than the control group. Thus, the results demonstrated that Metarhizium spp. extracts negatively affected the integument and ovaries, with potential implications for the control of R. microplus.