Entomopathogenic fungi in the control of Rhipicephalus microplus at different developmental stages: an in vitro study.

Given the need to develop sustainable strategies for the management of ectoparasites, the inclusion of eco-friendly mycoacaricide and/or mycoinsecticide products has become increasingly imperative. Rhipicephalus microplus is an ectoparasitic arthropod of major economic and sanitary importance in livestock production, acting as a vector of pathogens of veterinary relevance and causing substantial production losses. Control of this tick species has become progressively more challenging due to the widespread development of resistance to synthetic chemical acaricides commonly used in cattle production systems, highlighting the need for alternative approaches within integrated tick management programs. In this context, the present study evaluated the in vitro efficacy of the entomopathogenic fungi Beauveria bassiana IBCB66 and Metarhizium anisopliae IBCB425 against different developmental stages of R. microplus, including engorged females, eggs, and unfed larvae. Bioassays were conducted using conidial suspensions at concentrations ranging from 106 to 109 conidia/mL. Both fungal isolates exhibited high conidial viability (>90%) after 24 h of incubation. In the engorged-female immersion assay, B. bassiana IBCB66 at 109 conidia/mL significantly reduced egg mass and key reproductive parameters, whereas M. anisopliae IBCB425 affected hatchability of eggs laid by treated females. In the egg bioassay, direct exposure of eggs to conidial suspensions reduced hatching at the highest concentrations. In the unfed larval bioassay, both isolates caused significant larval mortality across the tested concentrations. These results demonstrate that B. bassiana IBCB66 and M. anisopliae IBCB425 exert biological effects at multiple stages of the R. microplus life cycle and support their potential use as environmentally sustainable components of integrated tick control strategies.