Cellular immune response of <i>Amblyomma sculptum</i> and <i>Amblyomma americanum</i> to entomopathogenic fungi: Implications for biological tick control

was used in assays to evaluate immune responses. Haemolymph was collected 24 h post-treatment, and smears were prepared for microscopy-based characterization of haemocyte responses. Confocal and fluorescence microscopy were used to classify, quantify and visualize the haemocyte types, including granulocytes, plasmatocytes, prohaemocytes, oenocytoids and spherulocytes. Our findings reveal that plasmatocytes dominate the haemocyte population in A. sculptum, whereas granulocytes are predominant in A. americanum, both showing reduced concentrations following B. bassiana exposure. Prohaemocytes and oenocytoids were present in all groups but at lower frequencies. Additionally, B. bassiana was more effective against A. sculptum, whereas M. robertsii exhibited greater efficacy against A. americanum, with phenoloxidase activity of ~29%. This study provides crucial insights into the cellular immune defences of Amblyomma ticks and highlights potential fungal strains that may overcome tick antifungal susceptibility. These findings establish a foundation for future research on haemocyte-mediated immunity in ixodid ticks, a topic with limited existing literature and contribute to the development of targeted biological control strategies.