Behavioral response of the tick Rhipicephalus linnaei to the entomopathogenic fungus Metarhizium anisopliae

The tick Rhipicephalus linnaei (Acari: Ixodidae), formerly recognized as the tropical lineage of Rhipicephalus sanguineus sensu lato (s.l.), is a globally distributed species. Entomopathogenic fungi offer a promising alternative to synthetic acaricides for tick control, yet little is known about the olfactory behavioral response of R. linnaei to fungal exposure. This study used a Y-tube olfactometer to investigate adult ticks' attraction or repellency to Metarhizium anisopliae conidia and fungal-colonized tick carcasses. Results showed that most adult R. linnaei moved toward the olfactometer arm containing the lowest conidial concentration (1 × 10⁵ conidia mL^-1 in mineral oil), indicating attraction. Similarly, most ticks preferred the arm with five fungal-colonized tick carcasses, which resulted from engorged females previously treated with oil conidial suspension. However, higher conidial concentrations or exposure to one or two fungal-colonized carcasses did not elicit attraction or repellency in ticks. This study is the first to report tick behavioral responses to M. anisopliae conidial suspensions and colonized tick carcasses. The observed attraction, although considered reasonably weak, indicates that volatile organic compounds from M. anisopliae IP 119 may affect tick behavior. In addition, oil formulation seems to stimulate the ticks' behavioral responses to the fungal conidia, potentially by enhancing or suppressing the production of volatile compounds. These findings provide new insights into tick-fungus interactions, supporting the potential use of M. anisopliae in tick management strategies.