Behavioural responses of off-host ticks (Ixodidae) to predators and pathogens

Ticks spend most of their life in moist off-host microhabitats, where they are protected from desiccation but susceptible to predators and entomopathogens. I investigated whether ticks avoid chemical cues indicative of ant predators and the entomopathogenic fungus Beauveria bassiana (Bb). In olfactometer bioassays, Ixodes scapularis ticks were significantly deterred by semiochemicals originating from the poison and Dufour's glands of Formica oreas thatching ants. Formic acid and hydrocarbons released from these glands deterred ticks but attracted worker ants. Contrary to my prediction, females and males of the ticks Amblyomma americanum, Dermacentor variabilis, Ixodes ricinus, and I. scapularis sought, rather than avoided, Bb. In further bioassays, I. scapularis oriented towards both harmful Bb and harmless soil-dwelling fungi, implying that fungi – regardless of their pathogenicity – signal habitat suitability to ticks. Responses to Bb were mediated by contact chemoreception of metabolites associated with cellulose breakdown. Ticks were deterred by the common fungal metabolite 2-methylisoborneol.