Attraction of the tropical bont tick, <i>Amblyomma variegatum</i>, to human breath and to the breath components acetone, NO and CO₂

Ticks are of medical and veterinary importance and employ several cues in search of a host. Olfaction is one modality by which ticks locate a blood-meal and breath is the major vent of gaseous and volatile metabolites from the host that could contribute to this search. We studied the responses of a hunter tick, <i>Amblyomma variegatum</i>, to diluted human breath and five of its components (acetone, CO₂, NO, isoprene and NH₃) while walking in an air stream on a locomotion compensator. Diluted breath elicited the greatest responses of all treatments in terms of time to onset of upwind walk, attraction, speed and local search behaviour after stimulus off. Acetone, NO and CO₂ also attracted, but with a reduced speed in the case of acetone and NO. Neither isoprene nor NH₃ induced any response. Our study indicates that breath was the most adequate stimulus tested. It also attracted two other ixodid tick species, <i>Rhipicephalus sanguineus</i> and <i>Ixodes ricinus</i>, as well as the argasid tick, <i>Ornithodorus moubata</i>. It appears that the evolution of resource tracking in ticks included sensory and behavioural adaptations for recognition and orientation to host metabolites that are regularly expelled in breath.