Host-Locating Behavior of Nymphal Ornithodoros Concanensis (Acarina: Argasidae)

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Abstract
Factors analyzed to determine the stimuli important to Ornithodoros concanensis nymphs in host detection included carbon dioxide, tick odor, host odor, contact, gravity, light, and heat. Tick odors and host-level concentrations of carbon dioxide did not elicit responses. Significantly reduced kinetic activity in response 10 increasing dorsoventral contact stimuli was observed in recently fed ticks followed by a progressive increase in activity through a period of 1–24 weeks, indicating that the longer nymphal O. concanensis remain unfed the more likely they are to become active and more sensitive to host-associated stimuli. Unfed ticks were negatively geotaxic and positively responsive to host-produced sounds. These traits are responsible for movement toward potential hosts situated in nests or roosts above their harborages and are doubtless the primary cues used by O. concanensis for long-distance host orientation and location. Heat (40°C) seems to be the stimulus for host procurement within 1 to 2 cm and contact with the skin elicits the feeding response. After engorging, ticks detach and exit the hosts' nest onto the cliff face where they display positive geotaxis, which apparently ensures movement down the cliff to suitable hiding sites. Entrance into and restriction to available refuges are evidently determined by the fed ticks' strong negative photokinetic and thigmokinetic responses.

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