Synergistic attraction of Western black-legged ticks, , to CO and odorant emissions from deer-associated microbes.

Foraging ticks reportedly exploit diverse cues to locate their hosts. Here, we tested the hypothesis that host-seeking Western black-legged ticks, , and black-legged ticks, , respond to microbes dwelling in sebaceous gland secretions of white-tailed deer, , the ticks' preferred host. Using sterile wet cotton swabs, microbes were collected from the pelage of a sedated deer near forehead, preorbital, tarsal, metatarsal and interdigital glands. Swabs were plated on agar, and isolated microbes were identified by 16S rRNA amplicon sequencing. Of 31 microbial isolates tested in still-air olfactometers, 10 microbes induced positive arrestment responses by ticks, whereas 10 others were deterrent. Of the 10 microbes prompting arrestment by ticks, four microbes-including (isolates A4)-also attracted ticks in moving-air Y-tube olfactometers. All four of these microbes emitted carbon dioxide and ammonia as well as volatile blends with overlapping blend constituents. The headspace volatile extract (HVE) of (HVE-A4) synergistically enhanced the attraction of . to CO. A synthetic blend of HVE-A4 headspace volatiles in combination with CO synergistically attracted more ticks than CO alone. Future research should aim to develop a least complex host volatile blend that is attractive to diverse tick taxa.