A laboratory study estimating blacklegged tick adhesion rates to host species of varying permissiveness

Host species vary tremendously in their permissiveness to blacklegged tick (Ixodes scapularis) feeding and their capacity to transmit pathogens to them. Thus, the host species ticks feed on impacts both tick population growth and infection prevalence. Given the importance of the bloodmeal to tick fitness there may be selection pressure for behavioral mechanisms that ensure they feed on more permissive hosts. We hypothesized that, if ticks have evolved host preferences, adhesion rates (when ticks get onto hosts) will increase with host permissiveness. We conducted a laboratory experiment to estimate larval and nymphal adhesion rates on four host species, representing a range of permissiveness (in descending order: Peromyscus leucopus, Tamias striatus, Sciurus carolinensis, and Didelphis virginiana) during standardized encounters using an apparatus designed to generate repeatable host-tick contacts. We found adhesion rates were essentially equivalent on the most (P. leucopus) and least permissive species (D. virginiana) and much higher on the second least permissive species (S. carolinensis). We also found the maximum adhesion probability for both larvae and nymphs declined with estimated time since emergence, though the effect was more pronounced in larvae. These results contradict both our expectation that adhesion to hosts is biased towards more permissive hosts and the widely held assumption that ticks equally attempt feeding on all host species. However, adhesion represents just one stage of ticks' host selection process, and whether these adhesion rates in our study translate into actual feeding rates, and thus impact tick population and infection dynamics, remains an open question.