Host specificity of a bird-specialised endophilic ectoparasite, the tree-hole tick Ixodes arboricola

Host specialisation in parasites can be due to either limited exposure or limited adaptation to different host types. When the first barrier is lifted experimentally, the degree of adaptive specialisation can be studied. The tree-hole tick Ixodes arboricola is an endophilic parasite with a narrow host range, found in nest boxes used mainly by great and blue tits (Parus major, Cyanistes caeruleus) and to a lesser extent by pied flycatchers (Ficedula hypoleuca) and nuthatches (Sitta europaea). In the current study, we exposed two nestlings per nestbox of pied flycatchers (N = 14), blue tits (N = 18), great tits (N = 14), and nuthatches (N = 16) to ten I. arboricola nymphs each. We found no differences in attachment success 2 days after infestation (56 ± 4% across species) nor were there any differences in tick engorgement weight (1.95 ± 0.03 mg across species), and moulting success was >90% for ticks from all bird species. Hence, our data suggest that all bird species investigated here are suitable host species. This may enhance the ticks' chances for persistence in cavities and dispersal among cavities inhabited by multiple host species, and supports the hypothesis that host use by ticks is limited by host ecology rather than by host specialisation.