Morphology of Pholeoixodes species associated with carnivores in the western Palearctic: Pictorial key based on molecularly identified Ixodes (Ph.) canisuga, I. (Ph.) hexagonus and I. (Ph.) kaiseri males, nymphs and larvae

Three Palearctic members of the subgenus Pholeoixodes, i.e., Ixodes canisuga, Ixodes hexagonus and Ixodes kaiseri are frequently collected from dogs, cats, red foxes, badgers and other carnivorous/insectivorous hosts in Europe. While a pictorial identification key has been reported for female Pholeoixodes ticks, a similar work has not been done on their male, nymphal and larval specimens. This study was initiated in order to clarify and re-examine those morphological characters of these three tick species, which can be used relatively easily to identify/distinguish them. In the case of larvae the aims included finding alternatives to chaetotaxy, which is difficult to observe and its usefulness is also affected by uncertainties in literature data. For this, 609 Pholeoixodes ticks (males, nymphs and larvae) were collected from carnivores, hedgehogs and their environment in six European countries (representing Western, Central and Southeastern Europe), followed by detailed morphological examination and/or molecular analyses to confirm the identity of their species. Based on the morphology of 84 molecularly analyzed specimens and a new identification key compiled accordingly, altogether 116 I. canisuga, 277 I. hexagonus and 216 I. kaiseri males, nymphs and larvae were identified. Ixodes kaiseri was not found in Western Europe, where I. canisuga predominated. In Central Europe, all three Pholeoixodes species were collected, the largest number of specimens represented by I. hexagonus. On the other hand, in Southeastern Europe I. kaiseri had the highest abundance. In conclusion, the morphology of internal spur on the first coxae (as the traditionally used character to distinguish I. hexagonus from other Pholeoixodes species) is trustworthy to recognize males but is less informative in the case of nymphs and larvae. The latter can be identified more properly by observing the morphology of basis capituli. In particular, nymphs and larvae of I. canisuga have anteriorly flattened basis capituli, forming a plateau that surrounds the base of the hypostome. On the other hand, nymphs and larvae of I. hexagonus and I. kaiseri lack a similar plateau, but (unlike I. canisuga) have cornuae, which are either posterolaterally or caudally directed, respectively.