Chorioptes mites: re-evaluation of species integrity

Chorioptes mites (Acari: Psoroptidae) are non-burrowing agents of mange which parasitize a wide range of domesticated and wild ungulates. Considerable historical confusion has surrounded the description and naming of the various species of Chorioptes. Here, the opisthosomal setae of male adult Chorioptes mites from a range of host species and geographic locations were subjected to detailed analysis. Discriminant analysis suggests the existence of three clear morphotypes. The first, Chorioptes bovis, is characterized by a very long seta 1 (ae) and short spatulate setae 2 (l4 and d5), whereas, in the second, Chorioptes texanus, setae 2 (l4 and d5) are longer and narrower than in C. bovis, but most of the other setae are shorter; this is particularly true for seta 1 (ae). A third morphotype is characterized by a seta 1 (ae) that is shorter than in C. bovis but longer than in C. texanus, long setae 2 (l4 and d5) and a long seta 6 (l5). The data are compared with previously published measurements. Although this analysis supports the validity of C. bovis and C. texanus as morphologically distinct, it also supports the existence of a proposed third species of Chorioptes, as described by Hestvik et al. in 2007, and suggests that the mites described by Sweatman in his classic 1958 description of C. texanus, which were obtained from the ears of semi-domesticated reindeer, are likely to have been specimens of this as yet unnamed species. The results show that there is a high degree of phenotypic plasticity in setal lengths. It is concluded that a statistical difference in the absolute measurement of any one seta is not a reliable species indicator; the relative sizes of groups of setae would appear to be more taxonomically informative and should be used when identifying Chorioptes morphologically.