Morphological and molecular comparison of host-derived populations of parasitic Psoroptes mites.

Infestation by parasitic Psoroptes mites (Acari: Psoroptidae) is an important cause of economic loss and welfare problems in livestock in many areas of the world. At least five species within this genus have been recognized, based on the host infested, the infestation site and differences in length of the opisthosomal setae of adult male mites. Here the integrity of these species is considered by subjecting populations of mites from a range of host species and geographical locations to simultaneous morphological and molecular genetic analyses. Morphological analysis showed that there were significant differences in shape and size between mite populations from different hosts, and that length of the outer opisthosomal setae in males and the homologous seta in females were the most important distinguishing character in adults. However, considerable variation in outer opisthosomal seta length was evident within and between populations of mites, and differences were not clearly related to host-species or geographical origin and did not support the accepted species differences. Molecular characterization using sequence data from the mitochondrial second internal transcribed spacer (ITS-2) region and microsatellite markers found little or no consistent host-related variation between the mite population samples. The results suggest that there is no case for considering the Psoroptes mites from the different hosts examined as separate species and that the morphological variation observed therefore may represent phenotypic adaptation to the local microenvironment on particular species of host.