Intraspecific variation of morphological traits backed up with molecular evidence votes for re-appraisal of hitherto distinguished Balaustium species-a case study of Balaustium murorum (Acariformes: Parasitengona, Erythraeidae).

Molecular examination of representatives of Balaustium from several populations in SW Poland, performed using the sequence data from the mitochondrial cytochrome c oxidase subunit I, confirmed their common specific affiliation and identity with Balaustium murorum. The potential presence of distinct species in the studied material, preliminarily inferred from the discovery of clusters as a result of Principal Component Analysis exploring the metric data sets, was rejected due to the finding of only one haplotype, at intra- and inter-population sampling. An insight into meristic traits in larvae, focused on chaetotaxy of legs, revealed wider variation than hitherto recognized for the species. The variation was higher in laboratory-reared larvae compared to field-collected ones. The overall deviations from the mean character values at intra- and interpopulation levels, higher than hitherto observed for the species, vote for the reappraisal of the criteria adopted for discrimination of members of Balaustium with the application of an integrative approach.