Osten Sacken, 1865 (Diptera, Limoniidae) in China: Taxonomic Review, Updated Distribution, and DNA Barcoding.

The genus Osten Sacken, 1865 from China is taxonomically reviewed using an integrative approach that combines detailed morphological examination and molecular analysis. (Alexander, 1947), a species widely distributed across the Palaearctic region, is newly recorded from China. Updated distributional data are presented for species known from China: (Linnaeus, 1758), (Alexander, 1942), Alexander, 1924, and (Alexander, 1930). Detailed redescriptions and illustrations, including intraspecific morphological variation, are provided for these species. An identification key to Chinese species is also presented. Geographical analysis reveals a higher species richness in southern China and the Qinghai-Tibet region, with a progressive decline toward northern and northwestern China. The first DNA barcode reference library for Chinese is established, comprising 15 mt sequences from five species. These sequences, analyzed alongside an additional 101 mt sequences from species in other countries, show that intraspecific divergence within the genus remains below 7.4%, while interspecific divergence ranges from 7.6% to 17.7%. These findings provide important insights into the taxonomy, species delimitation, and biogeography of in China, contributing to a more comprehensive understanding of diversity across the region.