Taxonomic complexity in the genus Merodon Meigen, 1803 (Diptera, Syrphidae)

The genusMerodonMeigen, 1803 is distributed across the Palaearctic and Afrotropical Regions. The present work summarizes the knowledge from recent taxonomic and systematic revisions and includes an identification key for the five monophyletic lineages (namelyalbifrons,aureus,avidus-nigritarsis,desuturinusandnatans), 24 species groups, two species subgroups and 10 unplaced species, along with diagnosis and illustrations. A list of 234 taxa, including 194 described and 40 undescribed species, is appended. Most of the species are distributed in the Palaearctic (209 taxa, 181 described), while 27 species (14 described) are known from the Afrotropical Region. Three lineages (aureus,desuturinusandnatans) are present in the Afrotropical Region, as well as in the Palaearctic. The Afrotropicalmelanocerusspecies group of thedesuturinuslineage and thebombiformisspecies group of theaureuslineage are endemic to the Afrotropical Region, and all other species groups belong to the Palaearctic fauna. Thealbifronslineage contains six species groups (albifrons,constans,equestris,geniculatus,ruficornisandrufus) and two unplaced taxa. Theaureuslineage includes five species groups (aureus,bombiformis,funestus,nanusandspinitarsis). Theavidus-nigritarsislineage is divided into 10 species groups (aberrans,aurifer,avidus,clavipes,fulcratus,italicus,nigritarsis,pruni,serrulatusandtarsatus) and eight unplaced taxa. Thedesuturinuslineage contains two species groups: the Afrotropicalmelanocerusgroup, with themelanocerusandplanifaciessubgroups plus the speciesM. cuthbertsoniCurran, 1939, and the Palaearcticmurorumspecies group. Thenatanslineage consists of thenatansspecies group plus the speciesM. segetumFabricius, 1794.