Déjà Vu in Merodon Taxonomy (Diptera: Syrphidae): Unveiling Hidden Species Inside Merodon caudatus and M. ottomanus Taxa

Two new species groups within the <i>avidus-nigritarsis</i> lineage of the hoverfly genus <i>Merodon</i> Meigen are here defined and assessed, i.e., the <i>Merodon caudatus</i> and <i>Merodon ottomanus</i> groups. Within the <i>M. caudatus</i> group, two species are recognised:<i>Merodon caudatus</i> Sack and a new species, <i>Merodon crispotarsus</i> sp. nov. Within the <i>M. ottomanus</i> group, an extensive examination of material from different collections revealed the presence of four new species, <i>Merodon auriolus</i> sp. nov., <i>Merodon paeninsula</i> sp. nov., <i>Merodon projectus</i> sp. nov., and <i>Merodon rostrum</i> sp. nov., apart from <i>Merodon ottomanus</i> Hurkmans. The genetic characterisation of species from the <i>M. ottomanus</i> group was performed through Maximum Parsimony (MP) and Maximum Likelihood (ML) analyses of the 5' end of mitochondrial COI gene sequences, and the existence of the five above-mentioned independent taxa was supported. In addition, we confirmed the validity of <i>M. auriolus</i> sp. nov., <i>M. paeninsula</i> sp. nov., and <i>M. ottomanus</i> by using an integrative taxonomic approach including wing shape differences. Diagnoses, keys for both species groups, and the species they consist of, as well as distribution maps for all studied species, are provided.