Six new species of the genus Eumerus Meigen, 1822 are here described from Iran. The new species and their four related groups are as follows: E. nadoosheni Gilasian & van Steenis sp. nov. of the Eumerus barbarus group; E. pollinipedes Gilasian & van Steenis sp. nov. of the Eumerus minotaurus group; E. effossus Gilasian & van Steenis sp. nov. and E. similis Gilasian & van Steenis sp. nov. of the Eumerus obliquus group, as well as E. intermedius Gilasian & van Steenis sp. nov. and E. khiabani Gilasian & van Steenis sp. nov. of the Eumerus ornatus group. In addition, the species E. argyropus Loew, 1848 and E. torsicus Grković & Vujić, 2015 are newly recorded from Iran. The illustrations of the male genitalia and images of the new species are provided.

The phytophagous hoverfly genus Merodon Meigen, 1803 (Diptera, Syrphidae) presently comprises 205 described species distributed in the Palaearctic and Afrotropical regions, and it is differentiated into multiple species groups. In this work, we revise the Merodon tarsatus species group, providing an illustrated key to species, a detailed discussion on relevant taxonomic characters, and a morphological diagnosis. We summarize morphological characteristics of the 12 species in the M. tarsatus group, together with available distributional data. Moreover, we provide descriptions for five new species, namely Merodon angustitarsis Vujić & Gilasian sp. nov., M. dumosus Vujić, Likov & Radenković sp. nov., M. latiantennatus Vujić, Popov & Prokhorov sp. nov., M. namaghijamii Vujić, Likov & Radenković sp. nov. and M. pakistanicus Vujić, Likov & Radenković sp. nov. Additionally, we describe one more species, Merodon nigroalatus Vujić, Likov & Radenković sp. nov., that belongs to the same lineage and is related to the Merodon tarsatus group based on molecular markers and structure of male genitalia, but lacks modifications of the metatarsus and sternum 4 that are the main diagnostic features of the group. Furthermore, we redefine and redescribe seven taxa of the M. tarsatus group. Following detailed analyses of type material, we revise the status of all available taxa related to M. tarsatus and we propose the following new synonyms: M. ankylogaster Hurkmans, 1993 syn. nov. (junior synonym of M. hypochrysos Hurkmans, 1993); M. persicus Hurkmans, 1993 syn. nov. (junior synonym of M. oidipous Hurkmans, 1993); and M. xanthipous Hurkmans, 1993 syn. nov. (junior synonym of M. marginicornis Hurkmans, 1993). We apply Maximum Parsimony and Maximum Likelihood analyses of the 5′ end of the mitochondrial COI gene sequences to genetically characterize species in the M. tarsatus group and the related species, M. nigroalatus Vujić, Likov & Radenković sp. nov.