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Hoverflies (Syrphidae) represent an insect group of great importance in ecosystems and indicators of ecosystem change. The genus Merodon Meigen, 1803 (tribe Merodontini) is one of the most species-rich hoverfly genera, distributed across the Palaearctic and Afrotropical regions. The genus Merodon Meigen, 1803 is less diverse in the Afrotropical Region than in the Palaearctic (11 versus 160 known species). An ongoing study of the genus Merodon in Africa has revealed the existence of two new species into the taxon previously known as Merodon planifacies Bezzi, 1915. The M. planifacies subgroup belongs to the Afrotropical lineage of the Merodon desuturinus group. Morphological analysis of male genitalia has classified the available specimens of the M. planifacies taxon into two sets: the first one corresponds to M. planifacies with folded theca, while the other with smooth theca, later named Merodon capi complex was found exclusively at the Drakensberg mountains in the Republic of South Africa, specifically in the Cathedral Peak National Park and the Royal Natal National Park. Further, molecular and morphometric evidences revealed two cryptic taxa within this complex: M. capi sp. nov. Vujić et Radenković and Merodon roni sp. nov. Radenković et Vujić. This work was funded by a project of the European Union: Horizon 2020, Marie Skłodowska-Curie action, Research and Innovation Staff Exchange (RISE) Programme: FlyHigh - Insect-plant relationships: insights into biodiversity and new applications (project number 645636, 2015e2018); and partially by the RSA SAEON network, a member of International Long-Term Ecological Research Network (ILTER) and Ministry of Education, Science and Technological Development of the Republic of Serbia (OI173002, III43002, III44006, 451-03-68/2020-14/200358 and 451-03-68/2020-14/200125).

The phytophagous hoverfly genusMerodonMeigen, 1803 (Diptera, Syrphidae), which comprises more than 160 species distributed in Palaearctic and Afrotropical regions, can be differentiated into multiple groups of species that harbor high levels of hidden diversity. In this work, theserrulatusspecies group ofMerodonis revised, providing an illustrated key to species, a detailed discussion on the taxonomic characters and a morphological diagnosis, including also the first data about the preimaginal morphology of this species group. The study includes characteristics of the 13 species of theM. serrulatusgroup, along with the available distributional data. Moreover, descriptions are provided for seven new species, namelyM. defectusVujić, Likov & Radenkovićsp. nov.,M. disjunctusVujić, Likov & Radenkovićsp. nov.,M. mediumVujić, Likov & Radenkovićsp. nov.,M. nigrocapillatusVujić, Likov & Radenkovićsp. nov.,M. nigropunctumVujić, Likov & Radenkovićsp. nov.,M. opacusVujić, Likov & Radenkovićsp. nov., andM. trianguloculusVujić, Likov & Radenkovićsp. nov.In addition, the taxaM. serrulatus(Wiedemann in Meigen, 1822),M. bequaertiHurkmans, 1993,M. hirsutusSack, 1913,M. kawamuraeMatsumura, 1916,M. sacki(Paramonov, 1936) andM. sophronHurkmans, 1993 are redefined and redescribed. Following a detailed study of the type material sourced from different entomological collections, the status of all available taxa related toM. serrulatusis revised and a new synonymy is proposed:M. tenerSack, 1913syn. nov.(junior synonym ofM. serrulatus). The identity ofM. trizonus(Szilády, 1940) could not be assessed as the type specimens are lost. Thus, the nameM. trizonusis considered asnomen dubium. The monophyly and composition of this species group are assessed through Maximum Parsimony and Maximum Likelihood analyses of the mitochondrial COI and nuclear 28S rRNA gene sequences.

In this study, we examined the morphology, genetics and distribution of the members of the Merodon chalybeus subgroup (M. aureus species group): M. chalybeus Wiedemann in Meigen, 1822, M. minutusStrobl, 1893 and M. robustusVeselić, Vujić & Radenković, 2017. Two of the species, M. chalybeus and M. minutus, are morphologically very similar and often misidentified in the literature. Here, by employing an integrative taxonomic approach we provide strong evidence for the separation of M. chalybeus and M. minutus. Our results show their clear allopatric distribution: M. minutus on the Balkan Peninsula, Sicily, Sardinia and Corsica, while M. chalybeus is a western Mediterranean species distributed on the Iberian Peninsula and northwest Africa. Data on the distribution of M. robustus were updated, with new records from Cyprus, Israel and Turkey, besides its type locality (Samos in Greece). We provide evidence for M. chalybeus and M. minutus representing a species complex, named the M. chalybeus complex, which together with M. robustus constitute the M. chalybeus subgroup. © 2021 Finnish Zoological and Botanical Publishing Board.