The Merodon nanus group (Diptera, Syrphidae) is a small group of closely related species with high morphological similarity. Until now, based on morphological characters, this group consisted of five species: M. nanus Sack, 1931; M. telmateia Hurkmans, 1987; M. kopensis Vujić et Hayat, 2015; M. neonanus Vujić et Taylor, 2015; and M. rasicus Vujić et Radenković, 2015. Here, using an integrative approach based on molecular characters (sequences of the D2–3 region of the nuclear 28S rRNA gene and the mitochondrial COI gene) and data obtained from geometric morphometry of wing shape, we distinguish all five previously morphologically defined species of the group. Additionally, we identify one species as being new to science, M. vladimiri Vujić et Kočiš Tubić sp. n. We emphasize the separation of this newly described species according to the sequences obtained from the slowly evolving 28S rRNA gene, which demonstrated four to five mutation positions between this species and morphologically the most similar M. neonanus species. Also, our results show a clear division of M. telmateia into at least three population groups that we designate as the subspecies: M. telmateia mediterraneus Ačanski et Kočiš Tubić subsp. n. and M. telmateia samosensis Ačanski et Kočiš Tubić subsp. n. exhibiting western distributions (western Anatolia and the Greek island of Samos, respectively) and the nominative subspecies M. telmateia telmateia with an eastern Anatolian distribution.

The putative monophyly and systematic position of Merodon nigritarsis group was assessed based on morphological and molecular data of the mitochondrial COI and nuclear 28S rRNA genes. The previously reported concept of the group has been redefined, and M. crassifemoris Paramonov, 1925 is now excluded. The related M. avidus group is redefined here, including the Merodon avidus complex and M. femoratus Sack, 1913. Species delimitation of morphologically defined species of M. nigritarsis group was well supported by COI gene analysis, with the exception of M. alagoezicus Paramonov, 1925 and M. lucasi Hurkmans, 1993. Descriptions are given for three new species of the M. nigritarsis species group: Merodon cohurnus Vujić, Likov et Radenković sp. n., Merodon longisetus Vujić, Radenković et Likov sp. n. and Merodon obstipus Vujić, Radenković et Likov sp. n., and one new species from the M. avidus group: Merodon rutitarsis Likov, Vujić et Radenković sp. n. A lectotype is designated for M. femoratus Sack, 1913, and two new synonymies of this species were proposed: M. biarcuatus Curran, 1939 and M. elegans Hurkmans, 1993. Here we review 18 species from the M. nigritarsis group and six species from the M. avidus group and provide morphological diagnoses of the species groups. Additionally, diagnosis of 12 branches (groups or individual taxa) of M. avidus-nigritarsis lineage, an illustrated diagnostic key for the males, and distribution map are provided for the new species.

Dehesas are typical Mediterranean habitats for extensive livestock raising. Hoverflies (Diptera: Syrphidae) may act as bioindicators in dehesas, but they are still poorly known in this habitat type. With the purpose of the present study, hoverfly diversity was surveyed in Campanarios de Azaba, a typical oak dehesa in Salamanca province, Spain. A total of 41 species were recorded, including Eumerus azabense sp. nov. This new species was found to belong to the Eumerus tricolor group, both in morphological and genetic terms, and clearly separated (DNA characters) from the similar Eumerus niveitibia, which is redescribed here. Genetic monophyly of the E. tricolor group is confirmed in the present paper. An updated hoverfly checklist of Salamanca province is provided (152 sp.) with indication of the 56 species recorded in Campanarios de Azaba. Obtained results address the importance of dehesa biodiversity, which includes species new to science.

The diversity in the Eumerus tricolor group, the largest group within the genus in Southeast Europe, is investigated. Two new, locally distributed species are described, E. crispus Vuji? & Grkovi?, sp. n. from Serbia and E. nigrorufus Grkovi? & Vuji?, sp. n. from Montenegro. In addition to Southeast European members, one related species E. arctus van Steenis, sp. n. is described from Switzerland. We designate lectotypes for E. ovatus Loew, 1848, E. tarsalis Loew, 1848, E. tricolor (Fabricius, 1798) and E. varius Meigen, 1822. A map of the distribution of members of the E. tricolor group in Southeast Europe is provided. In addition, records from other parts of Europe are listed and an illustrated identification key to the SE European species of the E. tricolor group provided. We also study and discuss the significance of small habitat patches for the preservation of species of Eumerus, because the three species described in this paper are currently known from such patches.