The Merodon clavipes and Merodon pruni species groups are two out of 10 established groups within the M. avidus-nigritarsis lineage. The both groups were primarily defined by Hurkmans (1988) and then revised by Likov et al. (2020) and Vujić et al. (2021). Likov et al. (2020) presented M. clavipes group in a much narrower sense compared to Hurkmans (1988), mentioning only two representatives: M. clavipes and M. velox. Vujić et al. (2021) added few diagnostic features and appended M. quadrinotatus and M. vandergooti Hurkmans, 1993 species to previous two species. Within M. pruni group, two species were mentioned in Likov et al. (2020): M. pallidus Macquart, 1842 and M. pruni Rossi, 1790, while the most recently, Vujić et al. (2021) listed four species belonging to this species group: M. cupreus Hurkmans, 1993, M. pallidus, M. pruni and one undescribed taxon from Israel. Here we analysed molecular data based on the sequences of the mitochondrial COI gene (cytochrome c oxidase subunit I) in addition to traditional morphological character with the aim to describe the hidden taxonomic complexity of the M. clavipes and M. pruni taxa. In the employed Maximum Parsimony approach, together with analysed species of the groups, we involved the representatives of previously described Merodon lineages by Vujić et al. (2021), as well as species from the groups of the avidus-nigritarsis lineage. The analysis based on 72 concatenated nucleotide sequences (612 bp of 5′ fragment of COI gene and 661 bp of 3′ fragment of the gene) revealed all five lineages as clades (Fig. 1). Within the avidus-nigritarsis lineage, the both analysed species groups resolved as monophyletic with 100 bootstrap support. Taxon M. aff. clavipes from Spain clearly separated (80 bootstrap) from the other analysed species of the groups (M. clavipes and M. velox), indicated existence of additional new species of the group. Within the M. pruni group, previously known variety Merodon pruni var. obscurus Gil Collado, 1929 proved to be valid species, revealing as separated clade with 99 bootstrap support on obtained MP tree.

References:
Hurkmans, W. 1988. Entomologische Berichten, 48(7), 107-114.
Likov, L., et al. 2020. Contrib. Zool., 89, 74–125.
Vujić, A., et. al. 2021. ZooKeys, 1031, 85–124.