Are Appearances Deceiving? Morpho-Genetic Complexity of the Eumerus tricolor Group (Diptera: Syrphidae) in Europe, with a Focus on the Iberian Peninsula

Simple Summary Hoverflies are a diverse group (6200+ species) of two-winged flies that provide important ecosystem services (e.g., plant pollination and regulation of populations of pest insects). The hoverfly genus Eumerus has caught the attention of scientists and entomology amateurs due to its high number of species worldwide (250+) and its wide range of body sizes and shapes. Nevertheless, some species show a similar overall appearance making both their separation from each other and the study of their classification/biology difficult. Thus, the aim of the present work is to update the knowledge of the Eumerus hoverflies in the Iberian Peninsula by assessing the diversity of the Eumerus tricolor group under an integrative approach (i.e., combining different techniques and data sources). We found and described two new species from Spain and provided the most comprehensive identification key for all known European species of this Eumerus group. Eumerus Meigen, 1822 is one of the largest Syrphidae genera in the Palaearctic Region, with the highest levels of taxonomic diversity found in the Eumerus tricolor species group. Despite its high diversity, the interspecific levels of morphological variability can be low. Additionally, some species may show certain levels of intraspecific variability. Hence, species delimitation may become challenging. In this work, we assessed the diversity of the E. tricolor group in the Iberian Peninsula through an integrative analysis of nomenclature, morphology and the 5 & PRIME; (COI-5 & PRIME;) and 3 & PRIME; (COI-3 & PRIME;) end regions of the Cytochrome c oxidase subunit I gene. Two new species, Eumerus ancylostylus Aguado-Aranda & Ricarte sp. n. and Eumerus petrarum Aguado-Aranda, Nedeljkovic & Ricarte sp. n., were described, and their intra- and interspecific variations discussed. In addition, the first barcodes of Iberian members of the E. tricolor group were obtained, and the distribution ranges of all species were mapped within the study area. The systematic position of the new species is discussed based on the resulting COI-based trees. The male genitalia of Eumerus hispanicus van der Goot, 1966 and Eumerus bayardi Seguy, 1961 were studied and illustrated. A lectotype was designated for Eumerus lateralis (Zetterstedt, 1819). An updated dichotomous key for all known European species of the E. tricolor group is provided. The egg of E. petrarum sp. n. is also described.