West Palaearctic species of Euura Newman, 1837 (Hymenoptera, Tenthredinidae)

Excluding 102 species of the previously revised West Palaearctic species groups of Euura Newman, 1837 (gall-making groups, 84 species; amentorum group, 8 species; bergmanni group, 8 species; and oligospila group, 2 species), we treat here the remaining 164 West Palaearctic species of the genus. 145 new synonymies are proposed (one in Platycampus, one in Nematus, two in Pristiphora, and the rest in Euura: see Table 4 for details). 153 lectotypes are designated (see Table 4). Four nominal species are reinstated (valid name in square brackets): Pteronidea fuscarima Benson, 1933 [E. fuscarima (Benson, 1933) comb. nov.], P. fuscodorsata Lindqvist, 1949 [Euura fuscodorsata (Lindqvist, 1949) comb. nov.], Pachynematus perkioemaekii Lindqvist, 1960 [E. perkioemaekii (Lindqvist, 1960) comb. nov.], and Pontania poppii Konow, 1904 [Euura poppii (Konow, 1904) comb. nov.]. Euura tiliae (Zinovjev, 1998) comb. nov. and E. wuyishanica (Wei, 2003) comb. nov. are transferred from Nematus. Euura memoriakaszabi (Haris, 2002) comb. nov. is transferred from Pristiphora. Five new species are described: Euura halo Prous, Liston & Mutanen sp. nov., E. histriato Prous, Liston & Mutanen sp. nov., E. minivittata Prous & Mutanen sp. nov., E. polepso Prous & Mutanen sp. nov., and E. serela Prous & Mutanen sp. nov. Euura telos Liston & Prous nom. nov. (an East Palaearctic species) is proposed for Amauronematus terminalis Malaise, 1931, a secondary homonym of Pontania terminalis Marlatt, 1896 [Euura terminalis (Marlatt, 1896)]. Three treated putative species based on single males (E. bergmanni and E. clitellata group) and a female (E. bipartita group) remain unidentified pending further research. An identification key is provided to separate the genus Euura from the other similar genera. Host plants are now known for 80% (132) of the treated species (88% for all West Palaearctic Euura). Genetic data (at least mitochondrial COI and nuclear NaK and POL2) are reported for 91% (151) of the treated species. The genetic data were obtained with Sanger and Nanopore sequencing. In numerous cases, identification of one sex of a species remains difficult using morphological characters but is clear when using genetic data. In a few cases, however, identification based on morphology is reliable, while support from available genetic data is weak. Often, large morphological and genetic variability makes species delimitation ambiguous. Within-species genetic diversity, as estimated from diploid females (i.e., within-individual genetic diversity, which is an underestimate of within-species diversity), is large in Euura, on average with 0.3% divergence between the haplotypes (max 1.4%), while between-species divergence for a given species group is often only slightly higher (on average varies between 0.5–2.1%). Strong mito-nuclear discordance is observed within most species groups, but in some cases even between species groups. Over 50% of the species cannot be reliably identified based on mitochondrial COI barcodes. While nuclear DNA is significantly more congruent with morphology, identification of about 15% of the species can be ambiguous due to large genetic variability. Remarkably, two or more apparently functional COI variants are frequently observed within the same individual, with variants diverging by up to 9.6% in Euura lappo (for the 658 bp barcoding region).