North-Western Palaearctic species of Pristiphora (Hymenoptera, Tenthredinidae)

North-Western Palaearctic species of Pristiphora Latreille, 1810 are revised. Altogether, 90 species are treated, two of which are described as new: P. caraganae Vikberg & Prous, sp. n. from Finland and P. dedeara Liston & Prous, sp. n. from Germany. Host plant of P. caraganae is Caragana arborescens Lam. Pristiphora dasiphorae (Zinovjev, 1993) (previously known from East Palaearctic) and P. cadma Wong & Ross, 1960 (previously known from North America) are recorded for the first time from Europe. Nematus nigricans Eversmann, 1847 [= Pristiphora nigricans (Eversmann, 1847), comb. n.], N. breviusculus Eversmann, 1847 [= Euura melanocephalus (Hartig, 1837)], and N. caudalis Eversmann, 1847 [= E. caudalis (Eversmann, 1847), comb. n.] are removed from synonymy with P. pallidiventris (Fallen, 1808), N. paralellus Hartig, 1840 [= P. paralella (Hartig, 1840), comb. n.] is removed from synonymy with P. bufo (Brischke, 1883), and P. mesatlantica Lacourt, 1976 is removed from synonymy with P. insularis Rohwer, 1910. The following 29 new synonymies are proposed: P. nigropuncticeps Haris, 2002, syn. n. with P. albitibia (Costa, 1859); Lygaeonematus karvoneni Lindqvist, 1952, syn. n. with P. alpestris (Konow, 1903); P. (P.) anivskiensis Haris, 2006, syn. n. with P. appendiculata (Hartig, 1837); Nematus canaliculatus Hartig, 1840, syn. n with P. carinata (Hartig, 1837); P. nigrogroenblomi Haris, 2002, syn. n. with P. cincta Newman, 1837; Tenthredo flavipes Zetterstedt, 1838, syn. n., Nematus congener W.F. Kirby, 1882, syn. n., and P. thomsoni Lindqvist, 1953, syn. n. with P. dochmocera (Thomson, 1871); P. atrata Lindqvist, 1975, syn. n. with P. friesei (Konow, 1904); P. gelida Wong, 1968, syn. n. with P. frigida (Boheman, 1865); Pachynematus nigricorpus Takagi, 1931, syn. n. with P. laricis (Hartig, 1837); Nematus (Pikonema) piceae Zhelochovtsev in Zhelochovtsev and Zinovjev, 1988, syn. n. and P. (P.) hoverlaensis Haris, 2001, syn. n. with P. leucopodia (Hartig, 1837); Mesoneura arctica Lindqvist, 1959, syn. n., Pachynematus incisus Lindqvist, 1970, syn. n., Pachynematus intermedius Verzhutskii, 1974, syn. n., and P. mongololaricis Haris, 2003, syn. n. with P. malaisei (Lindqvist, 1952); Nematus anderschi Zaddach, 1876, syn. n., P. inocreata Konow, 1902, syn. n., and P. discolor Lindqvist, 1975, syn. n. with P. nigricans (Eversmann, 1847); Lygaeonematus tenuicornis Lindqvist, 1955, syn. n. with P. paralella (Hartig, 1840); Lygaeonematus concolor Lindqvist, 1952, syn. n. with P. pseudocoactula (Lindqvist, 1952); P. flavipicta Lindqvist, 1975, syn. n., P. flavopleura Haris, 2002, syn. n., P. mongoloexigua Haris, 2002, syn. n., and P. mongolofausta Haris, 2003, syn. n. with P. punctifrons (Thomson, 1871); P. listoni Lacourt, 1998, syn. n. with P. sootryeni Lindqvist, 1955; P. gaunitzi Lindqvist, 1968, syn. n. with P. testacea (Jurine, 1807); and Nematus breviusculus Eversmann, 1847, syn. n. with Euura melanocephalus (Hartig, 1837). The valid name of Pachynematus (Pikonema) carpathiensis Haris, 2001 is Nematinus carpathiensis (Haris, 2001) comb. n. Lectotypes are designated for 43 taxa. An illustrated electronic key made with Lucid and a traditional dichotomous key are provided to facilitate identification of the species. Species belonging to the carinata (previously Lygaeotus), micronematica (previously Lygaeophora), and rufipes (also known as thalictri or aquilegiae) groups are not keyed to the species level, because additional research is needed to delimit the species more reliably in these groups. Phylogeny of Pristiphora is reconstructed based on one mitochondrial (COI) and two nuclear (NaK and TPI) genes. Remarkably, around 5060% (depending on the exclusion or inclusion of the carinata, micronematica, and rufipes groups) of the species cannot be reliably identified based on COI barcodes. Limited data from nuclear genes indicate a better identification potential (about 20% remain problematic).