Revision of the leachella group of Megachile subgenus Eutricharaea in the Western Palaearctic (Hymenoptera, Apoidea, Megachilidae): A renewed plea for DNA barcoding type material

The leafcutting bees of the leachella group of Megachile Latreille subgenus Eutricharaea Thomson are revised for the Western Palaearctic region using a combination of morphology and phylogenetic analyses of three genes (COI, LW-Rhodopsin, CAD). Although only seven species are recognized, much effort was needed to link delimitated taxonomic units to taxon names because of the difficulties in identifying type specimens. Numerous types were in a poor state of conservation, preventing straight-forward identification using morphology. This was in some cases aggravated by the fact that they often belonged to a sex that could not easily be identified; one type was a gynandromorph specimen whose identification is even more challenging. In several cases, the type locality was vague or unclear; in three cases, the type specimens originated from introduced populations for which the source of the introduction needed to be determined using DNA barcoding. In two cases, the type specimens consisted of several body parts not originating from a single individual but from two heterospecific specimens. We argue that this tedious nomenclatural work would have been greatly facilitated if a reference library of type specimens had been available. Our revision leads to the following taxonomic changes. Megachile argentata (Fabricius, 1793), described from northern Africa and with a convoluted taxonomic history, is demonstrated, based on morphometric analyses of its lectotype, to be conspecific with the species hitherto known as M. pilidens Alfken, 1924. After discussing and excluding several alternative options that would minimize nomenclatural changes, we place M. pilidens in synonymy with M. argentata (syn. nov.). Two new subspecies are described for morphologically slightly divergent insular populations, M. leachella cretica Praz, ssp. nov. from Crete, and M. leachella densipunctata Praz, ssp. nov. from Cyprus. In addition, M. albipila Pérez, 1895 is treated as a subspecies of M. leachella Curtis, 1828 (stat. nov.). The following new synonymies are proposed: M. compacta Pérez, 1895 (not M. compacta Smith, 1879) and the replacement name M. crassula Pérez, 1896, M. argyrea Cockerell, 1931 and Perezia maura Ferton, 1914, are placed in synonymy with M. argentata (syn. nov.). M. beaumonti Benoist, 1951, is newly treated as a valid species (stat. rev.). M. schmiedeknechti Costa, 1884 is treated as a subspecies of M. argentata (stat. nov.), and M. xanthopyga Pérez, 1895 is placed in synonymy with M. argentata schmiedeknechti (syn. nov.). M. bioculata Pérez, 1902, M. discriminata Rebmann, 1968 and M. ichnusae Rebmann, 1968 are placed in synonymy with M. leachella (syn. nov.). M. variscopa Pérez, 1895, M. timberlakei Cockerell, 1920, M. atratula Rebmann, 1968, M. striatella Rebmann, 1968 and M. sudai Ikudome, 1999 are placed in synonymy with M. pusilla Pérez, 1894. Lectotypes are designated for M. albipila, M. bioculata, M. compacta Pérez, M. pusilla, M. variscopa and M. xanthopyga