The genus Andrena Fabricius, 1775 in the southern Balkans (Hymenoptera, Andrenidae)

The southern Balkans (here comprising the countries of Albania, North Macedonia, Bulgaria, and Greece including the Greek islands) are known for their large bee faunas due to their mixture of Mediterranean, sub-Mediterranean, temperate, and montane habitats. The bee genus Andrena is particularly species-rich in this region, but has lacked a comprehensive modern revision. Here the fauna is comprehensively revised, producing a total of 273 species, with national totals of 243 (Greece), 186 (Bulgaria), 153 (North Macedonia), and 116 (Albania). A full identification key is presented to stimulate further work. The following taxonomic changes are necessary after genetic investigation and inspection of type material: Andrena (Graecandrena) repressa Warncke, 1975, stat. nov.; Andrena (Limbandrena) toelgiana Friese, 1921, sp. resurr.; Andrena (Holandrena) decipiens Schenck, 1861 = Andrena (Holandrena) flavilabris Schenck, 1874, syn. nov., Andrena (Holandrena) forsterella Osytshnjuk, 1978 = Andrena (Holandrena) wilhelmi Schuberth, 1995, syn. nov.; Andrena (Lepidandrena) caprimulga Warncke, 1975 = Andrena (Lepidandrena) statusa Gusenleitner, 1998, syn. nov.; Andrena (Melandrena) creticola stat. rev.; Andrena (Notandrena) meridionalis Dalla Torre & Friese, 1895, sp. resurr. = A. (Notandrena) langadensis Warncke, 1965, syn. nov.; Andrena (Notandrena) albipila Warncke, 1967, stat. nov.; Andrena (Notandrena) clanga Warncke, 1965, stat. nov.; Andrena (Notandrena) oblonga Warncke, 1967, stat. nov.; Andrena (Ulandrena) subglobosa Dours, 1873, sp. resurr. = A. (Ulandrena) kriechbaumeri Schmiedeknecht, 1883, syn. nov.; and Andrena (Campylogaster) erberi Morawitz, 1871 = Andrena kozarovi Nedialkov, 1914, syn. nov. Six new species are described: Andrena (Cryptandrena) testudo sp. nov. (Greece: Crete), Andrena (Euandrena) bulgarica sp. nov. (Bulgaria and Greece), Andrena (Euandrena) obscuricrus sp. nov. (Greece: Crete), Andrena (Graecandrena) cretica sp. nov. (Greece: Crete), Andrena (Lepidandrena) haladai sp. nov. (Greece), and Andrena (incertae sedis) lasithi sp. nov. (Greece: Crete). Finally, Leucandrena Haeckel, 1872, a name for a group of sponges, is considered to be a nomen oblitum and Andrena Subgenus Leucandrena Hedicke, 1933 is considered to be a nomen protectum. The final regional species total includes 28 endemic species (10.3%), giving the southern Balkans a comparable but slightly lower endemism rate than the Iberian Peninsula (15.7%) and Morocco (12.2%), but with a meaningfully higher species density per unit area, highlighting the southern Balkans as a global hotspot for the genus Andrena.