First nationally threatened mayfly (Ephemeroptera) species in Latvia assessed according to the IUCN criteria

Out of the 51 known Latvian Ephemeroptera species, five mayfly species are proposed for the inclusion in the new edition of the Red Data Book of Latvia, which for the first time will be IUCN criteria based. Arthroplea congener Bengtsson, 1908 is assessed vulnerable (VU) with a low number of localities, fragmented regional population and threats from pollution. Ephoron virgo (Olivier, 1791) is also VU, reported from ten localities and threats from light pollution, eutrophication and damming of rivers. Ephemerella mucronata (Bengtsson, 1909) is assessed as endangered (EN) with a fragmented regional population and declining water quality. Eurylophella karelica Tiensuu, 1935 is assessed as near threatened (NT) facing threats from the agricultural pollution. Prosopistoma pennigerum (O.F. Müller, 1785) is assessed as regionally extinct (RE) with the last observations from 1965 and previously known localities and habitats flooded by the hydropower plants (HPPs).