Resolving issues in the genus Dioxys (Hymenoptera, Megachilidae, Dioxyini) in the West Palaearctic with a new identification key

The bee genus <i>Dioxys</i> is widely distributed across the Holarctic from the Mediterranean basin to western North America but is species-poor, and individual species can prove challenging to identify. Consequently, there has been a lack of consensus as to how many species actually exist. In the West Palaearctic, the number of species has varied from six to ten, depending on the worker. Due to a previously incorrect assessment of publication dates, <i>Dioxysrotundatus</i> Pérez, 1884, <b>sp. resurr.</b> is restored as the senior synonym of <i>Dioxysmoestus</i> Costa, 1884, <b>syn. nov.</b> The relationship between this species and <i>Dioxysatlanticus</i> Saunders, 1904 is clarified, with the latter restricted to the islands of Gran Canaria and Tenerife (Spain). <i>Dioxysrufipes</i> Morawitz, 1875 is considered part of the West Palaearctic fauna, replacing "<i>D.moestus</i>" sensu Warncke (1977) in the eastern Mediterranean. <i>Dioxysmontanus</i> Heinrich, 1977, <b>sp. resurr.</b> is revalidated from synonymy with <i>Dioxyscinctus</i> (Jurine, 1807). <i>Dioxyspumilus</i> Gerstäcker, 1869 is found to consist of four species, <i>D.pumilus</i> (eastern Mediterranean), <i>Dioxysvaripes</i> De Stefani, 1887, <b>sp. resurr.</b> (western Mediterranean), <i>Dioxyscypriacus</i> Popov, 1944, <b>sp. resurr.</b> (Cyprus), and <i>Dioxyshermonensis</i> <b>sp. nov.</b> (Israel: Mount Hermon). A neotype is designated for <i>D.varipes</i>, and <i>Dioxysfalsificus</i> Engel, 2023, <b>syn. nov.</b> is synonymised with it. This contribution produces a total of 13 species for the West Palaearctic region, and illustrates the degree to which persistent taxonomic problems exist even within small bee genera.