Chelostoma emarginatum (Nylander, 1856)

Chelostoma emarginatum View in CoL species group

The three representatives of the Chelostoma emarginatum species group are characterised in both sexes by the short proboscis ( Fig. 1, 2 View FIGURES 1–9 ) in combination with the flat basal area of the polished propodeum, which lacks a raised ridge along its posterior margin, is crossed by rather fine longitudinal carinae and has a similar length as the metanotum ( Fig. 5 View FIGURES 1–9 ). Additional character of the females is the medially flat base of the labrum ( Fig. 3 View FIGURES 1–9 ). Additional characters of the males are the absence of tubercles or projections on the hypostomal area, the rather short and wide apical teeth of tergum 7 ( Fig. 8 View FIGURES 1–9 ), the lack of distinct and backwardly projecting lower teeth on tergum 7, the uninterrupted comb of long yellowish bristles along the apical margin of sternum 5 and the half-elliptical and ventrally slightly concave median projection of sternum 2, which is distinctly rising towards its posterior margin ( Fig. 9 View FIGURES 1–9 ). The ancestral pollen host of the clade to which the C. emarginatum species group belongs is Ranunculus ( Ranunculaceae ) ( Sedivy et al. 2008). Ranunculus is still the exclusive host of C. emarginatum , while C. edentulum has switched to Brassicaceae and C. levantense has become polylectic by incorporating – among others – the exclusive pollen hosts of its closest relatives into its diet, i.e. Ranunculus and Brassicaceae .