Chelostoma emarginatum species group

The three representatives of the Chelostoma emarginatum species group are characterised in both sexes by the short proboscis (Fig. 1, 2) 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). Additional character of the females is the medially flat base of the labrum (Fig. 3). 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), 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). 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 .