A polyectic bee, although it shows a marked preference for flowers of Lotus and Lathyrus (Fabaceae) (Banaszak & Romasenko, 1989). Müller et al., (2019) regrd this as a mesolectic species specialising in pollen from Fabaceae, Ericaceae and Cistaceae.
Müller et al. (2019) report that Osmia nigriventris collected the pollen almost exclusively from flowers of Fabaceae, Ericaceae and Cistaceae, with pollen from these three plant families constituting 96.6% of the total pollen grain volume. Among the Fabaceae, Lotus was by far the most important pollen source. Detailed analysis from the 50 nests conducted by Müller et al. shows pollen foraging at Lotus, Hippocrepis, Anthyllis, Trifolium, Lathyrus (Fabaceae); Rhododendron, Vaccinium (Ericaceae); Helianthemum (Cistaceae) and traces of Gentiana (Gentianaceae) and Echium (Boraginaceae).