Polylectic with a preference for Fabaceae; additional pollen sources include Ranunculaceae (Westrich, 1989; A. Müller, unpublished, based on 15 pollen samples from 4 different localities and on field observations).
Müller (2015) conducted microscopical analysis of female pollen loads and brood cell provisions and he revealed that H. tuberculata is polylectic with a strong preference for Fabaceae. Among the Fabaceae, Lotus and Hippocrepis were by far the most important pollen hosts. Non-Fabaceae taxa represented by substantial proportions in pollen loads or cell provisions were Helianthemum (Cistaceae), Vaccinium (Ericaceae) and Rubus (Rosaceae). Smaller quantities of pollen from Echium (Boraginaceae); Ranunculus (Ranunculaceae); Asteraceae and Lamiaceae were also found.
The host plant spectrum of H. tuberculata recorded by Müller (2015) is similar to that found in Finland (Käpylä 1978). Here, pollen of seven different plant families represented by at least 3% per load was recorded in 16 pollen loads of females collected both at flowers and nesting sites. As in the present study, Fabaceae (Caragana, Lathyrus, Lotus), Ericaceae (Vaccinium), Rosaceae (Geum, Potentilla, Rubus), Ranunculaceae (Anemone, Ranunculus) and Asteraceae (Leontodon) were among the plant families exploited for pollen. In addition, flowers of Asparagaceae (Convallaria, Polygonatum) and Violaceae (Viola) also served as pollen hosts, the former being the most important pollen sources followed by flowers of the Fabaceae.