Polylectic, but pollen sources not known in UK. Willow (2017) lists pollen sources in Iceland.
Flowers visited: Berberis (Berberidaceae); Viola (Violaceae); Silene dioica (Caryophyllaceae); Malva (Malvaceae); Ulex, Sarothamnus scoparius, Anthyllis vulneraria, Lotus (Fabaceae); Rubus, Cotoneaster, Crataegus, Pyrus (Rosaceae); Fuchsia (Onagraceae); Salix repens (Salicaceae); Calluna vulgaris, Erica tetralix, Erica cinerea, Vaccinium myrtillus (Ericaceae); Primula vulgaris (Primulaceae); Echium (Boraginaceae); Glechoma (Lamiaceae); Senecio, Cirsium vulgaris, Cirsium heterophyllum, Centaurea nigra, Taraxacum (Asteraceae); Allium triquetrum, Scilla and Hyacinthoides nonscriptus (Liliaceae).
Banaszak (1980) has described Veronica spicata (Scrophulariaceae) as an important species for bees in the xerothermal habitats of the lower Vistula in Poland.
In Spain, Ornosa & Ortiz-Sánchez (2004) list the following plant families as providing forage: Cupressaceae, Salicaceae and Rosaceae.
Willow (2017) presents along list of plants visited in Iceland, based on A total of 342 floral visits. These include Thymus praecox (Lamiaceae), Comarum palustre, Geum rivale (Rosaceae); Vicia cracca (Fabaceae); Calluna vulgaris (Ericaceae). Pollen loads of 38 B. jonellus workers were examined. These individuals were collected on ten different plant species. For all pollen loads analysed, the only plant species detected was that which the individual was collected on. Separation of the data into two time periods revealed a separation of dominant species assemblages in B. jonellus’s diet. From 14 June to 18 July, Thymus praecox (Lamiaceae) was the most visited species, representing 51% of all floral visits during this time period, followed by Geum rivale (26%), Geranium sylvaticum (Geraniaceae) (8%). From 21 July to 7 August, Comarum palustre was the site of 28% of recorded visits, followed by Vicia cracca (21%), Calluna vulgaris (20%), Thymus praecox (14%), Scorzoneroides autumnalis (Asteraceae) (8%), and Anthyllis vulneraria (Fabaceae) (6%). Other visits were noted to Vaccinium uliginosum (Ericaceae); Bartsia alpina (Orobanchaceae); Trifolium repens (Fabaceae); Aquilegia sp., Ranunculus acris (Ranunculaceae); Galium boreale; Galium verum (Rubiaceae).