As this is a cleptoparasitic species, all flower visits will be for nectar only.
Celary (1990) lists the following nectar sources in Poland: Convolvulus arvensis (Convolvulaceae); Echium vulgare (Boraginaceae); Knautia sp (Dipsacaceae); Jasione montana (Campanulaceae).
Westrich (2018) lists the following nectar source in Germany: Convolvulus arvensis (Convolvulaceae).