As this is a cleptoparasitic species, all flower visits will be for nectar only.
Westrich (1989) lists Vaccinium myrtillus (Ericaceae) as a nectar source. Celary (1995; 2007) additionally cites Galium spp. (Rubiaceae) as a nectar source. Dufrene (pers. comm) reports visitation to Euphorbia cyparissias (Euphorbiaceae).