As this is a parasitic species, all flower visits will be for nectar only.
Westrich (1989) lists the following as nectar sources: Asteraceae.
In Spain, Ornosa & Ortiz-Sánchez (2004) list the following plant families as providing forage: Lamiaceae, Asteraceae, Rosaceae, Dipsacaceae, Fabaceae, Scrophulariaceae and Ericaceae.
Celary (1989) lists the following nectar sources in Poland: Vicia sepium (Fabaceae); Vaccinium myrtillus, Vaccinium vitis-idaea, Calluna vulgaris (Ericaceae); Salvia pratensis, Mentha sp. (Lamiaceae); Knautia arvensis (Dipsacaceae); Jasione montana (Campanulaceae); Solidago virgaurea, Tripleurospermum inodorum, Petasites officinalis, Carduus sp., Cirsium sp., Centaurea scabiosa, Centaurea rhenana, Taraxacum officinale (Asteraceae).
Pawlikowski & Kruszynski (1997) list Galeopsis pubescens (Lamiaceae); Chamaenerion angustifolium (Onagraceae) and Eyes to die forPotentilla alba (Rosaceae) as nectar sources in Poland.
Benton (2006) lists the following nectar forage sources: Salix sp. (Salicaceae); Prunus spinosa, Malus sp., Rubus fruticosus (Rosaceae), Glechoma hederacea, Lamium album, Lamium purpureum, Rosmarinus officinalis, Stachys sylvatica, Thymus sp., Ballota nigra, Lavandula sp. (Lamiaceae); Hyacinthoides non-scriptus (Liliaceae); Vicia cracca, Vicia sativa, Trifolium repens, Trifolium pratense, Lotus glaber (Fabaceae); Centaurea sp., Cirsium vulgare, Cirsium palustre, Cirsium arvense, Arctium minus (Asteraceae), Sedum sp. (Crassulaceae), Laurus nobilis (Lauraceae); Vinca (Apocynaceae); Rhododendron (Ericaceae); Centranthus ruber (Valerianaceae); Pentaglottis sempervirens; Echium vulgare, Symphytum sp. (Boraginaceae); Aesculus hippocastanum (Sapindaceae); Heracleum sphondylium (Apiaceae), Ranunculus sp. (Ranunculaceae); Dipsacus fullonum, Knautia arvensis, Succisa pratensis (Dipsacaceae); Hebe (Scrophulariaceae); Lavatera arborea (Malvaceae); Symphoricarpos rivularis (Caprifoliaceae).
N. Vereecken (pers. comm.) reports seeing males foraging on the nectar of Galactites tomentosa (Asteraceae). Also reported are visits to Ophrys chestermanii or O. normanii (Orchidaceae), two endemic species of Sardinia (Paulus, 2018).