The species is a social parasite of Bombus pascuorum, and secondarily of Bombus humilis (Rasmont, 1988; Celary, 1989). It may occasionally parasitize Bombus pratorum (Løken, 1984; Celary, 1989). Peeters, Raemakers & Smit (1999) and Celary (1989) also list Bombus pomorum (May, 1937); Bombus muscorum, Bombus soroeensis and Bombus veteranus as possible hosts. Westrich (1980) adds Bombus ruderarius (citing Hoffer, 1988).