Probably oligolectic on Asteraceae. Müller and Bansac (2004) have shown that Megachile melanogaster has a distinct (e.g.) or exclusive preference for Asteraceae (Carduoideae) and that the species has a modified pollen collecting device is found under the hind trochanter and femur
Composition of scopal pollen contents were studied by Zander (1935). He showed that in a sample of 6 specimens of M. melanogaster, the pollen loads were all Asteraceae with 100% Centaurea jacea type.
Banaszak & Romasenko (1989) list Glycyrrhiza glabra (Fabaceae) as a forage source.