Oligolectic on Asteraceae with a clear preference for Cichorioideae and Asteroideae; species of the Carduoideae are rarely exploited, which might be due to the early seasonal flight activity of O. pinguis, when flowers of the Carduoideae are usually still rare (A. Müller, unpublished, based on 37 pollen samples from 22 different localities and on field observations).
Müller (2018) further shows that, based on 15 pollen loads, 11 exclusively consisted of pollen of Cichorioideae, and 4 Asteroideae, while a further four were mixed loads of pollen of both subfamilies.
Müller (2018) also lists the following visitation data: Chrysanthemum coronarium, Leontodon sp., Pallenis spinosa (Asteraceae).