[en] Represented by more than 16 000 described species, bees are the major pollinators of angiosperms in most ecosystems. Since early Cretaceous, they share a long and intimate evolutionary history with flowering plants.
Bees forage on pollen and nectar as the exclusive food source. Different foraging strategies have been described. Some taxa are specialized in their floral choices (oligolectic species or pollen specialists) while other bee species are more opportunistic and forage on a large plants spectrum (polylectic species or pollen generalists). Oligolecty is frequent in solitary bees (around 50 % of described species).
During evolution, host-plant shifts occured inside bee clades. They can be based on morphological or phylogenetical similarity with ancestral host-plant but host switches to unrelated plant families are also common. The constraints of these switches are not well known.
Because bees obtain all the proteins, lipids, minerals and vitamins they need for adult growth and development from pollen, and that the proportions of these nutrients can vary widely among pollens of di?erent plant species, ?oral specialisations in bees could be constrained by the chemical composition of the pollen.
We present the first analyses of pollen collected by two solitary bees of the genus Colletes, Colletes hederae foraging on Hedera helix and Colletes halophilus foraging on Aster tripolium.
