Abstract(s) :

(Anglais) 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. Interactions between flowering plants and wild bees are highly diverse. 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 plant spectrum (polylectic species or pollen generalists). Oligolecty is frequent in solitary bees (around 50 % of described species). Some clades of wild bees like the Melittidae include only oligolectic bees. Ancestral host-plant and specialist behavior seem both highly inherited. However some rare “host-plant shifts” occured during evolution inside clades. The origin and the mechanism of these host-plant shifts remain misunderstood. 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. Similar morphology of alternative host-plants could make the shift easier but the need of particular chemical (sterol, protein, ...) in pollen could reduce the range of suitable hosts. We present our first results in the analyses of chemical composition of pollen host-plants.