A fundamental question in bee-flower associations is whether flower selection and specialization in bees is determined by genetically based preferences or by the chemical imprinting of bees to odors of their larval pollen provisions. To evaluate the role of imprinting to pollen chemicals, females of two solitary bee species were forced to provision their nests with pollen of Brassica napus(Brassicaceae) and females of the next generation were tested for their preferences to flowers. In these multiple-choice behavioral experiments, bees were offered flowers from eight species and their responses to each were compared in terms of number of visits, duration of visits, and sequence of visits. In the pollen-generalist (polylectic) bee Osmia rufa (Megachilidae), no imprinting effect was observed. These findings will be compared to experiments conducted on a pollen-specialist (oligolectic) bee, Chelostoma florisomne (Megachilidae), and the implications on the development and evolution of flower/pollen specialization in bees will be discussed.

Key words: Brassica napus, chemical imprinting, flower selection, oligolectic bees, pollen odor, solitary bees