Missing from this discussion is the fact that there is strong selective
pressure for races of bees to develop preferences for foraging on pollen
sources that most benefit the colonies.  

I think the evidence is exactly the opposite. Bees are generalists and will forage on a large variety of flowers, regardless of the relative merit of the pollen. All pollen is highly nutritious, its germ plasm. Some might be better than others, but the best of all is a wide mix. Further, plenty of plants are successful without bees, including plants that are wind pollinated, ones that are self pollinating, and others that propagate via runners. 

As an example, one of our best bee plants (japanese knotweed) produces plenty of nectar and pollen but it apparently doesn't set much seed. It spreads underground and by sprouting from pieces that break off and float down creeks and rivers. There must be some seed produced or it would not appear in odd remote areas where these methods could not account for its presence, but seed is not its main route of propagation. 

PS. There aren't "races of bees" in most of the developed world, the bees are a mixture of pre-existing subspecies. These are seldom pure, even in their home regions.

PLB

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html