"There are 4,000 native bee species in America, 1,500 of which occur in California. Most have no colonies or small ones, so aren't easily amenable to "domestication." The honey bee is a bee of the "Old World"--of Europe and other nearby lands, brought here by Europeans in the 1600s.
Our agriculture has become dependent on monocultures--large acreages of the same crop. If the crops need pollination, they are mostly dependent on a bee monoculture--only European honey bees. So when this species is threatened, so is the pollination of crops like almonds, citrus, melons, strawberies, cotton, apples, pears and plums."
More at the link.
Bees are shaping up to be the big gardening story of 2007.