In the late 1990′s, bee biologists started to notice a decline in the abundance and distribution of several wild bumble bee species. Five of these species (western bumble bee, rusty patched bumble bee, yellowbanded bumble bee and the American bumble bee) were once very common and important crop pollinators over their ranges. Franklin's bumble bee was historically found only in a small area in southern Oregon and northern California, and it may now be extinct. The dramatic decline in wild populations of these five species occurred about the time that a disease outbreak was reported in populations of commercially raised western bumble bees, which were distributed for greenhouse pollination in western North America. The timing of this suggests that an escaped exotic disease organism may be the cause of this widespread loss.

This hypothesis was supported by a recent study led by Sydney Cameron, Ph.D., published in the Proceedings of the National Academy of Sciences. They found that the western bumble bee and the American bumble bee had significantly higher infection rates from a fungal parasite than more stable species. They also found that these two species had lower genetic diversity than species that were not in decline. Research is currently underway in Dr. Cameron's lab to determine whether or not this fungal parasite was introduced from Europe via the commercial bumble bee trade. You can read more about their study and its implications here.

A major threat to the survival of these wild bees may be the spread of diseases from commercially produced bees that are transported throughout the country. The Xerces Society is currently working to urge the USDA Animal and Plant Health Inspection Service to regulate the commercial bumble bee trade. You can read a status review that includes more details on this issue and the decline of three bumble bees that was written by Dr. Robbin Thorp and The Xerces Society.