The abundance of four common species of bumblebee in the US has dropped by 96% in just the past few decades, according to the most comprehensive national census of the insects. Scientists said the alarming decline, which could have devastating implications for the pollination of both wild and farmed plants, was likely to be a result of disease and low genetic diversity in bee populations.

Someone inquired into the location of the bumblebee species with declining populations.

Here's some supplemental information from the study, including a map of the species surveyed (look toward the end of the document for the maps) You might have to click on the supporting information link and then click on the supporting information PDF).

The four species listed are common to:
Bombus occidentalis - Western Bumblebee - No surprise that it is a western species, and its population declines are well documented. The Xerces Society is currently an effort to document nesting places for the remaining population.
B. pensylvanicus: Many places east of the Rockies
B. affinis: Northeast and Upper Midwest
B. terricola: Primarily Upper Midwest and New England