In article 2c7ac91f-b4a0-4236-ae20-c15158e6e3e1
@n2g2000pre.googlegroups.com, says...
Since you both expressed a concern on this subject,..

http://www.reuters.com/article/idUST...3?pageNumber=1

Researchers find "alarming" decline in bumblebees
By Maggie Fox, Health and Science Editor

WASHINGTON | Mon Jan 3, 2011 3:36pm
EST

Genetic tests show that the four affected bumblebee species are inbred
and other tests implicate a parasite called Nosema bombi, Cameron*
said...

They documented a 96 percent decline in the numbers of the four
species, and said their range had shrunk by as much as 87 percent. As
with honeybees, a pathogen is partly involved, but the researchers
also found evidence of inbreeding caused by habitat loss....

*Dr Cameron: http://www.life.illinois.edu/entomol...y/cameron.html

We've been watching this issue for awhile but hadn't run into Cameron's
work. We were hearing reports of bombus decline several years ago but
didn't know the extent.

As with honeybees it's likely complex.

In your explorations have you encountered Varroa Sensitive Hygeine and
have you tried googling 'sub-lethal neonicotinoid bees'.