ScienceDaily (July 26, 2009) — Declining bumblebee populations are at greater risk of inbreeding, which can trigger a downward spiral of further decline. Researchers have provided the first proof that inbreeding reduces colony fitness under natural conditions by increasing the production of reproductively inefficient ‘diploid’ males.
http://www.sciencedaily.com/releases/2009/07/090701190414.htm