The surviving bees of species in decline had lower genetic diversity than bees from healthy populations. The declining bees were also more likely to be infected with the parasite, Nosema bombi.
All hope is not lost for the declining bees.
"They could potentially recover; some of them might," said Cameron in a University of Illinois press release.
Besides the damage to ecosystems, humans suffer from the absence of bees. Agriculture depends on bees to pollinate crops. Declining bee populations and ranges have serious economic impacts.
"It may be that the role that these four species play in pollinating plants could be taken up by other species of bumble bees. But if additional species begin to fall out due to things we're not aware of, we could be in trouble," said Cameron.
IMAGE 1: Bumblebee (Bombus impatiens) on Rhododendron in Archbald, PA.; Wikimedia Commons IMAGE 2: University of Illinois entomology professor Sydney Cameron; Sydney Cameron