North American bumble bees are in trouble. The first large-scale study of bee population numbers and distribution in the U.S. brings bad news for vegetable farmers. Not to mention the balance of nature.

SEE ALSO: India Facing Crop Shortage as Pollinators Disappear

Eight species from a North American bumble bee genus (Bombus) were studied. Four out of the eight showed serious declines in both number and size of habitat since the late 1800's. The abundance of some bees had declined by 96 percent, while the ranges of some bees shrank by 23 to 87 percent, according to researchers led by Sydney Cameron of the University of Illinois at Urbana-Champaign.

Cameron worries that the four species in decline may be only the “tip of the iceberg.” There are still 42 species they didn't study, and they could be in trouble too.

The bee study was published recently in the Proceedings of the National Academy of Sciences.

SEE ALSO: Bee Die-Offs Worsened by Winter, Pesticides

For three years, Cameron and her team studied historical records and conducted field research at about 400 sites. They gathered data about changes in bumble bee population sizes, genetic diversity, and geographic distribution. The researchers created a database of 73,000 museum records and compared those to observations of 16,000 individual bees.

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.

SEE ALSO: An Island of Honeybees in the African Desert

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.

SEE ALSO: Bees : Discovery News

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