[Pollinator] Bumble bees in decline

[Sarina Jepsen]

Bumble Bees on the Brink?
Your help is needed
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In the late 1990's, bee researchers began to notice a decline in the 
abundance and distribution of several North American bumble bee 
species. Three of these species, the Western Bumble Bee (Bombus 
occidentalis), the Yellow-banded Bumble Bee (Bombus terricola) and 
the Rusty-patched Bumble Bee (Bombus affinis) were once among the 
most common bumble bees in North America. In recent years, these bees 
have become very rare in most parts of their ranges.

There are a number of threats facing bumble bees that may be causing 
the decline of these species, including: the spread of pests and 
diseases through commercial bee rearing, other pests and diseases, 
habitat loss, pesticides, invasive species, and climate change. Dr. 
Robbin Thorp has hypothesized that wild populations of Western, 
Rusty-patched and Yellow-banded Bumble Bees were infected by an 
introduced pathogen carried by commercially reared colonies of 
Western Bumble Bees and Eastern Bumble Bees (Bombus impatiens). 
Between 1992 and 1994, Western and Eastern Bumble Bees were sent to 
Europe where colonies were produced in facilities that also reared 
European Buff-tailed Bumble Bees (Bombus terrestris). Dr. Thorp 
suggests that these colonies were infected with a pathogen (probably 
a virulent strain of the microsporidian Nosema bombi) while in 
Europe.  When the colonies were returned to the U.S. for use as 
commercial pollinators, they may have spread pathogens to wild 
populations of bumble bees. While this hypothesis is still in need of 
validation, the timing, speed, and severity of the population crashes 
supports the idea that an introduced disease has led to the decline 
of these bumble bees.

To better understand the decline of these three species, the Xerces 
Society is documenting their former and current ranges. Please 
<mailto:info at xerces.org>contact us if you have any records of the 
Western Bumble Bee, the Yellow-banded Bumble Bee or the Rusty-patched 
Bumble Bee from field surveys, student collections, or other sources 
from the past ten years. We would also like to know if you have 
conducted surveys in the former ranges of any of these bees and have 
not encountered them. We have developed a series of WANTED posters to 
raise public awareness about the plight of these bumble bees. Please 
email (<mailto:info at xerces.org>info at xerces.org) or call the Xerces 
Society at 503-232-6639 to request a poster. To learn more about the 
identification and distribution of these bumble bees and our efforts 
to conserve them, please visit 
<http://www.xerces.org/bumblebees>www.xerces.org/bumblebees.



________________________________________
The Xerces Society for Invertebrate Conservation
The Xerces Society is an international, nonprofit organization that
protects wildlife through the conservation of invertebrates and their
habitat. To join the Society, make a contribution, or read about our
work, please visit <http://www.xerces.org/>www.xerces.org

Sarina Jepsen
Senior Conservation Associate
4828 SE Hawthorne Blvd.  Portland, OR  97215
tel: 503-232-6639     fax: 503-233-6794
email: sarina at xerces.org
________________________________________
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