The pollinator that got away

This is a story of how the eastern bumble bee, Bombus impatiens, came to be established in the western part of North America, outside its native range. It is still too early to determine any impacts to our native bees, but we need help continuing to monitor it. We will show how it got here and why, its current sightings, and what you can do to help us track it's range expansion.

Insects like the brown marmorated and southern green stink bugs, giant asian hornet, gypsy moth, and many other moth species have made their way into the U.S. and Washington state. Our work in the Pest Program is to mitigate potential destruction of our food supply and commodities by tracking movement of insects and keeping their populations down when necessary.

Food growers have used the help of pollinators for eons. Honey bees, bumble bees, many kinds of flies, and butterflies all contribute to human food production. Whether in open fields, or closed greenhouses, there simply would not be many of the foods we love, in the quantities we need, without their help.

For this help here in the western United States, farmers and growers use the native western bumble bee, Bombus occidentalis, to assist them in crop pollination. Healthy hives are bought from bee suppliers and shipped to farms. The hives are then set out in the fields and greenhouse and the bees get to work.

Assistance in the eastern United States comes from the eastern bumble bee, Bombus impatiens.

In the 1990's something crashed the captive western bumble bee population. A detrimental fungus called Nosema bombi, is attributed to infecting and decimating hives throughout the region. This left an alarming deficit of available, healthy bees for use in crop production. What were the growers going to do?

Enter Bombus impatiens

With this crisis, the governments of the US and British Columbia allowed for the importation of the eastern bumble bee within an emergency program. The agreement was that the bee was to be used solely within greenhouses and insurances had to be made to keep them from escaping. Although regulated softly, these courtesy permits stopped being regulated at all in 2000.

During a routine strawberry survey in 2003 near tomato greenhouses in Vancouver, B.C, a very interesting bycatch was discovered in the pan traps. A B. impatiens queens and worker were caught. It was a mystery where and how they came to be there. It wasn't long before the pieces came together. (This is a beautiful example of why our monitoring work is so important!)

Since then, an increase in B. impatiens sightings has been recorded on the internet. We have used Bugguide.net, BumblebeeWatch.org, and iNaturalist.org as the primary sources for the following maps:

As much as we'd like to be everywhere, WSDA has limited resources and funding. We rely on the enthusiastic help from citizen scientists and volunteers like the Master Gardener Program through WSU Extensions. This help adds invaluable information we wouldn't otherwise have by conducting studies and surveys in Washington.

Master Gardeners have assisted WSDA in better understanding overall pollinator health by running bee surveys in San Juan, Skagit, and Whatcom counties. Also, there was a survey on Japanese Beetle and the bycatch contributed to the knowledge of B. impatiens growing expansion.

The release of the eastern bumble bee was an accident and a good example that shows how easy it is for life to escape any circumstance. Bombus impatiens is out-competing our native western bees. They have been viewed more often out in the field. Their presence may not become a detrimental species in the west, but it will likely have an impact on the flora and fauna of this area. That all remains to be determined.

If you live in southwest British Columbia or western Washington and you spot a Bombus impatiens, please report your sighting on BumblebeeWatch.org, iNaturalist.org, or Bugguide.net. With this assistance, WSDA will be better equipped to continue monitoring its expansion south. Check out these resources online:

Author: Angela Yoder, Washington State Department of Agriculture Pest Program. 2019