Rusty-patched bumble-bee_Culver's root_Susan Day_UW-Madison Arboretum
A rusty patched bumblebee on Culver’s root at the University of Wisconsin-Madison Arboretum (Susan Day/UW-Madison Arboretum)

By Anna Yellin

On March 21, the rusty patched bumblebee (Bombus affinis) became the first bumblebee listed as endangered under the Endangered Species Act.

Before the 1990s, rusty patched bumblebees were abundant and seen throughout the Canadian provinces of Ontario and Quebec as well as in 28 states from the eastern U.S. to the Midwest. Mountainous North Georgia marked the southern extent of the species’ range.

In the last few decades, however, the population of rusty patched bumblebees has crashed. It is believed the species now persists in only a few scattered locations in approximately 0.1 percent of its known range. None of these locations are in Georgia.

But given that most people do not pay much attention to the type of bumblebees they see, and very few would previously have been on the lookout for this species, it’s possible there are some rusty patched bumblebees still in Georgia. That means we should be watching for them!

The loss of this pollinator has likely led to significant agricultural and economic losses. For growers of cranberries, apples, plums, alfalfa and onion seed, crop yields may already be lower. The rusty patched is known as a generalist forager, tirelessly pollinating hundreds of plant species. It also flies for an exceptionally long season. In fact, specimens held in the Smithsonian Institution insect collection from Georgia were collected in Neels Gap near Suches at the end of November!

In addition to the bee’s prolonged season, this species is a specialist in “buzz pollination.” In this especially efficient and effective method, rusty patched bumblebees assist plants in producing fruit. Some plants, like blueberries, tomatoes and eggplants, buzz pollination is required to shed the pollen from the anther (the part of the stamen where pollen is produced) and enter the pistil for the production of fruit. (The rapid movement of flight muscles by buzz pollinators is transmitted to the anther through their legs and mouth, vibrating loose more pollen grains. Watch this video.)

We are fortunate that the rusty patched bumblebee is not our only native buzz pollinator! Despite efforts by some commercial growers to ensure pollination, such as renting honeybee hives, many crops will not be pollinated if we lose buzz pollinators.

Primary threats to the rusty patched bumblebee are hypothesized to include habitat loss, pesticides (including systemic neonicotinoids), climate change and disease. Many also think that the population crash of this and other Bombus species is due to disease spreading from honeybees, a non-native species imported by European settlers. At least two significant diseases found in honeybees – deformed wing virus (DWV) and the fungus Nosema ceranae – have been found to also kill bumblebees.

The hope in this case is that the genetic diversity the rusty patched bumblebee has evolved to include, over time and geographic variability, may prevent the species from being driven to extinction by disease. Field surveys seem to support the idea that some of the bees have persisted through a resistance to the illnesses, because in the isolated areas the species is still found their numbers are good.

Others point to changes in the types of pesticides used in the 1990s and suggest that chemicals are to blame for the species’ decline. In truth, why this bumblebee is disappearing is unknown.

Considering the wide extent of its historic range, discovery of the rusty patched bumblebee in areas where it’s not known or hasn’t been documented in years will likely be done by the public. The protection of those areas that results from such finds and research to understand why the bees persist there would help scientists protect the species.

So, grab a pair of binoculars and a camera and be on the lookout for rusty patched bumblebees, especially if you live in the Georgia mountains or are hiking on or around the Appalachian Trail. The males and worker bees of this colonial species have a distinctive rusty patch on the back, giving the species its name. If you do spot what you
think is a rusty patched, send a GPS coordinate (or map of the site), the date and a photo – all are essential! — to Bumble Bee Watch (www.bumblebeewatch.org) and to Georgia DNR at anna.yellin@dnr.ga.gov.

Here’s The Xerces Society’s pocket guide to identifying rusty patched bumblebees.

Anna Yellin is environmental review coordinator for DNR’s Nongame Conservation Section.

BombusAffinis_ID_USFWS
Bombus affinis (U.S. Fish and Wildlife Service)
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