Scientists Complete Detailed Genome Map of Endangered Rusty Patched Bumble Bee

The rusty patched bumble bee is one of the many bees facing threats to its survival, from toxic insecticides to loss of habitat and global heating. Once prevalent throughout the upper midwestern and northeastern U.S., this unique bumble bee species has declined more than 85 percent and now lives only in the northernmost portion of its original range, according to the U.S. Forest Service.

Rusty patched bumble bees are productive pollinators of milkweed, bergamot and other wildflowers, as well as many foods like apple, alfalfa and plum. Bumble bees perform the specialized “buzz pollination” method to release otherwise inaccessible pollen, which is essential for crops like peppers, tomatoes and cranberries.

Now, a high-resolution map of the genome of the rusty patched bumble bee has been put together by scientists from the U.S. Department of Agriculture (USDA), the U.S. Fish and Wildlife Service and the Agricultural Research Service (ARS), a USDA press release said. The detailed map may offer new insights on how to help this native pollinator with the rust-colored patch avoid extinction.

“With the amount of detailed information that we and other researchers now have access to in this newly sequenced genome, we have an opportunity to find a whole different approach to strengthening rusty patched bumble bee populations,” said research entomologist Jonathan B. Uhaud Koch with the ARS Pollinating Insect-Biology, Management, Systematics Research Unit in Logan, Utah, in the press release.

Assembling the genome of this special bumble bee was part of a first-of-its kind endeavor called the Beenome 100 project, for which scientists from the University of Illinois and ARS created extremely detailed genome maps of 100-plus diverse U.S. bee species.

It is hoped that the collection of genome maps will assist researchers in finding answers to issues such as whether a specific bee species will likely have a heightened vulnerability to a pesticide or what genetic differences make certain bee species more susceptible to climate change.

The rusty patched bumble bee has been listed as endangered since 2017. The bumble bees used to be common in 28 states, as well as two provinces in Canada, but their range now consists of fragmented areas in one Canadian province and 13 states.

Some factors contributing to the decline of the rusty patched bumble bee include exposure to toxic pesticides, habitat loss, climate change, less variety of nectar sources and an increased number of pests and pathogens, Koch said in the press release.

Scientists have been well aware of the prevalence of the fungal pathogen Varimorpha bombi (formerly known as Nosema bombi), which adversely affects many populations of rusty patched bumble bees. However, Koch was surprised by the amount of Varimorpha genetic material that was found in the sample used in the development of the genome map.

“We used a small piece of abdominal tissue from a single male collected from a nest in Minnesota, which, given the endangered status of the rusty patched bumble bee, seemed like a very good idea,” Koch said in the press release. “It’s only with the most cutting-edge equipment that you could resolve an entire genome of 15,252 genes and 18 chromosomes from a tiny bit of one bumble bee.”

Approximately 4.5 percent of the sequenced DNA came from the fungal group Microsporidia, which includes Varimorpha bombi.

“That’s a massive amount of genetic information from the bee tissue sample to be associated with Varimorpha bombi. It demonstrates how pervasive the pathogen is,” Koch said.

After the researchers identify which genes are more successful for a certain type of local condition, they can use that knowledge, along with captive breeding programs, to boost the rusty patched bumble bee population in a particular area.

“Having this high-quality genome will support the identification of genetic differences between rusty patched bumble bee populations that appear to be doing well versus where they are in decline. This may give us a handle on identifying the genes that give the more capable population its flexibility to deal with its environment,” Koch added. “We may also gain a better understanding of the genetic basis of bumble bee behavior, physiology and adaptation to changing environmental conditions.”