AMES, IA – Once widespread throughout the eastern United States and the upper Midwest, the population of rusty patchwork bumblebees has decreased by nearly 90% since the 1990s.
Researchers at Iowa State University are part of a multi-state effort to map where the federally endangered pollinator lives, determine the habitat it prefers and gather clues about population genetic diversity and public health. The findings could help wildlife and land officials reverse the decline of bumblebees and support other pollinators more broadly.
Amy Toth, professor in the Departments of Ecology, Evolution, Organism Biology, Plant Pathology, Entomology, and Microbiology at Iowa, is leading a 2.5-year project in Iowa with Anna Tucker, associate professor of natural resource ecology and management and unit leader with the United States Geological Survey (USGS) at the Iowa Collaborative for Fish and Wildlife Research.
While the researchers collect data on the rusty patchwork bumblebee, they are also documenting where they found its larger cousin – the American bumblebee – which has experienced a recent population decline estimated at 51%.
“If we know where surviving populations of rust and American bee populations are and what they need to thrive, we can better target areas in Iowa and the upper Midwest for conservation and restoration, as well as for future research,” Toth said.
Toth adds that Iowa represents a “primary site” for rusty patched bumblebee conservation in the United States as the western edge of the pollinator range. Isolated wild populations, such as those the team found near Ames and Fort Dodge this summer, may carry genetic variations that could aid species recovery efforts.
Prairie surveys and ‘zombie cold’
Using data from the Iowa Department of Natural Resources, the US Fish and Wildlife Service, and iNaturalist (an app for sharing and identifying plants and animals), the research team identified 50 survey sites in Iowa. Most of them were in the northeast corner of Iowa, but they extended as far west as Spencer and south of Iowa City.
two graduate students, Kelsey Shepherd and Erica Ibarra Garibai; ISU alumna Danielle Holthouse; Denis Camarena, the current ISU Chief Officer, did the bulk of the data collection over the summer. Additional help came from undergraduates Stephanie Paris and Alex Court, and graduate student Morgan Moore.
At each location, the team recorded GPS coordinates and planted flags along the perimeter of an area roughly the size of a hockey rink. They then walked across the place with hand nets, pausing for 30 minutes each time they caught a bee.
If they find a rusty bee or American bee, Ibarra-Garibay will return for a second survey. To collect her data, she put each bee on ice to create “coma goosebumps.”
“I probably had five minutes before they started getting up, so I had to work really fast to collect my measurements.”
After weighing a coma bee, Ibarra-Garibay slides between graph paper and a microscope slide to measure the size of its head and the distance between its wings. She assessed if it had any damage to the wing and took pictures, which she will analyze with other software this winter.
“The idea in our lab is that wing wear equals the effort of foraging. Therefore, the bees may experience more wear and tear if they fly longer distances in search of food or have to increase their effort to forage. It is the idea that the more hard they have to work, The more likely they are to wear their wings.”
Ibarra-Garibay also collected a small tissue sample for DNA analysis, and pollen from the rusty patched legs of bumblebees to share with the USGS for a larger study looking at the species’ genetic diversity and dietary preferences.
At sites where the team has found rust bees or American bees, Shepherd and Holthaus have also conducted habitat assessments (for example, whether the site is within 20 meters of a body of water; what flowering plants are) and will work with Tucker on a landscape analysis using maps Geographical Information System (GIS).
Of the 50 sites surveyed twice this summer, the research team detected the presence of American bees in a third. They found rusty bumblebee patches in four locations.
“At two locations, including here in Ames, rusty bumblebees were fairly abundant, suggesting there were survivor populations there. So, it’s not too late for conservation action here in Iowa,” Toth said.
The other three sites included the Brushy Creek State Recreation area near Fort Dodge, and two sites near Dubuque and Yellow River State Forest, one of which is part of the USFWS Partners for Wildlife Program.
“Most of our discoveries this summer have been along the gorges of the Des Moines and Mississippi Rivers — areas of banks where there’s a river and then trees and meadows, but there’s still a lot we don’t know about the rusty bumblebees of Iowa,” shepherd.
More than a bee
Some people might ask, ‘Who cares? It’s just one type of little bee. However, both Rust and American are two large, attractive species that act as symbols of a much larger problem – the massive global decline in pollinators,” Toth said.
Efforts to help rust and Americans recover could benefit other pollinators that depend on the same habitats and face similar threats, such as pesticides and climate change.
“Conserving pollinator populations on a large scale is important because we humans depend on them for pollination services, because they play important roles in natural ecosystems, and, in my opinion, because they are essentially wonderful and beautiful animals,” Toth said.
The researchers stress that the project, which is funded by the US Fish and Wildlife Service, is still in its early stages. This winter, they will analyze the data and collect a second round of data next summer.