Bumblebees’ Favorite Flowers Identified to Aid Conservation

(CN) – Deep in California’s Sierra Nevada mountain range, field biologists have identified the flowers most frequently nibbled by bumblebees as part of research to improve pollination of critical plants as bee species face declines nationwide, according to a study published Tuesday.

Bees play an essential role as pollinators in agriculture – and in pollinating native and non-native plants – in particular because of their ability to fly at higher elevations in cold climates.

In the Plumas National Forest of Northern California, a Vosnesensky bumblebee and a Nevada bumblebee feed on Rydberg’s penstamon flowers. (Travis DuBridge / Institute for Bird Populations)

But North American bumblebees have seen significant declines in recent decades, a phenomenon attributed to a host of factors including fading availability of flowers that attract bees.

Research teams combed California’s Plumas National Forest, capturing and studying thousands of bumblebees to determine which flowers each species uses more frequently.

Once a bee was captured on a flower, biologists estimated the number of those flowers in a given plot of forest.

Researchers found that bee species each selected different flowers even though they foraged across the same landscape, according to research published Tuesday in the journal Environmental Entomology.

Of the 100 different species of flowers examined by researchers, they found that only 14 were selected by any of the bee species, the study said.

Land stewards and other managers will apply that information when restoring meadows and other riparian habitat for native bumblebees. That adjustment may lead to increased availability of plants the bees need in order to thrive.

Jerry Cole, a biologist with the Institute for Bird Populations and lead author of the study, said in a statement the use of comparative analysis was key for researchers.

“Often studies will use the proportion of captures on a plant species alone to determine which plants are most important to bees,” said Cole. “Without comparison to how available those plants are, you might think a plant is preferentially selected by bees, when it is simply very abundant.”

Researchers collected 13 different bee species, each selecting at least one flower not selected by any other species, the study found.

Field biologist Alma Schrage watches on as two Vosnesensky bumble bee (bombus vosnesenskii) queens absorb warmth on her sleeve. (Courtesy of the Institute for Bird Populations)

New bee-flower combinations were also documented for the first time, with biologists noting that two-form bumblebees (bombus bifarius) select thick-stem aster flowers Eurybia integrifolia, while the black tail bumblebee (bombus melanopygus) selected Rydberg’s penstemon flowers.

Helen Loffland with the Institute for Bird Populations said in a statement that as early, summer-blooming flowers were replaced by late bloomers, bees used the flowers at different levels.

“We discovered plants that were big winners for all bumblebee species but, just as importantly, plant species that were very important for only a single bumblebee species,” said Loffland. “This study allowed us to provide a concise, scientifically based list of important plant species to use in habitat restoration that will meet the needs of multiple bumblebee species and provide blooms across the entire annual lifecycle.”

Matthew Johnson, a U.S. Forest Service manager, said in a statement the research is already being applied in the field.

“Restoration planning on the Plumas National Forest is already using these results to identify areas where restoration efforts may increase availability or improve quality of bumblebee habitat,” said Johnson, a study co-author, adding that researchers have also collected seeds in order to build more effective seed mixes.

In an email, Cole said wildfires can play a key role in boosting bee populations that have been in decline.

“It’s still not really exactly clear why some species of bumblebees have declined, but it may be related decreased habitat quality, sharing of parasites from honey bees, shifts in when plants flower relative to the emergence of bees, and many other factors,” Cole said. “If a site has lacked wildfire for an extended period of time it may have a less diverse flower community, and potentially support fewer bumblebee species.”

Cole said the presence of stable plants in the forest – and an uptick in insects that call those plants home – provides benefits for bird populations, too.

“Birds typically feed their young a large amount of lepidoptera larvae (butterfly and moth caterpillars) and a more robust plant community may support larger populations of caterpillar,” Cole said.

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