Low-infection plants included sunflower and thyme, while high-infection plants included swamp milkweed and purple loosestrife. (Credit: lalo_pangue/Flickr )

Flowering strips for bumble bees offer perks and risks

Although there are pros and cons to flowering strips for bumble bees, they're a good way to offset pollinator declines, say researchers.

Mick Kulikowski-NC State • futurity
May 13, 2020 6 minSource

There are both pros and cons to flowering strips, pollinator-friendly rows of plants that offer foraging habitats for bees, report researchers.

Researchers show that flowering strip plants generally benefitted bee colony reproduction by adding floral resources for common eastern bumble bees ( Bombus impatiens ). The results came with a tradeoff, however, as bumble bees exposed to certain plants showed higher rates of infection by a bee pathogen acquired on flowers— Crithidia bombi , which is associated with reduced bee-foraging abilities as well as mortality in food-compromised bees.

The study showed that certain “high-infection” plants doubled C. bombi infection intensity when compared with “low-infection” plant species. Bees feeding mostly on canola plants—a major bee foraging plant and important US crop—showed infection levels between high- and low-infection plants.

“…providing flowering resources in pollinator habitat is still the best path forward.”

Nonetheless, all bee colonies that foraged on flowering strips—both low-infection and high-infection types—showed increases in reproduction relative to bees that only had access to canola.

“We wanted to know the effects of flowering strip plant species on the health and reproduction of bumble bees,” says Rebecca E. Irwin, professor of applied ecology at North Carolina State University and a coauthor of a paper on the research in the Proceedings of the National Academy of Sciences . “Flowering strips are becoming more common as people look for ways to mitigate pollinator declines .”

The researchers used information gleaned from a previous study to split flowering strips into low- and high-infection portions. Low-infection plants included sunflower and thyme, while high-infection plants included swamp milkweed and purple loosestrife.

“In a prior study, we evaluated 15 plant species by putting the same amount of C. bombi on each, letting a bee forage, and then seeing whether and how bad of an infection it developed,” says Lynn S. Adler, professor of biology at the University of Massachusetts Amherst and the corresponding author of the paper. “We used that to designate plant species as ‘high/low infection’ for this study.”

Researchers placed bees in tents with the crop plants and either high-infection flowering strips, low-infection flowering strips, or no flowering strips.

“The bees were all infected with the same amount of pathogen and then allowed to forage, so the plants could increase or decrease infection,” Adler says.

Adler said the flowering-strip tradeoff—more bee reproduction but higher pathogen infection rates—may be acceptable.

“It depends on how critical food versus the pathogen is for pollinators,” she says. “ Crithidia is somewhat benign, but if these patterns hold for other pathogens like Nosema , a common honey bee disease, it may be more of a concern. Right now I would not recommend stopping our investment in flowering strips.”

The researchers hope to continue examining the effects of flowering strips on bee populations and health by including other bee species and pathogen types.

“I think we need a much more comprehensive program to evaluate how pollinator habitat characteristics affect pathogen spread to make informed choices,” Adler says. “In the meantime, providing flowering resources in pollinator habitat is still the best path forward.”

Additional coauthors of the paper are from San Diego State University and Thomas Jefferson University.

Funding for the study came from the US Department of Agriculture’s Agriculture and Food Research Initiative, the National Institutes of Health, the National Science Foundation, and the US Department of Agriculture’s Cooperative State Research Education and Extension Service.

Source: NC State

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