Conservation strategy found to increase disease in bumble bees

Rows of plants known as flowering strips are designed to be pollinator-friendly, but a new study suggests they have some drawbacks.

Researchers at NC State University have found that while flowering strips can help boost bumble bee reproduction, they also facilitate higher rates of disease. 

The team demonstrated that flowering strip plants supported bee colony reproduction by adding floral resources for common eastern bumble bees. 

On the other hand, bumble bees exposed to certain plants showed higher rates of infection by a bee pathogen, Crithidia bombi, which is associated with reduced foraging abilities and can be fatal.

The study revealed that certain “high-infection” plants doubled C. bombi infection when compared with “low-infection” plant species. A control group of bees that only had access to canola was found to have infection rates that fell somewhere in between.

Regardless of their level of infection, bee colonies that foraged on flowering strips were more reproductively successful than bees in the control group.

“We wanted to know the effects of flowering strip plant species on the health and reproduction of bumble bees,” said study co-author Professor Rebecca E. Irwin. “Flowering strips are becoming more common as people look for ways to mitigate pollinator declines.”

The low-infection plants used for the study included sunflower and thyme, and the 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,” said study co-author Professor Lynn S. Adler of UMass Amherst. “We used that to designate plant species as ‘high/low infection’ for this study.”

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

Professor Adler explained that the tradeoff of higher pathogen infection in exchange for better reproductive rates may be acceptable.

“It depends on how critical food versus the pathogen is for pollinators. 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 study is published in PNAS.

—

By Chrissy Sexton, Earth.com Staff Writer