Most popular weed killer linked to declining bee populations

Researchers at The University of Texas at Austin have discovered that the most commonly used weed killer in the world may be inadvertently killing bees. The study provides evidence that weed killers are contributing to the declines of honey bees and other bee populations worldwide.

When bees are exposed to the active ingredient in Roundup called glyphosate, they lose important gut bacteria and become more susceptible to infection and death from harmful bacteria.

Graduate student Erick Motta co-led the study with Professor Nancy Moran.

“We need better guidelines for glyphosate use, especially regarding bee exposure, because right now the guidelines assume bees are not harmed by the herbicide,” said Motta. “Our study shows that’s not true.”

While glyphosate has long been assumed to be non toxic to animals, including humans and bees, the current research suggests otherwise. Glyphosate compromises a bee’s ability to fight infection by modifying the gut microbiome, which plays an important role in health and disease.

For their investigation, the researchers exposed honey bees to glyphosate at levels that would be common in crop fields or anywhere that the herbicides are used. Three days later, they observed that exposure to the weed killer significantly reduced healthy gut microbiota.

Of the eight dominant species of healthy bacteria, four were found to be less abundant after exposure. Snodgrassella alvi, a microbe that helps bees process food and defend against pathogens, was affected the most.

The study also revealed that the bees with impaired gut microbiomes were far more likely to die from Serratia marcescens, a widespread opportunistic pathogen that infects bees around the world.

“Studies in humans, bees and other animals have shown that the gut microbiome is a stable community that resists infection by opportunistic invaders,” said Professor Moran. “So if you disrupt the normal, stable community, you are more susceptible to this invasion of pathogens.”

The study authors recommend that farmers, landscapers, and homeowners avoid spraying glyphosate-based herbicides on flowering plants that bees are likely to visit.

“It’s not the only thing causing all these bee deaths, but it is definitely something people should worry about because glyphosate is used everywhere,” said Motta.

The study is published in the Proceedings of the National Academy of Sciences.

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By Chrissy Sexton, Earth.com Staff Writer

Image Credit: Alex Wild/University of Texas at Austin