Active ingredient in Monsanto’s Roundup hurts honey bee guts
Credit: Vivian Abagiu, The University of Texas at Austin

Active ingredient in Monsanto’s Roundup hurts honey bee guts

The weedkiller glyphosate decreases microorganisms in honey bee guts and these changes leave them more susceptible to death, according to a new study.

Honey bees exposed to levels of glyphosate commonly found in the environment had decreased amounts of microbiota in their gut—which leaves them prone to early death, according to a study released today.


Honey bees' health is directly tied to the helpful organisms in their gut. These "microbiota" help the bees' metabolism, weight gain and immune system. The new findings go against previous claims that glyphosate — the active ingredient in Bayer's Monsanto Roundup weedkiller — does not harm wildlife, and offers another possible clue as to why honey bee colonies are dying at an increased rate.

"Gut microbiota is involved in nutrition for bees, helping break down components of cell walls in pollen grains and protecting against different pathogens," Nancy Moran, senior author of the study and evolutionary biologist at the University of Texas, told EHN.

She and colleagues published the study today in the Proceedings of the National Academy of Sciences (PNAS).

The researchers collected hundreds of honey bees from a single hive and exposed some of them to levels of glyphosate commonly found in the environment, and then returned them to the hive. After three days, the total gut bacteria already decreased in the treated bees. When treated bees were exposed to a harmful pathogen, they were more likely to die if they had the reduced microbiota in their gut.

They repeated the experiment with other hives and bees and saw the same impacts.

More pollinator problems 

The colored markings were used to track individual bees during the study. (Credit: Vivian Abagiu, The University of Texas at Austin)

It was previously thought that glyphosate was harmless to bees since it targets an enzyme usually found only in plants and microorganisms—however, bee gut bacteria contain that same enzyme, Moran said. "It's true the bee itself has no molecular targets from glyphosate but its gut bacteria do have targets," she said. "It's similar to humans taking antibiotics where there can be trouble if you upset the normal microbiota."

She said honey bees are relatives to bumble bees and share similar gut microbiota. So, glyphosate is bad for bumble bees as well.

The experiment is concerning as the value of insect pollination to U.S. farming is about $16 billion a year, and honey bee colonies — and pollinators in general — are in trouble.

A third of our food relies on pollinators, and while honey bees are one of many species that pollinate, the U.S. Department of Agriculture estimates about a 30 percent overwinter colony loss annually for honey bees over the past decade.

Over the past year, the Bee Informed Partnership, a nonprofit working with beekeepers, research labs and universities to better understand honey bee declines in the U.S., estimated beekeepers lost 40 percent of their managed colonies.

The culprits for the colony collapses are unclear: Researchers have previously pointed to diseases, parasites, habitat loss, pesticides, and a combination of all of these stressors.

Latest Monsanto woe 

Glyphosate is the world's most heavily used herbicide. More than 3.5 billion pounds have been applied in the U.S. alone over the past four decades—two-thirds of which were applied over the past decade, according to a 2016 study.

Moran said the new study isn't enough evidence to say if glyphosate is having population level impacts on the honey bees, "but there really is a lot of [glyphosate] in both agricultural and urban areas," she said.

"At the moment, there are no guidelines that you should avoid spraying glyphosate on or near bees, since it's considered completely innocuous," she added.

The study is the latest blow to Monsanto's popular weedkiller. The company was ordered to pay a $289 million award last month to a former groundskeeper with terminal cancer who said Roundup exposure gave him the illness. The company is now fighting that ruling.

However, the agribusiness is facing an estimated 8,000 similar lawsuits.

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