Common weed killer linked to bee deaths

Common weed killer linked to bee deaths
Honeybee. Credit: Alex Wild/University of Texas at Austin

The world's most widely used weed killer may also be indirectly killing bees. New research from The University of Texas at Austin shows that honey bees exposed to glyphosate, the active ingredient in Roundup, lose some of the beneficial bacteria in their guts and are more susceptible to infection and death from harmful bacteria.

Scientists believe this is evidence that might be contributing to the decline of honey and around the world.

"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 Erick Motta, the graduate student who led the research, along with professor Nancy Moran. "Our study shows that's not true."

The findings are published this week in the journal Proceedings of the National Academy of Sciences.

Because glyphosate interferes with an important enzyme found in plants and microorganisms, but not in animals, it has long been assumed to be nontoxic to animals, including humans and bees. But this latest study shows that by altering a bee's gut —the ecosystem of bacteria living in the bee's digestive tract, including those that protect it from harmful bacteria—glyphosate compromises its ability to fight infection.

The researchers exposed honey bees to glyphosate at levels known to occur in crop fields, yards and roadsides. The researchers painted the bees' backs with colored dots so they could be tracked and later recaptured. Three days later, they observed that the herbicide significantly reduced healthy gut microbiota. Of eight dominant species of healthy bacteria in the exposed bees, four were found to be less abundant. The hardest hit bacterial species, Snodgrassella alvi, is a critical microbe that helps bees process food and defend against pathogens.

Common weed killer linked to bee deaths
Honeybee. Credit: Alex Wild/University of Texas at Austin

The bees with impaired gut microbiomes also were far more likely to die when later exposed to an opportunistic pathogen, Serratia marcescens, compared with bees with healthy guts. Serratia is a widespread opportunistic pathogen that infects bees around the world. About half of bees with a healthy microbiome were still alive eight days after exposure to the pathogen, while only about a tenth of bees whose microbiomes had been altered by exposure to the herbicide were still alive.

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

Based on their results, Motta and Moran recommend that farmers, landscapers and homeowners avoid spraying glyphosate-based herbicides on flowering plants that bees are likely to visit.

More than a decade ago, U.S. beekeepers began finding their hives decimated by what became known as colony collapse disorder. Millions of bees mysteriously disappeared, leaving farms with fewer pollinators for crops. Explanations for the phenomenon have included exposure to pesticides or antibiotics, habitat loss and bacterial infections. This latest study adds herbicides as a possible contributing factor.

Common weed killer linked to bee deaths
Honeybee. Credit: Alex Wild/University of Texas at Austin

"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.

Native bumble bees have microbiomes similar to honey bees, so Moran said it's likely that they would be affected by glyphosate in a similar way.

Explore further

Overuse of antibiotics brings risks for bees—and for us

More information: Erick V. S. Motta el al., "Glyphosate perturbs the gut microbiota of honey bees," PNAS (2018).
Citation: Common weed killer linked to bee deaths (2018, September 24) retrieved 19 October 2019 from
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Feedback to editors

User comments

Sep 24, 2018
Glyphosate and nicotinoids in general should be banned. There are other chemicals and techniques that can be used instead.
We are very slowly killing ourselves with chemicals especially petrochemical based ones.

Sep 24, 2018
Well, there are not too many good choices. Out of a study of 42 common pesticides, fungicide and herbicides used in spray applications, these are the compounds with the least toxicity to bees:

34 Acetamiprid Aphid 0.95 711 0.77 0.00 <1%
36 Etoxazole Mite 0.83 622 0.70 0.00 <1%
37 Novaluron TPB/SB/BW 10.5 7,864 1.33 0.00 1%
39 Flubendiamide BW/TBW 2.5 1,872 2.13 0.00 1%
40 Chlorantraniliprole BW/TBW 20.5 15,353 1.37 0.00 1%
41 Spiromesifen Mite/WF 8 5,991 3.25 0.00 1%
42 Glyphosate Weed/Grass 125 93,614 0.03 0.00 <1%


Sep 24, 2018
Given the number of unconvincing articles lately on RoundUp - clearly, there is an organized effort to eliminate RoundUp from the market. It's doubtful that such an effort is entirely environmentally based, but much more likely to be competitor - economically based. This is they new face media and public opinion manipulation. There seem to be no neutral or untainted information sources these days - including

Sep 25, 2018
How is this article unconvincing, Dug? is not the publishing journal. The scientists published their data and their report in Proceedings of the National Academy of Sciences of the United States of America, the official scientific journal of the National Academy of Sciences, published since 1915. PNAS papers are published after peer-review, and revision. Do you really mistrust the scientific and journalistic integrity of the authors, the reviewers and the editorial boards of PNAS and

Sep 25, 2018
Bees are dying because of the cessation of use of pesticides. Proliferation of bee-killing mites due to lack of pesticides is what is destroying bee populations. This can be seen in urban areas where pesticide use was discontinued bees began dying between 2-5 years AFTER use was discontiued.

Sep 25, 2018
@Thorium Boy

I must say that is the dumbest argument I have heard in some time.
It's the equivalent to saying bees were a dying race until we started farming them.
There's no doubt, bee population is in decline directly and indirectly due to human activity.
Given that the bees are dying due to bacteria, and that the gut hosts most of the beneficial and toxic bacterial, it follows that pesticides could reek even more havoc on bees than on us; which if true means we now have an excellent benchmark for testing pesticide toxicity. However, likely as important are the "probiotics" which for bees could be pollen diversity. Also, one must wonder if honey extraction, done improperly or too frequently, if that could allow harmful bacteria to infect the honeycomb which would devastate a colony. Sometimes I wish I would have ventured into biology.

Sep 25, 2018
I just do not get the idea that we know (fairly certain) for a scientific fact that Round-Up is killing the insects that work for us to pollinate. This is not good. This is one of many signs that humans are acting just like mold in a Petry dish over-consuming and over-polluting ourselves into oblivion. At the same time our species is all ga-ga over going to Mars, spending incredible amounts of resources as well as capital. Why can't we devote the same scientific effort to working out how to save our home planet before we jet off to another. Another that is about as inhospitable as anyone can imagine. Yet they plan to create a sustainable environment there. It seems like it would be easier to maintain the one we already are blessed to have.

Sep 25, 2018
Given the number of unconvincing articles lately on RoundUp ... -Dug
That's odd, RoundUp wasn't mentioned anywhere in the article nor in the comments until you brought it up. And then Anonym981200, a new account, pops up and also defends Roundup.
There seem to be no neutral or untainted information sources these days - including
If the taint is coming from corporate shills in the comments section, I'd have to agree.

Sep 25, 2018
the shill also plays the game of attempting to conflate and make the point they desire to make. Which is the shill moment of trying to deflect and cause doubt.

These are modern evolved shilling and interference tactics.

Sep 26, 2018
going to Mars, spending incredible amounts of resources

I think you have your priorities a little messed up.

Pentagon spending last year (not counting Black Budget and intel agencies) - $700 billion
Pentagon percentage of budget - 45%
All NASA budgets combined since the beginning (including Apollo) - $800 billion
NASA percentage of the budget - 0.5%
Peak NASA percentage, during Apollo - 4.5%

Just think of what we could do if we stopped spending more than the next 10 countries combined (most of whom are allies) on killing people.

Sep 26, 2018
HAWW...HEE...That's odd, RoundUp wasn't mentioned anywhere in the article nor in the comments until you brought it up. And then Anonym981200, a new account, pops up and also defends Roundup.

The barakn jackass brays.
The very first paragraph clearly mentions -- Roundup.

Sep 26, 2018
By jove, you're right. And I even did a text search in the browser to make sure I didn't miss it, not sure how I did.

Sep 27, 2018
Much like a broken clock, even the likes of antigoracle can be right twice a day, though twice a year seems closer to truth.

Sep 27, 2018
"The barakn jackass brays."
Even commenting on an article like this, anti refuses to bee have.

Oct 01, 2018
It's hardly "news" that glyphosates, nicotinoids and similar compounds are damaging and killing pollinators and animals that prey on them. The problem is that it is not only Bayer-Monsanto in the environmental crosshairs; because of a host of commercial licenses to produce the same poisons internationally, the challenge is far, far larger and more pervasive that most of us realise. Also, public education about the dangers is lacking. I live in Portugal, and am appalled at how little awareness and training exists; almost any fool can get a local Council license to spray any chemicals anywhere, without notifying neighbours or taking simple precautions. Also, big business uses big money to influence decision makers, and despite all the evidence that the toxins are killing and damaging insects, birds, mammals and the soil, there is not the clear political will to ban them. Witness the EU's own cowardly and foolish extension of another five years to Bayer-Monsanto (and others) to continue.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more