Herbicides, Bacteria Killers, and Honey Bees

Recently, I learned that herbicides such as Roundup and 2-4-D kill bacteria. Not only do they do a fine job of killing broadleaf pollen producers, they also kill some microbes. This information didn’t come from the tin-hat doom-sayer who lives on the other side of my computer screen. I saw it written up on the pro-business Forbes website, so it might be true.

For years, I’ve puzzled over the complaint that herbicides kill bees. I thought this was a mistype. Surely they meant insecticides kill bees. Herbicides are supposed to just kill weeds. Nasty weeds that choke farmers’ fields.

But now I learn that herbicides kill bacteria. You will see in a moment why that’s not so good for bees. A lot of chemicals are antiseptics – rubbing alcohol, iodine, and fire, for example. Honey, of course, also kills bacteria. So it should not surprise us that some of the ingredients of the most popular herbicides are also bactericides. These are either antiseptics (killing bacteria locally and topically) or antibiotics (disrupting bacterial growth, including internally). Here’s a brief summary of a few favourite herb-killers:

2,4-Dichlorophenoxyacetic acid (usually called 2,4-D) is an organic compound. Yes, folks, it’s organic. Its chemical formula is about as complicated as sour dough’s: C8H6Cl2O3.   2,4-D is a systemic herbicide which causes uncontrolled growth in most broadleaf plants, killing them, while most grasses such as cereals, lawns, and grassland are relatively unaffected.  2,4-D has been around since 1945.  Its patent expired long ago so any company with a chemistry lab can make it. As a result, over 1,500 herbicide products contain 2,4-D as an active ingredient.

Roundup’s key ingredient is glyphosate. A Monsanto chemist, John E. Franz, discovered that glyphosate is  an herbicide in 1970.  Its patent has also expired, but Monsanto cleverly and profitably created glyphosate-resistant Roundup Ready crops, enabling farmers to kill a very wide range of weeds without killing crops.  This allows even better (and actually cheaper) weed control for farmers, but they need to buy seeds developed specifically to tolerate the organophosphorus compounds.  Monsanto sells those seeds, of course. Unfortunately, in the same way that Monsanto was able to find genes that resist glyphosate, Mother Nature (a semi-independent unincorporated entity only partially owned by Monsanto) enabled weeds to evolve and become glyphosate-resistant. This is not as bad as it sounds, the weeds are only partially resistant and are killed by increasing the amount of glyphosate applied. (Of course, in a few years, the weeds will evolve to be even more tolerant. But then the farmer simply increases the dosage again. Meanwhile, the World Health Organization found that glyphosate is carcinogenic.  In 2007, glyphosate was the most-used herbicide in the United States’ agricultural sector’s arsenal and the second-most used in home and garden, government and industry and commerce.   But what’s to worry?

what me worry

Dicamba is sold under names like Banvel, Diablo, Oracle and Vanquish. Is it just me, or do those sound like Satan’s nom de plumes? The Dicamba family is made of organochlorines derived from benzoids. In this 25-year-old fact sheet on Cornell University’s website,  dicamba is described as a highly corrosive acid that can cause skin irritation and “severe and permanent eye damage.”   Sprayed on broadleaf plants, it kills.

We have our pick of dandelion killers:  2-4,D, glyphosate, dicamba. There are others. Now let’s consider if these herbicides kill bees. I can see how they’d make a bee’s life less enjoyable. Just as the bee approaches a bright yellow dandelion flower, grounds-keeper Willie floods the septal nectaries with glyphosate. That shouldn’t kill the bee, but it might make her groggy. Hopefully, she can still return to her nest with her slightly damp pollen. But that’s where the real problem may start.

Bees use bacteria to make pollen more palatable. The bacteria, mixed with pollen in beebread (the bees’ staple protein dinner), makes the pollen more easily digested. Herbicides kill bacteria. Obviously, if the herbicides kill bee-friendly pollen-reducing bacteria, herbicides may result in malnourished bees. This alone does not cause colony collapse disorder, nor has it alone caused the demise of bumblebees and other creatures. But it’s probably one more ingredient in the toxic soup that makes a bees’ life brief and dreary.

About Ron Miksha

Ron Miksha is a bee ecologist working at the University of Calgary. He is also a geophysicist and does a bit of science writing and blogging. Ron has worked as a radio broadcaster, a beekeeper, and Earth scientist. (Ask him about seismic waves.) He's based in Calgary, Alberta, Canada.
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5 Responses to Herbicides, Bacteria Killers, and Honey Bees

  1. Pingback: Herbicides, Bacteria Killers, and Honey Bees | Bad Beekeeping Blog – WORLD ORGANIC NEWS

  2. BeeNuts says:

    The problem with all the scare stories about chemicals is they usually fail to consider the dose/response curve. Many chemicals are bacteriocidal if the dose is high enough – common salt is a good example, which is why it makes a good preservative. So simply demonstrating an effect (like carcinogenicity/bacteriocidal activity) whilst interesting (and headline grabbing) does not necessarily mean it is relevant. If a herbicide was shown to kill the bacteria responsible for making beebread (I thought they were yeasts?), and the minimum inhibitory concentration was established, and it was shown that such concentrations are occurring in pollen collected by bees, then there’s a problem. That’s not to say we shouldn’t be concerned, but neither should we leap to conclusions.
    As for the publication in the link under ‘Herbicides kill bacteria’ my understanding is that the authors are reporting that herbicides may, under certain conditions INCREASE antibiotic resistance of certain bacteria by inducing activity of pumps on the cell membrane. These pumps also pump out antibiotics, which makes the bugs more resistant. Sometimes they found the opposite effect, and the bacteria became more susceptible to antibiotics. Either way, what this paper doesn’t show is that herbicides kill bacteria – though I’m sure if the dose was high enough, they would!
    All that said – I wish folk wouldn’t spray dandelions – the bees love them.


    • Vera Strogolova says:

      Glyphosate is an antibiotic, as it inhibits the Shikimate physiological pathway, which is essential for life of bacteria in Lactobacillus spp. and Bifidobacterium spp. and other microorganisms. All antibiotics also follow a dose/response curve, of course, and don’t kill bacteria at low doses. Yet, drug interactions lead to worse outcomes than single drugs.


  3. Sherman pillis says:

    Systemic herbicides have been found in the body’s of bees. It may be a cause of colony collapse. Europe has banned the products made by bayer. Colony collapse has ended in Europe. When will the EPA get their act together in the USA ?


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