#GMOFAQ How Bt corn and Roundup Ready soy work, and why they should not scare you


Last week I wrote about the anti-science campaign being waged by opponents of the use of genetically modified organisms in agriculture. In that post, I promised to address a series of questions/fears about GMOs that seem to underly peoples’ objections to the technology. I’m not going to try to make this a comprehensive reference site about GMOs and the literature on their use and safety. I’m compiling some general resources here, and a list of all FAQs here.

Question 2) Maybe GMOs aren’t automatically bad, but isn’t it obvious that it’s dangerous to consume crops that produce their own pesticides and can tolerate high doses of herbicides?

Approximately 90% of soybeans, maize, cotton and sugar beets grown in the US are have been genetically modified to produce a protein that kills common insect pests or to make them highly tolerant of an herbicide used to control weeds, or in some cases both. To make a rational judgment about whether these specific GMOs are good or bad, it’s important to understand exactly what they are and how they work.

Bt soy and corn

The pesticide resistant plants have been engineered to produce a protein isolated from the bacterium Bacillus thuringiensis (known generally Bt). Each strain of Bt produces a different version of the protein, known as Cry, each highly specific to a limited number of related species. Bt has evolved these proteins as a key part of a reproductive strategy in which they kill insects that ingest them and then eat nutrients released by the dying host. The Cry protein found in Bt spores must be activated by a protein-cleaving enzyme found in the host gut and then bind to a specific protein on the surface of cells in the digestive system, which Cry then destroys. Insects, who are not huge fans of this strategy, eventually evolve resistance by modifying one or both of these proteins. Bt stains that rely on this insect adapt in turn, creating highly-specific strain-insect relationships.

The irony of Cry becoming a major bugaboo of the anti-GMO movement is that, until the gene that produces it was inserted into corn, it was the poster-child of a “natural” insecticide, preferred over chemical pesticides because of the potential for extreme host specificity and complete biodegradability.  Bt spores were sprayed on crops for decades, and are still widely used to control pests by organic farmers. But the effectiveness of Bt as an insecticide is limited because it degrades in the matter of days – more rapidly when it rains. This led agricultural biotechnology companies to try and insert Cry genes directly into the plants, and there are now many varieties on the market, each targeting pests that are a particular problem for a given crop (some varieties of Bt corn, for example, targets the European corn borer).

Given what we know about  Cry proteins, there is very little reason to be concerned about the safety of eating it. These are proteins that have evolved to kill insects – and not just insects in general, but very specific subsets of insects. And humans are not insects. Regulatory agencies in the US and Europe have consistently rejected claims that plants that produce their own Cry cause problems in either humans or farm animals.

Nonetheless, anti-GMO activists continually raise the spectre of “plants that make their own pesticide” as if this alone was sufficient reason to not only avoid them, but to ban them. Here is a banner running on the website of one of the organizations pushing the CA GMO-labeling initiative:

If you don’t know a lot about plants, I can see how this would seem threatening. But this picture and the anti-GMO campaign it accompanies are based on the flawed premise that “normal” plants are pesticide free. This could not be farther from the truth. Almost since they first appeared on Earth, plants have had to reckon with a diverse array of animals determined to eat them. And this is a battle that continues today, as anyone who has tried to garden, or wandered through a forest, can attest. To fight off these pests, plants have evolved a dizzying array of defense mechanisms, including the production of a diverse arsenal of chemicals targeted at the insects and other pests that afflict them.

As far as I know, natural pesticides have been found in every plant in which they have been sought, including all conventionally grown crops. Wheat makes a family of proteins lethal to hessian flies, peas contain the insecticidal protein PA1b, tomatoes tomatine, and so on. And even if the corn in that picture was not genetically modified, that cute little girl is about to get a mouthful of the insecticide maysin. Indeed almost any mouthful of unprocessed plants from any source will likely contain some kind of natural pesticide that is inert in humans. There is nothing at all unusual, or particularly worrisome, about eating plants that contain the Bt Cry protein as we’ve been eating insecticides for eons.

I’m sure some people will say that we may have been eating insecticides all along, but we haven’t been eating Bt Cry protein and, under the “you never know” principle, should just avoid it. This would all be fine and good if there weren’t strong evidence supporting the value of Bt corn and soy in reducing pesticide use on farms and limiting collateral damage to insects that are in the vicinity of, but not eating, the relevant crop. As a panel of the US National Academies of Science reported in a 2010 study of GMOs:

The evidence shows that the planting of GE crops has largely resulted in less adverse or equivalent effects on the farm environment compared with the conventional non-GE systems that GE crops replaced. A key  improvement has been the change to pesticide regimens that apply less pesticide or that use pesticides with lower toxicity to the environment but that have more consistent efficacy than conventional pesticide regimens used on non-GE versions of the crops.

To me, the demonization of Bt in anti-GMO rhetoric is a emblematic of everything that is wrong with the GMO debates. The producers of Bt crops have done a horrible job of explaining why plants expressing a single insecticidal protein should not – and do not – harm humans. And the anti-GMO advocates either have not bothered to understand the science behind their activity, or (worse) are cynically exploiting peoples’ fears of pesticides to promote their cause.

Glyphosate tolerant crops

The second major class of GMOs (mostly soy) have been engineered to be tolerant of the herbicide glyphosate (Roundup). Glyphosate is a small molecule that inhibits an enzyme, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), which catalyzes an essential step in the biosynthesis of the amino acids  phenylalanine, tyrosine and tryptophan. By denying rapidly growing plants these amino acids, it is able to rapidly inhibit grown of plants onto which it has been sprayed. Glyphosate is generally considered to be inert in humans, who get these amino acids from their food, and do not have an EPSPS.

The obvious problem with using glyphosate to control weeds is that it will, under normal circumstances, also kill crop plants. However, plants that have been engineered to express an alternative form of EPSPS that functions normally even in the presence of glyphosate. These plants are thus “Roundup Ready“, and will survive doses of glyphosate used to kill weeds in the field.

Although the EPSPS gene used in Roundup Ready plants comes from a bacterium, the necessary changes could now easily be made to the plant’s own copy of EPSPS. Thus Roundup Ready crops, which produce no new proteins not found prior to genetic manipulation,  shouldn’t really be places in the same class of GMOs as Bt expressing plants, which are expressing a new protein. And there is absolutely no reason to expect that there are any health risks associated with eating the altered form of EPSPS found in glyphosate resistant transgenic plants.

Concern about Roundup Ready plants focuses instead on the adverse effect of glyphosate on people and the environment. There are some suggestions that high doses of glyphosate are bad for humans, though these studies are hotly contested (note this was a Monsanto-funded study and must be assessed with that in mind). But the more important question is whether the use of glyphosate in conjunction with Roundup Ready crops is better for humans and the environment than the alternatives. Here, the aforementioned NRC report concluded that:

GE soybeans, corn, and cotton are designed to be resistant to the herbicide glyphosate, which has fewer adverse environmental effects compared with most other herbicides used to control weeds.

This does not argue that glyphosate is safe. However, it suggests that the net effect of the GMO – Roundup Ready- has been positive. There is a bigger discussion to be had about the role of herbicides in farming – but this is really orthogonal to issues of genetic modification.

NEXT: Question 3) Why should I trust the big companies that develop these crops? Didn’t it take years to realize PCBs, DDT etc. were bad for us?

About me

I am a molecular biologist with a background in infectious diseases, cancer genomics, developmental biology, classical genetics, evolution and ecology. I am not a plant biologist, but I understand the underlying technology and relevant areas of biology. I would put myself firmly in the “pro GMO” camp, but I have absolutely nothing material to gain from this position. My lab is supported by the Howard Hughes Medical Institute, the National Institutes of Health and the National Science Foundation. I am not currently, have never been in the past, and do not plan in the future, to receive any personal or laboratory support from any company that makes or otherwise has a vested interest in GMOs. My vested interest here is science, and what I write here, I write to defend it.

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  1. Cornelius
    Posted October 22, 2012 at 4:08 pm | Permalink

    @Ewan R, I know these comments are old, but is there a way that I can correspond with you either via email or some other way about this issue?

  2. Posted November 11, 2012 at 12:38 pm | Permalink

    The desire to know about more the foods we’re eating still exists despite the disappointing failure of the GMO labeling mandate of Proposition 37. If you want to avoid GMOs in your food, there are still alternatives, including buying organic, as any product that carries the USDA organic seal cannot contain GMOs. In addition, be sure to pay attention to the little stickers on your grocery store produce. The numbers on these sticker indicate how the produce was farmed: 4 digits = conventionally farmed, likely subjected to herbicides and/or pesticides; 5 digits, beginning with 9 = organic certified, no GMOs, pesticides, or herbicides; 5 digits, beginning with 8 = conventionally farmed and GMO, almost certainly subjected to herbicides and/or pesticides. Stay healthy!

  3. Mitch W
    Posted November 24, 2012 at 8:59 pm | Permalink

    India’s cotton production for 2012:


  4. Posted March 21, 2013 at 4:02 pm | Permalink

    There are a lot of forces acting for and against introduction of GM crops in India.

    I live in Canada but was born in India and have quite a lot of links with grassroots organizations in India involved in many fields of work mostly to do with preservation of ecology and addressing poverty related issues for the marginal people in India.

    For the Indian context, there are many issues relating to GM crops and why these are resisted at the grassroots level. I shall cover in this post only one of them :


    Often this issue slips under the radar, under the weight of other related issues of GM crops. Basically, this recent act, coming under the Ministry of Environment and Forest, and in force since 2002 – has in its scope the following opening text :

    The Biological Diversity Act 2002 was born out of India’s attempt to realize the objectives enshrined in the United Nations Convention on Biological Diversity (CBD) 1992 which recognizes the sovereign rights of states to use their own Biological Resources. The Act aims at the conservation of biological resources and associated knowledge as well as facilitating access to them in a sustainable manner and through a just process For purposes of implementing the objects of the Act it establishes the National Biodiversity Authority in Chennai.

    What it means, in the case of plant, animals and micro-organism families that are not imported but locally evolved, or had been imported in the long lost past and has evolved further within India to acquire region specific traits that make it suitable to the soil and the climate – including those that have been used by the folk and indigenous people of India for medicinal purposes, as tonics or as cure to some illness or injury, and those plants that are used as food, either cultivated or wildly grown, are the collective intellectual property of the nation.

    This means, the genome of this biomass may not be copied or studied, or tinkered with, without explicit permission of the Government of India.

    So, studying the genome without explicit conditional permission, and then genetic ally tinkering of same and eventual patenting of any modified life form, essentially violates the Biodiversity Preservation Act of 2002. A new term has been coined to represent this violation – Biopiracy.

    So, in the case of Bt.Brinjal, where 4 different types of Indian Brinjal were studied, genome sequenced and Bt.variety developed, violated the above act. This was more or less outside of the public brouhaha about if Bt. Bringal should or should not be introduced on Indian farms.

    Between 2002 and now, India has a different Govt in place, and essentially in cahoots with the GM corporations. Nonetheless, the act has not been repealed, There is enough prima facie evidence that the law has been violated. The Govt of India, according to this law, should not only ban introduction of BT. Cotton, it should sue Monsanto and its Indian partner for violation of the act and penalize them, perhaps removing their license to do any further business in India.

    But, as I said, the new Govt is a different animal, and was dragging its feet on the issue. So an NGO firm has initiated a Public Interest Litigation in a provincial high court, against the Govt of India, in order to force it to sue Monsanto. The case has progressed to the stage where the court has ordered the relevant provincial authority to issue a notice to the Govt to file a case against Monsanto. A lot of strange drama is going on about it, with Govt officials involved in the case suddenly getting transferred etc.

    This case is catching peoples attention. There is another one pending at the Supreme court about banning or putting a moratorium on a majority of the GM crops till various long term effects are known – being investigated by an expert committee comprising of six scientists, three on behalf of the Govt and three for the petitioners.
These two cases are sending a bit of a shiver in the whole GM wagon train, and a worry creeping in – if my grassroots friends are correct – that if the cards are not played well at this time by the GMO lobby, the whole game might be lost.

    This issue – basically of Biopiracy, is the first of my many objections to the issue of GM crops in India.


  5. CanolaPatientZero
    Posted March 21, 2013 at 4:35 pm | Permalink

    I decided that your article was tl;dr….. once I saw that you went to Berkley… They get money from Monsanto so anything you have to say has most likely been paid for by them….. Just because you can’t see that doesn’t mean others don’t.

    And for the people like me who can prove harm we are SOL since the 2013 farm bill includes a Monsanto rider so they can’t be sued… Now ask yourself….who benefits from that?

    If their products are so safe why would that part of the farm bill? Why would it be needed? How the hell do you even PRETEND that is even legal?

    Journalism fail :/

  6. Daniel
    Posted June 4, 2013 at 5:45 pm | Permalink

    The real problem with GMO’s is they’re allowed to be developed FOR PROFIT.
    People rarely realize, GMO’s aren’t the enemy – multi-national corporate empires (Monsanto) are the enemy here.

  7. Karl Hayden
    Posted November 17, 2013 at 7:22 pm | Permalink

    I get diarrhea or intense stomach cramps whenever I consume soybean oil. I trust my gut, no pun intended.

    consuming round up is not in my best interest.

    • Simon Says
      Posted February 24, 2014 at 3:20 pm | Permalink

      there is no Roundup in GMO soybeans, they have a gene that produces a different version of an enzyme that is not effected by roundup. you probably need to have your gallblader checked….

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