Michael Eisen: How Bt corn and Roundup Ready soy work, and why they should not scare you

Michael Eisen addresses the second of his #GMOFAQ rebuttals:

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?

Here’s a short fragment

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.


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.

6 thoughts on “Michael Eisen: How Bt corn and Roundup Ready soy work, and why they should not scare you

  1. I’m not about to demonize GM crops, but I do believe that some caution is necessary. It seems to me that those who reject the possibility of risk are being just as unreasonable as those who totally reject GM crops.

    Certainly it is true that plants have for millenia been producing their own pesticides, but not all the plants that do so are safe; poison ivy, oleander, and hemlock come to mind. Thus, it should not be assumed that all crops engineered to produce their own pesticides are safe. Perhaps all of them produced to date are safe, but the fact that people in the business of developing and using them apparently assume that there could never be a risk makes me very uncomfortable.

    I’d be much more comfortable with GM crops if it weren’t for claims that there isn’t the slightest possibility that they could create serious problems. To me, failing even to admit the possibility of risk indicates a lack of objectivity. Exaggerating the risk also indicates a lack of objectivity.

  2. My point was not that there is no possibility of risk, rather that the risk from GM foods is no greater than the risk from, say, conventionally selected insect resistant lines. We should always be cautious about food – but the idea that GM=risky and conventional=safe is absurd and leads people to propose bad policies, like blanket bans on GMOs.

    • I wouldn’t propose a blank ban on GM foods, especially since some of them could significantly and safely increase food production. However, I have no faith in some of the companies producing GM crops and I see some as ill-advised. For example, Roundup-ready crops don’t make much sense. Constantly using Roundup will result in weeds’ becoming resistant to Roundup so any benefits of Roundup-ready crops are likely to be very temporary.

      It looks as though the development of Roundup-ready crops was intended to increase the demand for Roundup thereby increasing the profits from selling it.

      Why not develop corn and other crops that fix their own nitrogen, like peanuts? It seems to me that that would make more sense, except of course, that it would reduce the profits made from selling nitrogen fertilizer.

  3. Almost every useful technology has certain risks. Fire, grid electricity, internet. Michael didn’t claim GMO crops are zero-risk. We have to choose amongst imperfect options. Michael’s Bt example is one where we now have extensive deployed-experience that the benefits are very large in relation to risks. My view is most of those risk can be managed by apply best practices.

    The anti-GMO activists share a platform with the anti-nuclear lobby. In both cases their intuition says “scary things could happen”, but they do not ask “what are the relative risk-benefits of my alternatives”? They also need to ask “How can we affordably feed 9 billion?”. And for energy policy options, substitute power for feed.

  4. We shouldn’t forget that BT-toxins are allowed even by organic farming. It is very interesting! (But stupid…)

    If an organic farmer uses bt-toxins then everything is ok (and safe); if BT-toxin is produced by corn then the “evil multinational companies” are trying to kill us.

    (I’m not native english-speaker, sorry for grammar)

    • >>If an organic farmer uses bt-toxins then everything is ok (and safe); if BT-toxin is produced by corn then the “evil multinational companies” are trying to kill us.<<

      You summed it up succinctly, and your grammar is excellent. Thanks for your comments.

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