Bt FAQ

Bt effectively and selectively kills certain insects. Images from the Bacillus thuringiensis info page.

Bt, short for Bacillus thuringiensis, is a bacteria that produces a protein that kills certain types of insects. Different types of the gene that produces thais protein have been engineered into crops to make them resistant to those insects. The approach has been quite successful but the details can be confusing.
If you’re looking for science-based information on Bt crops, check out the Bacillus thuringiensis info page that was developed by Karen Chien of the University of California, San Diego, with the assistance of Raffi Aroian. The material is a little dated, but it’s still a great resource. I especially enjoy the cartoons!  🙂

The Aroian lab studies the ways that “target pests develop resistance to Bacillus thuringiensis crystal proteins in order to protect this valuable natural resource.” They’re also studying how Bt could be used to treat parasites in animals and people, as in their recent article in PLoS: Bacillus thuringiensis Cry5B protein is highly efficacious as a single-dose therapy against an intestinal roundworm infection in mice (full text).
Thanks to Mica Veihman (@Mica_MON on Twitter) for reminding me about this great resource.

Written by Anastasia Bodnar

Anastasia Bodnar is a science communicator and science policy expert with a PhD in plant genetics and sustainable agriculture from Iowa State University. Anastasia has had various risk analysis roles in US government and military service. She serves as BFI's Director of Policy and as Co-Executive Editor of the Biofortified Blog.

20 comments

  1. The graphic of ‘Bt man’ is misleading and inaccurate. The Bt currently in use are highly targeted, which means that many crop pests are immune.
    So, “He will get rid of all your crop pests!!” is a bit off the mark. (I also wonder about the masculinization of a crystal protein.)
    There’s also a lack of a full account of how Bt works. It was originally thought that the protein causes digestive failure in crop pests, and on that theory, Bt resistance would quickly emerge.
    However, Bt resistance has been slow to emerge. According to another school of thought, Bt allows ‘benign’ bacteria in the insect gut to pass through the gut to infect and kill the insect. A resistant insect would have to develop resistance to beneficial bacteria in the gut, which is not an advantageous evolutionary development.
    People have tried to demonstrate Bt-resistant insects in cotton fields in the US and India, but the results are equivocal at best.
    Bottom line: the mode of action of Bt remains up for grabs, but it is certain that Bt does *not* get rid of all pests.

    1. Maybe we can help update the resource? I bet the author would be amenable to some help. Heck, I wonder if we might adopt part or all of it here at Biofortified – with credit of course. Ah, so many resources, so little time!

      1. We are Biofortified. Lower your firewalls and surrender your sites. We will add your informational and creative distinctiveness to our own. Your resources will adapt to service us. Resistance is futile.

        1. Hey! That’s not what I meant! I like their style a lot, especially the cartoons, and I don’t think all that much actually needs to be changed. A site doesn’t have to be 100% including every detail especially if the target audience is non-scientists. I just think it’s a well done resource that could use a little updating, preferably by people in the originating lab. If someone really wants an up-to-date all-inclusive resource, though, they should make it, and it might be appropriate to host it here. There’s nothing wrong with saying that, I think. I should have been more clear before, that’s what I get for trying to comment on my phone :p

          1. Anastasia,
            Saying “A site doesn’t have to be 100% including every detail especially if the target audience is non-scientists” is playing with fire. Anti-agro biotechnology activists will take a 1% deviation and use it to condemn the other 99%. It’s a standard ploy in their arsenal, and it works.

          2. Shame it doesnt work the other way round =/
            Bt still apparently causes Indian farmers to commit suicide.

          3. By that logic, we should all just give up and go home. Are we supposed to include everything from explaining what an atom is all the way up to every intricate detail of every study published in the field? I don’t think so.

          4. It’s one thing to not explain agro biotechnology starting from the level of atoms. It’s another thing altogether to explicitly state the explanation is not 100%.
            Those who hate agro biotechnology attach themselves like leeches to honest statements which they feel they can capitalize upon.
            As far as Bt causing farmers in India to commit suicide, it’s a combination of predatory lending practices and farmers borrowing money to purchase fake Bt seed.
            Imagine how bad that is and multiply by a significant factor. Enough to kill yourself over.
            Yeah, that’s how bad it is.

  2. Eric – by any math I’ve done the thing that causes farmers to kill themselves is a crop failure (which can occur in GMOs just as it can in non-GMOs), be that from Bt, regular cotton, or fake seed – the abject lack of the suicide rate to change following the introduction of Bt pretty much excludes it as a causitive factor, be that real Bt seed, or fake seed.

  3. Ewan,
    About a year ago someone published a paper comparing suicides among farmers in India with the number of acres devoted to Bt cotton. Turns out that increased Bt acres correlated with decreased suicides. Which makes sense if you figure farmers are getting roughly 50 percent better harvest yields.
    But when Bt cotton was first catching on, there was a brief up-tick in suicides. Bt seed costs more than conventional. Farmers spent their pesticide money on the more costly seed. When the seed turns out to be fake Bt, and your pesticide money is already spent, you’re facing crop failure.
    India has tremendous, and continuing, problems with fake seed and fake crop protection chemicals.

  4. Eric – do you have a link to anything showing the uptick, or the subsequent downtick – because any paper I’ve seen, and the Indian government stats on suicide rates in general and farmer suicide rates specifically don’t really show any change whatsoever in rates – particularly around the time of adoption.

    1. Ewan,
      Here you go — Bt Cotton and farmer suicides in India: Reviewing the evidence. International Food Policy Research Institute, IFPRI Discussion Paper 00808, October 2008. Available at:
      http://www.ifpri.org/sites/default/files/publications/ifpridp00808.pdf (64 pp.)
      You will note that the authors inexplicably did not draw my conclusion from their evidence. But if you look at the graphs at the end of the paper, you’ll see that it’s unmistakable.
      Enjoy!

  5. Eric – I don’t necessarily agree with your conclusion which if I’m not mistaken (and I often am, so I’ll repeat exactly what I think you’re saying…)

    But when Bt cotton was first catching on, there was a brief up-tick in suicides. Bt seed costs more than conventional. Farmers spent their pesticide money on the more costly seed. When the seed turns out to be fake Bt, and your pesticide money is already spent, you’re facing crop failure.

    To me first catching on would have to be the second or third year of adoption – particularly as the first year of adoption in all cases has practically no coverage whatsoever
    Fig A1 – shows Bt introduction in 2002, and while there does appear to be an uptick in suicide rate in 2003 the corresponding adoption of Bt in 2002 and 2003 seems to be so small as to be incapable of explaining this uptick – correlation and not causation – there is a clear multi-year correlation between Bt acreage and reduced suicides however (which I’d put down as causative due to increased income etc)
    Fig A2’s uptick occurs in a year with significant adoption, and then is followed by a reduction in rate with an apparent correlation with adoption
    Fig A3 shows suicide rates staying relatively flat and being unaffected by adoption
    Fig A4 shows essentially the same as A3
    As such I don’t think you can conclude that Bt had any effect on suicide rates close to adoption, but there does appear to be a correlation between acreage of Bt and a reduction in suicide rate in two regions.
    It also looks to me that the “upticks” in suicide rate are actually just part of the normal variation year on year, with the only “real” effects of anything occuring in FigA1 and A2 – the drops in rate there look too big to be variation, and show a year on year consistency – although as A3 and A4 show no real drop due to adoption which would suggest to me that something else may be the cause of a drop in the first two areas.
    I’ll need to actually read the full paper to tighten up my conclusions, but based on those 4 figures the hypothesis that Bt cotton had zero effect on suicide rate after adoption appears to remain very strong to me in the short term, and still relatively strong in the longer term (with some regional variation which may or may not be down to the effects of the Bt)

  6. Indian farmers commit suicide because the seeds being sold by companies like MOnsanto are too expensive. MOnsanto holds a patent on Bt seeds and therefore sues anyone who saves seed. Seed saving has been how humans have survived for thousands of years. GMO seeds are built to withstand spraying of toxins. The argument that Bt farmers might pay more in seeds evens out with no longer spraying – is a serious lack of information. These seeds are not pest proof, they are pest SPRAY proof. Bt and GM crops tend to have higher need for spray because pests become immune to the poison. Mono-cultures are bad. The only way to reduce pests is to stop farming this way and to bring bio-diversity into every field. Nature is pretty smart – heck of a lot smarter than humans. Let her do her thing.

    1. Dhanna, you are confusing two different traits that GE cotton can have. The first, which is herbicide tolerance, allows the plant to withstand weed killers. Since this often allows the farmer to switch from one form of herbicide to another, this doesn’t change very much about that. But the “BT” in BT cotton does reduce sprays of insecticides, as it kills some of the major pests of cotton, such as the bollworm. This has not only been demonstrated by several scientific studies, but even the anti-GE Organic Center agrees that Bt cotton reduces insect sprays susbstantially.

    2. “Indian farmers commit suicide because the seeds being sold by companies like MOnsanto are too expensive.”
      No, they don’t.
      “GMO seeds are built to withstand spraying of toxins” Some are, some aren’t. The seeds you’re discussing are in fact designed to reduce the spraying of “toxins” as you so emotively put it, regardless of the fact that the “toxins” that the most commonly used GM herbicide tolerant varieties withstand are amongst the least toxic of the available herbicides (and therefore reduce the toxicity of herbicide useage in general)
      “The argument that Bt farmers might pay more in seeds evens out with no longer spraying – is a serious lack of information.”
      This appears to be a case of the pot calling the grass black. Bt farmers in general do have to spray less insecticide, and the insecticides that are still sprayed are those which are less toxic. It is bizarre to the extreme that someone who believes Bt confers resistance to pest sprays and not to pests can accuse anyone of a serious lack of information.
      “Bt and GM crops tend to have higher need for spray because pests become immune to the poison.”
      Pests have only shown resistance to Bt in a few areas, the resistance is not immunity, and other Bt products exist to counter this – at worst the crop would require the same spray regime as non-Bt, in which case farmers would switch to non-Bt and use old spray regimes – spraying will be the same, or less, than in a non-Bt operation (otherwise using Bt makes no sense, and as much as you don’t want to believe it farmers who remain in operation do have a modicom of sense)
      “The only way to reduce pests is to stop farming this way and to bring bio-diversity into every field.”
      This categorically isn’t true. Spraying insecticides reduces pest numbers. Using Bt reduces pest numbers. You could bring bio-diversity into every field but you will suffer reductions in yield because of it (every ounce of biomass in the field that is not crop comes at the expense of crop – particularly in terms of other plants, insects etc etc – there’s a level you probably need to maintain soil health etc (bacteria, fungi, earthworms and the like)
      “Nature is pretty smart – heck of a lot smarter than humans. Let her do her thing.”
      Nature isn’t smart, nature is unthinking. Letting nature do “her” thing essentially means don’t farm at all, ever. I’m guessing that you live in a cave sans electricity or any of the conveniences of modern life and made this post by way of an internet connected squirrel? If not why aren’t you letting nature do “his” thing?

    3. I’m always curious about the whole “mother nature knows best” idea. Nature is a pretty horrible place. It’s full of disease and death. If we didn’t use the big brains that “nature” gave us, we’d still be living in caves, lucky if we live to be 30 years old.

  7. Thought this was interesting, particularly the conclusion “The tight linkage between corn fields and streams warrants further research into how corn byproducts, including Cr1Ab insecticidal proteins, potentially impact non-target ecosystems, such as streams and wetlands.”
    http://www.sciencecodex.com/insecticides_from_genetically_modified_corn_present_in_adjacent_streams
    Insecticides from genetically modified corn present in adjacent streams
    September 27, 2010
    In a paper published this week in the Proceedings of the National Academy of Sciences, Cary Institute aquatic ecologist Dr. Emma Rosi-Marshall and colleagues report that streams throughout the Midwestern Corn Belt are receiving insecticidal proteins that originate from adjacent GE crops. The protein enters streams through runoff and when corn leaves, stalks, and plant parts are washed into stream channels.
    Corn engineered to release an insecticide that wards off the European corn borer, commonly referred to as Bt corn, comprised 63% of crops. The tissue of these plants has been modified to express insecticidal proteins, one of which is commonly known as Cry1Ab.
    Following an assessment of 217 stream sites in Indiana, the paper’s authors found dissolved Cry1Ab proteins from Bt corn present in stream water at nearly a quarter of the sites, including headwater streams. Eighty-six percent of the sampled sites contained corn leaves, husks, stalks, or cobs in their channels; at 13% of these sites corn byproducts contained detectable Cry1Ab proteins. The study was conducted six months after crop harvest, indicating that the insecticidal proteins in crop byproducts can persist in the landscape.
    Using these data, USDA land cover data, and GIS modeling, the authors found that all of the stream sites with detectable Cry1Ab insecticidal proteins were located within 500 meters of a corn field. Furthermore, given current agricultural land use patterns, 91% percent of the streams and rivers throughout Iowa, Illinois, and Indiana -some 159,000 miles of waterways-are also located within 500 meters of corn fields.
    Rosi-Marshall comments, “Our research adds to the growing body of evidence that corn crop byproducts can be dispersed throughout a stream network, and that the compounds associated with genetically-modified crops, such as insecticidal proteins, can enter nearby water bodies.”
    After corn crops are harvested, a common agricultural practice is to leave discarded plant material on the fields. This “no-till” form of agriculture minimizes soil erosion, but it also sets the stage for corn byproducts to enter nearby stream channels.
    Rosi-Marshall concludes, “The tight linkage between corn fields and streams warrants further research into how corn byproducts, including Cr1Ab insecticidal proteins, potentially impact non-target ecosystems, such as streams and wetlands.” These corn byproducts may alter the health of freshwaters. Ultimately, streams that originate in the Corn Belt drain into the Mississippi River and the Great Lakes.

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