Ah, the Fox News question mark, which absolves the author of actually adhering to a statement. But it sucks you in, doesn't it? Let me say straight away, that unless you are from a limited subset of crop eating moths, Bt is unlikely to be a bombshell for you. But if you do have moth genes--perhaps you should beware.
There pesticide known as Bt, or Bacillus thuringiensis for the organism source's name, has been known for over 100 years. For decades it has been used safely in both organic and conventional farming. A review paper recently came out that provided a very nice overview of the history and context of Bt, which some here may be interested to read. It is available here, in PDF or web page form:
Bacillus thuringiensis: a century of research, development and commercial applications by Georgina Sanahuja, Raviraj Banakar, Richard M. Twyman, Teresa Capell, Paul Christou. The author's affiliations and sources of support are found over on the paper.
This peer-reviewed article is a very nice reference--it links to a large number of quality sources to support its claims, which are all listed in the extensive collection of references. I'll be providing a sort of summary and overview, but I encourage you to explore the primary material as well.
But first let's do some basics and ask what is Bt, and how it works.
Bt and how it works
The protein known as Bt really represents a number of related proteins of similar characteristics. The real symbol nicknames of the proteins are Cry or Cyt, whereas the individual and unique protein versions get names that look more like Cry1Ab or Cry9Ca or Cry8Ca, for example. The "full toxin list" at the University of Sussex is pretty informative, and provides the sequence IDs and links for those who want to look at the primary sequence data.
It's important to realized that there isn't just one Bt. These are very specific for a narrow range of species. Some work better on mosquitoes. Some that work better on corn borers may have little activity on pea aphids. A lot of study has gone on to explore the affected species, and a very nice summary of that can be seen at The Bacillus thuringiensis Toxin Specificity Database.
The way it works--the biological mechanism, in reader's digest form, is this:
- the Bt bacteria makes the crystal protein
- the target organism ingests the protein
- the crystal is cleaved by a specific enzyme in the alkaline gut of the target organism, and becomes active.
- the active protein binds to a specific receptor in the gut of the target, and pokes holes in the gut, essentially...
- the organism dies, and more Bt can get made by the bacteria remaining in the detritus.
It may sound scary--and knowing that people use Bt on your organic veggies might freak you out. But not to worry: key points from the summary illustrate the reality, quoted directly from the review:
The requirement for alkaline conditions, specific proteases and specific receptors explains why Bt is harmless to mammals (which have an acidic gut and lack the corresponding receptors) and why each toxin has a narrow host range.
This naturally-occurring system, which is harmless to mammals, is what farmers began to harness a century ago for protection of their crops.
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One analogous example I've seen used is this: Chocolate. You know that chocolate is bad and toxic for your dog, right? Do you still eat it, and offer it to children? It's because you are capable of understanding species differences and dosage issues that you can push chocolate on other humans. If you can understand that situation--you can understand this one. |
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The paper gives an interesting description of the historical development of the commercial pesticides, and provides a look at the advantages and disadvantages of them.
As with most pesticides, the people at highest risk of exposure are farmers and farm staff. But despite the extensive use of this pesticide over the decades, there's only one incident of a farmer getting Bt spores detectable on his body as a result, according to this paper. Some mice will die, if exposed intranasally, to 1 billion times the amount ever seen in a field spraying. But means to safely deliver effective proteins has been studied heavily still. So those of you who are buying organic product that may have been treated with Bt should be calmed by the reality of Bt biology.
Bt in transgenic crops
Many of you will also know that Bt is one of the proteins that has been spliced into some transgenic crops. There's a whole section in the paper about that. It was put into tobacco, potato, cotton, corn, and rice, too (See Table 6 in the paper). The paper also has a Box 1 diagram of the major corporate providers of these productions.
These crops have been rapidly adopted by farmers in the US and worldwide. Figure 3 illustrates that. And I know some people will blame one particular company for all of this. But you need to know that some governments are, in fact, the primary drivers of the work--especially in developing nations (Crops With Attitude: Poor nations are now starting to shake off the old 'Frankenfood' taboo).
The biological mechanism of Bt action has not changed in the plant systems. It still requires the same conditions to affect the agricultural insects. It will still not affect you. Pam Ronald, a respected plant geneticist, offers a list of things that people who are concerned about this can explore: 10 Things about GE crops to Scratch From Your Worry List
5. GE crops harm human health. [scratch from your worry list]
There is virtually universal scientific consensus that GE crops currently on the market are safe to eat. After over 10 years of consumption there has not been a single validated report of negative health effects from any GE crop. In contrast every year there are thousands of reported pesticide poisonings (ca. 1200 each year in California alone)....
Ecological aspects of Bt crops
A whole section of the paper is devoted to the ecology and impact these crops have. You'll see here decades of research that has investigate the issues. As with any biological control mechanism, resistance is always possible. There are strategies that can be employed, including planting refuges, which has been remarkably successful:
The widespread use of this strategy is probably responsible for the remarkable lack of resistant populations even in areas devoted to high-intensity Bt agriculture for 15 years.
But this continues to be monitored, of course. It's not to anyone's benefit to have resistant organisms develop. And other strategies are being used as well.
Who benefits?
One of the arguments I hear in the discussions about the current genetically-modified crops is that there are no benefits to average folks. I don't agree--because I think these things benefit me:
The deployment of Bt crops has reduced the use of pesticides, also saving on fossil fuels required for spraying, reducing CO2 emissions by limiting the need for ploughing, and conserving soil and moisture by encouraging no-tilling agriculture. The cumulative reduction in pesticide use for the period 1996–2008 was approximately 356 000 tonnes (8.4%), which is equivalent to a 16.1% reduction in the associated net environmental impact as measured by the environmental impact quotient (EIQ).
Benefits me?
☑ reduced pesticides
☑ saving on fossil fuels
☑ conserving soil and moisture
I also support things that benefit farmers, especially in the developing world--even if it's not as direct a benefit to me personally:
In countries such as India, China, Argentina and Brazil, which are the most enthusiastic adopters of Bt agriculture after the United States, the greatest impact of Bt has been the reduction in the number of pesticide sprays (from 16 down to 2–3 per growing season) and a concomitant reduction in the number of poisonings caused by chemical exposure. These factors, together with average yield increases of up to 10%, have raised net income by as much as 40% (Subramanian and Qaim, 2010).
☑ I want farmers around the world to be more effective growers, with increased safety, and profit if they can.
The section of the paper on beneficial insects and secondary pests is informative as well. What's been observed is that these targeted strategies are actually better for other insects in the field than application of broad-spectrum pesticides. (And before someone comments on organic pesticides, I'll just point you to this paper that shows they are not necessarily more environmentally beneficial.) There was also a study that came out last year that indicated that a secondary pest that had been kept in check with the chemicals before was affecting some other crops. So yes, it's possible farmers are no longer killing enough with broad-spectrum pesticides. But this also shows that reducing chemicals reduces non-target species deaths. That's sort of the point, actually.
☑ Reduce killing of non-target species.
So this was a long essay about Bt. I wanted to write it because I see a lot of mis-representation about what Bt is and does. And I know that people here are able to grasp reality when it's presented to them.
Yes, some of you will continue to hate Big Ag's business model, and that's fine to hate. And some of you will hate other types of genetically engineered crops. And that's certain to appear in the comments. But if you could clear that fog away for a minute to understand the biology of Bt, the people who use your fears against you will have less ground to stand on. If you could also clear that fog to understand that there are beneficial applications of genetic engineering technologies, entirely unrelated to the business models and to the use of chemicals, it would be great.
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Don't let fear win over science. Look at the facts. |
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Supplemental activity for über-geeks: to check out a Bt crystal protein yourself, go to this page at the Protein Data Bank. Under the graphic on the right that says "Biological Assembly" click the "View in Jmol" button. A new page will load, and if you have a computer with java enabled you can view the protein, and swing it around, and look at different models of it. Very fun stuff. That specific protein comes from this publication. And that's how I created the movie of the protein.