ABOUT |
| Anthony Shelton is a professor of International Agriculture and Associate Director of International Agriculture at Cornell University. Dr. Shelton serves as the co-chair of the CALS Advisory Committee on Agricultural Biotechnology, and as the associate director of Research and Associate director of the Cornell Agricultural Experiment Station. |
| Dr. Shelton's area of expertise is pest management, biological control, host plant resistance, agricultural biotechnology, insecticide resistance, insect ecology and economic entomology. |
| INTERVIEW |
| My background is in classics and philosophy. I was also very interested in biology, environmental issues and world food production issues, so entomology blended all those together. |
| Reading Rachel Carson's The Silent Spring had a huge impact on me. What it talked about was having more sustainable, more environmentally friendly methods to manage pests, like insects. Really, that book started the whole environmental movement, at least in the United States, and it certainly has moved around the world. |
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| "Bt has been used as a foliage spray for about fifty years." |
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| In the last chapter of her book, Rachel Carson talks about using Bt as an insecticide, this was back in 1962. Bt had been around for a while but it had never been largely used because it is not as effective as the other alternatives when it's sprayed onto plants. However, when the genes for Bt are incorporated into a plant, it becomes a very, very effective way of controlling insect pest and is not toxic to humans or to other non-target organisms. |
| Bt has been used as a foliage spray for about fifty years. We used it thirty years ago when I was in graduate school. So yes, we have some experience with it. It has some deficiencies when used as spray: it breaks down rapidly in the sunlight, it only lasts for about two or three days and it is very difficult to get the insecticide to where the insects are, which is generally in concealed areas. And although it had many good properties, it also had many negative properties, and that is, in fact, why it accounted for less than two percent of insecticide sales worldwide. |
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| "The genes for producing these particular Bt proteins are being incorporated into plants." |
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| Bt stands for Bacillus thuringiensis. It is a bacterium which is found in soil and on the foliage of plants; it is very widespread. Now something unique about Bt is that during the reproduction of the bacterium or when it regenerates, it produces a protein which, when ingested by some insects, paralyzes its gut and after a couple of days the insect dies. |
| There are lots of subspecies of Bt: There is a Bt that is effective against flies; there is another Bt that is effective against caterpillars; and there is another Bt that is effective against beetles. Depending upon which Bt you have, you have to either spray it against the particular target insect, or what is being done now is that the genes for producing these particular Bt proteins are being incorporated into plants. |
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| "Bt is far safer than the alternatives, including many of those used in organic agriculture." |
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| There are some questions people have about the Bt when it is incorporated into a plant. One concern is that insects can develop resistance to the Bt proteins. Another one is what will be the effect on non-target organisms like the monarch butterfly? These are things that one has to look at regardless of whether Bt is incorporated into a plant or whether it is sprayed onto the plant. |
| A lot of research has been done on the monarch butterfly. The conclusions of a multi-disciplinary, multi-institutional study indicate that the effect of Bt corn pollen on monarch butterflies is negligible and much less than if you sprayed a synthetic insecticide. The same is true of other non-target insects and beneficial insects. Bt is far safer than the alternatives, including many of those used in organic agriculture. |
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| "It is actually easier for the insect to develop resistance to the Bt when it is sprayed on the plant, rather than when the genes for Bt are put into the plant." |
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| We know that some insect species can develop resistance to Bt; it has already occurred in some areas for the diamondback moth and the cabbage looper. These insects developed resistance to the foliage sprays of Bt, not to Bt plants. So we know that some insects have the capacity to develop a resistance to Bt. The real question is: Is it more likely that they will develop resistance to Bt when applied as a foliage spray or when it is incorporated into plants? It is actually easier for the insect to develop resistance to the Bt when it is sprayed on the plant, rather than when the genes for Bt are put into the plant. Let me explain. |
| When you apply an insecticide as a foliage spray, the problem is that you have a mosaic of residue deposits on the plant and different doses on different parts of the plant. Some parts of the plant will have the correct dose but other parts of the plant will have low doses, and it is these low doses which are conducive to allowing an insect to develop resistance to the insecticide. On the other hand, when the insecticide is incorporated into the plant, the plant can express it at a high enough level throughout the tissue that resistance evolution is actually minimized. |
| The EPA mandates that Bt plants use this "high dose" strategy for resistance management and this is combined with a refuge of plants that do not have Bt in them. This refuge serves to maintain susceptibility in the population. The U.S. EPA mandates a very strong resistance management program, requiring farmers to set aside some property for Bt-free plants to serve as a refuge for insects. This mandated resistance management strategy is probably the reason that even after 10 years of use there have not been any documented cases of insects having developed resistance to Bt plants. This is remarkable. Resistance to conventional insecticides usually occurs with 2-4 years. |
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| "In my laboratory, we have been working on having the Bt toxin expressed only when it is needed in the plant." |
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| In 2004 Bt plants were grown on nearly 55 million acres, so this technology has been rapidly adopted since its introduction in 1996. While there are no examples of insects that have developed resistance to Bt plants, we continue to try to stay a step ahead of them so they do not develop such resistance. |
| What we have now is the first generation of Bt plants, which are always expressing the toxin at a high dose. In my laboratory, we have been working on having the Bt toxin expressed only when it is needed in the plant. For example, if you have a sweet corn plant, you are really only trying to protect the ear of that plant. Most of the time you can tolerate some injury in the stalk or in the leaves. What we are working on now is a system where the plant will have the capacity to express these Bt proteins but only when you turn that gene on. This is a way to effectively apply the Bt only when necessary in the plant and protect the ear. |
| We can also develop plants that are expressing the Bt in certain ways, say in particular parts of the plant or at particular times in the plant. What we can also do is what we call "pyramid", add two Bt proteins into a plant. Some recent work we have done and some theoretical models have shown that this is a great way to delay the onset of resistance. |
| To get this to work, the two Bt proteins need to act differently so one Bt protein might affect one part of the gut of an insect and another Bt protein might affect another part of the gut of an insect. So essentially what you do is you have the ability to delay the onset of resistance with what we call pyramided proteins in a plant. |
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| "There are many, many different types of Bt and they produce different proteins." |
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| There are many, many different types of Bt and they produce different proteins. Over one hundred Bt proteins have already been identified. What one can do is to have new Bt proteins introduced in the plant over time, so this would further delay the onset of resistance. This is fundamentally different than many other kinds of insecticides. |
| For example, pyrethroid insecticide are the most common insecticides used today and there are many different pyrethroids. But if an insect becomes resistant to one pyrethroid, it has essentially become resistant to all the other pyrethroid insecticides. In the case of Bt, however, because the proteins have different targets sites in the insect, an insect can become resistant to one particular protein but not the other, so in theory you can manage resistance by introducing new Bt genes in the plant. |
| If you know how the particular protein binds in the insect gut, you can actually manufacture different Bt proteins. There are different parts of a Bt protein and people have been able to adjust these parts of the Bt protein so the whole protein becomes more active. |
| It is unlikely that we will ever have an endless supply of Bt proteins, but at least we have much more flexibility with this class of insecticides called Bt than we do with most other classes of insecticides. |
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| "That is a tremendous advantage for human health and the environment." |
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| What about the benefits of Bt? I think you really have to look at it on the crop by crop basis. For example in cotton, which is about the most intensively sprayed crop in world, the use of Bt plants has reduced the number of insecticide sprays by 60-80 percent. That is a dramatic reduction of the hazardous materials that would otherwise be in the environment. In the case of developing countries like China or India which has recently registered Bt cotton, this not only reduces the amount of sprays, it also really has a direct effect on the farm workers. In countries like in India or China much of the population is actually working on the farm so the health benefits of Bt cotton have been substantial. |
| Bt corn is a major food crop. "Field corn" is manufactured into cereals, into corn syrup and a whole series of other things. "Sweet corn", the kind we eat as fresh, frozen or canned corn gets sprayed a lot. Much of our corn comes from the southeastern U.S. where, during the spring and the fall, armyworm is a tremendous problem. Farmers might have to spray fifteen to thirty times to try to control it. But with Bt corn, they may only have to spray twice. That is a tremendous advantage for human health and the environment. |
| Apples are being transformed to express Bt proteins. Crucifers like cabbage and broccoli--which is what I work on--are also being transformed to express Bt proteins and they work very, very well. There is a new project in India with Bt eggplant and it appears that it may save the majority of the 80 or so foliar sprays applied during the crop cycle. Again, this will have tremendous benefits to human health and the environment. |
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| "It is not just food products that are being transformed through biotechnology." |
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| We are in the first generation of biotech crops, which are mostly pest management crops--herbicide resistance, virus resistance or insect resistance. Hopefully, the second generation crops will have qualities that are much more consumer oriented, not just farmer oriented. Consumer oriented qualities could include reducing certain fats in animals, or having better nutritional content in the oils in the plants. |
| It is not just food products that are being transformed through biotechnology, but it is also the non-food products such as fuels, paints, varnishes, fiberboard, and clothing material. Biotechnology will play a role in all of the uses of agricultural crops, including crops which are producing some of the proteins being used in medicine. |
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| "Engineering resistance into the plant is a good solution and is really a low-tech solution, even though it is done through biotechnology. " |
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| A good example of a biotech crop is papaya, which has been bred to resist the papaya ringspot virus, a devastating papaya disease. Cornell researchers Dennis Gonsalves and colleagues at the University of Hawaii realized that they were not able to control this virus by spraying for the insects, which transmit the virus, or by using cultural controls. So they genetically engineered the papaya so the papaya plant is essentially immune to the virus attack. Now you may think of papaya as just a luxury crop, but it is a major source of vitamin C throughout the developing world. This is an example of how the use of biotechnology can help people in developing countries. |
| There are many similar kinds of devastating diseases in various parts of the world. Engineering resistance into the plant is a good solution and is really a low-tech solution, even though it is done through biotechnology. |
| Now biotechnology is not the only solution that is going to help feed the world, but I think we are realizing it is a part of an overall solution. We also have to make sure that we have good food distribution systems because there is a lot of food that simply rots in storage or on the way from the field to the market. Biotech is one component, but I think we are realizing it's a pretty important component. |
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| "What we really want to try to do is to produce our food and fiber products in the most environmentally friendly fashion that we possibly can." |
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| Besides Bt proteins, there will be other proteins which plants can express that will be able to control insect populations. One thing that can be done is to introduce lethal genes into an insect population and so as the insects breed, they actually decline in population because the offspring carry the lethal gene. There has been some success with this "sterile insect technique" for screwworm, a major pest of cattle. |
| In the past scientists have to use radiation to alter the chromosomes of insects and then mass produce them and release them in the field to mate with the wild population to produce offspring that are infertile. Another way of doing this besides radiation is to genetically engineer the insects in the laboratory so they have a lethal gene and then release them. Using this technique is much more exact and can produce better control of the pest. |
| What we really want to try to do is to produce our food and fiber products in the most environmentally friendly fashion that we possibly can. How can we do that? It could include some organic agricultural practices and also some products of biotechnology. I look at it from the standpoint of: What end do we want? I believe the answer is a more environmentally friendly agricultural system and one that is safer for humans. There are some things that organic agriculture does that are very, very good, especially for what I would call preventative pest management. But organic agriculture uses pesticides and some of these pesticides definitely have deleterious environmental effects. |
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| "Some of the most educated organic growers I work with would love to use biotechnology if it were allowed by organic standards." |
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| Organic agriculture is regulated so that farmers have to use natural products, but not all natural products are safe. We really have to step back and think about it: It is not a question of what is natural or unnatural, but what has the least environmental effect. For example, organic agriculture can use compounds like sulfur to control some diseases but it is a general biocide and causes disruption of some arthropod pests. Organic growers can also use pyrethroid-like insecticides, which, again, are natural but they still have some of the same deleterious environmental effects as pyrethroid insecticides used by conventional growers. |
| I work with a number of organic growers, and I respect the way they do things. Some of the most educated organic growers I work with would love to use biotechnology if it were allowed by organic standards. They see it as an opportunity to reduce overall pesticide input. So, again, it is not a question of whether something is biotech or organic, it is a question of how do you achieve a more environmentally sustainable way of producing your plants. |
| Organic growers and conventional growers both use Bt as a foliage spray and it has the same environmental effects and the same effects on the target insects. However, organic growers will not allow Bt to be used when it is incorporate into a plant. I find that a fairly fine distinction and from an environmental standpoint, I do not think is a legitimate distinction. |
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| "There are ways that you can regulate the plant to try and minimize the risk of genetic drift." |
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| Regarding the gene flow issue and whether a genetically engineered crop can actually go into another crop and persist, those issues are complex. There are no wild relatives of Bt cotton in the major cotton growing areas of the U.S. so you really do not have the problem of Bt cotton going into wild cotton. However, in the center of origin for corn, which is Mexico, I think the issues are more complex. |
| Although Mexico has banned the use of Bt maize or any other genetically engineered maize, seed does get into these areas and it will mix with these wild land races. Plants hybridize easily, so this will occur. The real question is: Will it give the plant any particular selective advantage? Those are the hard questions that have to be answered and it takes research to do that. There are also some techniques that are being developed right now to transform a plant so that the Bt is expressed in the chloroplasts but not in the pollen, so if the pollen moves out of that field, the Bt gene will not since pollen does not contain chloroplasts. So there are ways that you can regulate the plant to try and minimize the risk of genetic drift. |
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| "If Bt plants were banned, essentially what many growers would do is to use some of the other materials that are more toxic." |
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| We certainly know a lot more about Bt plants now than we did when they were first deployed back in 1996. Will we ever know everything? No, I do not think we will. Nor do we know everything about the alternatives of not using Bt. For example, if Bt plants were banned, essentially what many growers would do is to use some of the other materials that are more toxic. Now we do not know everything about the consequences of using those other insecticides, those non Bt insecticides, but research tells us those consequences would be more severe than using Bt plants. |
| In the case of Bt potatoes, for example, they first came onto the market in 1996. Bt potatoes had at one time about four percent of the overall potato market, but because of some misinformation and selective pressure by some anti-GMO advocates, they were dropped like hot potatoes. As a substitute, another new foliage-insecticide came onto the market and growers adopted it and anti-GMO felt them won a victory. The new insecticide was a neo-nicotinic, very much related to nicotine. The growers still had insects attacking their crop so they used this new insecticide rather than the safer Bt potatoes. Who won? |
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| "Some of the claims against Bt plants or agricultural biotechnology are really the same claims that were made against pasteurization." |
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| There is a controversy about agricultural technology. There have been controversies about many, many things introduced into agriculture in the past hundreds of years including the pasteurization of milk. Some of the claims against Bt plants or agricultural biotechnology are really the same claims that were made against pasteurization. That is: "It is unsafe. We don't know the long term consequences of it, etc." We know many of the positive things about agricultural biotechnology are subject to the controversy. It is not going to be immune to controversy but I think all the data that have been presented in the scientific literature indicate that, at least in the case of Bt plants, they are far safer than the alternatives. |
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