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Biotechnology Sample Lesson
BT129 Developing Crops that Fight Insects
Genetic engineers have succeeded in producing crop varieties that resist insects. These insect-resistant varieties can help producers save on the cost of chemicals and reduce the risk of chemical pollution of the environment. The cost savings and effectiveness of insect resistant varieties have made them very popular with producers. Insect-resistant acreage of cotton and corn increased rapidly as soon as the new varieties became available. Some environmentalists, however, have raised concerns about the potential of genetic pollution and the risk to wildlife. UNDERSTANDING THE SCIENCE Insect-resistant cotton, corn and other crops were developed using genes from a common soil bacterium, Bacillus thuringiensis (Bt). Some strains of Bt have long been used to produce biological pesticides. These Bt strains produce proteins that kill certain insects by disrupting their digestive systems. Different strains of the bacterium kill different insects and only those insects. That helps to avoid harming beneficial insects. Genetic engineers have been able to produce insect-resistant varieties by using DNA technology to insert Bt genes into plants. Then these plants can produce their own Bt toxin. The first step is to identify a strain of Bt that kills the targeted insect. In the case of Bt corn, scientists looked for strains that could kill corn borers. Then the scientists isolate the gene that produces the lethal protein. That gene and another gene that can be used as a marker are removed from the Bt bacterium. These genes are then inserted into plant cells. The altered plant cells are then grown and tested to see if the marker gene is present. If it is, the transfer has been successful and the scientists will know that the gene that produces the lethal protein will also be present. These genetically transformed plant cells are then grown into whole plants by a process called tissue culture. The modified plants will then produce the same lethal Bt protein produced by Bt bacteria because the plants now have the same gene. EARLY SUCCESSES Cotton growers were among the first to get an insect resistant variety. Insect control on cotton is especially costly because chemical control is expensive and insect losses can be high. In addition, the use of chemicals is environmentally risky. Thus, insect-resistant Bt cotton was considered to be an important advancement for agriculture and the environment. Plant breeders working with the Agricultural Group of the Monsanto Company started field trials with cotton in 1989. The objective was to produce cotton varieties with a defense mechanism against certain caterpillars. These are insects that damage millions of acres of cotton crops each year. The start of field trials came after eight years of research on insect control in plants. It took until 1993 for the company to complete research and development work, including over 60 cotton field trials in over 40 locations. At that point the results were ready to be presented to federal regulatory agencies for review. By 1995 the company had received final Environmental Protection Agency (EPA) and USDA approval to expand acreage. Some 30,000 acres were planted to increase seed supply. The first insect-resistant cotton became available for planting by producers in 1996. By 1998 over 25 percent of all U.S. cotton acreage and 60 percent of the cotton acreage in Alabama, Arizona, Louisiana and Mississippi was planted with Bt cotton. These are states where the early Bt cotton varieties were best suited to local growing conditions and local pests. The Bt toxins produced by the altered cotton plants can control several pests. The pests controlled include the tobacco budworm, pink bollworm and cotton bollworm. CORN WAS NEXT In midsummer 1995, the Environmental Protection Agency (EPA) approved genetically engineered corn hybrids developed by the Mycogen Corp. Insect-resistant corn became available to producers in 1996. Since then a number of other seed companies have also introduced hybrids that are resistant to certain insects, including the European corn borer and southwestern corn borer. Like insect-resistant cotton, corn plants of the new hybrids have been genetically engineered to contain the Bt protein that serves as a biopesticide. The new Bt hybrids became so popular that by 1998 nearly 20 percent of U.S. corn acreage was planted to these new hybrids. Some experts believed that within five years, half the corn crop would be insect-resistant hybrids. PROBLEMS EMERGE The rapid rise of this new insect-resistant technology soon raised several concerns among scientists, environmentalists and the general public. Scientists soon pointed out that without proper management the targeted insects could quickly become resistant to the Bt toxin. That would make the new Bt corn and Bt cotton ineffective against the new generations of pests. Environmentalists raised questions about the impact on wildlife. Early research by a New York researcher indicated that pollen from the Bt corn could poison monarch butterflies. But after additional research, the USDA reached the conclusion that there was not an immediate significant risk to Monarch butterflies from Bt pollen. Meanwhile, corn exporters soon ran into another problem. Buyers in several importing countries began to reject U.S. commodities with genetically engineered content. That was troublesome, because commodity markets were not prepared to keep the genetically altered commodities separated in market channels. In addition, corn from one of the Bt corn hybrids that was approved for only livestock feed was detected in food products and in corn being delivered to food processors. That hybrid, sold under the trade name StarLink, raised many new questions about the safety of this new technology. SOLVING PROBLEMS Market concerns have dampened the enthusiasm among producers for genetically altered crops, especially corn. Meanwhile, scientists have been reviewing the problems that have emerged and are looking for solutions. Here are some examples, Managing insect resistance: Insect resistance management guides have been developed for both Bt corn and Bt cotton growers. Whenever a pesticide of any kind is used, a certain number of insects will be able to survive. These survivors will mate and produce the next generation of insects. The new generation will then be dominated by the genetic characteristics of insects that can survive the pesticide. Resistance can easily build up with insect-resistant crops, unless growers follow resistance management practices. Unlike periodic spray treatments, the insect population is exposed to the Bt toxin from the crop throughout the growing season. This makes it quite effective. It also increases the risk that only tolerant insects will survive and mate to produce the next generation. Refuge plantings are the main tool used to prevent insect populations from becoming resistant to the Bt toxin. A refuge is simply an acreage of corn or cotton that does not contain the Bt gene. The purpose is to provide a source of susceptible insects to mate with those that survive from the Bt acreage. In general this requires about 20 percent to 25 percent of the entire acreage in the area. In addition, the refuge must be located and treated in ways that will increase that chances that a high percentage of Bt survivors will mate with susceptible insects from the refuge. Beneficial insects: Beneficial insects are getting a great deal of attention from researchers working with Bt crop varieties. Many nontarget beneficial insects will actually thrive better with Bt crops. Remember that the Bt toxin is very selective. It kills only the targeted pest. Meanwhile, researchers around the country have studied the potential impact on the monarch butterfly. Extensive research was done by a group of scientists from many separate institutions using research procedures designed to more accurately reflect actual interaction of the butterflies and Bt corn fields. Their findings, published in October 2001 in the Proceedings of the National Academy of Sciences, put the issue to rest. They concluded that Monarch caterpillars are not very sensitive to pollen from most types of Bt corn, and that caterpillar exposure to Bt pollen in any case is too low to be significant. The USDA BT Corn and Monarch Butterfly Web site listed under Internet Resources gives more details about this study. Meanwhile, growers can do things that will help to protect beneficial insects from exposure to pollen from Bt plants. Planting refuge corn around the edges of Bt cornfields can reduce this risk of exposure. The Starlink problem: The Starlink problem was discovered in late summer of 2000. The EPA and Aventis CropScience, the company that developed and sold the hybrid, took action immediately. Aventis discontinued sales of StarLink seed and the EPA agreed to review its approval of the hybrid. The EPA had approved StarLink for livestock feed only. It was not approved for human food because it contained a protein identified as Cry9C. There was concern that the Cry9C protein might cause an allergic reaction in some people. By late 2000, however, it had not been established whether or not Cry9C was an allergen. To find an answer, the EPA asked its Scientific Advisory Panel to provide an independent scientific assessment of the Cry9C protein as a potential allergen. Meanwhile, Aventis said it would not resume sales of StarLink seed until it had received a food clearance from the EPA. Aventis also supported the release of protein test kits to grain dealers to help them keep StarLink corn out of sales to food processors. BOTTOM LINE: As you can conclude from the above, the idea of insect-resistant crops has a great deal of promise along with many problems that need to be solved. You also can see that the picture is changing rapidly. Anyone interested in this topic will need to review recent developments frequently in order to be well-informed. EXERCISES: Discuss in class or write a brief report on each of the following: 1. Why would insect-resistant cotton or corn be important in your area? How many acres of corn or cotton are grown in your county? Estimate how much is spent on chemical controls. 2. What environmental benefits could be gained if crops could be grown in your county without using chemical insect controls? 3. Contact local seed dealers, producers and/or an extension agent to determine what insect-resistant varieties have been used in your area. Some things to ask:
INTERNET RESOURCES:
** Environmental Protection Agency (EPA) - Home Page
** EPA - Pesticides
** USDA - Research Q&A: Bt Corn and Monarch Butterflies TEST: 1. Why is insect resistance especially important for cotton growers? 2. Trials on insect-resistant cotton varieties began in 1994 and became available for planting by growers in 1996. TRUE or FALSE? 3. The main benefit of insect resistance in crops is that it reduces the cost of chemicals. TRUE or FALSE? Explain.
4. Name an insect pest being controlled with Bt corn hybrids.
5. Name an insect pest that can be controlled with Bt cotton. 6. What is the one most important tool used to prevent a buildup of insect populations that are resistant to the toxin produced by Bt crops? 7. The company that produced and sold the StarLink Bt corn hybrid removed it from the market because it was found to contain the protein Cry9C. TRUE or FALSE?
---------------------------------------------------------------------------- END STUDENT SECTION BT129 Developing Crops that Fight Insects
TEACHER'S GUIDEOBJECTIVE: Students will be able to explain how an insect-resistant crop variety can be produced, and will be able to list and discuss the benefits and the problems that have emerged following the rapid increase in acreage of Bt cotton and Bt corn hybrids. PREPARATION: Review the lesson content and be ready to help students complete the suggested exercises. Help them find contacts who can help them learn more about the local impact of this method of insect control. Follow recent technology news and EPA reviews related to insect-resistant crops. INTERNET RESOURCES:
** Environmental Protection Agency (EPA) - Home Page
** EPA - Pesticides
** USDA - Research Q&A: Bt Corn and Monarch Butterflies IMPORTANT TERMS: Bacillus thuringiensis (Bt), bacterium, bollworm, caterpillars, EPA, monarch butterfly, pink bollworm, refuge, resistance management, StarLink, tobacco budworm. EXTENSION: Offer extra credit for students who research and report on current developments on an insect-resistant crop grown in your area. Ask them to check out the latest regulations and recent reports from Ag extension or research sources. Sources could include your state Cooperative Extension Service, a search of Internet sites and the EPA Internet sites listed above. EXERCISE ANSWERS: 1. Students may be able to make estimates of chemical usage and costs per acre from extension recommendations, or from a local supplier. A visit with producers may also be helpful. 2. Possible benefits are protection of local streams, birds and other wildlife. In addition, there are fewer health risks for workers and farm family members. Bt toxins are not harmful to people, birds, fish or wildlife. The monarch butterfly is an exception, and it also may benefit more than it is harmed. 3. Answers depend upon the area and who the students are able to contact. In some areas, the marketing problems were quite difficult, especially where StarLink hybrids were planted and became mixed in grain supplies. TEST KEY: 1. Why is insect resistance especially important for cotton growers? There are three reasons insect resistance is especially important for cotton growers. Any of these three would be correct: 1) the high cost of chemical control, 2) the high level of potential insect losses and 3) the environmental risk of chemical treatments. 2. Trials on insect-resistant cotton varieties began in 1994 and became available for planting by growers in 1996. TRUE or FALSE? FALSE. While the new varieties were available in 1996, it took many years of research to reach that point. 3. The main benefit of insect resistance in crops is that it reduces the cost of chemicals. TRUE or FALSE? Explain. TRUE from the economic perspective. In many situations, the added cost of seed for the Bt variety is lower than the cost of effective chemical controls. A FALSE answer is correct if the student considers noneconomic factors as more important benefits. There is less health risk for workers and less risk of chemical pollution of the environment. 4. Name an insect pest being controlled with Bt corn hybrids. Correct answer: both European corn borer and Southwestern corn borer are mentioned in the lesson. 5. Name an insect pest that can be controlled with Bt cotton. Correct answer: Tobacco budworm, pink bollworm and cotton bollworm are all mentioned in the lesson text. 6. What is the one most important tool used to prevent a buildup of insect populations that are resistant to the toxin produced by Bt crops? Planting of a nonresistant refuge where susceptible insects can thrive and mate with insects surviving the Bt plantings. 7. The company that produced and sold the StarLink Bt corn hybrid removed it from the market because it was found to contain the protein Cry9C. TRUE or FALSE? FALSE. The company and EPA knew that it contained Cry9C, which was suspected of being an allergen. That is why it was approved only as livestock feed. The company removed StarLink from the market after the Cry9C protein was found in food products for humans when it had not been approved for human consumption. CROSSWORD PUZZLE ANSWERS:
Across: 2. Monarch, 5. Mycogen, 7. StarLink, 8. Cotton, 9. Refuge, 11. Toxin, 12. Budworm. END TEACHER'S GUIDE
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