Answer:Where the story began
For centuries, humans have searched for crop plants that can survive and produce in spite of insect pests. Knowingly or unknowingly, ancient farmers selected for pest resistance genes in their crops, sometimes by actions as simple as collecting seed from only the highest-yielding plants in their fields.
With the advent of genetic engineering, genes for insect resistance now can be moved into plants more quickly and deliberately. Bt technology is only one example of ways genetic engineering may be used to develop insect-resistant crops now and in the future.
(opens in new window)The Bt chapter
Bacillus thuringiensis, commonly known as Bt, is a bacterium that occurs naturally in the soil. For years, bacteriologists have known that some strains of Bt produce proteins that kill certain insects with alkaline digestive tracts. When these insects ingest the protein produced by Bt, the function of their digestive systems is disrupted, producing slow growth and, ultimately, death.
Bt is very selective — different strains of the bacterium kill different insects and only those insects. Strains of Bt are effective against European corn borers and cotton bollworms (Lepidoptera), Colorado potato beetles (Coleoptera), and certain flies and mosquitoes (Diptera). Bt is not harmful to humans, other mammals, birds, fish or beneficial insects.
Bt was first identified in 1911 when it was discovered that it killed the larvae of flour moths. Bt was registered as a biopesticide in the U.S. in 1961. Today it is used in insecticide sprays sold to home gardeners and others worldwide.
In 1983, the World Health Organization used Bt in West Africa to control disease-carrying blackflies. In the U.S., various strains of Bt are used to control spruce budworms and gypsy moths in forests, cabbage worms in broccoli and cauliflower, loopers or budworms in cotton and tobacco, and leaf rollers in fruits.
However, less than one percent of all pesticides used in the U.S. each year contain Bt (Monsanto). As an ingredient of commercial sprays, Bt is relatively expensive and has some drawbacks. Although some pesticides kill on contact, Bt must be eaten by insects to be effective. Sunlight breaks down Bt, and rain washes it from the plants. Therefore, Bt must be applied exactly where and when the target insects are feeding, and they must consume it quickly before it disappears.
(opens in new window)Bt and biotechnology
Today, plants can be genetically engineered to produce their own Bt. Genetic (recombinant DNA) engineering is the modification of DNA molecules to produce changes in plants, animals or other organisms. DNA (deoxyribonucleic acid) is a double-stranded molecule that is present in every cell of an organism and contains the hereditary information that passes from parents to offspring. This hereditary information is contained in individual units or sections of DNA called genes. The genes that are passed from parent to offspring determine the traits that the offspring will have.
In the last twenty years, scientists made a surprising discovery — DNA is interchangeable among animals, plants, bacteria ... any organism! In addition to using traditional breeding methods of improving plants and animals through years of cross-breeding and selection, scientists can now isolate the gene or genes for the traits they want in one animal or plant and move them into another. Of course, when a trait is controlled by several genes, the transfer process is more difficult. The plants or animals modified in this way are called transgenic.
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