Case study: Bt crops : A novel mode of insect control

The bacterium Bacillus thuringiensis (Bt) is distinguished from other bacilli by the production of large crystals during sporulation composed of one or more insecticidal proteins. These proteins have served as the principal active ingredient of numerous commercial bacterial insecticides used worldwide for more than 40 years to protect crops against caterpillar pests, and more recently to control coleopterous insects and mosquito and blackfly vectors of human and animal diseases (Federici, 1999). The first genes encoding insecticidal Bt proteins were cloned early in the 1980s. This led quickly to their use to construct recombinant bacterial insecticides containing novel combinations of these proteins and insect-resistant Bt crops (Estruch et al., 1996). The first Bt crops became commercially available in the United States in the mid-1990s, and have been widely adopted by farmers despite higher seed costs in comparison with conventional crops. During the 1999 growing season, farmers in the United States planted over 20 million hectares of insect-resistant Bt transgenic crops, including over 10 million hectares of Bt maize (corn), 1.5 million hectares of Bt cotton, and about 30 000 hectares of Bt potatoes (Thayer, 1999; Shelton et al., 2002). This acreage is expected to grow to about 15 million hectares of corn and 3 million hectares of cotton within five years, representing, respectively, about a third of the corn and half of the cotton acreage in the United States. Bt crops are also being grown in China and Argentina, and their potential deployment is being assessed in several other countries. In addition, more than 30 other Bt crops, including rice, sorghum, most major vegetable crops as well as many tree crops used for fruit, nut and fiber production are under development (Schuler et al., 1998).