Genetically Modified Crops: Assessing Safety

By Keith T. Atherton | Go to book overview

Chapter 8

Case study: Bt crops

A novel mode of insect control

Brian A. Federici


Introduction

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).

For farmers, Bt crops offer advantages over conventional crops in that the insecticidal proteins are produced directly by the plants, and continuously during most of the growing season, thereby reducing the material and application costs of using synthetic chemical insecticides. Growers have reported improved profit margins over conventional varieties averaging $60 to $100 per hectare during the first few years of Bt cotton plantings in the southeastern United States. Consumers and the environment benefit from reductions in the use of synthetic chemical insecticides. For example, it is estimated that the use of Bt cotton in the United States reduced chemical insecticide applications in cotton for lepidopterous pests by 2.7 million pounds in 1999 (Shelton et al., 2002). This represented a reduction of 15 million insecticide applications (22%) in comparison to the number used in 1995 prior to the use of Bt cotton. These reductions preserve populations of insect natural enemies such as

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