Bt (Bacillus thuringiensis)

Bacillus thuringiensis (bt) is a bacterium that naturally occurs in soil and on both wild and domesticated plant species. Some varieties of this bacterium produce a protein that acts as a natural insecticide, toxic to certain classes of insect larvae, including moth and butterfly as well as some varieties of beetle and fly larvae. As a result, Bt is a natural insecticide used in traditional agricultural production systems, as well as applied in higher-intensity modern agriculture, usually sprayed directly on crops. In the latter form, the bacterium is a product marketed as an insecticide under numerous trade names. Because the toxins break down quickly when exposed to ultraviolet light and other environmental factors, Bt is considered an attractive, organic, and environmentally friendly form of pesticide, especially when [Page 174]compared to more persistent compounds that have the tendency to bioaccumulate (such as chlorinated hydrocarbons), and nerve-based substances (e.g., organophosphates).

Some varieties of Bt produce a protein that acts as a natural insecticide, toxic to certain insect larvae.

Far more controversially, Bt toxins have become widely used in transgenic crops, where genetic modification creates new crop plant breeds (especially corn, cotton, and potatoes) that produce Bt. Critics warn that although Bt itself is a relatively safe insecticide, the new breeds present human and environmental risks. Specifically, they raise concerns about human health exposure, resistance of insect species over time, and the possible transfer of the gene through crosspollination to wild relatives that may result in the creation of new, especially persistent super-weeds, whose new genetic advantages make them immune to healthy predation by pests.

Industry has responded by suggesting that since commerical Bt is already safely applied, the new genetic applications pose a minimal risk. While it is true that the scientific evidence on Bt as applied in spray form is well developed, the broader ecosystemic effects of the Bt transgene are essentially unknown. Nevertheless, the acreage of Bt crops has expanded rapidly in the last several years, making Bt crop acreage roughly one fifth of the global total of transgenic crops, demonstrating a violation of the precautionary principle.