In 1996, maize, cotton, and potato farmers in the USA became the first farmers in the world to grow transgenic insect-resistant cultivars. These cultivars contain genes from the bacterium Bacillus thuringiensis (Bt) that encode insecticidal proteins known as delta-endotoxins. Delta-endotoxins have two properties that are essential for toxins used in transgenic crops: they are highly toxic to certain insect pests, and they are generally safe for human consumption (NRC 2000). Bt crops have been a large commercial success. In 1999, 11.7 million ha of Bt crops were grown by farmers in 10 countries, including Australia, Canada, China, South Africa, Spain, and the USA (James 1999).
Many laboratories around the world have transformed rice with Bt genes and have evaluated their effectiveness under greenhouse conditions (e.g., Cheng et al 1998, Datta et al 1998, Maqbool et al 1998). No Bt rice varieties have yet been released to farmers, but field testing began at two sites in China in 1998 (Datta 1999, Ye et al 2000). The target pests for control by Bt rice are caterpillars, most importantly the yellow stem borer (YSB, Scirpophaga incertulas), the striped stem borer (SSB, Chilo suppressalis), and leaffolders such as Cnaphalocrocis medinalis. It has not been possible to produce rice with high resistance to these pests through conventional breeding, although short-duration semidwarf varieties are generally less damaged by stem borers than are traditional varieties (Khan et al 1991).