During its long growing season, cotton is exposed to numerous insect pests. Heliothis caterpillars (native budworm) are the most significant with the potential to significantly reduce yield. Consequendy they are the target for much of the $200 million spent annually on pest control in cotton.
Reliance on pesticides brings significant environmental liabilities with increasing concern over off-target drift, residues and pesticide resistance. Genetically modified, or transgenic, cottons offer one means to reduce this pesticide requirement.
Transgenic cotton contains a gene from the soil bacterium Bacillus thuringiensis (Bt), which produces an insecticidal protein giving protection against heliothis and similar pests when they feed on the plant. Because these Bt proteins are very specific in their activity, they have no effect on most other insects in cotton fields, particularly the beneficial insects, nor on mammals or birds.
Bt cottons have been grown commercially in Australia for three years. In that time they have resulted in significant reductions in pesticide use of 40-60 per cent with no reduction in yield. While cotton growers do not necessarily see increased returns, there is a huge environmental and community health benefit and potential for greatly enhanced sustainability of production in the long term.
Another critical advantage is that Bt cottons provide the foundation for more robust integrated pest management (IPM) systems. A wide range of nonchemical pest control techniques for heliothis and other pests can be readily combined with Bt cotton to give a more sustainable IPM system. Many of these approaches (e.g. enhancing the numbers and activity of beneficial insects) were not possible with conventional cottons because of the disruption caused by pesticides.
Potential for resistance?
While the first generation of Bt cottons are not perfect in controlling heliothis, they augur well for future improved varieties which will require even less pesticide. One significant concern for Bt cottons is the potential that heliothis may become resistant to the Bt protein, as it has to many other pesticides. To guard against this, the use of Bt cotton is associated with a comprehensive resistance management strategy. Developed in association with growers, the strategy should protect the value of this technology. Work is also under way to develop varieties containing two different Bt genes which would make the possibility of resistance less likely.