CropGenFriday, 28th July, 2006
That's Biology for YouThe introduction of Bt-cotton some years ago brought enormous benefit, especially to China. Not only were yields enhanced, but the use of noxious insecticide to keep down the boll-weevils was lowered in some cases by as much as 80%. That in turn kept down the cost and also saved much illness and lives because insecticides are poisonous substances and poor farmers, like many in China, cannot afford expensive spraying equipment but depend on back-packs.
The anti-GM doomsters were always certain Bt-crops would have a limited value because insects resistant to the Bt-toxin would certainly arise, they said, and we would be back where we started. Biology has a long history of variation and adaptation: introduce a constraint, particularly with rapidly breeding organisms like insects, and a resistant mutant will emerge spontaneously which, before long, will come to dominant the population.
But while that is not what happened (see http://www.cropgen.org/article_43.html); something else did, also well-known in biology. After a number of years of growing Bt-cotton in China – but not in the US – secondary pests such as mirids have increased so much that farmers are now said to have to spray their crops up to 20 times a growing season to control them. Farmers seem to be back where they started with labour and chemical costs: the boll weevils have gone but the mirids are just as bad. Incidentally, it shows that, contrary to the oft repeated claims of the anti-GM brigade, the use of Bt-crops does not affect non-target insects.
So what happened in China and what might be done?
There is actually nothing surprising: it is just biology at work. Control the primary pest, and former secondary pests become the new primaries. We can therefore expect in time to see new cotton varieties developed with new traits (Bt-based, stacked, and altogether different characteristics), new agronomic strategies (rotation, use of beneficial, heterogeneous plantings and modified refugia), and new pricing regimes, all jockeying to contribute various aspects to the evolution of a new, metastable paradigm that will emerge and last until the next perturbation, economic or entomological. Those who cannot adapt will move into other lines of business.
As happens with all products in a free market, customers will vote with their chequebooks, with market forces determining whether a product thrives or fails. It may be that the most effective strategy for adopting Bt-cotton (at least in certain parts of China) would be to use a variety only as long as it remains net-positive (that is, profitable), and then to change to other varieties.
The particular problem identified in the Cornell study may be amenable to the introduction of additional Bt toxins ("stacking") into new varieties of Bt-cotton, as well as to coming up with remedial actions for the Bt-cotton farmers. That will depend upon more detailed information.
And why did it not happen in America? Perhaps because of better management: the use of refugia and a greater measure of crop rotation.
Seven-year glitch: Cornell warns that Chinese GM cotton farmers are losing money due to 'secondary' pests. Cornell University (July 26, 2006) (http://www.news.cornell.edu/stories/July06/Bt.cotton.China.ssl.html)
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