Monday, May 17, 2010

Cotton wars

A few weeks ago we commented on a story in the New York Times about increasing resistance to herbicides in weeds around the world, some of it because of plants genetically modified to resist glyphosate, or RoundUp, but all of it because of the widespread use of herbicides. And we've also written about the increasing resistance to pesticides because of genetically modified plants that produce a Bacillus thuringiensis (Bt) toxin that is lethal to many plant pests. A report in Nature this week (about a paper published in Science) describes the boon the use of Bt cotton in China has been to previously inconsequential cotton pests.

Bollworm moth larvae outbreaks were particularly destructive to cotton yields and profits in the early 1990s in China, so in response, the government approved the use of Bt cotton. Currently, according to the Nature story, more than 4 million hectares of the crop are under cultivation in China. And, as a result, previously minor pests, which were once outcompeted by the bollworm, have become major problems. The Nature piece reports:
Numbers of mirid bugs (insects of the Miridae family), previously only minor pests in northern China, have increased 12-fold since 1997, they found. "Mirids are now a main pest in the region," says [entomologist Kongming] Wu. "Their rise in abundance is associated with the scale of Bt cotton cultivation."
"Mirids can reduce cotton yields just as much as bollworms, up to 50% when no controlled," Wu adds. The insects are also emerging as a threat to crops such as green beans, cereals, vegetables and various fruits.
The rise of mirids has driven Chinese farmers back to pesticides — they are currently using about two-thirds as much as they did beforeBt cotton was introduced. As mirids develop resistance to the pesticides, Wu expects that farmers will soon spray as much as they ever did.
The Science paper is apparently the first study of the effect of GM plants on non-target pests.
Our work highlights a critical need to predict landscape-level impacts of transgenic crops on (potentially) pestiferous organisms in future ecological agricultural risk assessment. Such more comprehensive risk management may be crucial to help advance integrated pest management and ensure sustainability of transgenic technologies.
It might seem odd that an ecological perspective has been lacking when decisions are made about such things as the use of pesticides or herbicides in ecological systems, whether they are introduced into plants or sprayed on fields, but a narrow view of the problem and its solution is apparently the norm.  It is not clear (to us) why removing bollworms would make space for mirids. Was it that before, there were not seats at the cotton-table for them? Whatever the answer, it adds to the importance of ecological perspectives.

But this is true of much of science. Reducing a problem to a single cause-and-effect relationship is what our methods do best, whether it's determining the metabolic effect of a single nutrient in a single food, or of a single gene, or a parenting method or a teaching technique. The unintended consequences that can result from such approaches, such as the upsurge in non-target pests, or herbicide resistant weeks, are increasingly well-documented -- and we certainly haven't discovered 'the' way to teach math.

And this is without even mentioning the obvious lesson, that artificial selection can have fast and sweeping consequences. And that when short-term gains (in the case of Bt cotton, profit) drive decision making, whatever we actually do know about long-term consequences may not even be factored in.

Perhaps, as industrial genetics is likely to argue, we are able to use technology to keep at least a half-step ahead. The definition of 'winning' in Pest vs Crop wars would be that, rather than any dream of a pest-free world. But as the human population and its demands grow, so likely will high-volume monocropping, and along with that more vulnerability. If the pace of biotechnology can be kept greater than that of artificial selection, then the current approach will work reasonably well, at least in the short term -- or that's what industrial genetics will argue. Maybe it's true -- until another ecological aspect, the toll on soil and water of monocropping, takes over.

Like any organism -- such as a human -- the human-made and human-affected world is made of many parts that exist and evolve together. Organisms can go extinct, and so can ecosystems. That is, they could change in ways that we who are responsible cannot adopt. Whether that's in the near-term offing is of course highly debated. Whoever wins....

1 comment:

Jennifer said...

Yup. What I find amazing, is that those scientists are surprised!