Scientists have found that cultivating pest-resistant GM crop strains can paradoxically create a whole new breed of bugs!
Writing in Science, Beijing-based researcher Yanhui Lu and colleagues show that after ten years of growing GM cotton in northern China, a previously low-level pest, called the mirid bug, has now risen to prominence and become a serious problem.
The cotton plants in question have been engineered to produce a toxin made by the bacterium Bacillus thuringiensis (Bt), which kills off susceptible pests that try to devour the cotton plants, including one notorious nuisance, the cotton bollworm, Helicoverpa armigera.
In China, the modified plants account for over 95% of the cotton grown. This has, in turn, translated into a dramatic reduction in pesticide use, but therein lies a problem.
Prior to the introduction of GM Bt cotton, farmers sprayed regularly against bollworm, which also had the effect of killing off other low-level pests like mirid bugs. But with the introduction of the GM cotton strain, and the cessation of spraying, the researchers found that the mirid bugs, which are actually not affected by the Bt toxin, have increased their numbers dramatically.
But more significantly, they don't remain confined to the cotton field. Being fairly unfussy eaters, they also spread to and infest other local crop species nearby.
This shows, say the scientists, that "area-wide cultivation of transgenic crops may bring various (direct and indirect) effects on ecological status of different organisms, which should be assessed or anticipated in a comprehensive fashion."
I believe that the greatest problem with GM plants is that there has been insufficient time to fully assess their effects and consequences. Our relationship with food crops has developed over many thousands of years yet GM crops are being claimed to be safe and have to have known effects and consequences after considerably less than half a century of testing.
it is these possibilities that cause many people to invoke the precautionary principle in dealing with GMOs.
The precautionary principle bans progress. Why try penicillin when we don't know the long term consequences?
BC - the precautionary principle does not ban progress - it seeks to force policy-makers to understand risk before an irreversible decision is taken. the penicillin argument is almost as much of a straw man as the mouse/cow hybrid. the pp does not look to eliminate risk, it seeks to limit those situations in which unquantified and unquantifiable risks are taken.
Since it is impossible to foresee all possible risks, the precautionary principle (as used by GM opponents) bans progress.
BC - the risks of prescription a drug with side-effects can and must be quantified - once this is done a cost-benefit analysis is carried out and advice given accordingly. the idea behind the precautionary principle is that in some cases the present position of scientific knowledge allows no quantification of risks. As you say yourself "The sensible action is to look at the risk and ask if it is outweighed by the benefit" but in many cases the risks CANNOT be weighed against the benefit.
The people who talk about the precautionary principle WRT GMO are not in the real world.
At this point in the development of GMOs, the people who advocate the precautionary principle are just saying that they don't want to be lab rats.