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."