Pest and pesticide problems

June 2014
CC photo by Roger Smith on Flickr
A recent report on GM crop-growing in America since 1996 prepared by the US Department of Agriculture made specific mention of the burgeoning problem of weeds resistant to glyphosate herbicide which is used on most GM crops (see THE GM DEBATE: 'OVER', OR BARELY STARTED? - June 2014).
The report came just too late to include the latest study on what may be the next big problem with GM crops: emerging pest-resistance to the 'Bt' insecticides generated by GM maize.
Pest-resistance has previously been found in laboratory studies, but these have been shrugged off as too artificial to extrapolate to what would actually happen in the field.
Successful insecticidal action depends on the biotech plant maintaining a high level of Bt production to ensure all the pests are killed. If, or when, the Bt level becomes inadequate, the pests that aren't killed will tend to evolve to tolerate the toxic effect. In the case of one major maize pest, western corn rootworm, 2% can survive on Bt crops designed to kill them.
The answer to this has, of course, been more GM. Bt proteins can take a huge variety of forms, and several different forms can be stacked into a single GM crop. The reasoning has been that, with such an armory of pesticides to deploy, pests could never possibly survive, and resistance to such formidable crops would simply never get a chance to happen.
However, the newly published study has poured cold water on these resistance-beating GM tactics as applied to western corn rootworm in the field.
It was found that, where the same GM crops are grown year-on-year, resistance to a Bt toxin can emerge within just three years. Unexpectedly, it was also apparent that some of the 'different forms' of Bt aren't different enough: cross-resistance between the Bt toxins is evident. In the case of, western corn rootworm, there has been a fast-emerging resistance to two out of the three Bt toxins now on the market. As the lead author points out “It's a substantial part of the available technology”.
The authors note that actual levels of insect-resistance may be underestimated because Bt crop-growing farmers aren't looking for them.


The lead author concludes from his study that “There needs to be a fundamental change in how the technology is used.”  Perhaps he should be considering whether the technology should be used at all.
The suggestion of pests going unnoticed is of particular concern.
It seems farmers' belief in the biotech industry hype on GM crops may be blinding them to the reality. Our food supply could be collapsing before their very eyes and no one will notice.
  • Aaron J. Gassmann, et al., 2014, Field-evolved resistance by western corn rootworm to multiple Bacillus thuringiensis toxins in transgenic maize, PNAS
  • Brian Owens, Pests worm their way into genetecally modified maize, Nature 17.03.14
  • Doug Gurian-Sherman, New science sounds the alarm about destructive beetles on GMO corn, 20.03.14
  • Brandon Keim, Voracious worm evolves to eat biotech corn engineered to kill it, 15.03.14
  • B.E. Tabashnik, et al., 2003, Insect resistance to transgenic Bt crops: lessons from the laboratory and field, Journal Economic Entomology 96(4)

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