Now, it's ten years that the United States has been launched in the extensive cultivation of the transgenic corn "Bt," capable of producing its own toxins to protect itself from the corn borer, a devastating insect. Farmers who choose this type of seed must follow procedures that aim to delay the appearance of resistant insects as long as possible.

The strategy adopted - the so-called "high dose-refuge (HDR)" - consists of cultivating surfaces (20%) of conventional corn alongside GMO fields. These havens allow for the preservation of "resident" corn borers whose function, if the need arises, is to "dilute" the genetic make-up of resistant insects through cross-breeding so that their descendants remain sensitive to Bt.

Now, "This strategy might not be as optimal as thought," deems Denis Bourguet (INRA-Montpellier). His team has, in fact, just observed that a key element was not evaluated correctly: To whit, when and how these butterflies mate.
http://biology.plosjournals.org/perlserv?request=get-document&doi=10.1371/journal.pbio.0040181

In a study published May 30 in PLoS Biology, the French researchers - who proceeded to mark and capture hundreds of insects in the field - revealed that copulation very frequently takes place (in up to 57% of all cases for females) in the parcel where the butterfly was born and not in the refuge zone where it is supposed to disperse its genes. This behavior increases the risks of seeing individuals from a resistant strain multiplying.

These observations suggest that the maximal distance (800 meters) allowed by the American rules may perhaps be too high. In Europe, where Bt corn is still only very marginally cultivated (several thousands of hectares in France), the authorities are tempted to copy the American discoverers' recommendations. But they should look again.

New Experiments

Many points need to be determined before rejecting the American doctrine, which has, all the same, allowed the appearance of resistant insects to be avoided for over a decade. Why is the influence of these local couplings according to whether or not crop rotation is practiced? Are the females definitively stay-at-homes, or do they distance themselves from their field of birth to lay eggs?

These questions necessitate new field experiments. "Our results do not necessarily imply that the HDR strategy cannot work," summarizes Denis Bourguet and his colleagues. "However, they caution that model assumptions must be carefully investigated before relying on them."

Translation: truthout French language correspondent Leslie Thatcher This email address is being protected from spambots. You need JavaScript enabled to view it.