Genetically modifying crops to protect them against pests may not work, according to research published in Science Journal.

A US laboratory study concludes that one of the main pests responsible for damaging crops may be rapidly developing a resistance to GM products.

Insect damage to crops like maize costs farmers billions of dollars a year.

It is one of the arguments for planting crops that have been modified to produce an insecticide capable of killing the pests that feed on them.

But this latest research, carried out at Kansas State University, is likely to fuel the debate over GM crops.

Immunity through exposure

The researchers found that insects can become immune to insecticide through over-exposure, in the same way that bacteria, responsible for human diseases, can become resistant when exposed to too many antibiotics.

The report confirms that corn borers, which attack maize, develop immunity to insecticide much more quickly than was previously thought.

And this could spread rapidly as the insects breed.

So far these experiments have only been carried out in the laboratory.