By Stephen Evans BBC North America Business Correspondent

A quiet battle between genetic engineers is underway in the cotton fields of Arizona.

The adult moth: The trial is the first of several experiments

At a secret location there, genetically modified pink bollworms (Pectinophora gossypiella) have just been released to see how they behave in the wild.

They are the first GM insects to be released anywhere, and they have been freed under netting. But if the experiment is deemed a success, the insects will be further modified and released into the great wide spaces where they will breed but produce no offspring that survive.

In effect, they will have been modified to destroy their own species - which is where the competition between engineers comes in.

High price to pay

Such a mutant insect would be bad news for Monsanto; the chemical company already sells genetically engineered cotton plants to farmers who complain bitterly about the price.

Monsanto's modified cotton is resistant to the bollworm which devours cotton.

Pink bollworm

Larvae feed inside the growing cotton boll, destroying the cotton Adult moths are greyish brown, with a wingspan of 15 to 20 mm The most destructive pest of cotton worldwide In Egypt, China, and Brazil, it commonly causes cotton losses up to 20%

So, the farmers are backing the alternative genetic modification of the insect itself.

At the moment, farmers can use chemical sprays to kill the insects, or they can irradiate them in a laboratory - radiation makes the insects sterile.

Both measures are expensive. To find a cheaper way, the idea is to alter the insect's genes so the bug is sterile.

In a laboratory in Phoenix, insects have been modified, initially in a harmless way: they have been released under netting just to see whether they survive, whether they thrive even, whether they mate.

The idea then is to introduce a new gene from a fly into their make-up, and this gene will make them non-productive. The insects will mate as normal but no destructive off-spring will result.

If that works, the farmers would then not have to buy modified cotton plants from Monsanto. But will it work, and will it be safe?

The scientists involved say the strictest safeguards are in place.

Measured risk

Opponents say that already there are questions about the ability of insects to pass mutations to bacteria in the soil, for example. And once bacteria mutate, the mutation could take on unpredictable paths, they claim.

The difficulty is that there are no certain ways of predicting consequences. It is a matter of balancing risk.

Cotton: A major world crop

On the one hand, the benefits of cheaper cotton are huge, not just for American farmers but for poorer farmers in India or Mexico, and for consumers the world over.

On the other, though, the cost of getting it wrong in terms of destroyed ecosystems could be high.

Much depends on how tough the United States Department of Agriculture decides to be in its monitoring of the tests.

There is intense pressure from the farmers to get the modified insects approved.

The unanswerable question is whether the USDA would stand against the producers if doubts about potential danger started to surface in the tests that are now underway.