Diamondback moths are major crop pests around the world

Genetically modified male diamondback moths designed to wipe out pest populations have been released in New York state. The field trial shows that these GM moths, whose female offspring die soon after hatching, could help control this major crop pest.

Oxitec, the British biotechnology company behind the trial, has already carried out field trials of this method for controlling mosquitoes that spread diseases such as dengue. However, the moth field trial is the first for a crop pest, the company says.

The larvae of the diamondback moth (Plutella xylostella) eat the leaves of brassica plants such as cabbage, kale, broccoli and oilseed rape (canola). The moths are a major pest worldwide, causing damage estimated at $5 billion a year.

To create its GM moths, Oxitec added two genes to moths that are still susceptible to pesticides. One gene simply codes for a red fluorescent protein, so the insects can easily be identified in the wild.

The other gene kills larvae soon after they hatch – but it switches on only in females. When male GM moths mate with wild females, all the female offspring die, but the males survive and pass the lethal gene on to their offspring.

Because half the offspring of the GM males die each generation, the lethal gene should disappear after just a few generations. To continue to suppress wild populations, more GM males would need to be released.

In field trials in August and September 2017 at the Cornell University Agricultural Experiment Station in New York, between 1000 and 2500 males were released on six separate occasions. The researchers then recaptured some of the moths to confirm that they survived in the wild. They say the moths should be as competitive with wild male moths in mating with females as they were in lab trials done in the US and UK.

As expected, the GM strain didn’t persist in the wild. “We did not detect any of them hanging around,” says Neil Morrison of Oxitec.

The company hopes to get approval to start selling its GM diamondback moths to farmers in the US. It also plans to use the same technology to tackle other crop pests, such as the fall armyworm.

The diamondback moth is a huge problem globally and evolves resistance to pesticides very rapidly, says Michael Bonsall at the University of Oxford. “It’s super-invasive. We need new tools in the toolbox,” he says.

But the GM moth will need to be used with other methods as part of an integrated approach, Bonsall says. “It’s not a silver bullet. It’s just another tool.”

This isn’t the first release of GM insects in the US. In 2007, pink bollworm with an added fluorescence gene were released in Arizona. There have also been releases of mosquitoes infected with a bacterial parasite called Wolbachia, which some people regard as a form of genetic modification. These insects do persist in the wild.

Oxitec has carried out field trials of its GM mosquitoes in the Cayman Islands, Brazil, Panama and Malaysia. A second trial is now under way in Brazil, and Oxitec hopes to get the go-ahead for a trial in the US.

Journal reference: Frontiers in Bioengineering and Biotechnology, DOI: 10.3389/fbioe.2019.00482

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