Flotilla of designer insects is new weapon in pest control

GM insects are go. Genetically modified versions of a fly that decimates olive trees could soon be released in Spain in an attempt to control the pests. And in Brazil, GM mosquitoes are already at large as part of the biggest project yet involving engineered insects. The aim is to stamp out their natural counterparts, which carry dengue fever.

The techniques are opposed by anti-GM groups, but advocates say they offer a real alternative to spraying insecticides, and have the potential to provide a better and more precise tool to combat agricultural pests and insects that spread human diseases.

The olive fruit fly is a major pest to olive growers in the Mediterranean and California. Females lay their eggs in the fruit and the larvae destroy 15 to 30 per cent of the crop each year as they munch their way to freedom. To tackle this, Oxitec, a biotech company based in Oxford, UK, has submitted an application to the National Biosafety Commission in Spain to release a small contingent of male GM olive flies, in what would be the first field trial of its kind in Europe.

The males are equipped with genes that cause any female offspring they sire to die while they are still in the larval stage, before they have had a chance to reproduce. The idea is that the male offspring inherit the lethal genes and continue to propagate them through the population, until the number of females dwindles to zero and the species crashes.

In lab experiments, the designer flies successfully competed with non-GM males for mates and caused the population to nosedive within 10 weeks (BMC Biology, doi.org/nvd). To check this happens in the wild, the trial would involve releasing the engineered flies under six olive trees in the Tarragona province, draped in mesh netting to prevent escape.

As the Spanish authorities mull the application, Oxitec is continuing with an even bigger trial to combat dengue fever in Jacobina, a city of 50,000 people in the Brazilian state of Bahia. The aim: to run local mosquitoes that transmit dengue out of town.

The principle is almost the same as with the olive flies ? send out an army of male mosquitoes equipped with genes that prevent any offspring, male or female, from reaching breeding age. "Our males are mating at the frequency we'd hoped," says Luke Alphey, co-founder of Oxitec.

In a preparatory field study elsewhere, the team showed its mosquitoes reduced the native population by between 80 and 96 per cent within six months. "The new programme is less about 'does this work?', and more about the first operational roll-out of this technology," says Alphey.

The main benefit of the GM insect method, says Tony Nolan from Imperial College, London, is that it is "strictly species-specific" as the insects only seek out mates of the same species. Controlling the pests with insecticides wouldn't be so discriminating.

However, opponents, such as GeneWatch UK, say there are unanswered questions about the insects, whether they will spread unpredictably, for example. They also point out that sites cleared of insects would eventually be reinvaded. Alphey counters that similar work using males sterilised with radiation has shown that reinvasions can be controlled for decades by simply releasing more insects.

This article appeared in print under the headline "Designer insects join fight against pests and disease"

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