Allowing genetically engineered insects to fly free is controversial. (So far, insects are the only genetically modified animals that companies have released into the wild. U.S. officials are considering allowing a company to sell genetically modified salmon that would be farmed in inland tanks.) The BBC talked with Helen Wallace, a spokeswoman from Genewatch, an opposing group. The modified olive fruit flies may have other, unwanted genetic traits, such as pesticide resistance, that they'll spread among wild flies, Wallace said. The group is also concerned about GM maggots living for some time in olives before their genes kill them off.