"This allows us to test the transgenic technology in a very safe way that overcomes the previous environmental and safety concerns. Releasing males only would ensure people were not bitten by GM mosquitoes," he said.
Sue Mayer of Genewatch agreed that the new GM insect did address some of the previous concerns, but she called for thorough testing of the mosquitoes before they were considered for release.
"Changing one gene can some-times affect others, so there are still questions to ask," she said.
There are political barriers too. The London group's insect is best suited to tackling malaria in impoverished urban areas of southeast Asia and India, where World Health Organization (WHO) trials of sterile male mosquitoes to fight dengue fever collapsed in the 1970s amid a flurry of biowarfare accusations.
The males of the mosquito involved in the Delhi trials could be separated because their pupae were smaller, but they were never released after newspaper articles claimed the experiment might secretly be used to gather data on how to spread yellow fever.
Chris Curtis, a malaria expert with the London School of Hygiene and Tropical Medicine who worked on the WHO project in India, said: "We were all set to go and there was a huge uproar. You have to handle the public relations very carefully."
Female mosquitoes can travel several kilometers after mating, he said, so the sterile-male technique is best suited to isolated insect populations, such as in large cities.
"If females that have already mated fly in from outside your release area then they carry on laying fertile eggs. That's fatal," Curtis said.
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