A British-American research team has created female mosquitoes incapable of flight using a genetic engineering trick that some scientists hope to use in India to control mosquitoes that spread dengue.

Researchers at Oxford University and the University of California, Irvine, have genetically altered male mosquitoes so that they pass on a gene that selectively disables only their female progeny to make them flightless.

Their work, reported on Monday in the Proceedings of the National Academy of Science, is part of an effort to curb mosquito population by genetically disabling female mosquitoes that feed on human blood and transmit diseases. Male mosquitoes do not bite humans or other animals. The scientists have developed two strains of genetically disabled Aedes aegypti, the mosquito that carries viruses that cause dengue and other viral diseases.

"Flightless females cannot escape predators, seek hosts, or mate - therefore these females will die without producing progeny and the size of the wild population will decline," said Luke Alphey, a team member and a visiting professor at Oxford.

"We release males who carry a gene that makes females flightless. When they mate with wild females, their daughters are flightless. This decreases the number of females in the next generation causing the population shrink," Alphey said.

The researchers hope that repeated releases of such altered males will continue to reduce the wild population of female mosquitoes until their number falls below the critical threshold required to cause major public health outbreaks of diseases.

About five years ago, Alphey and his colleagues had used similar genetic engineering technology to develop a strain of Aedes aegypti called OX513A, genetically-disabled to ensure that its larvae do not survive into adulthood.

But a senior government scientist involved in mosquito control in India appeared sceptical, arguing that while he appreciates the novelty in this research, it is a high technology strategy for a problem for which solutions are already available .

"India had tried a slightly different method to suppress mosquito populations using sterile males in the 1970s - but it failed miserably," said a researcher at the National Institute of Malaria Research, who requested anonymity.

"Continuous infiltration of wild mosquitoes from outside the experimental area frustrated attempts to curb populations," he said, describing the results of the failed field experiments in northern India during the 1970s.

But theoretical studies have suggested that the new approach based on genetically disabled mosquitoes - to remain flightless or to die as larvae - can lead to strong suppression of wild populations in over six to nine months in an area of the size of a city.

"These mosquitoes represent a replacement or a supplement to insecticides and result in decreased mosquito populations," said Anthony James, a team member and molecular biologist at the University of California, Irvine.

The OX513A strain has been tested in laboratories in France, the UK, and in semi-field conditions in Thailand and Malaysia, said Seshadri Vasan, head of public health with Oxitec, a company set up by Alphey to pursue novel insect-control technologies.

The International Institute of Biotechnology and Toxicology, a non-governmental research centre in Chennai, has received permission from Indian biotechnology regulators to import the OX513A strain for studies in a contained laboratory, Vasan said.

Scientists concede that there are concerns about potential ecological impacts of reducing mosquito populations, but point out that such possible consequences need to be considered on a case-by-case basis for each pest and each region. "But, mosquitoes are invasive species whose spread is facilitated by humans.

"There is no evidence that they are a keystone species in any natural ecological habitat,".

Alphey said the Aedes aegypti mosquito is native to Africa and was over the centuries inadvertently carried by humans into Asia and the Americas. "As a recent invader, one would not expect native species to be dependent on it. Indeed eliminating invasive species would be considered environmental remediation," Alphey said.

An Indian malaria researcher cautioned that flightless mosquitoes could adapt and turn into crawling insects that would still seek out bloodmeals. "Insects can adapt really well to different situations," he said.

"There's no single magic solution for mosquito control," said Vasan. Colonisation of OX513A strain has been completed at the IIBAT and a panel of government scientists is expected to instruct the institution on the next steps, he said.