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[KUALA LUMPUR] Malaysia will soon take the controversial step of releasing genetically modified (GM) mosquitoes into the wild as part of an experiment to test their survival in natural conditions.

The move was approved by the country's National Biosafety Board last month (10 October) and will make the nation the first major country in the world to release GM Aedes aegypti mosquitoes for field testing — second only after the Cayman Islands in 2009.

The mosquitoes, known as OX513A, have been developed by Malaysia's Institute for Medical Research (IMR) and the UK-based biotech company Oxitec to control the dengue virus, which is transmitted by A. aegypti.

A total of 4,000–6,000 male GM mosquitoes are expected to be released within the next couple of months, along with a similar number of unmodified male mosquitoes.

The male GM mosquitoes mate with normal females to produce larvae that are unusual because of an extra enzyme they produce. This enzyme accumulates in the larvae to a level where it becomes toxic and kills them. The larvae's only hope for survival is if the antibiotic tetracycline is present — because it mops up the enzyme.

The developers hope male GM mosquitoes will compete with normal males for females so that repeated releases cut numbers of A. aegypti in dengue-prone areas.

The mosquitoes will be released in the inland districts of Bentong in the state of Pahang, and Alor Gajah and Melaka in the state of Malacca, according to the National Biosafety Board. Each location will have two release phases: the first at a site 0.5–1 kilometres from the nearest human settlement, and the second at an inhabited site.

They will be recaptured using mosquito traps, which will be monitored for at least one month, while the inhabited release sites will also be fogged with insecticide when the experiment is over.

The board made its decision after its Genetic Modifications Advisory Committee (GMAC) analysed the risk factors for the experiment. The issue was opened for public consultation from 5 August to 4 September.

Ahmad Parveez Ghulam Kadir, head of the GMAC, told reporters last month (29 October) that the committee had been concerned that lab tests had shown that three per cent of the offspring of male GM mosquitoes and normal females actually survive into adulthood rather than dying as larvae as intended.

Ricarda Steinbrecher, a geneticist and co-director of EcoNexus, a UK-based non-profit research organisation, said that it is not clear how the offspring of the male GM mosquitoes survive into adulthood and do not die as 'programmed', but it raises the possibility that they could breed and pass on this — as yet unknown — mechanism for overcoming the lethality.

"I would suggest that it is far too early for any open field releases. More data are needed from laboratory experiments. Furthermore, trials in field cages [large outdoor enclosures made from netting, i.e. confined field trials] are needed," she said.

The advisory committee had also been worried that female GM mosquitoes might accidentally be released. The technicians separate the male from the female GM mosquitoes based on the size of the  pupae — the stage after the larval stage — and is therefore not completely accurate.

Because of this, Parveez said, the board has insisted that scientists sort through the pupae twice — first mechanically and then manually.     

The 'self-limiting' strategy theoretically poses little threat of genes being released uncontrolled into the environment because of the death of the offspring. But future strategies, in which the aim is to overwhelm mosquito populations with those that are resistant to disease, are more controversial because the mosquitoes survive and breed.

A Malaysian geneticist, who declined to be named, said he hopes the experiments will be carried out under rigorous safety protocols.

"We have the best laws on biosafety in the world, but the problem is the enforcement," he said.

Liow Tiong Lai, health minister of Malaysia, told a press conference last month (10 October) that the Malaysian government views the GM mosquitoes "as one of the most efficient and fast ways of getting rid of the Aedes mosquito from our local environment".