Even as several issues of field testing of genetically modified mosquitoes to fight malaria and dengue are being debated, Oxitec, a British company founded and part-owned by the University of Oxford, carried out the world's first open field trial last year. The trials to test the efficacy of genetically modified Aedes aegypti mosquitoes that cause dengue were conducted without much publicity in the Grand Cayman Island in the Caribbean Sea. A bigger trial was conducted this year in 16 hectares in the town of East End. Oxitec had worked with the Mosquito Research and Control Unit of the Cayman Islands for the trial. The results presented recently at a meeting of the American Society of Tropical Medicine and Hygiene in Atlanta show that the technology holds great promise. The release of altered and naturally occurring males in a 10:1 ratio resulted in 80 per cent reduction in adult dengue-causing mosquitoes in the study area. The technology is based on the premise that any offspring from the mating of genetically altered male A. aegypti mosquitoes with female mosquitoes would be killed in the larval or pupal stage. As male mosquitoes do not bite humans, the release of GM males will not increase the risk of dengue. Reducing the insect population using sterile male insects is not a new practice and many agricultural pests are controlled by this approach.

Yet there are some concerns about the release of GM mosquitoes. Field testing that was scheduled to start in December in Malaysia in the inland districts of Bentong in the State of Pahang, and Alor Gajah and Melaka in the State of Malacca has been postponed following questions raised by environmental groups. Among them is the possibility of female transgenic mosquitoes also being released when the sex-selection procedure based on pupal size is not strictly and consistently adhered to. According to Malaysia's Genetic Modifications Advisory Committee, laboratory tests showed that three per cent of offspring produced by mating of transgenic male mosquitoes with normal females actually survived into adulthood. This warrants more laboratory studies before undertaking further field trials as the chances of larvae growing into adult mosquitoes are greater in the field as tetracycline, a widely used antibiotic, is common in the environment. Though the mosquitoes would be recaptured and the area fogged once the trials are completed, further evaluation through caged field studies would be needed before open field trials are taken up, given particularly that the areas involved are densely populated.

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