GENETICALLY modified(GM) mosquitoes helping scientists find a new way to combat malaria cannot compete against unmodified insects, a study has revealed.
The introduced genes disappear within 16 generations when they are allowed to breed with â€œwildâ€ mosquitoes, researchers found.
The findings are a set back in attempts to develop a GM mosquito that cannot transmit the malaria parasite to humans. However, the scientists are confident the obstacle will be overcome.
Researchers at the Imperial College London created the first GM mosquito three years ago. The ultimate aim is to release insects into the wild that are modified to make them harmless.
Eventually, it is hoped, the trait would be passed on to other insects. But the new study revealed that engineered mosquitoes would lose out to their natural cousins in the wild. Imperial College researchers and a team of Italian colleagues studied laboratory populations of the mosquito Anopheles stephensi, the major carrier of malaria in India.
Among them were four lines of mosquitoes modified with a fluorescent marker gene that made them glow green or red under ultraviolet light. In control populations containing GM mosquitoes only, the marker was maintained intact and passed on for more than 30 generations.
But when GM insects were allowed to breed with unmodified mosquitoes, the number carrying marker genes decreased sharply. In some experiments, the marker disappeared entirely within four to 16 generations, the researchers reported in the journal â€œScience.â€
The introduced gene was thought to be associated with one or more mutations that gave the GM mosquitoes a competitive disadvantage, they said. Though these deleterious genes do not kill the GM mosquito, they â€œcause it to lose out in competition with normal mosquitoes,â€ they wrote. The problem could probably be reduced by minimising the effects of in-breeding.
Professor Andrea Crisanti, who led the research, said such studies were crucial to evaluating the environmental effects of releasing GM insects into the wild.
â€œThey will help to assess the overall feasibility of using GM mosquitoes to fight malaria., yellow fever and dengue and banish these major scourges,â€ she said.
GM mosquitoes flop