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The Aedes aegypti mosquito is the sole transmitter of the virus behind dengue fever. Credit: Derric Nimmo/Oxitec Ltd |
The first open field tests of genetically engineered mosquitoes,
carried out in the Cayman Islands, show that the insects can
successfully compete with their wild counterparts for mates. The
mosquitoes are designed to help combat dengue fever, a potentially fatal
infection that afflicts 50 to 100 million people per year, mostly in
tropical countries. No drugs or vaccines exist to treat or prevent the
disease, so prevention efforts are focused on eradicating the carriers, a
single species of mosquito.
The mosquitoes, created by a U.K. based start-up called Oxitec, are
engineered to carry a mutation that makes them die if not fed a specific
chemical. Larval insects can survive in the lab with special food; but
once the males are released in the wild and mate, subsequent generations
die, reducing the population as a whole.
According to unpublished research from Oxitec, releasing 3.3 million
engineered mosquitoes in Grand Cayman Island reduced population by 80
percent. The findings follow a smaller study carried out in 2009, whose
results were published Sunday in the journal
Nature Biotechnology.
Previous insect control efforts have included sterilizing male
animals and releasing them to the wild, where they mate but produce no
offspring. Sterile male Mediterranean fruit flies, for example, are used
worldwide to protect fruit and vegetable crops. But this does not work
for mosquitoes, because the technique used to sterilize the insects
also weakens them, meaning they cannot compete for mates.
The lethal gene strategy, which theoretically stops genetically
engineered organisms from spreading, is somewhat similar to that used in
the fictional Jurassic Park; like the dinosaurs in the movie, the
mosquitoes are engineered to require a certain substance to survive. But
just as in Jurassic Park, experts say it isn't foolproof.
"The progeny of crosses between [genetically engineered] males and
wild females in the laboratory survived at the disturbingly high rate of
3.5%," writes Todd Shelly, a researcher at the US Department of
Agriculture-Animal and Plant Health Inspection, Waimanalo, Hawaii, in a
commentary accompanying the publication in Nature Biotech.
A second concern is that the engineered lethality gene could somehow
be transferred to other environmentally-important insects, such as those
vital for pollination.
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Larvae
engineered to require a certain chemical to survive are marked with red
or green fluorescent proteins. Credit: Derric Nimmo/Oxitec Ltd The
Aedes aegypti mosquito is the sole transmitter of the virus behind
dengue fever. Credit: Derric Nimmo/Oxitec Ltd |
Florida is already considering trying the new mosquitoes. According to an
article in the New York Times,
Authorities in the Florida Keys, which in 2009
experienced its first cases of dengue fever in decades, hope to conduct
an open-air test of the modified mosquitoes as early as December,
pending approval from the Agriculture Department.
...The Agriculture
Department, meanwhile, is looking at using genetic engineering to help
control farm pests like the Mediterranean fruit fly, or medfly, and the
cotton-munching pink bollworm, according to an environmental impact statement it published in 2008. Millions of genetically engineered bollworms have been released over cotton fields in Yuma County, Ariz.
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