Oxitec this week said its first study of genetically engineered mosquitoes in the U.S. produced “positive” results, but critics said the experiment so far hasn’t stemmed the spread of mosquito-borne illness.
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Oxitec this week announced results of the first open-air study of genetically engineered mosquitoes in the U.S.
The U.K.-based firm described the results as “positive,” but said, “Larger tests are still needed to determine whether the insects can achieve the ultimate goal of suppressing a wild population of potentially virus-carrying mosquitoes.”
The company’s self-reported results are not yet independently confirmed or peer-reviewed.
The company completed the first stage of the study with the release over seven months of nearly 5 million engineered Aedes aegypti mosquitoes.
The pilot study was conducted under an experimental use permit issued by the U.S. Environmental Protection Agency (EPA). It was the first to be approved in the U.S., though the company has since received a permit to conduct a similar experiment in California.
Reporting this week on Oxitec’s announcement about its Florida results, Nature stated:
“Wild A. aegypti mosquitoes can carry viruses such as chikungunya, dengue, Zika and yellow fever, so scientists have sought ways to reduce their populations. Oxitec’s engineered males carry a gene that is lethal to female offspring.
“If all goes to plan, when released into the environment, the engineered males should mate with wild females, and their female offspring will die before they can reproduce. Male offspring will carry the gene and pass it on to half of their progeny. As each generation mates, more females die, and the A. aegypti population should dwindle.”
Oxitec’s pilot project in the Florida Keys involves releasing up to 1 billion OX5034 mosquitoes — the first genetically modified (GM) mosquito approved for release in the U.S — in Monroe County over a two-year period.
Oxitec said the mosquitoes have a “self-limiting” gene that makes the females dependent on the antibiotic tetracycline. Without the drug, they will die.
Mosquitoes require water to mature from an egg to an adult. By adding water to the boxes the mosquitoes are deployed in, both GM males and GM females will hatch.
However, with no tetracycline present in the box, the GM females are expected to die in early larval stages.
The male mosquitoes will survive and carry the gene. When they leave the boxes, according to Oxitec, the insects will fly away to mate with wild females to pass the gene to the next wild generation.
In an April 6 webinar about the Florida pilot study, Oxitec claimed the first stage of the experiment was a success.
Oxitec’s researchers collected more than 22,000 eggs from traps set as part of the pilot study, Nature reported. They found the males that hatched from the eggs typically traveled within a one-hectare area around the release box.
This represents the same range over which wild A. aegypti mosquitoes fly.
Oxitec reported all females that inherited the lethal gene died before reaching adulthood, and said researchers could determine this because mosquitoes carrying the lethal gene fluoresce under certain light.
According to Nature, however, reducing A. aegypti populations won’t reduce the need for anti-mosquito pesticides, at least in the Florida Keys, as this specific mosquito type represents only 4% of the local population.
Other mosquito types, such as the black salt marsh mosquito (Aeges taeniorhynchus), described as “more of a nuisance than a disease vector,” have much larger populations in the region.
Nature also cited other limitations of Oxitec’s study results:
“[L]arger tests are still needed to determine whether the insects can achieve the ultimate goal of suppressing a wild population of potentially virus-carrying mosquitoes
“The pilot study was not intended to determine how well the method suppresses the wild population.”
Oxitec said it plans to gather this additional data in an extension of the Florida Keys study, which requires approval from state regulators.
Thomas Scott, an entomologist at the University of California, Davis, expressed reservations about any results Oxitec’s expanded studies would provide.