They fear "Franken-skeeter" over dengue fever.
Almost 100,000 people have joined a Key West mother's online campaign asking the U.S. Food and Drug Administration to deny a British biotech company's application to release genetically modified mosquitoes in the Keys.
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The Florida Keys Mosquito Control District is pushing the plan as way to combat dengue fever.
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Oxitec, short for Oxford Insect Technologies, would let loose its male mosquitoes in the Keys to breed with wild females. Only female mosquitoes bite, so the company would release males with an altered gene that ultimately kills them and whatever larvae that results from their mating.
Mila de Mier, a Key West mother of three, launched the petition drive against the plan on Change.org, a website that uses online petitions to spur social change. As of Thursday, 99,460 had signed it.
"As a community we've already said we don't want these mosquitoes in our backyards, but Oxitec isn't listening," de Mier said.
She and other Key West residents say they want more definitive scientific studies of potential long-term effects on humans and the environment.
The city of Key West passed a resolution in April banning the release of Oxitec's mosquitoes until more is known about how they might impact other wildlife.
Oxitec's application has elicited fears of mutant mosquitoes that won't die as advertised, females that inadvertently slip in with the released batch of insects, increasing risk of dengue - males and females are separated in the laboratory by hand - and other ill impacts.
"Nearly all experiments with genetically-modified crops have eventually resulted in unintended consequences: super weeds more resistant to herbicides, mutated and resistant insects and collateral damage to ecosystems," de Mier's petition says.
"Why would we not expect GM insects, especially those that bite humans, to have similar unintended negative consequences?"
Oxitec says their way is more environmentally friendly than pesticides and that the U.S. Department of Agriculture has found the approach "environmentally preferable" to available alternatives.
The company tried a large trial release of the mosquitoes in the Grand Cayman Islands in 2010, reducing mosquitoes there by 80 percent for three months.
Brazil released some of the mosquitoes last year, and reportedly saw 90 percent decrease in mosquitoes.
Other trials are planned in Panama, Malaysia and France.
The plan in Key West comes as the result of an increase in recent years of in rates of dengue fever, which has jumped 30-fold in the past half-century, according to the World Health Organization.
Dengue (pronounced DENG-gay) occurs in more than 100 countries. The disease emerged in Key West in 2009 and 2010 and in Miami in 2011.
Also known as "breakbone fever," the disease often causes its victims to have contortions due to intense joint and muscle pain.
Other symptoms are flu-like and include a flat, red rash over most of the body and increased skin sensitivity.
WHO estimates 100 million people get the disease annually. Last year, the Centers for Disease Control and Prevention issued a travel advisory for the Bahamas, after 1,000 suspected dengue fever cases were reported in just one month.
The mosquito species that spread dengue fever are difficult to kill.
"They are very hard to control because they are daytime fliers," said Chris Richmond, an environmental specialist with Brevard Mosquito Control.
"You really can't spray during the day: it's too hot, the spray won't work, and you kill a lot of non-targets."
The technology could conceivably eliminate the need for insecticides, said Alfred Handler, a geneticist at the USDA in Gainesville.
He has concerns, however.
Handler says mutations in mosquitoes bred in the lab might result in them growing resistant to the lethal gene and getting inadvertently released in the wild.
The mosquito under evaluation has been bred at Oxitec for 10 years (over 100 generations) "with no signs of mutations or changes in performance," according to Florida Keys Mosquito Control District.
Handler said he's more concerned with public perception and reactions to this type of research than the actual risks to the environment.
He'd prefer these insects over insecticides, which carry their own risks.
"It's not expected that they will persist in the environment," Handler said.
Even if they did, "It's quite possible there is no worst-case scenario," he added.
"With many things, you can always come up with theorized worst-case scenarios that can never be tested."