The federal government on Friday moved to clear the way for the
release of genetically engineered mosquitoes into the wild for the first
time in the United States, tentatively approving a field test that
might help slow the spread of the Zika virus.
The genetically engineered insects, which contain a gene that will kill
their offspring, have already shown effectiveness in small tests in
Brazil and other countries in suppressing the populations of the
mosquitoes that transmit both Zika and dengue fever.
But an application to test the mosquitoes in the Florida Keys had
appeared to languish in regulatory review. It has also faced fierce
opposition from some residents in the state.
The threat of Zika virus, which is running rampant in Latin America and
threatening the United States, spurred the government to speed up its
review. On Friday, The Food and Drug Administration said it had
determined that the field trial of the mosquitoes was unlikely to cause
any harm to people, animals or the environment.
However, a final approval for the trial will not be made until the
F.D.A. receives and assesses comments from the public, which is likely
to take months.
The mosquitoes, developed by a British company, Oxitec, contain a gene
that kills the insect. Male mosquitoes containing the gene are released
to mate with wild females. Offspring from such matings die before they
reach adulthood, in that way suppressing the population of wild
mosquitoes that spread Zika, dengue fever and some other diseases.
The field test, to be conducted by Oxitec and the Florida Keys Mosquito
Control District, would take place in Key Haven, a small community
outside Key West. The genetically modified mosquitoes would be released
up to three times a week for as long as 22 months, to assess whether the
population of wild mosquitoes is reduced.
The F.D.A. based its decision largely on a nearly 300-page draft
environmental assessment submitted by Oxitec, which is now owned by the
American biotechnology company Intrexon. That document was also released
Both the company and F.D.A. documents said that the genetically
engineered mosquitoes were unlikely to establish themselves in the wild
or beyond the Florida Keys area, particularly because they are
programmed to die.
They were also unlikely to cause harm to people because the male
mosquitoes being released do not bite, they said. While small numbers of
genetically engineered females, which could bite, may be released, the
extra proteins they contain from the genetic engineering do not look
either toxic or allergenic and do not get into the insects' saliva in
The F.D.A. also said that if the population of Aedes aegypti mosquitoes,
the main type that transmits Zika and dengue, was suppressed, it did
not think that the population of other mosquitoes would increase to fill
the void. That outcome has been a theoretical concern of entomologists.
The F.D.A. said this was not likely because the trial would be short and
because aegypti mosquitoes "occupy a fairly uncontested ecological
"The consequences of escape, survival and establishment of OX513A in
the environment have been extensively studied: Data and information from
those studies indicate that there are unlikely to be any adverse
effects on nontarget species, including humans,'' the F.D.A. wrote,
using Oxitec's name for the mosquitoes.
Under federal rules, genetically engineered animals are regulated as
animal drugs, giving jurisdiction to the veterinary medicine division of
the F.D.A. This was done in order to regulate genetic engineering using
existing rules and agencies.
Critics have said that it does not make sense to regulate animals as
drugs and that the F.D.A. is not the best agency to evaluate ecological
effects. The F.D.A. said it was assisted in its review by the
Environmental Protection Agency and the Centers for Disease Control and
Most experts agree that traditional methods of controlling mosquitoes -
including spraying insecticides and removing standing water where the
insects breed - have not been sufficient, at least in Latin America, and
new methods must be tried.
However, federal officials and those at the World Health Organization
have said that newer techniques, including the Oxitec mosquitoes, need
to be tested more extensively and probably cannot be scaled up quickly
enough to make a big difference in the near future.
Oxitec argues that its technique is safe because it targets only Aedes
aegypti mosquitoes. By contrast, chemical sprays kill many nontarget
But that has not assuaged the opponents of the field trial.
"I don't want my kids to be guinea pigs,'' said Mila de Mier, who owns a
real estate company in Key West and has three sons. She organized a
petition on Change.org that drew more than 160,000 signatures.
Interest in using the mosquitoes arose after the Florida Keys
experienced its first locally transmitted cases of dengue fever in
decades, in 2009 and 2010. There have been no locally transmitted cases
of dengue since then, giving ammunition to opponents of the mosquitoes.
A big question now is whether the threat of Zika will reduce the
opposition to the mosquitoes. Judging from Ms. de Mier, it will not.
She said on Friday that even if the technique could reduce the wild
mosquito population, it had not been proved to reduce the spread of
Zika. She said she and some residents of Key Haven would contemplate
filing a lawsuit if the F.D.A. gave the final approval to the field
Intrexon, whose stock closed up more than 8 percent on Friday, also
wants to deploy the mosquitoes in Puerto Rico, which already has wild
mosquitoes spreading Zika virus.
Some lawmakers, saying that Zika posed an emergency, have pressed for
faster action, including shortening or suspending the public comment
period on the Florida trial.
Dr. Luciana Borio, acting chief scientist of the F.D.A., has said the
F.D.A. would not do that given the great public interest in the issue.
She also said that the agency could not authorize emergency use of the
mosquitoes in Puerto Rico before it won regulatory approval.