The first genetically modified mosquitoes to be allowed to fly for free outdoors in the United States began reaching mating age in the Florida Keys.
In a test of GM mosquitoes from biotechnology company Oxitec for pest control, these Aedes aegypti began to grow from small eggs laid in toaster-sized hexagonal boxes on suburban private properties in late April. On May 12, the experiment monitors confirmed that the males had matured enough to start flying on their own to woo American female mosquitoes.
This short-term experiment in Florida marks the first outdoor test in the United States of a strain of transgenic male mosquitoes as a highly targeted pest control strategy. This strain is designed to reduce local Ae populations. aegypti, a species of mosquito that spreads dengue and Zika (SN: 29/07/16). This could start to happen now that transgenic mosquitoes have reached mating age because their genetics make them such terrible choices as parents.
Mosquitoes that now wave distinctively male (extra spongy) antennae in Florida carry genetic supplements that block development in females. No female larva should survive into adulthood in the wild, says molecular biologist Nathan Rose, head of regulatory affairs at Oxitec. Half of the children of the freed men, however, will carry the trait of killing the father’s daughter. Children of bad parents can trick a new generation of females into making reckless mating decisions and doomed daughters (SN: 08/08/09).
Sign up to receive the latest from Science News
Headlines and summaries of the latest Science News articles, delivered in your inbox
However, the stroke is not designed to last in mosquitoes in an area. Genetics follows the same old rules of natural inheritance that mosquitoes and people follow: traits pass to some descendants and not others. Only bad half-father sons will carry the trait of killing daughters. The others will have normal families of mosquitoes.
Imagined versions of live mosquito pest control in Florida have been glorified and savaged at lively community gatherings for some time (SN: 22/08/20). But now it’s real. “I’m sure you can understand why we’re so excited,” Andrea Leal, executive director of the Florida Keys Mosquito Control District, said at the start of the (virtual) mosquito test on April 29th.
The debate over these GMOs Ae. the aegypti mosquitoes lasted so long that Oxitec updated its original version more coded with one that is essentially plug and play. The new strain, nicknamed OX5034, no longer needs a breeding colony with its females (biters) and antibiotics within reach of the release zone to produce fresh males.
Instead, Oxitec can send eggs in a suspended development phase from its base in Abingdon, England, to anywhere in the world, high-tech or not, that it wishes to deploy. Brazil has already tested this OX5034 strain and gone through the regulatory process to allow Oxitec to sell it there.
The targets of these possible live pest controls will be of their kind only. They represent only about 4 percent of the combined populations of the 45 species of mosquitoes complaining around the Keys. Other species are bothered and a more recent invader, Ae. albopictus, can also spread dengue and Zika to some extent. However, Leal blames Ae for almost every human disease spread by mosquitoes on the keys, including last year’s dengue outbreak. aegypti.
It is one of the three most important mosquitoes in the world in number of diseases that can spread, says Don Yee, an aquatic ecologist at the University of Southern Mississippi in Hattiesburg who studies mosquitoes (SN: 31/03/21). His lab has linked at least three dozen human pathogens, including some viruses and worms, to Ae. aegypti. Although most mosquitoes hide outdoors in vegetation, it loves humanity. In the tropics, “adults literally rest on the walls or ceiling,” he says. "They're hanging around the bathroom." The species bites humans for more than half of its blood meals.
In a long battle against this beast, Florida staff in late April added water to boxes of eggs sent and placed them on selected suburban private properties in Cow, Cudjoe and Ramrod Keys. Other points, with no mosquitoes added, will be seen as controls. All locations were chosen in part because females of the same species with American incubation were already there to be slaughtered, Rose says.
Males usually do not emerge from the boxes in a gray cloud, but emerge sporadically, few at a time. If all goes well in this preliminary test, up to 12,000 GMO mosquitoes in total at the release sites will be released into the air each week for 12 weeks.
Neighboring homes will house mosquito traps to control the distance from kindergartens that Oxitec GM males tend to fly. These are data that the U.S. Environmental Protection Agency wants to see. Based on distance tests elsewhere, 50 meters could be the median, Rose estimates.
Distance matters because pest controllers want to keep transgenic mosquitoes from flying free from outdoor sources of the antibiotic tetracycline. That is the substance that genetic engineers use as a shut-off switch for the self-destruct mechanism in female larvae. Breeding facilities provide the antibiotic to the larvae, disabling lethal genetics and letting the females survive in a laboratory to lay eggs for the next generation.
If transgenic males released in Florida were bred with a female laying eggs in some pond of water with adequate concentration of tetracycline, the daughters who inherited the switch could survive into adulthood as biters and breeders. The main possible sources in the keys would be the sewage treatment plants, Rose says. Test designers say they selected sites far removed from them.
After the distance tests, there are even larger releases that analyze the good condition of the males and the pests decrease. Up to 20 million Oxitec mosquitoes in total could be released in tests coming up in the fall.
Despite some high-level protests, it hasn’t been hard to find people to welcome the boxes, Rose says. "We were overly subscribed." In public hearings, project critics usually excite fans. However, there is also support. In a 2016 non-binding referendum on the use of GMO mosquitoes, 31 of Monroe County’s 33 enclosures, comprising the Keys, voted yes for the release of the evidence. Twenty of those wins were competitive, not reaching 60 percent.
Released males depend on a strategy of living sons / dead daughters. This is a change from the previous Oxitec mosquito strain. Those males sabotaged all offspring regardless of gender. The change occurred during the genetic redesign that allows for an egg-sending strategy. However, surviving offspring mean that the non-engineered genes of the new Oxitec strain can be mixed in the Florida population more than in the original version.
Those mixed test genes are “unlikely” to strengthen the power of Floridian mosquitoes to spread disease, researchers from the EPA and the U.S. Centers for Disease Control and Prevention wrote in a May 1, 2020 memorandum. factors in addition to the genetics of mosquitoes affect the spread of a disease. Oxitec will oversee the mix.
There may be at least one advantage in the mix, Rose says. Laboratory colonies have little resistance to some common pesticides such as permethrin that Floridian mosquitoes barely seem to notice.
Pesticide resistance in the keys is what takes a lot of interest in GMO techniques, says chemist Phil Goodman, who chairs the local mosquito control district commissioners ’board. During the dengue outbreak in 2009 and 2010, the first in decades, the district discovered that its spray program had almost no effect on Ae. aegypti. With some rethinking of the program’s chemicals, the control district may now kill 50 percent of mosquitoes of this species in a treated area. That’s not a big control, at best. Then, when bad weather intervenes for days on end, mosquitoes bounce back, Goodman says.
Joao Paulo Burini / Moment / Getty Images Plus
Since that 2009-2010 outbreak, dengue in Florida instead of traveling abroad has become more common. In 2020, an unusually bad year for dengue, Florida reported 70 locally captured cases, according to the CDC’s provisional balance sheet.
Traditional pesticides can get in the way of creatures in addition to their pest targets, and some critics of transgenic mosquitoes are also concerned about unexpected ecological effects. However, the success of Oxitec mosquitoes in striking current pests should not cause a disastrous food shortage or pollination for the natives, Yee says. Ae. aegypti has invaded North America in the last four centuries, probably too short a time to be absolutely necessary for any predator or plant native to North America.
For more details on pre-trial evidence and data, the Mosquito Control District has now released a swarm of documents on transgenic mosquitoes. The EPA summary of Oxitec tests, for example, reports no observed effects on feeding aquatic mosquito larvae to crayfish.
Yee doesn’t care much about either crustaceans or fish that eat the larvae. “That’s something analogous to say: well, we’re worried about releasing buffaloes back to the Midwest prairies because they can be eaten by lions,” he says. Crayfish and fish, he points out, do not naturally inhabit the small still water containers where Ae. aegypti mosquitoes breed.
Still, new mosquito control options are emerging: radiation techniques may be accurate enough to sterilize males but leave them attractive enough to trick females into a meaningless mating. And researchers are developing other genetic ways to arm mosquitoes against their species.
A technique that does not use transgenic sorcery only infects mosquitoes with Wolbachia bacteria that cause the sting not to spread dengue. The latest data from Mexico and Columbia suggest that this infection "could be effective in the southern United States and throughout the Caribbean," says biologist Scott O'Neil, based in Ho Chi Minh City, Vietnam, founder of the World Mosquito Program.
He has no plans to work in the United States, but focuses on places with much worse dengue problems. His version of the Wolbachia strategy makes the bites less dangerous (SN: 29/06/12). The mosquito population does not shrink or thirst for blood, so this approach may not appeal to Floridians.