Researchers have completed the first outdoor study of genetically modified mosquitoes in the United States. The results, according to the biotech company running the experiment, are positive. But more extensive tests are still needed to determine whether insects can achieve the ultimate goal of killing a wild population of potentially virus-carrying mosquitoes.
The experiment has been running since April 2021 in the Florida Keys, a chain of tropical islands near the southern tip of Florida. Oxitec, which developed insects, has released nearly five million engineers Aedes aegypti mosquitoes over the course of seven months and has now nearly completed monitoring of release sites.
Based in Abingdon, UK, the company reported the first results of the experiment during a webinar on April 6, although it has not yet released the data.
Following the plan
Wild A. Egypt mosquitoes can carry viruses such as chikungunya, dengue, Zika, and yellow fever, so scientists have been looking for ways to reduce their populations. Oxitec’s engineered males carry a gene that is lethal to female offspring. If all goes to plan, once released into the environment, the engineered males will mate with wild females and their female offspring will die before they can reproduce. The male offspring will carry the gene and pass it on to half of their offspring. As each generation mates, more females die and the A. Egypt the population is expected to decline.
To make sure the mosquitoes follow this pattern, the researchers placed Oxitec mosquito egg boxes on private properties in the Keys and surrounded them with traps, covering a radius of over 400 meters. Some traps served as egg-laying sites and others caught adult mosquitoes.
The researchers found that males that hatched from eggs typically traveled within a one-hectare area around the release box – the same range over which they were found in the wild. A. Egypt fly. Artificial mosquitoes, which do not bite, have mated with the wild population and wild females have laid their eggs in Oxitec traps, as well as in sites such as flower pots, garbage can lids and soda cans.
Oxitec researchers collected more than 22,000 eggs from the traps and brought them back to their lab to hatch for observation. The company reported that all females who inherited the lethal gene died before reaching adulthood. (Researchers can determine this because mosquitoes carrying the lethal gene fluoresce under a certain light.)
Furthermore, the team found that the lethal gene persisted in the wild population for two to three months, or about three generations of mosquito descendants, and then disappeared. No mosquitoes carrying the lethal gene have been found beyond 400 meters from the release points, even after several generations. Oxitec monitors the sites for ten weeks after the last mosquito carrying the lethal gene was found.
“I like the way they’re doing it,” says Thomas Scott, an entomologist at the University of California, Davis. “They are doing it in a systematic and thoughtful way. So I’m encouraged, but they have a lot of work ahead of them, ”he says.
The pilot study was not intended to determine how well the method suppresses wild populations. Oxitec plans to collect this data in an extension of the Florida Keys study. It needs approval from state regulators, but hopes to get started soon. The company plans to release mosquitoes at a second study site in Visalia, California, where it is building a research and development facility.
But these extensive studies will not assess whether Oxitec’s method reduces the transmission of dengue or other viruses carried. A. Egypt. “They won’t be able to do a test to show that it actually has an impact on public health,” says Scott. “There isn’t enough Aedes“Viral infection transmitted in the Florida Keys,” or anywhere in the continental United States to do that kind of study, he says. To run such an experiment, the company would have to invest in a controlled trial elsewhere and conduct the study as a clinical trial, the which would be enormously expensive.
Disease outbreaks can also occur when A. Egypt populations are low, so reducing the mosquito population won’t necessarily result in disease suppression, Scott adds. “It’s just not that simple.”
Suppress A. Egypt it will also not reduce the need for pesticides. Aedes aegypti it constitutes only about 4% of the mosquito population in the Keys. The black mosquito of the salt flats (Aedes taeniorhynchus) – more of a nuisance than a vector of disease – probably accounts for around 80% of the mosquito population on the islands.
However, the Florida Keys Mosquito Control District (FKMCD), the local culling group, supports Oxitec’s evidence. “We have faced multiple disease outbreaks, so we must do everything we can to protect our people down here and the economy,” says Andrea Leal, Executive Director of FKMCD. That means trying new things, she says. “We are looking into any tools that might be useful.”
According to the FKMCD, the Keys experienced a dengue fever outbreak in 2010, with 68 cases transmitted locally, and again in 2020, with 72 cases transmitted locally. In 2017, the group worked with MosquitoMate, a biotech company in Lexington, Kentucky, to release A. Egypt males who have been infected with the bacterium Wolbachia pipientis. Lab-grown males mate with members of the wild population to produce eggs that do not hatch.
In 2020, the FKMCD approved Oxitec’s process after asking for community input. In a 2016 referendum, 31 out of 33 districts in Monroe County, where the Keys are located, voted in favor of the project, although some local residents and environmental groups protested the plan. It is particularly important, says Scott, that FKMCD and Oxitec have made an effort to interact with the community, especially “for something as controversial as genetically modified mosquitoes.”
The US Environmental Protection Agency (EPA) and the state of Florida also granted Oxitec permission to execute the 2021 project. The company’s plans for 2022 in Florida and California were approved by the EPA in March, and the company awaits permission from both states.