Innovations in Mosquito Control

Part 3: Genetic Control of Mosquitoes

While we enjoy sunshine and vacations, it may seem that mosquitoes serve no other purpose than to ruin our summer fun. While that is not true, mosquitoes can be vectors for harmful viruses, including Dengue, Zika, and West Nile Virus—even in the United States, and controlling mosquito populations is a matter of public health.

Historically, we have tried to solve the mosquito problem with heavy use of synthetic chemical pesticides which have been proven to be highly toxic to other insects, including important pollinators, like bees. Fortunately, mounting pressure from environmentally-minded citizens has inspired scientists to investigate innovative solutions to the problem of mosquito control in recent years.

From nanotechnology to predator biocontrol to genetic solutions, scientists have made incredible strides in effective, environmentally-friendly mosquito population control methods. In this three-part blog series, we’ll explore a few exciting avenues of research currently under investigation.

In our final post, we take a look at new scientific advancements in mosquito control through genetic modification.

Genetic engineering

Perhaps the most innovative mosquito control solution comes from Oxitec, where scientists have been exploring genetic engineering as a potent way to manage mosquitoes for over a decade. In this method, male mosquitoes bred from wild stock are genetically altered to carry a gene lethal to females, then released in hopes of passing that lethal gene on to wild populations. Lethal genes do not act on living adults, but rather cause female mosquito eggs or larvae to perish during development. 

While in the lab, mosquitoes are given an antidote to the lethal gene which allows them to develop to adulthood. This antidote is called tetracycline—a chemical commonly used in antibiotics and acne treatments. Once released into the wild, those males will mate with wild females, producing eggs that fail to develop and effectively reducing the size of the next generation of mosquitoes.

Lethal genes cause female mosquitoes to perish sometime before or during the larval stage (pictured), before they are able to bite. Credit: Peyman Zehtab Fard

This revolutionary method has been intentionally fail-safed in a few ways. First, lethal genes are time-limited, meaning that fewer and fewer mosquitoes will carry the gene in each subsequent generation. Self-limiting male mosquitoes will not persist in the environment, as they will disappear from the environment a few generations after releases stop. 

Second, altered males are given a gene for fluorescence in addition to the lethal gene, allowing researchers to quickly identify altered mosquitoes in the wild using a special light.

Finally, in an extreme case, if the target mosquito population needs to be recovered for any reason wild mosquito breeding pools can be treated with tetracycline, allowing generations to survive to adulthood and repopulate the area once more. However, it is unclear how such a treatment may affect native wildlife, and some research suggests that environmental tetracycline can inhibit the growth of some aquatic organisms.

Past Successes and New Experiments

Excitingly, newer versions of these lethal genes do not kill mosquitoes at the egg stage, but rather delay its effects until it is a larva. While no other wildlife species depend on mosquitoes as a primary food source, mosquitoes are part of the natural food web–larvae in particular. Delaying lethal gene effects until the larval state largely avoids the issue of removing a food supply for native wildlife and reduces the risk of unforeseen effects across the food web. Additionally, the EPA has determined that these releases pose no risk to people, other animals, or the environment.

This process has been extremely successful so far. Lethal genes have effectively repressed wild, disease-carrying mosquito populations in the Cayman Islands and Brazil, and in 2021, testing also began in the Florida Keys. This garnered national attention due to concerns over using Florida as a ‘GMO testing ground,’ but the truth is that these methods have already been in development for nearly fifteen years and have been successful in every previous field trial. Past field tests have shown no direct effects on non-target species and no effects on target mosquitoes outside of the lethal gene. These experiments have successfully eliminated 97-98% of mosquitoes that are capable of carrying Zika, Dengue virus, and yellow fever in target areas.

In some areas of the Florida Keys, mosquito populations are so dense that field researchers must wear protective suits. Credit: Florida Fish and Wildlife

Altered male mosquitoes released in Brazil were found to transfer genes into a natural population through a few rare, viable hybrids. These mosquitoes were actually three-way hybrids because the altered males were themselves hybrids from Cuban and Mexican populations. They are quite genetically distinct and are unlikely to persist in the population, but it is unclear how their existence might affect future efforts.

Back in the Florida Keys, preliminary results from the 2021 release have already been announced. Like the others, the experiment was considered a success—edited males mated with wild females, and all of the resulting female offspring inherited the lethal gene and died before maturity. As planned, the lethal gene persisted in the population for two to three months before disappearing and, just like wild males, edited males remained within about one acre of the release site. In March, the EPA approved additional releases in Florida and California between 2022 and 2024. These experiments will focus on assessing how scheduled releases of edited males will affect wild mosquito populations.

This is one example of many exciting advancements in technology that have allowed scientists to explore methods of mosquito control that are not only more effective than past methods, but reduce the negative environmental impacts of human health management.

Mosquitoes carry a slough of deadly diseases, including Zika, West Nile, Dengue, and yellow viruses in addition to malaria. Even today, over one million people die from mosquito-borne illnesses across the world every year. Additionally, mosquitoes carry diseases that can be deadly to domestic pets, including horses and dogs, as well as several wildlife species. Scientific advancements in mosquito control like those explored in this series are crucial for eliminating these deadly threats–not just for humans, but for our wild animals and ecosystems, too.

In this series

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