Amanda Maxwell

Sep 29th 2021

Genetically Modified Mosquitoes Tackle the World’s Deadliest Animal

Pest control in the skies over the Florida Keys is taking on a distinctive buzz this year. Thousands of genetically modified mosquitoes are being released to evaluate their impact on local populations. As a strategy, releasing modified mosquitoes into the wild could help to reduce arbovirus infections such as Zika virus, chikungunya and dengue. Since climate change is already expanding the range of many disease-bearing flying vectors into the United States, scientists and clinicians alike are eager to find out if this strategy is a winner.

Pest Control Over the Florida Keys

In April, the first ever release of genetically modified mosquitoes in the U.S. launched, according to Nature. Tens of thousands of eggs carrying modified Aedes aegypti males were placed in secret locations around Monroe County’s Cudjoe Key, Ramrod Key and Vaca Key. These males, each carrying a gene that’s lethal to female larval development, will hatch and fly off to interact with the resident population. In breeding with the locals, they’ll create generations where the females do not survive.

Within several rounds of breeding, the number of female A. aegypti will hopefully decline to a point where the wild population itself is severely suppressed. Additionally, since it’s only the females of this species that bites, Scientific American notes that this should also reduce transmission of serious arbovirus diseases such as dengue, chikungunya and Zika virus.

Genetic Modification Tech at Work

The bioengineering tech at work in the modified A. aegypti males buzzing around the Florida Keys is highly specific. Science Magazine describes how the modification adds a tetracycline transcriptional activator variant (tTAV) gene to the male genome. The engineered males carry the dominant lethal gene that they transmit to female offspring. In the lab, the gene’s lethality is suppressed simply by adding the antibiotic tetracycline to the mosquitoes’ food. Since this is not available in the wild, lethality activates and renders the females non-viable.

The Centers for Disease Control notes that, although this is the first time this has been deployed over U.S. soil, more than one billion genetically modified mosquitoes have been released safely and successfully in other areas around the world. Brazil, the Cayman Islands and Malaysia have all been involved in trials carried out by U.K.-based firm Oxitec, testing the technology’s ability to control wild populations and suppress arbovirus transmission.

An Engineered Future to Pest Control

Globally, according to the number of people killed, mosquitoes are the world’s deadliest animal. As CNET notes, mosquitoes kill more people than sharks, snakes, hippos and even humans per year — all due to the transmission of fatal and debilitating viral diseases. With the expansion of flying insect vector ranges due to global warming, as well as the increasing resistance to insecticides, public health strategies have had to evolve to protect people effectively.

Genetic modification (GM) is only one approach, but it does seem to be more efficient than traditional methods, such as insecticide use or releasing irradiated insects to suppress populations. Insecticide gets tricky once species become resistant. And irradiation, although successful at sterilizing males, needs huge numbers of insects for success because the process renders them weaker than unmodified males. The World Health Organization (WHO) has accepted GM, advising that it avoids increased insecticide use due to resistance.

The Oxitec approach, known as Release of Insects carrying a Dominant Lethal (RIDL), is one GM technique. Other high-tech tools for insect control include infecting breeding populations with debilitating Wolbachia bacteria species, modifying insect foods for lethality and other precision molecular approaches.

For example, Bt maize suppresses local insect populations by giving them something poisonous to chew on. Nature describes how the engineered maize species kills off caterpillars and grubs by incorporating a protein derived from a common soil bacterium that kills the pests and is harmless to people. When the larvae start feeding, they ingest the toxic Cry proteins and die rapidly, so the crop is protected.

Another GM approach uses highly specific CRISPR targeting. Researchers created populations containing the Cas-9 targeting modification alongside individuals with the guide RNA targets. A BioRxiv preprint describes how the scientists homed in on genes that destroyed functionality in both male and female A. aegyptii populations. Using CRISPR, they disrupted spermatogenesis and attacked the gene responsible for flight. Not only did the genetically modified mosquitoes produce sterile males, but they also created non-viable females. Without being able to fly, female mosquitoes could not mate or reproduce. Furthermore, because they also could not search for humans for a blood meal, this modification could also impact disease transmission.

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