[Narrator] Mosquitoes.

They're a sign of summer in many parts of the US.

They're also vectors of pathogens, spreading diseases,

especially this species, the Aedes Aegypti Mosquito.

It's really hard to control this mosquito.

It's resistant to a lot of the chemical insecticides

which can be used for it.

And there are no effective vaccines or drugs

for most of the diseases which it can actually carry.

[Narrator] So Florida Keys mosquito control district

is turning to a novel tool,

releasing millions of genetically modified male mosquitoes

designed to reduce the population of Aedes Aegypti.

Here's how it works.

It might seem strange that a tool

to combat the spread of mosquitoes

relies on the release of well, more mosquitoes.

The entire strategy focuses on

getting rid of female mosquitoes,

since they're the only mosquitoes that bite.

Fewer female mosquitoes means fewer eggs,

which hopefully means fewer future mosquitoes.

So the OX5034 mosquito,

this is what we call our friendly male mosquito.

And this male mosquito really has one job

and that's to go and find invasive female mosquitoes,

mate with them and pass on to them two genes.

[Narrator] The first genetic modification

they'll pass on to their offspring

is found in the tTAV gene.

It's called a self-limiting gene.

It stops the development of female mosquitoes

that carry this gene.

So males can carry the gene.

It doesn't impact them at all.

But the female offspring that get the self-limiting gene,

they're gonna die before they become

adult female mosquitoes.

[Narrator] The other genetic modification

these male mosquitoes will pass on to their offspring

will be a color marker.

So we put the DsRed2 gene into our male mosquitoes

and this is a color marker which helps us

to tell our mosquitoes apart from the invasive wild ones.

So that means that if we've released

our male mosquitoes in the field,

we can look at any mosquito that we catch

and we can see whether it's one of our mosquitoes or not.

The other thing we can do is we can look at

the offspring of our male mosquitoes,

and if they carry this color marker

which is visible under a microscope,

then you can tell whether they've actually been

fathered by one of the male mosquitoes.

[Narrator] It's a novel approach

that specifically targets the Aedes Aegypti population.

And while the United States is home

to more than 200 species of mosquitoes,

Aedes Aegypti isn't native,

and is, according to scientists,

an annoying biting pest and the species

most responsible for transmitting dengue,

chikungunya, yellow fever and Zika viruses to humans.

So there's a lot of factors that are involved

in influencing what makes a mosquito species

such as Aedes Aegypti such a great vector of viruses.

Certainly the ability of the virus to pass through

all of the transmission barriers within the mosquito

and go from the mid gut of the mosquito

to the salivary gland,

so that it can be able to transmit that virus.

When we talk about the extrinsic factors

or the factors outside of the mosquito,

some of the things that make Aedes Aegypti

such a wonderful vector of viruses to humans

is that it does live in such close association with us.

The species is known to take frequent

and multiple blood meals.

Every time it takes a blood meal from a human,

it increases the likelihood of either being able

to pick up an infection, or if it's already infected,

transmitting that infection to an uninfected person.

[Narrator] The spread of exotic viruses by mosquitoes

is a problem in Florida and around the world.

Oxitec's technology to create a self-limiting mosquito

has been a decade in the making.

So genetically modifying any insect is challenging.

You have to take the eggs of that insect,

put them under a microscope,

and then you actually take DNA that carries these genes

that we're putting into that insect,

and we insert it, we inject it into those eggs.

And then we wait to see if that DNA

becomes part of the chromosomes

that are in that mosquito egg.

And then what we can do is once it's been incorporated

into those chromosomes and we can then breed

from that genetically modified mosquito.

So that's what we did.

Back in 2013 we first injected that DNA

into these mosquito eggs.

And then since then, we've just been breeding

from that stock that have incorporated these two genes.

But along the way what we also have to do

is we have to do a lot of experiments in the lab

to see whether these genes are functioning

the way that we expect.

So are they killing all the female offspring as we expect?

Can we see this color marker properly?

And can these mosquitoes mate effectively?

Can they fly properly?

All the kind of things you need to check

before you can go from the lab into the field.

[Narrator] The mosquito eggs are produced

in facilities in the UK.

Then they're shipped to the project areas.

Add water, and in under two weeks,

you'll have about a thousand

genetically modified mosquitoes.

We've done this in Brazil in the past.

We've seen that the neighborhoods

where we released our male mosquitoes,

we have more than 95% reduction in the mosquito population

in that neighborhood.

[Narrator] The release in Florida began in 2021.

This year, the Florida Keys mosquito control district

is approved to release up to 196 million mosquitoes

between 2022 and 2023.

It'll be monitored by Oxitec

and the mosquito control district.

These type of trials, they can be expensive.

To be able to really monitor the success of these trials,

it's going to require a lot of labor

to be able to document the impacts of the releases

on the multiple stages of the mosquito life cycle

or the mosquito populations.

And so this is not something that is going to

be used everywhere.

What I can say is that the best long term solution

for mosquito control is going to be an integrated

mosquito management plant that incorporates

the multiple tools.

For example, using maybe genetically modified mosquitoes,

source reduction.

That means getting rid of sites around houses

or within neighborhoods that could be used

as the larval habitat.

And then following up with larvicide.

Using all these different tools together

is going to be the best long term solution.

[Narrator] The tools typically used to combat mosquitoes,

source reduction and insecticide,

will need to adapt to the realities of a warming world.

As temperatures increase,

then the length of the larval stage is going to decrease.

You're gonna be able to go through that life cycle faster

and you're gonna end up with more mosquitoes.

So certainly in these areas that are becoming warmer,

it's going to allow for species that like the warmth

like Aedes Aegypti to increase their range

and also increase their population size.