By Angus Dalton
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Deadly genetically modified mosquitoes that glow fluorescent red are bound for Australian shores.
British company Oxitec has lodged an application with Australia’s Gene Technology Regulator to approve the release in Queensland of gene-edited Aedes aegypti mosquitoes, which carry dengue and yellow fever.
Genetically modified mosquitoes are often tagged with a fluorescent gene for identification, as shown here in a separate CSIRO study into dengue-resistant mozzies.Credit: CSIRO
But these mozzies will be deadly only to themselves. Oxitec’s insects pass on a DNA tweak that kills off female larvae before they develop into blood-hungry biters. Another gene tags the mozzies with a red fluorescent marker – borrowed from coral – for identification.
On Tuesday, Oxitec announced the launch of an Australian wing of its operations, in partnership with the CSIRO, to create more gene-edited organisms designed to slash populations of unwanted insects.
They’re already working on a gene-edited version of the Asian tiger mosquito, another aggressive, disease-causing species that threatens to infiltrate mainland Australia.
How does this approach work, what are the concerns — and how will the DNA-tweaked mosquitoes get here?
There’s a chance, in fact, you’ll be hatching them yourself.
How does GM mozzie control work?
About a million people perish from mosquito-borne diseases each year. One researcher estimated mosquitoes have killed half of all people who ever lived. (It’s probably more like one in 20.)
Extreme weather events propelled by climate change including floods and heatwaves are fanning a spike in malaria and dengue outbreaks. Mosquitoes are also evolving to resist insecticides.
Only female mosquitoes bite and drink blood.Credit:
That’s why Oxitec, which grew out of Oxford University, has developed a line of self-limiting or what they call “friendly” Aedes aegypti mosquitoes, a sub-Saharan species that spread around the world via the slave trade. The species spreads dengue and yellow fever, and chikungunya and Zika virus.
Oxitec’s mosquitoes are edited to carry a lab-designed gene that’s based on elements of DNA found in E. coli, fruit flies, cabbage looper moths and the herpes virus. (The gene doesn’t encode for actual E. coli or herpes but was rather inspired by tiny structural sequences of their DNA.)
When the modified males mate with wild females, the gene passes into their offspring and overloads mosquito cells with a protein called tTAV.
The protein isn’t toxic or harmful but the larval cells are so flooded with tTAV they can’t produce other vital proteins and they die.
The gene only kills females, which are the ones that bite and spread disease because they need blood to nourish their eggs. The non-biting males live on to deliver the deathly gene to a new generation.
Just like sea monkeys
Dengue-ravaged communities in Brazil have already recruited Oxitec mosquitoes. The company produces eggs in a “mosquito factory” in Sao Paulo and they’re shipped out in boxes to businesses and homes in mozzie-plagued neighbourhoods.
The next part is like breeding sea monkeys: you just add water, and the eggs hatch. A few hundred harmless males spawn from each box and begin their work, bringing down the mosquito population in the surrounding hectare.
An Oxitec release box of genetically modified Aedes aegypti in Brazil.Credit: Oxitec
Some towns have reported a 96 per cent plunge in Aedes aegypti numbers as a result.
An advantage of Oxitec’s approach is that male mosquitoes are female-seeking precision missiles, unlike the blunt instrument of “fogging” or spraying large areas with insecticide.
“Our approach leaves other beneficial insects like butterflies and bees completely unharmed,” Oxitec’s chief strategy officer Neil Morrison says. “Predators like birds or bats, that feed on our mosquitoes, are completely unharmed, too.”
Director of health and biosecurity at CSIRO Dr Brett Sutton says another advantage is that the genetically modified mosquitoes don’t last by themselves in the wild.
“It’s not like a genetically altered species that carries that gene on ad infinitum,” he says. “The gene is only inherited by the male mosquitoes, and so with every generation it’s halved, and therefore it doesn’t last beyond a fixed number of generations.”
But there have been teething issues.
Community distrust and a controversial paper
A controversial 2019 paper in Scientific Reports by an independent team of researchers found something troubling: wild populations had inherited fragments of the genetically modified mosquitoes’ genome during a Brazilian trial.
Back then, Oxitec’s method targeted both male and female larvae. But 3 to 5 per cent of the offspring survived despite the deadly gene. The paper sparked concern that surviving mosquitoes could adapt to withstand Oxitec’s approach or even create hybrid insects more resistant to pesticides and more likely to spread disease.
Oxitec mosquitoes and larvae glow red under a special light.Credit: Oxitec
That speculation was unfounded – the paper didn’t test for such resistance – but nevertheless sparked headlines such as “Failed GM mosquito control experiment may have strengthened wild bugs”.
The paper was soon hit with a string of scientific and editorial concerns, including that many of the issues raised in the report were not backed up by data. (Oxitec’s mosquitoes are more susceptible to insecticides.)
“That paper was somewhat discredited,” Morrison says. “It also describes a version of the friendly mosquito that was generation one. We’re now on generation-two mosquitoes – no females survive. So the same question marks don’t apply.”
But the saga does underscore the risk of distrust and sceptical community sentiment towards the release of genetically modified insects. In a Florida Keys neighbourhood in 2018, 65 per cent of residents voted to reject a trial release of Oxitec’s mosquitoes.
Other communities voted in favour, however, and Morrison says Oxitec has ended up “oversubscribed for households wanting to host egg boxes in their front yard”.
Where the mozzies could be released first
Working in tandem with locals is top of mind for Morrison and Sutton as they eye the Torres Strait as a potential launchpad for Australian trials of Oxitec mozzies.
“Backlash tends to happen when there aren’t open, honest conversations with those communities,” Sutton says. “We don’t want to push for this against community wishes.”
Oxitec and the CSIRO are already working on a population-suppressing version of the Asian tiger mosquito to go with the existing genetically modified Aedes aegypti males. Both are invasive to Australia.
A helicopter sprays a pond to fight a mosquito infestation in Liverpool in November.Credit: Sydney Water
“We think there’s an opportunity right now for control of those mosquitoes in the Torres Strait,” Sutton says. “The Asian tiger mosquito could easily expand into mainland Australia.
“There is a lot of value in having a technology that can be applied to the invasions that will come.”
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