Rise of the indestructible mutant mosquito

Nets and traps no longer work against some strains as scientists labour to find new control methods

MUTANT mosquitoes are evolving to evade insecticide nets and traps, scientists have warned, as new ways are sought to control the insects.

Mosquitoes transmit diseases such as zika, dengue, yellow fever and malaria, the most deadly vector-borne sickness.

Malaria alone results in more than 600,000 deaths each year, and scientists are working to understand how mosquitoes’ behaviour has changed – and the best way to design new traps to stop them.

The UK has around 30 species of native mosquitoes, some of which cause nuisance biting. Manuela Carnaghi, a postgraduate researcher at the University of Greenwich, said there are parallels with the Covid pandemic, during which new strains of virus emerged.

She said: “All living organisms try to evolve and continue to infect. Human interventions have made mosquitoes adapt. We need to constantly find new ways of controlling them.

“When we started using insecticides, decades ago, the first generation of mosquitoes developed resistance. When you kill off mosquitoes, you’re left with the ones that have mutated, they become the strong ones.”

Harrison Lambert, a postgraduate researcher at the University of Greenwich, added: “Mosquitoes are becoming more ‘generalist’. They can survive in more seasons and breed just about anywhere now.”

Mosquitoes have proven a tough adversary and researchers are constantly looking for innovative ways to fight them – from gene editing to devel- devel oping different pesticides. Professor Tom Churcher, of Imperial College London, said the emergency of insecticide resistance has been “really quite dramatic and quick”.

“Mosquitoes have quickly evolved to overcome insecticide on bed nets. Everywhere in Africa pretty much has some resistance – some places have very high resistance, which has a substantial impact on public health.”

However, Prof Churcher said bed nets do still provide some protection. “We’ve been relying on this single insecticide for 20 years now, it’s no surprise there’s some resistance, but we do need more research and more insecticides.”

Ms Carnaghi warned that some mosquito species, of which there are more than 3,000, have also adapted how they feed.

“Rather than just feeding [on humans] at dusk or dawn, now they’re feeding in broad daylight,” daylight, she said. “Nets used to protect us at night, but what can we build to protect us in the day?”

The Greenwich researchers are studying mosquito behaviour, including how they mate, the significance of their buzzing, and what attracts them to a target.

Ms Carnaghi has been experimenting with human smells, colours and heat to tweak existing traps.

She said: “We’re looking at their behaviour and understanding their responses, to exploit that,” she said.

One innovation developed at the university is the ‘host decoy trap’, designed by Prof Gabriella Gibson and Dr Frances

Hawkes. The trap lures mosquitoes by mimicking the sensory stimuli that they follow when searching for a person to bite, then captures them when they land.

Part of the university’s research involves developing efficient traps which are also cost effective. “Some areas might not have power, or running water.

“We need a trap that is cheap to run, that can be easily fixed, and has a basic design,” said Ms Carnaghi.

Mr Lambert warned that a globalised world, and particularly transport, also poses a threat to malaria transmission.

For example, in Djibouti, a mosquito from India called Anopheles stephensi is thought to have prompted malaria cases to soar in recent years. Experts believe it arrived in the country on a cargo container.

Prof Churcher said: “The stephensi is something I’m hugely worried about. They’re very good at living with humans. If it establishes itself in Ethiopia, we could see malaria cases doubling.”

In 2020, there was a spike in malaria cases and deaths across the world.

According to figures in the World Malaria Report, there were an estimated 241 million malaria cases and 627,000 deaths from the mosquitoborne disease in 2020 – the majority of which were in children under the age of five in sub-Saharan Africa.

This equates to an additional 14 million cases and 69,000 deaths compared with 2019.

It is thought that the spike was caused by Covid shutdowns and disruptions to prevention programmes, such as insecticide spraying.

With malaria and other vector-borne diseases still putting significant pressure on health systems, and their detrimental impact on the global economy, the scientists warned that now is not the time for complacency.

‘Rather than just feeding [on humans] at dusk and dawn, now they’re feeding in broad daylight’