An adult female Anopheles mosquito bites a human.
Soumyabrata Roy/NurPhoto/Getty Images/FILE
https://edition.cnn.com/-By Ritu Prasad, CNN
Why mosquitoes choose you
CNN — At this point in the year, we’re all quite familiar with the sounds of summer: the breeze through the trees, the birdsong, the chatter of children playing outside – and the persistent buzz of a mosquito.
These insects have been nibbling on us since our earliest days. And with those bites came a plethora of diseases from viruses and parasites hitching a ride, everything from malaria to West Nile, Zika, dengue and more.
The US Centers for Disease Control and Prevention has dubbed mosquitoes the world’s deadliest animal, and they are responsible for hundreds of thousands of deaths worldwide each year. Add in a world warming thanks to climate change, the problem could be getting worse.
We’ve got some issues with our itty-bitty bloodthirsty cohabitants and it may seem like getting rid of them entirely would eliminate a source of irritation, not to mention save lives.
But could we simply get rid of all of them? We asked the experts.
Some mosquitoes are actually helpful
The first problem to tackle here is the word “all.” There are more than 3,000 recognized mosquito species worldwide.
“And each one of those mosquitoes is very different in terms of their ecology, the places that they exist, if they bite people, if they bite frogs, or if they bite birds,” notes Kristen Healy, an assistant professor in the Department of Entomology at Louisiana State University. “So, their whole ecological cycle is very different depending on the mosquitoes we’re talking about.”
Given this diversity, there are a lot of ecological cycles – in other words, the relationships between species and their environment – to consider.
Healy, who is also president of the American Mosquito Control Association, offered Louisiana, which is home to many swamps where mosquitoes thrive, as an example. “Those mosquitoes might serve an excellent purpose in, you know, the ecology of those swamp life cycles, and feeding fish and other small invertebrates in the aquatic system. And maybe there’s other small animals that might feed on the adults (mosquitoes).”
Other mosquitoes might play similar roles in their native habitats, so complete eradication could end up having some adverse effects. On top of that, experts say it’s unlikely we’d be able to totally exterminate all mosquitoes given their massive (think hundreds of billions) and widespread population.
But, we don’t necessarily have to get rid of all mosquitoes.
It turns out the species we’re most familiar with – the ones causing all those itchy, red bumps, as well as the more notorious diseases – are few in number.
And as Laura Harrington, professor of entomology at Cornell University, puts it: “Eradication of all mosquitoes would likely have an impact on the food chain. Eradication of one or two species would likely not have any impact.”
OK, so who’s the problem?
The Aedes, Anopheles and Culex genuses, to be exact. The species within those genuses can each transmit multiple viruses or parasites. Anopheles carries malaria, Culex carries West Nile, and the Aedes genus alone includes mosquitoes that can carry yellow fever, chikungunya, dengue and Zika, among others.
And we may not need them in our ecosystems.
“Disease-transmitting mosquito species, such as Aedes aegypti and Aedes albopictus, are invasive species in many parts of the world. … We were fine without them,” John Marshall, a professor in residence of biostatistics and epidemiology at the University of California, Berkeley, told CNN.
“There are thousands of species of mosquitoes, only a few of which transmit human pathogens, so if the disease-transmitting species were eliminated, non-disease-transmitting species would often be available to fill their ecological niches.”
Marshall added: “Disease-transmitting mosquitoes have been eliminated from many parts of the world throughout history, so local elimination is certainly possible.”
Healy noted these species also have “a very close relationship” with the viruses or parasites they carry. That means while sister species could theoretically mutate and become able to transmit the same diseases, it’s unlikely we’d see completely unrelated species suddenly become carriers if we eliminated the problem ones.
Looking more specifically at the US, Culex mosquitoes – namely, the common house mosquito –are a big target for control efforts. These mosquitoes prefer feeding on birds, which is where they pick up West Nile virus, and humans are “accidental hosts,” Healy said. But as larvae and pupae, these mosquitoes love living in very polluted environments, like septic water, retention and detention ponds, and anywhere with sewer runoff.
The other kind of mosquitoes being targeted in the US are the ones living in your backyard, like the Asian tiger mosquito (part of the Aedes genus). Early in their life cycle, “they live in backyard containers, like tires, watering cans, bird baths.”
Importantly, those ecosystems don’t have much going on by way of other species that might be affected – so eliminating those specific species of mosquitoes wouldn’t upset the natural balance, Healy said.
As for the Anopheles mosquitoes, which transmit malaria, things are a little different. They prefer swamps, Healy said, which are a much more diverse ecosystem.
“If you were to go out and target the larva of that species, you’d have to really think about what types of products that you’d be using in those environments,” she said.
But while some recent cases of malaria have made headlines, it’s still rare in the US.
What are we trying?
Gone are the days of problematic chemicals with unintended ecosystem effects – control strategies are getting more and more specialized, the experts say.
“For example, some success has been achieved with Wolbachia (a bacterial infection of mosquitoes) as a tool to ‘sterilize’ Aedes aegypti mosquito (a major vector of dengue, Zika and yellow fever viruses),” said Harrington.
Wolbachia, for example, has been used to sterilize male mosquitoes. The bacteria also doesn’t allow the viruses that cause Zika, dengue, yellow fever and chikungunya to replicate inside the Aedes aegypti mosquito.
Gene editing is offering other promising strategies, including additional ways to render mosquito populations sterile. Other avenues include using non-chemical options to kill immature mosquitoes – like bringing in fish to eat the larvae – setting sugar traps and using drones to find stagnant water for removal, Healy said.
But there’s no denying we haven’t yet won the war.
“It has been challenging,” Harrington said. “Mosquitoes have short generation times, they can mutate, adapt, and change very rapidly in response to some strategies. In addition, there is still much we don’t know about their basic biology and behavior that is critical to developing effective means to eliminate them.”
She added, “Much research needs to be done to develop and evaluate tools that will be affordable and acceptable, especially to those in resource poor settings who suffer from the greatest burden of disease.”
Education about mosquito control is also key – incorrect use of sprays, for example, could harm other insects, like bees. “But thankfully, those misapplications are not the norm,” said Healy, who has conducted research on these practices alongside the beekeeping industry.
“We’ve had organized mosquito control for over a century. And our research with the USDA bee lab continues to emphasize that there are more important stressors to honey bee health. … We are constantly educating mosquito control workers to follow these practices. And when followed, we don’t anticipate harm to these insects.”
What can we do now?
Is elimination of the worst of the mosquitoes that plague us possible? Yes. But it’s going to take time.
For now, here’s what the experts recommend to stay safe:
- Check your local health department website or the CDC’s traveler health website to stay aware of mosquito-borne risks
- Use EPA-registered repellents
- When outdoors, wear light, loose-fitting clothing; long sleeves and long pants if possible
- Make sure your doors, windows and screens are secured to prevent mosquitoes from coming in through cracks or tears
- When visiting areas with disease-carrying mosquitoes, invest in a bed net
- Check your backyard once a week for standing water; empty out any buckets or trash cans after rain or watering