Dear Science: I seem to be a total mosquito magnet, and nothing I try keeps the biters at bay. With serious illnesses such as Zika to worry about, why don’t we just get rid of the pests once and for all. What good do mosquitoes do?
Mosquitoes are our most deadly adversaries in the animal kingdom. While the “factoid” that floats around about malaria causing “half of all human deaths” throughout history is not true, we do have the insects to thank for some devastating diseases. More than 400,000 people were killed by malaria in 2015. Warming climates and increased global travel have helped previously obscure viruses such as Zika and chikungunya gain footholds across the globe. And even if you never face a life-threatening disease because of a mosquito bite, swelling and itching is hardly a pleasant experience.
So why don’t we just zap them all? Unfortunately, you won’t read about the total eradication of mosquitoes anytime soon.
Only female mosquitoes bite, and only for a very brief portion of their life cycle — when they need nutrients to create eggs.
“They’re trying to do the right thing,” said Ole Vielemeyer, infectious-disease expert at Weill Cornell Medicine and NewYork-Presbyterian. “They’re just trying to have enough food for their offspring.”
But during that stage of life, they might bite multiple victims (including those of different species). If a mosquito bites someone infected with an illness that can replicate inside the insect’s gut instead of simply being digested, that virus or parasite can then sneak into a new host when the bug’s saliva slips into a bite. It’s not the infected blood itself being passed along, which is why you can’t get HIV from a bug bite. Still, plenty of pathogens have evolved to thrive in mosquito saliva.
“Most of mosquitoes are harmless. But when they transmit diseases, horrible things can happen,” Vielemeyer added. “The ones that carry disease have caused human suffering for millennia. So it’s kind of a mixed bag.”
Many mosquitoes serve an important biological purpose. They can help pollinate plants as they feed on nectar (their usual food source, outside of that crucial blood meal period) and provide a vital source of food for larger animals. They’re vital components of a complex ecosystem, just like every other living thing. Researchers in the Arctic worried that climate change would lead more animals to feast upon local mosquitoes, throwing the food web out of whack and leaving plants unpollinated. As it turns out, warmer water has actually produced an Arctic mosquito boom — but that’s not great news for the baby caribou they feed upon.
The point is that just because humans hate mosquitoes doesn’t mean that they can be wiped out without consequences.
“We see the mosquito as sort of this evil thing,” Vielemeyer said. “But there are lots of positive things that they do in the ecosystem.”
That doesn’t mean that scientists have a live-and-let-live philosophy about these insects: Researchers are trying to eradicate mosquitoes. But they’re focusing on the ones that cause the most harm. The aegypti mosquitoes that cause Zika and the like — mosquitoes that have evolved to live in urban areas — are a particularly attractive target.
“There is no visible end to this except a war against aegypti,” Jo Lines of the London School of Hygiene and Tropical Medicine recently told The Guardian. “Otherwise this is going to go on for a thousand years.”
Many scientists are working on creating genetically modified male mosquitoes that can only father sterile offspring. If released into the population, these males could trick deadly mosquitoes into wasting their blood meals on useless eggs.
