Mosquitoes are developing resistance to insecticides

Aug 4, 2015

Humans have used everything from screens to chemical repellants to protect themselves from mosquitoes and the diseases they carry. Now, however, scientists say mosquitoes are finding ways to adapt to insecticides and other recent changes in their environments.

A new study on mosquito adaptability has big ramifications for public health workers, and for anyone out on a warm night, trying to avoid both mosquito bites, and the itchiness and disease those bites might bring.

Hosssein Asgharian, a molecular biology Ph.D. candidate at USC, and lead author of a study on mosquito evolution began with a question. He wanted to know if mosquitoes were able to adapt to changes to the environment made by humans, including the use of pesticides.

Asgharian and a group of scientists focused their study on two different strands of mosquitoes found in two different parts of the world: Russia and California. The first strand, Culex pipiens, is known as an urban or suburban mosquito. It can be found near puddles at California bus stops, buzzing around Moscow railway stations, or feasting on human blood at backyard suburban parties. The second strand, Culex torrentium, is a rural mosquito that would be found in Californian or Russian forests and meadows, and prefers animal hosts to human hosts.

“Our finding was that basically geographical location is the most important factor in determining genetic similarity. In other words, urban and suburban mosquitoes from Moscow are more alike and urban and suburban mosquitoes from Sacramento look more alike,” Asgharian said.

Asgharian and his team estimated that between five and 20 percent of the mosquito genome, depending on the population, had undergone recent adaptive change.

“The interpretation is that these mosquitoes are becoming resistant to insecticides and many of these adaptations are happening locally. In other words, different populations are becoming resistant to different chemicals,” Asgharian says.

For public health officials, and those who develop bug repellants, Asgharian’s findings mean that the strategy for fighting mosquitoes will have to be different in different parts of the world.

“If we want to plan defensive strategies we will have to sample each population separately and plan specifically for that population,” Asgharian says.

Asgharian also has advice for dealing with the diseases mosquitoes carry as climate change modifies the insects’ behavior.

“Each mosquito, each species basically prefers a specific environmental set of conditions,” Asgharian says, “When climate change happens, they shift their range, and when they shift their range, they will carry different diseases. So if you can basically anticipate the response of these mosquitoes to climate change, and we can anticipate the shift in their range, we can expect what will be the profile of the more common infections, diseases in each area that these mosquitoes carry.”

This story first aired as an interview on PRI's Living on Earth.