For many poorer nations, mosquitoes are more than just a nuisance at the picnic table. They’re a lethal menace to public health, especially in the humid tropical regions where mosquitoes thrive.
Mosquitoes are the prime carriers of a host of diseases which have killed millions over the course of human civilization. Fortunately, the last century has seen major advances in medical science that have drastically reduced the toll from mosquito-borne diseases like malaria and yellow fever. Understanding how weather and climate impact mosquito populations has been a key part of this process.
Weather and Climate Impacts on Mosquito Populations
Mosquitoes prefer to breed in covered, stagnant pools of water, especially those containing decaying organic matter such as leaves. Any regions which receive a lot of rainfall (such as the Southeast US) will be much more hospitable.
Chemicals released by sweating during hot weather, among other factors, can make a person more appetizing to a passing mosquito. Mosquitoes take more frequent blood meals during warmer weather. Even the virus itself grows faster in a warmer environment, meaning the mosquito will spend more of its two-four week lifespan being infectious.
Zika and Climate
In the last few years, a new virus called Zika has made global headlines. The risk is not so much to adult health, but to unborn babies in infected mothers. The rate of birth defects caused by Zika infection has been much higher in tropical climates like Brazil that offer the best environment for mosquitoes to breed.
So far, more moderate climates, including much of the United States, have been spared. Scientists predict, however, that the northward spread of Zika may be just a matter of time. The species responsible for transmission of the Zika virus, Aedes Aegypti, has a range that already spans the southern half of the US (see figure below from the Centers for Disease Control).
Evidence suggests a previously underestimated ability of the species to adapt to climate conditions at the cooler northern margins. Climate change may further expand the living space for Aedes Aegypti. While the Zika virus has not spread to include the full Aegypti range yet, cases of local infection have been reported in Florida and Texas.
Prevention
The CDC has already issued travel warnings cautioning pregnant women traveling to certain countries in the tropics. But even at home, efforts are already being made to prevent the spread of Zika, for which there is currently no vaccine and no cure. Large-scale pesticide spraying efforts are underway across the southern tier to suppress mosquito population. However, there are grave concerns about the harmful effects of these poisons on beneficial insect populations like bees.
The FDA approved testing for a safer, more targeted method this year. It would involve infiltrating mosquito populations with genetically altered males carrying a gene designed to stunt the reproductive process. This method has claimed an 80-90% population reduction in parts of Brazil hardest hit by the Zika epidemic.