The mosquito's ability to adapt to changing temperatures may be contributing to the spread of diseases, like dengue fever, Zika virus, and chikungunya virus.
“We've been interested in climate change for awhile trying to understand why we get more disease in one location than another. And how these patterns of risk might change, as climate warms,” said Matthew Thomas, the director of the Invasion Science Research Institute within the University of Florida’s Institute of Food and Agricultural Science.
Mosquitoes are around the world now, he said, due to the globalization of transport and trade, as humans continually alter the local environment. Through urban expansion, species like the Aedes aegypti mosquitoes have become domesticated.
“Its main breeding habitats in the natural environment would be things like tree holes, so small bodies of water, isolated bodies of water. But, of course, in our urban environments, we create those all the time,” Thomas said.
Discarded cans, bottles, car tires, and flower pots are prime breeding grounds for these insects now.
“We are constantly growing, and particularly increasing urbanization, without management of water and management of these potential breeding sites, which creates the sort of perfect storm for spread of these diseases,” Thomas said.
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His team looked at how specifically, the Aedes aegypti mosquitoes, tolerate various temperatures between cold and hot, and how their tolerance evolved over 10 generations.
"We found out that the mosquitoes were better adapted to their local environment,” said Thomas.
That means mosquitos, which are transported to other locations, can adapt to colder or warmer temperatures over time, which makes tracking them based on temperature and location difficult.
They used mosquitoes from five different regions of Mexico, not only because they had access to these populations, but also because it enabled the researchers to observe different types of environments.
“We could sample mosquitoes from a north-south gradient, but also… high altitudes and low altitudes. And that allows us to maximize the differences in local temperature conditions,” Thomas said.
They put thousands of mosquitoes into small glass vials and then those vials were plunged into a hot water bath. The scientists were watching for when the mosquitoes would fall over.
“And so that's obviously not very realistic. Mosquitoes don't do that in nature, but what we were using it for is to say, how tolerant are they. So, if they fell over very quickly, then they weren't very temperature tolerant. And if they lived, they lasted rather longer without falling over, then they were more tolerant,” Thomas said.
This past summer, a handful of dengue fever cases were reported in Broward and Miami-Dade counties. Also a handful of malaria cases were reported in Sarasota County, but that disease is transmitted by the female mosquitoes of the genus Anopheles.
It’s important to understand why and where mosquito-transmitted diseases occur, Thomas said, and how that might change in the future as the planet continues to warm.
"We can be on the lookout for diseases cropping up in areas where we weren't expecting them, and then we can deal with appropriate measures to manage the mosquito populations," he said.
The study, Phenotypic adaptation to temperature in the mosquito vector, Aedes aegypti was recently published in the journal Global Change Biology, but Thomas said documenting this is just the first step.
More experiments and models need to be done to discover how important this finding is in terms of disease transmission.
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