Certain populations of mosquitoes are more heat tolerant and better equipped to survive heat waves than others, according to new research from Washington University in St. Louis. Most models that scientists use to estimate vector-borne disease risk currently assume that mosquito heat tolerances do not vary. As a result, these models may underestimate mosquitoes' ability to spread diseases in a warming world. Researchers led by Katie M. Westby, a senior scientist at Tyson Research Center, Washington University's environmental field station, conducted a new study that measured the critical thermal maximum (CTmax), an organism's upper thermal tolerance limit, of eight populations of the globally invasive tiger mosquito, Aedes albopictus.

The scientists collected eggs in the wild and raised larvae from the different geographic locations to adult stages in the lab, tending the mosquito populations separately as they continued to breed and grow. The scientists then used adults and larvae from subsequent generations of these captive-raised mosquitoes in trials to determine CTmax values, ramping up air and water temperatures at a rate of 1 degree Celsius per minute using established research protocols. Mosquito populations from locations with higher precipitation had higher CTmax values. Overall, the results reveal that mean and maximum seasonal temperatures, relative humidity and annual precipitation may all be important climatic factors in determining CTmax.

This study is one of the few to consider the upper limits of survivability in high temperatures -- akin to heat waves -- as opposed to the limits imposed by cold winters. That's why it was important for us to experimentally determine if this mosquito exhibits variation before we can begin to test how, or if, it will adapt to a warmer world. Future research in the lab aims to determine the upper limits that mosquitoes will seek out hosts for blood meals in the field, where they spend the hottest parts of the day when temperatures get above those thresholds, and if they are already adapting to higher temperatures. Determining this is key to understanding how climate change will impact disease transmission in the real world.