Wherever you go in Virginia in summertime, there they are.
Mosquitoes are the nearly constant companion of every Virginian from late spring into the fall, breeding in pools of water and lying in wait for any chance at human blood. And some researchers say they may soon become even more omnipresent as climate change gives rise to the warmer, wetter conditions in which many mosquito species thrive.
“There’s already a dramatic impact of mosquitoes on human populations, but it’s going to increase,” said Virginia Tech biologist Clément Vinauger. “It can only increase because of climate change.”
But how mosquitoes are managing to so smoothly adapt to changing conditions, whether environmental or stemming from human efforts at controlling the insect, remains hazy.
“We have very good examples in the U.S. of several species of mosquitoes that are invasive and are basically efficient at invading because they can adapt pretty well to changing temperature,” said biologist Chloé Lahondère. “What we are trying to do in the lab is to try to understand how do they adapt so well?”
Over the next five years, Vinauger, Lahondère and another colleague in Virginia Tech’s Department of Biochemistry, Jake Tu, are aiming to tease out the ways these insects adapt their biological rhythms in response to changes in human behavior.
How they’ll investigate that sounds like something out of science fiction: The team uses a 3-D printer to make a platform that can fit around a captive mosquito’s head as well as electrodes that can be attached to its brain. Then the mosquito is exposed to different stimuli — “kind of like having a mosquito in a flight simulator, if you will,” said Vinauger — while the researchers record the activity of its neurons to pinpoint the exact times and places where the brain is processing the information in the environment.
The research is more than a matter of scientific curiosity, and the National Institute of Allergy and Infectious Diseases has put $2.7 million in grant funds behind it. As carriers of diseases such as malaria, dengue and the Zika and West Nile viruses, mosquitoes are sometimes called “the deadliest animal on earth.” For centuries humans have tried countless strategies to get rid of them, from pesticides to electric shocks to drainage improvements.
Mosquitoes, however, have been persistent. Species like Aedes japonicus and Aedes albopictus — the latter more commonly known as the Asian tiger mosquito — that originated in eastern Asia have managed through international trade to establish robust populations in North America, as well as Europe.
Other species have altered their behavior in response to human efforts to defend themselves. One of the triggers for the present Virginia Tech research was the observation that mosquitoes in parts of Africa were altering their feeding times in response to humans’ use of netting at night.
“They are shifting and becoming active either later the next morning or earlier in the evening when people are outside,” said Vinauger. “We don’t know how they do that, and that would be really important to understand how they are capable of adapting to our control strategies so that we can prevent them from doing that.”
Two potential factors make uncovering the inner workings of mosquito brains more pressing. First, scientists have noted rising resistance to insecticides among several common types of mosquitoes. And second, climate change is likely to impact the spread of mosquito species, although a number of factors influence their distribution and behaviors, and uncertainty remains about how exactly those changes will play out.
“Although we may be seeing some global warming trends here in Virginia and elsewhere in the United States, mosquito behavior is genetically built into all mosquito species, and it does not change rapidly in response to changing environmental conditions or cues,” said Virginia State Public Health Entomologist David Gaines in an email.
Day length is an important driver of mosquitoes’ reproductive and feeding activity, “so even if our climate warmed appreciably here in Virginia, and the last frost date in the spring and first frost date in the fall were made a month earlier into the spring, and a month later into the fall, many mosquito species would not extend their seasonal activity,” Gaines said.
However, other scientists have discovered connections between environmental shifts related to climate change and alterations in mosquito populations.
“Unlike ticks, mosquitoes have short life cycles and respond more quickly to climate drivers over relatively short timescales of days to weeks,” wrote researchers examining the impacts of climate change on human health in a 2016 study through the U.S Global Change Research Program.
“Based on the evidence, there is high confidence that climate change is very likely to influence mosquito distribution, abundance and infection prevalence by altering habitat availability and mosquito and viral reproduction rates,” they concluded.
According to Lahondère, warming temperatures have been shown to affect mosquito growth rates and adult sizes, as well as activity levels.
“We’ve shown that basically when it’s warmer, mosquitoes tend to fly more, so if they fly more, they can disperse more, and so on and so forth,” she said.
Ongoing work she and Vinauger are conducting in the Blue Ridge Mountains to compare mosquito behavior at different elevations is also revealing links.
“Even if they are small in terms of degrees of temperature, we see huge differences in the composition, the species composition of mosquito populations, and behavior — which plants, which hosts they look for,” said Vinauger.
What consequences these changes in mosquito behavior and distribution will have when it comes to disease is a matter of pressing concern for health officials. The Centers for Disease Control and Prevention have identified the Southeast, a region including Virginia, as facing “the greatest threat from diseases the mosquito carries.”
“Summer increases in dengue cases are expected across every state in the Southeast,” the agency wrote in a brief on regional health effects of climate change. “Warmer conditions may have facilitated expansion of the geographic range of mosquito populations and could potentially increase their capacity to transmit Zika virus.”
Gaines, the Virginia entomologist, also described the potential for climate change to “cause some unwanted consequences” in the transmission of diseases carried by mosquitos, including changes in habitat that could be more favorable to mosquitoes carrying West Nile virus or malaria.
Furthermore, because “some mosquito-borne pathogens replicate and/or go through life cycles more quickly at higher environmental temperatures, and because a mosquito’s body temperature is always the same as the ambient outdoor temperature,” such pathogens “will replicate and or develop faster in mosquitoes when the mosquito’s body temperatures are higher,” he said.
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