For most of us, mosquitoes are irritating creatures. Their itchy bites, the whiny hum of buzzing wings, ubiquitous presence, and uncanny abilities to sense human presence not only ruin our beautiful evenings in the backyard of our homes but also spoil our sleeps in our bedrooms at night.
Most people are not aware of the fact that only female mosquitoes bite humans (or birds/animals) to suck blood. They use their proboscis to insert two tubes into the skin: one to suck blood and the other to inject an enzyme to inhibit blood clotting. Blood provides female mosquitoes required proteins to lay eggs. For food, both male and female mosquitoes depend on nectar and other plant sugars.
A new study from researchers from the University of Cincinnati claims that female mosquitoes bite humans not only to get the protein from the blood but also to quench their thirst during hot, dry conditions—a finding that could help scientists find new strategies to fight mosquito-borne diseases.
“It makes sense,” UC biology student and study co-author Elise Didion said.
“We find the highest transmission rates of West Nile virus during droughts because mosquitoes may use blood meals to replace the water they lose.”
According to researchers, mosquitoes are among the deadliest animal threat to people. Every year, more than 400,000 people are killed from the disease (malaria, dengue, yellow fever, etc.) spread by mosquitoes.
UC biology professor Joshua Benoit says new findings about the physiology and behavior of mosquitoes could help researchers and health agencies find some new techniques to fight mosquito-borne illness.
“It will make for better modeling for when disease outbreaks occur,” Benoit said.
“When it’s dry, it might be easier for a mosquito to locate a host than limited supplies of water or nectar.”
In their current work, UC students studied a batch of thirsty, dehydrated female mosquitoes. They noticed that the mosquitoes that escaped from a vial were “unusually aggressive” and were trying to bite. They also found that dehydration prompted as many as 30 percent of female mosquitoes to seek a blood meal.
“Normally only 5 or 10 percent of female mosquitoes will feed at any time, depending on the species,” Benoit said.
“Dehydration has a big impact on whether they feed normally or not.”
To confirm results, researchers conducted more experiments in natural but controlled conditions at the UC Center for Field Studies. They released adult mosquitoes in a mesocosm (a large mesh enclosure), which imitated conditions found in nature.
After a week, researchers put a membrane-covered disk of blood (mimicking a bird/animal host). They found that dehydrated mosquitoes in the mesocosm were more likely to search for a blood meal compared to mosquitoes that were not thirsty.
According to Benoit, it does not take long for mosquitoes to become dehydrated to the point where they might seek a blood meal.
“We saw the behavioral effects within two or three hours under low humidity and higher temperatures,” Benoit said. “It was completely changing their behavior.”
The UC study was presented at the Society for Integrative and Comparative Biology conference in January this year. Its detailed findings have now been published in journal Scientific Reports.