Tired Mosquitoes Would Rather Sleep Than Bite

You know how sometimes you’re so tired, you can’t eat? Mosquitoes feel the same.

Researchers recently discovered that mosquitoes who have their sleep disrupted would rather get rest than go looking for their next meal. The findings show how critical restorative sleep is even for insects.

“It was a bit surprising. Sleep deprived or not, a blood meal should appeal to them,” said University of Cincinnati doctoral student Oluwaseun Ajayi, who was the lead author of the study.

Ajayi says the research was necessary because of the need for mosquito control and management other than chemical insecticides.

“We were surprised that sleep is understudied in mosquitoes, despite the fact that circadian rhythms, which are tightly linked to sleep in other systems and determine the biting time and rate of mosquitoes, have been well studied in these disease vectors,” Ajayi tells Treehugger. “This further piqued our interest in this area of research.”

Setting Up an Ideal Experiment

To study mosquitoes, researchers spent more than a year developing ways to analyze how they sleep.

“We employed analysis of images to define the posture of mosquitoes and also used an infrared-based monitoring system to quantify the timing and amount of sleep in three different mosquito species,” Ajayi explains.

It was particularly challenging because of something researchers call the “observer effect.” This is when the act of just observing something can change its outcome.

In the case of mosquitoes, they’re able to sense that people are nearby due to their body heat, movement, smells, and the carbon dioxide exhaled during breathing and emitted from the skin.

So just walking into the room to watch them can have an impact on how the insects react.

“Mosquitoes are typically attracted to host sensation and stimulation, and this portends a problem of accurately quantifying sleep in mosquitoes,” Ajayi says. “This required us to have our experiments in isolated rooms and incubators away from humans. Images taken for the postural analyses were actually taken remotely to forestall the mosquito interaction with the human host.”

In order to deal with those circumstances, researchers set up the experiment in a quiet lab where the mosquitoes were several rooms away from anybody who might pass by. They placed cameras and infrared sensors in the room so they could record whenever the mosquitoes moved without any risk of disturbing them.

Watching Mosquitoes Sleep

Researchers found that the mosquitoes in the lab slept between 16 and 19 hours each day.

It took them some time to determine when a mosquito was actually asleep. When they’re not hunting for something to eat, they can stay still and perch for a long time in order to not expend energy. But researchers discovered that when mosquitoes were actually in a sleep-like state, their hind legs are lowered and they bring in their bodies closer to the surface where they are resting.

The mosquitoes were left alone for about a week in order to get used to the new environment. Researchers studied their sleep and feeding when they first came in. Then, researchers vibrated their enclosures regularly at night or during the day to subject them to sleep deprivation.

More than three-quarters of the mosquitoes that got to sleep normally went hunting for a blood meal when they were awake. But less than one-quarter wanted to eat after a sleepless night. They found that the sleepy mosquitoes landed less on a human both in the lab and when they watched them in the field.

The findings were published in the Journal of Experimental Biology. 

Sleep Deprivation

Scientists know the effect of prolonged sleep loss on humans, ranging from impacts on health to decreased longevity.

“Sleep deprivation also has negative consequences on the biological functionality of insects,” Ajayi says. “Honeybees that experienced nighttime sleep loss were not able to forage well in the subsequent day due to impaired waggle dance signaling. Fruit flies developed defects in short- and long-term memory as a result of nighttime sleep deprivation.”

Mosquitoes can transmit serious diseases to humans including malaria, dengue virus, Zika, and West Nile virus. They can also spread diseases to dogs and horses such as heartworms, eastern equine encephalitis, and West Nile virus.

By understanding the circadian rhythms of insects, researchers hope to find new methods to prevent the spread of infections.

“In fruit flies, a link between sleep and immunity has been established. And immunity is an important factor for disease transmission in mosquitoes,” Ajayi says. “Based on this, this research would provide us with an understanding of the role of sleep on disease transmission in mosquitoes.”