Sleep-deprived mosquitoes are less interested in feeding

Mosquitoes need sleep in order to function well, just like we do. In fact, mosquitoes in the lab sleep between 16 and 19 hours a day, depending on the species and the levels of activity going on around them. 

Sleep in humans is important in maintaining the immune system and in restorative functions such as tissue repair and protein synthesis. It has also been demonstrated that sleep is vital for peak memory and brain function. Sleep deprivation, on the other hand, can blur cognitive function and is associated with the development of numerous ill health conditions.

In a recent study from the University of Cincinnati, researchers demonstrated the importance of sleep to mosquitoes. The study revealed that mosquitoes whose slumber was disturbed the night before were more likely to spend the next day catching up on rest rather than seeking out a host on which to feed. The research highlights how vital this biological function is, even in insects.

“It was a bit surprising. Sleep deprived or not, a blood meal should appeal to them,” said UC doctoral student and study lead author Oluwaseun Ajayi.

Sleep is an evolutionarily conserved process that has been observed and described in different animal systems, including insects. But sleep in mosquitoes, which are important vectors of disease-causing pathogens, has not been directly examined. This is surprising as circadian rhythms, which have been well studied in mosquitoes, influence sleep in other systems. In addition, the phenomenon of catching up on missed sleep, called sleep rebound, has been observed in other insects such as honeybees and fruit flies, and is also well known in humans.

The researchers from UC’s College of Arts and Sciences and Virginia Tech’s Department of Biochemistry, found it challenging to study sleep patterns in mosquitoes. They spent more than a year developing protocols to study the phenomenon effectively – mosquitoes are easily disturbed by the presence of an observer, whom they detect as a potential host. This means that any experiments on mosquito sleep are likely to be confounded by the presence of the observer – a phenomenon called the observer effect – according to UC biologist Joshua Benoit.

“It’s really hard to quantify sleep in mosquitoes when, as soon as you walk in the room, you’re considered their Thanksgiving dinner,” Benoit said.

Mosquitoes detect the presence of potential hosts through their body heat, odors, movement, vibrations and the carbon dioxide they exhale from their lungs and emit from their skin. Because of this sensitivity, the researchers had to install the mosquitoes in rooms isolated within other rooms, and make use of cameras and infrared sensors that could record when the mosquitoes were moving around, without disturbing them. Virginia Tech researcher and study co-author Clément Vinauger used these video observations to document mosquito behavior.

In this way, the researchers studied the sleeping and feeding behavior of three species of mosquitoes for about a week, once they were acclimatized to their laboratory homes. Mosquitoes spend a lot of time perching between activities, in order to conserve energy, and it is not easy to detect when they are actually sleeping. However, the scientists identified a subtle postural change that occurs when a mosquito falls asleep. 

“When mosquitoes enter a sleep-like state, their hind legs droop and their body comes closer to the surface,” Ajayi said.

Using this knowledge, the researchers were able to establish from the video footage how much time mosquitoes spent asleep. The three species under investigation slept at different times of the 24 hour cycle – Aedes aegypti, a “day biter,” slept mostly at night while Anopheles stephensi, which is most active at night, slept during the daytime. Culex pipiens, which seeks a meal at dusk, could be found sleeping during the daytime and the night.

In a second experiment, researchers subjected the mosquitoes to sleep deprivation during their normal sleep time by vibrating their enclosures at regular intervals during. 

The results of the experiments, published in the Journal of Experimental Biology, showed that, while more than 75 percent of mosquitoes fly around actively seeking a blood meal when they are not subjected to sleep deprivation, less than one-quarter of them had any interest in food after a sleepless night. This represented a 54 percent decrease in the propensity to feed among sleep-deprived mosquitoes.

“What’s surprising to me is that as much as mosquitoes need blood to produce eggs, they will give it up to recover the sleep they lost,” Benoit said. “They might not be aroused as much because of the need to catch up on sleep.”

The overtired mosquitoes were also less likely to land on a host in both laboratory and field settings, suggesting that the same behaviors would occur in natural settings like your back yard. Tiredness also impaired blood feeding on a human host at times when mosquitoes would normally be active. 

Lucas Gleitz participated in the research project as a UC undergraduate biology student. In his opinion, the study’s findings are relatable to the lives of college students, given the sleepless nights most of them endure.

Mosquitoes cause more human suffering than any other animal, according to the World Health Organization. Malaria alone kills more than 400,000 people annually. And mosquitoes carry pathogens for other deadly diseases such as dengue and yellow fever. By understanding the mosquitoes’ circadian rhythms, researchers hope to find better ways to prevent infection.

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By Alison Bosman, Earth.com Staff Writer