Sleepless mosquitoes lose their taste for blood

It turns out there is rest for the wicked: Sleepy mosquitoes are more likely to make up for missed z than to drink blood, a new study has found.

Most people are aware of the consequences of a bad night’s sleep. Insects also suffer; for example, sleepy honey bees struggle to perform their characteristic rocking dance, and tired fruit flies show signs of memory loss. In the case of sleep-deprived mosquitoes, they give up valuable eating time in favor of sleeping overtime, researchers said on June 1 in Journal of Experimental Biology.

The preference for a nap in front of the dining room is surprising, given that “we know that mosquitoes love blood very much,” said Oluvasen Ajayi, a disease ecologist at the University of Cincinnati.

Scientists have long been interested in the circadian rhythms of mosquitoes, the internal clock that determines the time for sleep and wakefulness (SN: 2.10.17). Knowing when a mosquito is awake – and biting – is important for understanding and limiting the transmission of the disease. For example, malaria, often transmitted by night mosquitoes, is kept under control by placing a net around the beds. But new research shows that mosquitoes that feed during the day can also spread the disease.

The challenge is to study sleeping bloodsuckers in the lab. This is partly because awake mosquitoes are aroused by the presence of food – the experimenter. And when mosquitoes fall asleep, they look a lot like their peers, who just rest to save energy.

This is the difficult and often species-specific question: “How can you understand [when] insect sleeping? “says Samuel Rund, a circadian mosquito biologist at the University of Notre Dame in Indiana who was not involved in the study.

One way to find out is by tracking the behavior of the insect. So Ajayi and his colleagues watched the mosquitoes sleep. The team focuses on three species known to transmit diseases, including malaria: Temples of the Egyptianswho are active during the day; Culex pipienswho prefer twilight; and night Anopheles Stephanie. The mosquitoes were left alone in a room in small enclosures, where the team used cameras and infrared sensors to spy on them.

After about two hours, the mosquitoes seemed to nod. Their bellies dropped to the ground and their hind legs drooped, the footage shows. Over time, C. pipiens and A. aegypti showed a reduced response when the experimenter entered the room, suggesting that the delicious odor is less likely to wake these species when they are in deep sleep. Taken together, posture change, periods of inactivity, and lower arousal were determined to identify dormant mosquitoes.

What began as a relaxing mosquito experiment quickly changed gears. Insects are placed in transparent tubes that receive vibrational pulses every few minutes, preventing them from falling into deep sleep. After 4 to 12 hours of this sleep deprivation, the team mimics the presence of a host with a pad of heated artificial sweat. In another experiment, a brave volunteer offered a leg to be fed for five minutes by sleep-deprived and well-rested A. aegypti in batches of 10 insects.

In both cases, mosquitoes that have had a complete night’s rest are much more likely to land on the host than those that have been deprived of sleep. And the leg exposed to sleeping mosquitoes performed much better than when exposed to the control group: in eight tests, an average of 77 percent of well-rested mosquitoes went for blood nutrition, compared to only 23 percent of sleepy mosquitoes.

The findings, Rund said, pave the way for research to control mosquito populations and reduce disease using the circadian rhythms of insects.

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