World Mosquito Day丨Do mosquitoes also have to "take turns"? Let's take a look at the mosquito work schedule

Produced by: Science Popularization China

Author: Yang Cihan (PhD in Biology)

Producer: China Science Expo

As the temperature rises, beautiful skirts and delicious ice cream are getting closer and closer to us, but the ultimate enemy of summer is also quietly approaching, that is, mosquitoes that not only disturb people's dreams but also drink human blood. In every sleepless night due to mosquitoes, we may have thought of a question: do mosquitoes not need to sleep?

Let me tell you a secret today: mosquitoes also take turns to rest and take turns on duty . Without you knowing, the mosquitoes have already had a good sleep, and the mosquitoes that bite you during the day and at night may not be the same species!

(Photo source: veer photo gallery)

The common mosquitoes we see generally belong to the genera of Aedes, Culex and Anopheles, among which Aedes albopictus, Culex tritaeniorhynchus, Culex pipiens pallens (in northern China), Culex pipiens quinquefasciatus (in southern China) and Anopheles sinensis are the most common. The common mosquitoes in cities are Aedes albopictus, Culex pipiens pallens and Culex pipiens quinquefasciatus, while in suburbs and rural areas, Culex tritaeniorhynchus or Anopheles sinensis are the main mosquitoes.

Since male mosquitoes feed on plant juice or nectar, and female mosquitoes need blood to supplement nutrition in order to lay eggs and reproduce offspring, it is the female mosquitoes that bite us. So, when do these female mosquitoes start to forage for food every day? According to research and investigation, different mosquito species have different active time periods every day, that is, different mosquito species have different peak foraging periods every day.

As the main vector of Japanese encephalitis, Culex mosquitoes generally reach their first peak of activity 1-2 hours after sunset (19:00-21:00), which is called the dusk peak. In areas with higher temperatures, the dusk peak can even extend to 23:00. Then the number of active mosquitoes will gradually decrease, and a second peak of activity will form 1-2 hours before sunrise (4:00-6:00), which is called the morning peak. Generally speaking, the dusk peak value will be higher than the morning peak value, that is, the blood-sucking activity of mosquitoes 1-2 hours after sunset will be higher than that of mosquitoes 1-2 hours before sunrise. Outside of the peak period, mosquitoes are basically in a resting state and will not actively seek food.

Culex pipiens pallens

(Image source: Wikipedia)

Aedes albopictus (commonly known as "flower-legged mosquito") can spread a variety of infectious diseases including dengue fever and Zika virus disease. In addition to the dusk and morning peaks, it sucks blood all day long, and there is a phenomenon that it does not suck blood enough once and sucks blood multiple times, resulting in an increase in the number of bites. So when we find that we are bitten several times at once, it is very likely that the culprit is Aedes albopictus. Anopheles sinensis is the main vector of malaria and filarial worms. Its main outdoor foraging peak at night is 19:00-21:00, and there is also a small peak at 4:00-5:00.

Aedes albopictus

(Image source: Wikipedia)

Anopheles sinensis

(Image source: Wikipedia)

So what are the factors that affect the different foraging peaks of mosquitoes? Simply put, they are all affected by environmental factors, among which temperature and light intensity play a big role. Generally, as the temperature and light intensity increase, the activity of mosquitoes also increases accordingly, and their foraging activity increases. In addition, relative humidity and wind speed also have a certain impact on it. As the relative humidity increases and the wind speed increases, the activity of mosquitoes at night will tend to decrease, and rainfall has the weakest impact on it.

In addition to the differences in daily foraging peaks, different mosquito species also appear in different seasons throughout the year. According to statistics, the peak period for mosquitoes is generally concentrated in July and August, but because Aedes albopictus is not as cold-resistant as other mosquito species, it appears later and hibernates for a longer time. Their active period in most parts of my country is from April to October each year, and in some subtropical areas it can be advanced to late March. Similarly, the activities of Culex tritaeniorhynchus and Anopheles sinensis generally begin in May and June, respectively, and basically disappear by late October. Their occurrence and prevalence are greatly affected by temperature.

However, Culex pipiens pallens and Culex pipiens quinquefasciatus are highly cold-resistant and will remain active even in cold weather. Those larger, light yellow mosquitoes that we occasionally see indoors in autumn and winter are most likely these two types of mosquitoes.

Culex pipiens (male on the left, female on the right)

(Image source: Wikipedia)

In addition, have you ever encountered groups of mosquitoes flying up and down together? In fact, this is the male mosquitoes starting to work. Male mosquitoes gather in groups and fly in the air to attract female mosquitoes to fly in for courtship and mating. This phenomenon is called nuptial flight. Different mosquito species have different mating active times. Under natural conditions, the nuptial flight of Anopheles mosquitoes mainly occurs at dusk, especially in the peak period of Anopheles mosquito activity in summer. We can often see groups of mosquitoes flying on both sides of the road or next to trees.

A swarm of mosquitoes flying in mating at dusk

(Image source: pixabay)

However, researchers observed that the mating activities of Aedes albopictus raised in the laboratory mostly occurred during the day, with two peak periods, mainly 3 hours after light and 3 hours before darkness, while the mating peak of Culex pipiens was only 3 hours after darkness. Further research found that this is actually a physiological behavior regulated by genes. Mosquitoes, like humans, have biological clocks, and the nuptial flight behavior of mosquitoes is regulated by the biological clock genes in the mosquitoes, and the biological clock genes of mosquitoes can also integrate exogenous light and temperature signals to coordinately regulate the occurrence of nuptial flights.

In our daily lives, we always feel that mosquitoes are everywhere, and we have inadvertently received the "big red envelope" from mosquitoes. With the development of urbanization, mosquitoes are becoming more and more adapted to coexisting with humans and gradually becoming "domesticated" insects. Since mosquitoes can be used as a vector for a variety of diseases and top the list of the top ten most dangerous animals all year round, mosquito prevention and control is also an important part of daily life. We can reduce the probability of being bitten by understanding the living habits of different mosquitoes, which is also an effective way to reduce risks. The most dangerous enemy is hidden around us, and understanding the enemy is to protect ourselves.

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