Mosquito bites
Why do we experience more mosquito bites at night?
K. ANANTHANARAYANAN, Kanyakumari, Tamil Nadu
Adult mosquitoes usually feed on nectar, juice and decaying matter, which serve as the energy sources. However, female mosquitoes need to ingest the blood meal that serves as the protein source for developing the eggs.
Hence, they usually feed on humans and other animals including frog, birds and cattle. Most mosquito species are crepuscular (active at dawn and dusk). However, they are all not active at night.
For instance, Aedes mosquitoes that transmit virus diseases such as dengue fever, yellow fever and chikungunya are active during the day time. On the other hand, Anopheles mosquitoes, which transmit malaria, are active during the night time.
The predominant flight and feeding activities of Anopheles mosquitoes during the night time is regulated by the in-built circadian rhythm, which is driven by a circadian clock. These rhythms are adjusted by the external cues, especially the daylight.
Hence, it is their body clock that makes them active during the night time like in other nocturnal animals. The mosquitoes also use the carbon dioxide that emanates from the humans during expiration, to locate the host.
Since the carbon dioxide is present in abundance in the environment, an extremely higher concentration of carbon dioxide combined with the host odour is required to track the blood hosts.
The humidity also helps them to easily locate their hosts. The thermal receptors present in the antennae enable the mosquitoes to locate the blood, when they are few metres away from their hosts. However, the range of these receptors substantially increases under higher humidity. Thus, the environmental cues and the body clock direct the Anopheles mosquitoes to be active during the night time.
DR. R. SRINIVASAN
Entomologist, AVRDC
The World Vegetable Center
Tainan, Taiwan Republic of China
