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Skip to 0 minutes and 14 secondsWhy, where, and when to Aedes adults bite? It's only females that bite, so that's where we're going to focus on.

Skip to 0 minutes and 23 secondsWhy do Aedes adults bite me? As seen in the previous video about the lifecycle, the female mosquito needs nutrients in the blood in order to produce her eggs. Aedes aegypti females mainly show a preference toward humans whilst they can feed on other animals, blood of other vertebrate species have only been found in small proportions of their blood meals. Host preference is a trait to select a certain blood host species above others. It is determined by external and internal factors. Host preference differs between mosquito species, but also within species and even on the individual level.

Skip to 1 minute and 0 secondsThe unique composition of human blood is associated with Aedes aegypti's preference for humans. Feeding on human blood increases the mosquitoes'fitness, which means it increases their reproductive success. Aedes mosquitoes tend to be quite aggressive biters, which often results in a high biting rate. They will also feed multiple times of different individuals. The human biting rate, which means the number of bites received per hour, is directly related to disease transmission. Another statistic that epidemiologists are interested in, as it is also important to disease transmission, is the entomological inoculation rate. This is calculated as the number of bites a person receives in a given time period multiplied by the proportion of bites that come from infected mosquitoes.

Skip to 1 minute and 49 secondsMosquitoes are attracted to human odours, carbon dioxide, and other compounds produced in the breath, and a mixture of other chemicals produced by the skin and bacteria that live on the skin. Some of these chemicals, such as lactic acid, are attractants, but some are natural repellents. Differences in these compounds between individuals is the main reason some people get bitten more than others. The mosquito's head, which can be seen in the above picture, shows the antennae, which are covered in tiny hairs called sensilla. Olfactory receptor cells that detect odours can be found at the base of these hairs. Scientists can study what odours mosquitoes respond to by connecting microelectrodes to the antennae or cells within the antennae.

Skip to 2 minutes and 37 secondsThis has helped in the identification of new attractants and repellents for many mosquito species in recent years. The host-seeking flight of a mosquito can generally be classified into long, medium, and short-range attraction. Long-distance attraction involves detection of carbon dioxide and other highly volatile chemicals in the body, odour, and breath. Almost all mosquito species use carbon dioxide, which is given off from hosts with breath as an activating and attractive signal. Medium-distance attraction is determined by less volatile compounds that signify the odour of a particular host species. The skin of humans and other vertebrates produced natural chemicals which evaporate into the air and thus give each individual a unique scent. Examples of these volatile chemicals are lactic acid, ammonia, and carboxylic acids.

Skip to 3 minutes and 33 secondsAttraction from a short-distance is determined by the previously mentioned odours, but also by other types of cues, like heat, body moisture, and visual signals.

Skip to 3 minutes and 43 secondsWhere do Aedes adults bite? There are very few studies done on where mosquito species prefer to bite. It is known that Anopheles gambiae is attracted to feet. But for Aedes aegypti, however, preference for a certain body parts remains unclear. One source indicates preference for the head and mainly upper side of the body. But in reality, they can bite you anywhere.

Skip to 4 minutes and 8 secondsSo here's the last question: when do Aedes adults bite me? Aedes aegypti is generally found to be most active during the day and early evening. However, there has been some evidence for different biting times in different populations and locations. Some studies have even observed night-time feeding. Natural resting places are found outside in vegetation, where it is cool and shady. But most mosquitoes, however, are found indoors. They have adapted to a more urban lifestyle because of human presence. They can, for example, be found in cupboards and other dark places inside houses.

Skip to 4 minutes and 43 secondsBecause they are mainly active during the day, traditional mosquito control methods, such as sleeping under a bed net at night, are not normally recommend for Aedes aegypti control, but should still be used, especially if sleeping during the day. Other methods that can be used during the day are needed as well, and these will be discussed later in the course.

Why, where, and when do Aedes bite me?

In this step Tessa Visser continues her examination of Aedes adults and highlights an aspect of their relationship with humans: biting!

For what reasons do Aedes aegypti adults prefer to bite humans? Do they show any preference for particular parts of the body? In what parts of the day or night are they most active? Being better informed about the why, where, and when of biting can help us to better protect ourselves, and we will cover this in greater detail in Week 3 of the course.

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This video is from the free online course:

Preventing the Zika Virus: Understanding and Controlling the Aedes Mosquito

London School of Hygiene & Tropical Medicine

Course highlights Get a taste of this course before you join: