5.7 Behaviour of mosquitoes that transmit malaria

To help you work effectively to prevent malaria transmission, you need to learn about the most important behaviours of a malaria-transmitting mosquito.

Female mosquitoes can feed on animals and humans. Most species show a preference for certain animals or for humans. They are attracted by the body odours, carbon dioxide and heat emitted from the animal or person. Species of mosquitoes that prefer to feed on animals are usually not very effective in transmitting diseases from person to person. Those who prefer to take human blood are the most dangerous as they are more likely to transmit diseases between people. One of the reasons why An. arabiensis mosquitoes are better vectors of malaria than other mosquitoes is that they feed mostly on humans and very little on cattle.

Most anopheline mosquitoes bite at night. Some species bite just after sunset while others bite later, around midnight or in the early morning. Those that bite in the early evening may be more difficult to avoid than species that feed at night.

Some species prefer to feed in forests, some outside houses and others indoors. Mosquitoes that enter a house usually rest on a wall, under furniture or on clothes hanging in the house. Mosquitoes that bite outside usually rest on plants, in holes, in trees, or on the ground, or in other cool dark places. Mosquitoes that rest indoors are the easiest to control, as you will learn in Study Session 6.

Because digestion of the blood-meal and development of the eggs takes 2‒3 days, a blood-fed mosquito looks for a safe resting place that is shaded and offers protection from drying out. Some species prefer to rest in houses or cattle sheds, while others prefer to rest outdoors, on vegetation or at other natural sites. After the mosquito takes a blood meal indoors, it usually rests inside the house, some for a short period and some for days. Mosquitoes do not usually bite while eggs are developing.

Adult females can normally live between 20 days and one month. The average survival is much shorter at 6‒9 days. The average life-span of the female has direct relevance to its efficiency as a malaria vector, because it has to live long enough to transmit malaria (i.e. long enough for the parasite to complete its life cycle in the mosquito host, approximately 10 days).

On average, the flight range of adult Anopheles is between a few hundred metres and 2 kilometres. Therefore water collections very close to houses are more important sources of vectors than those located far away from houses. As you will see in Study Session 9, this is something that could be important when considering vector control measures to prevent vectors from breeding in water collections.

Summary of Study Session 5