Mosquitoes

Mosquitoes are common insects from the family Culicidae (Order Diptera or ‘true flies’) which have mouthparts adapted for piercing and sucking. There are more than 3000 species of mosquito in the world.

Mosquitoes undergo a complete metamorphosis, meaning that they have a four stage life-cycle which includes eggs, larvae, pupae and adults. Adults lay eggs on or near standing water and the larvae complete their development in the aquatic environment. Adults that emerge usually remain within a one mile radius of this breeding site. The lifespan of a female mosquito, from egg through adult, varies according to ambient temperature and species, but can be up to about 100 days.

Male mosquitoes live on nectar and plant juices whilst female mosquitoes supplement their diet with blood-meals in order to produce eggs. Mosquitoes have poor eyesight but females are able locate a blood source through a combination of scent, sight and heat. Humans are the preferred blood meal source for only a relatively few mosquito species, with other mammals, reptiles and birds also representing sources for other species. Female mosquitoes inject saliva into the bite site in order to prevent coagulation of the blood during feeding. It is through this process that pathogenic organisms such as viruses and protozoa can be transmitted.

After taking a blood meal female mosquitoes must rest in order to digest the blood and generate eggs. This resting period can vary but is usually about 2 to 3 days in tropical conditions. After laying eggs the female will resume host seeking behaviour.

The age of a mosquito is an important factor in its ability to transmit disease.

The three most important mosquitoes which impact man are from the genera Anopheles, Aedes and Culex. These are collectively responsible for the transmission of malaria, dengue, filariasis, chikungunya, Japanese encephalitis and many other viral diseases.

Different species of mosquito can have different behaviours in terms of biting preferences and resting sites (e.g. indoors or outdoors) and host preferences (e.g. humans vs animals). These factors are important in the choice of intervention method for disease vectors. For example, if the principal vector species within a given area is predominantly indoor resting then this suggests that indoor residual spraying could be an effective intervention technique. If a species feeds and rests indoors late at night then the use of insecticide treated bed nets should be appropriate.

An illustration of this variety can be seen in the table below for a selection of important Anopheles species.

Species	Region found	Biting site	Resting site	Host preference	Peak biting time	Breeding sites
Anopheles gambiae	Africa	Indoors	Mostly indoors	Human	Late	Sunlit shallow temporary water bodies, rice fields
Anopheles arabiensis	Africa	Indoors and outdoors	Indoors and outdoors	Human and animal	Late	Temporary water bodies, rice fields
Anopheles culicifacies	India/ Asia	Indoors and outdoors	Indoors	Mainly animal	21.00 to 23.00 hours	Various clean and polluted water bodies
Anopheles dirus	Asia	Indoors and outdoors	Outdoors	Human	Late	Small shaded water bodies in forested areas
Anopheles sundaicus	South East Asia	Indoors and outdoors	Indoors and outdoors	Human and animal	All night	Brackish water in coastal areas
Anopheles albimanus	Central America	Outdoors	Outdoors and Indoors	Human and animal	Evening	Open, sunlit clear water
Anopheles stephensi	Asia and middle East	Indoors and outdoors	Indoors	Animal	Before midnight	Gutters, wells, rainwater tanks, grassy pools