Anopheles

Anopheles, (genus Anopheles), genus of more than 450 species of mosquitoes, some members of which are serious biting nuisances and vectors of disease, sometimes transmitting potentially deadly pathogens (disease-causing organisms) to humans and other animals. Anopheles mosquitoes are the only known carriers of malaria and can also transmit encephalitis and lymphatic filariasis to humans and dog heartworm to dogs and other mammals. Given that malaria is responsible for more than 600,000 deaths every year, control of the 30–40 Anopheles species largely responsible for the disease’s transmission is a major public health priority in many places around the world.

Anopheles mosquitoes are found nearly worldwide, especially in tropical and subtropical regions, and have been introduced to temperate regions. They are uncommon in extremely cold regions and are not found in Antarctica.

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Physical description

Anopheles mosquitoes are typically smaller than other mosquitoes, with spotted coloring on the wings due to colored scales. The adults have a slender elongated body with long fragile-looking legs and elongated piercing mouthparts. Tactile feelers on either side of the proboscis, called palps, are a distinguishing feature of Anopheles species.

Anopheles mosquitoes are easily recognized from their resting position, in which the proboscis, head, and body are held in a straight line with one another but at an angle to the surface. Other mosquito genera such as Aedes have their body parallel to the ground when in a resting position.

Life cycle and natural history

Anopheles mosquitoes are typically active at dusk or at night. Only the females are biting insects and require the proteins obtained from a blood meal to mature their eggs. Interestingly, some species have adapted to human measures such as mosquito nets and consume blood during the day as well. The majority of Anopheles species do not bite humans and use the blood of birds, nonhuman mammals, reptiles, or even amphibians.

The female rests for two to three days after a full blood meal, during which time the blood is digested and the fertilized eggs develop within her body. She then deposits her eggs singly on the water surface. Egg laying usually occurs in still water such as in puddles or ponds and even in water storage pots, though many species lay their eggs in water containing heavy vegetation, such as marshes and rice paddies. The eggs hatch after one or two days.

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mosquito: Anopheles mosquitoes

Anopheles larvae lie parallel to the water surface and breathe through posterior spiracular plates on the abdomen instead of through a tube, as do most other mosquito larvae. After a period of 10–12 days, the adult mosquito emerges from the final pupal stage. Female adults are capable of consuming blood within three days, and the entire life cycle is from 18 days to several weeks, depending on the species and environmental conditions. Males typically feed on flower nectar and are known pollinators.

(Read Britannica’s essay “What Purpose Do Mosquitoes Serve in Ecosystems?”)

Malaria

Malaria is caused by five related protozoan parasites spread by the bite of infected female Anopheles mosquitoes. When engaged in a blood meal, an infected mosquito injects immature forms of the parasite into the host’s bloodstream. The parasites are then transported to the host’s liver, where they mature and multiply. They eventually reenter the bloodstream, invading red blood cells and destroying them in the process.

The British doctor Sir Ronald Ross was the first to detect the malarial parasite in the gastrointestinal tract of Anopheles mosquitoes. This led to the realization that malaria was transmitted by Anopheles mosquitoes and laid the foundation for combating the disease.

The World Health Organization (WHO) advocates for prevention of malaria through medicines and avoidance of mosquito bites as well as through eradication of the Anopheles mosquito vectors. However, progress is threatened by increasing resistance to insecticides and the advance of vector species into novel, formerly inhospitable areas because of climate change.