The malaria mosquito, found in all major zoogeographical regions. The adult females transmit a malaria-causing agent when taking blood from vertebrates. The males feed on nectar and plant fluids. The larvae are aquatic, feeding at the water surface using short feeding bristles. (Order: Diptera. Family: Culicidae.)
| iAnopheles Mosquitoes | ||||||||||||
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Anopheles stephensi |
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| Some Species | ||||||||||||
| Anopheles atroparvus Anopheles beklemishevi Anopheles coustani Anopheles crypticus Anopheles culicifacies Anopheles farauti Anopheles fluviatilis Anopheles forattinii Anopheles funestus Anopheles gambiae Anopheles grabhamii Anopheles hailarensis Anopheles halophylus Anopheles hyrcanus Anopheles introlatus Anopheles kosiensis Anopheles latens Anopheles maculipennis Anopheles minimus Anopheles moucheti Anopheles nili Anopheles ovengensis Anopheles pampanae Anopheles peytoni Anopheles quadrimaculatus Anopheles rennellensis Anopheles rivulorum Anopheles stephensi Anopheles triannulatus |
Anopheles is a genus of mosquito (Culicidae).
Some species of Anopheles also can serve as the vectors for canine heartworm Dirofilaria immitis, the Filariidae Wuchereria bancrofti and Brugia malayi, and viruses like the one that is the cause of O'nyong'nyong fever.
Life stages
Like all mosquitoes, anophelines go through four stages in their life cycle: egg, larva, pupa, and adult. The adult stage is when the female Anopheles mosquito acts as malaria vector.
Eggs
Adult females lay 50-200 eggs per oviposition.
Larvae
Mosquito larvae have a well-developed head with mouth brushes used for feeding, a large thorax and a segmented abdomen. In contrast to other mosquitoes, Anopheles larvae lack a respiratory siphon and for this reason position themselves so that their body is parallel to the surface of the water. Larvae of Anopheles mosquitoes have been found in fresh- or salt-water marshes, mangrove swamps, rice fields, grassy ditches, the edges of streams and rivers, and small, temporary rain pools. After a few days as a pupae, the dorsal surface of the cephalothorax splits and the adult mosquito emerges.
Adults
The duration from egg to adult varies considerably among species and is strongly influenced by ambient temperature. Mosquitoes can develop from egg to adult in as little as 5 days but usually take 10-14 days in tropical conditions.
Like all mosquitoes, adult anophelines have slender bodies with 3 sections: head, thorax and abdomen.
Anopheles mosquitoes can be distinguished from other mosquitoes by the palps, which are as long as the proboscis, and by the presence of discrete blocks of black and white scales on the wings.
Adult mosquitoes usually mate within a few days after emerging from the pupal stage.
Malaria transmission and control
Understanding the biology and behavior of Anopheles mosquitoes can help understand how malaria is transmitted and can aid in designing appropriate control strategies. Factors that affect a mosquito's ability to transmit malaria include its innate susceptibility to Plasmodium, its host choice and its longevity. Factors that should be taken into consideration when designing a control program include the susceptibility of malaria vectors to insecticides and the preferred feeding and resting location of adult mosquitoes.
Preferred sources for blood meals
One important behavioral factor is the degree to which an Anopheles species prefers to feed on humans (anthropophily) or animals such as cattle (zoophily).
Once ingested by a mosquito, malaria parasites must undergo development within the mosquito before they are infectious to humans. The time required for development in the mosquito (the extrinsic incubation period) ranges from 10-21 days, depending on the parasite species and the temperature. If a mosquito does not survive longer than the extrinsic incubation period, then she will not be able to transmit any malaria parasites.
It is not possible to measure directly the life span of mosquitoes in nature.
Assuming this is constant through the adult life of a mosquito, less than 10% of female A. If daily survivorship increased to 0.9, over 20% of mosquitoes would survive longer than a 14-day extrinsic incubation period. indoor residual spraying) may actually impact malaria transmission more through their effect on adult longevity than through their effect on the population of adult mosquitoes.
Patterns of feeding and resting
Most Anopheles mosquitoes are crepuscular (active at dusk or dawn) or nocturnal (active at night). Some Anopheles mosquitoes feed indoors (endophagic) while others feed outdoors (exophagic). After blood feeding, some Anopheles mosquitoes prefer to rest indoors (endophilic) while others prefer to rest outdoors (exophilic), though this can differ regionally based on local vector ecotype, and vector chromosomal makeup, as well as housing type and local microclimatic conditions. Biting by nocturnal, endophagic Anopheles mosquitoes can be markedly reduced through the use of insecticide-treated bed nets (ITNs) or through improved housing construction to prevent mosquito entry (e.g.
Insecticide resistance
Insecticide-based control measures (e.g. indoor spraying with insecticides, ITNs) are the principal way to kill mosquitoes that bite indoors. However, after prolonged exposure to an insecticide over several generations, mosquitoes, like other insects, may develop resistance, a capacity to survive contact with an insecticide. Resistance of mosquitoes to some insecticides has been documented with just within a few years after the insecticides were introduced. There are over 125 mosquito species with documented resistance to one or more insecticides. Judicious use of insecticides for mosquito control can limit the development and spread of resistance. It is possible to detect developing resistance in mosquitoes and control programs are well advised to conduct surveillance for this potential problem.
Susceptibility
Some Anopheles species are poor vectors of malaria, as the parasites do not develop well (or at all) within them. It is hoped that some day, genetically modified mosquitoes that are refractory to malaria can replace wild mosquitoes, thereby limiting or eliminating malaria transmission.
Habitat
Although malaria is nowadays limited to tropical areas, most notoriously regions of sub-Saharan Africa, many Anopheles species live in colder lattitudes (see this map from the CDC).
The CDC warns, however, that "Anophelines that can transmit malaria are found not only in malaria-endemic areas, but also in areas where malaria has been eliminated.
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