''Anopheles'' (
) is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
mosquito first described and named by
J. W. Meigen in 1818. About 460 species are recognised; while over 100 can transmit human
malaria
Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. S ...
, only 30–40 commonly transmit parasites of the genus ''
Plasmodium
''Plasmodium'' is a genus of unicellular eukaryotes that are obligate parasites of vertebrates and insects. The life cycles of ''Plasmodium'' species involve development in a blood-feeding insect host which then injects parasites into a vert ...
'', which cause malaria in humans in
endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
areas. ''
Anopheles gambiae
The ''Anopheles gambiae'' complex consists of at least seven morphologically indistinguishable species of mosquitoes in the genus ''Anopheles''. The complex was recognised in the 1960s and includes the most important vectors of malaria in sub- ...
'' is one of the best known, because of its predominant role in the transmission of the most dangerous malaria parasite species (to humans) – ''
Plasmodium falciparum
''Plasmodium falciparum'' is a Unicellular organism, unicellular protozoan parasite of humans, and the deadliest species of ''Plasmodium'' that causes malaria in humans. The parasite is transmitted through the bite of a female ''Anopheles'' mosqu ...
''.
The name comes from the
Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...
word 'useless', derived from , 'not', 'un-' and 'profit'.
Mosquitoes in other genera (''
Aedes'', ''
Culex'', ''
Culiseta
''Culiseta'' is a genus (biology), genus of mosquitoes. Most ''Culiseta'' species are cold-adapted, and only occur in warmer climates during the colder parts of the year or at higher elevations where temperatures are lower. Species found in South ...
'', ''
Haemagogus
''Haemagogus'' is a genus of mosquitoes in the dipteran family Culicidae. They mainly occur in Central America and northern South America (including Trinidad), although some species inhabit forested areas of Brazil, and range as far as northern A ...
'', and ''
Ochlerotatus'') can also serve as
vectors of disease agents, but not human malaria.
Evolution
The ancestors of ''
Drosophila
''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species ...
'' and the mosquitoes diverged .
The
culicine and ''Anopheles'' clades of mosquitoes diverged between and .
The Old and New World ''Anopheles'' species subsequently diverged between and .
''
Anopheles darlingi
''Anopheles darlingi'', the American malaria mosquito, is a species of mosquito in the family Culicidae. ''A. darlingi'' is one of the major species of mosquito known to be responsible for malaria in the Amazonian regions. It has a wide range of ...
'' diverged from the African and Asian malaria vectors ~.
[Marinotti O, Cerqueira GC, de Almeida LG, Ferro MI, Loreto EL, Zaha A, Teixeira SM, Wespiser AR, Almeida E Silva A, Schlindwein AD, Pacheco AC, da Silva AL, Graveley BR, Walenz BP, de Araujo Lima B, Ribeiro CA, Nunes-Silva CG, de Carvalho CR, de Almeida Soares CM, de Menezes CB, Matiolli C, Caffrey D, Araújo DA, de Oliveira DM, Golenbock D, Grisard EC, Fantinatti-Garboggini F, de Carvalho FM, Barcellos FG, Prosdocimi F, May G, de Azevedo GM Junior, Guimarães GM, Goldman GH, Padilha IQ, Batista JD, Ferro JA, Ribeiro JM, Fietto JL, Dabbas KM, Cerdeira L, Agnez-Lima LF, Brocchi M, de Carvalho MO, Teixeira MD, de Mascena Diniz Maia M, Goldman MH, Cruz Schneider MP, Felipe MS, Hungria M, Nicolás MF, Pereira M, Montes MA, Cantão ME, Vincentz M, Rafael MS, Silverman N, Stoco PH, Souza RC, Vicentini R, Gazzinelli RT, Neves RD, Silva R, Astolfi-Filho S, Maciel TE, Urményi TP, Tadei WP, Camargo EP, de Vasconcelos AT. The genome of ''Anopheles darlingi'', the main neotropical malaria vector. Nucleic Acids Res] The ''
Anopheles gambiae
The ''Anopheles gambiae'' complex consists of at least seven morphologically indistinguishable species of mosquitoes in the genus ''Anopheles''. The complex was recognised in the 1960s and includes the most important vectors of malaria in sub- ...
'' and ''
Anopheles funestus'' clades diverged between and . A molecular study of several genes in seven species has provided additional support for an expansion of this genus during the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
period.
The ''Anopheles'' genome, at 230–284 million base pairs (Mbp), is comparable in size to that of ''
Drosophila
''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species ...
'', but considerably smaller than those found in other culicine genomes (528 Mbp–1.9 Gbp). Like most culicine species, the genome is
diploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
with six
chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
s.
The only known
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
s of this genus are those of ''Anopheles (Nyssorhynchus) dominicanus''
Zavortink & Poinar contained in
Dominican amber
Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In Ma ...
from the Late
Eocene
The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
( to ) and ''
Anopheles rottensis
''Anopheles'' () is a genus of mosquito first described and named by J. W. Meigen in 1818. About 460 species are recognised; while over 100 can transmit human malaria, only 30–40 commonly transmit parasites of the genus ''Plasmodium'', which c ...
''
Statz contained in
German
German(s) may refer to:
* Germany (of or related to)
**Germania (historical use)
* Germans, citizens of Germany, people of German ancestry, or native speakers of the German language
** For citizens of Germany, see also German nationality law
**Ger ...
amber from the Late
Oligocene
The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
( to ).
Systematics
The genus ''Anopheles'' Meigen (nearly worldwide distribution) belongs to the subfamily Anophelinae together with another two genera: ''
Bironella
''Bironella'' is one of the three mosquito genera in the subfamily Anophelinae. The other two genera are ''Anopheles'' Meigen (nearly worldwide distribution) and ''Chagasia'' Cruz (Neotropics).
''Bironella'' is found in Australia but one species ...
'' Theobald (
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
only) and ''
Chagasia'' Cruz (
Neotropics). The taxonomy remains incompletely settled. Classification into species is based on morphological characteristics – wing spots, head anatomy, larval and pupal anatomy, chromosome structure, and more recently, on DNA sequences. In the taxonomy published by Harbach et al in 2016, it was shown that three species of ''Bironella: confusa, gracilis,'' and ''hollandi'' are phylogenetically similar ''Anopheles kyondawensis'' than other ''Bironella'' species. The same phylogeny also argues that, based on genetic similarity, ''Anopheles implexus'' is actually divergent from the common ancestor to the ''Anopheles'' genus, raising new questions regarding taxonomy and classification.
The genus has been subdivided into seven subgenera based primarily on the number and positions of specialized
setae
In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms.
Animal setae
Protostomes
Annelid setae are stiff bristles present on the body. Th ...
on the
gonocoxites of the
male
Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization.
A male organism cannot reproduce sexually without access to ...
genitalia. The system of subgenera originated with the work of Christophers, who in 1915 described three subgenera: ''Anopheles'' (widely distributed), ''Myzomyia'' (later renamed ''
Cellia'') (
Old World
The "Old World" is a term for Afro-Eurasia that originated in Europe , after Europeans became aware of the existence of the Americas. It is used to contrast the continents of Africa, Europe, and Asia, which were previously thought of by the ...
) and ''Nyssorhynchus'' (Neotropical). ''Nyssorhynchus'' was first described as ''Lavernia'' by
Frederick Vincent Theobald.
Frederick Wallace Edwards in 1932 added the subgenus ''
Stethomyia'' (Neotropical distribution). ''
Kerteszia
The subgenus ''Kerteszia'' are Neotropical anopheline mosquitoes originally described in 1905 by Frederick V. Theobald as genus ''Kertészia'' with ''Kertészia boliviensis'' as the type species.Theobald, F. V. 1905. A catalogue of the Culicidae ...
'' was also described by Edwards in 1932, but then recognised as a subgrouping of ''Nyssorhynchus''. It was elevated to subgenus status by Komp in 1937, and it is also found in the Neotropics. Two additional subgenera have since been recognised: ''
Baimaia'' (Southeast Asia only) by Harbach ''et al.'' in 2005 and ''
Lophopodomyia'' (Neotropical) by Antunes in 1937.
Two main groupings within the genus ''Anopheles'' are used: one formed by the ''Celia'' and ''Anopheles'' subgenera and a second by ''
Kerteszia
The subgenus ''Kerteszia'' are Neotropical anopheline mosquitoes originally described in 1905 by Frederick V. Theobald as genus ''Kertészia'' with ''Kertészia boliviensis'' as the type species.Theobald, F. V. 1905. A catalogue of the Culicidae ...
'', ''Lophopodomyia'' and ''Nyssorhynchus''. Subgenus ''Stethomyia'' is an outlier with respect to these two taxa. Within the second group, ''
Kerteszia
The subgenus ''Kerteszia'' are Neotropical anopheline mosquitoes originally described in 1905 by Frederick V. Theobald as genus ''Kertészia'' with ''Kertészia boliviensis'' as the type species.Theobald, F. V. 1905. A catalogue of the Culicidae ...
'' and ''Nyssorhynchus'' appear to be sister taxa.
The number of species currently recognised within the subgenera is given here in parentheses: ''Anopheles'' (206 species), ''Baimaia'' (1), ''Cellia'' (216), ''
Kerteszia
The subgenus ''Kerteszia'' are Neotropical anopheline mosquitoes originally described in 1905 by Frederick V. Theobald as genus ''Kertészia'' with ''Kertészia boliviensis'' as the type species.Theobald, F. V. 1905. A catalogue of the Culicidae ...
'' (12), ''Lophopodomyia'' (6), ''Nyssorhynchus'' (34) and ''Stethomyia'' (5).
Taxonomic units between subgenus and species are not currently recognised as official zoological names. In practice, a number of taxonomic levels have been introduced. The larger subgenera (''Anopheles'', ''Cellia'' and ''Nyssorhynchus'') have been subdivided into sections and series which in turn have been divided into groups and subgroups. Below subgroup but above species level is the species complex. Taxonomic levels above species complex can be distinguished on morphological grounds. Species within a species complex are either morphologically identical or extremely similar and can only be reliably separated by microscopic examination of the chromosomes or DNA sequencing. The classification continues to be revised.
Subgenus ''Nyssorhynchus'' has been divided in three sections: ''Albimanus'' (19 species), ''Argyritarsis'' (11 species) and ''Myzorhynchella'' (4 species). The ''Argyritarsis'' section has been subdivided into ''Albitarsis'' and ''Argyritarsis'' groups.
The ''Anopheles'' group was divided by Edwards into four series: ''Anopheles'' (worldwide), ''Myzorhynchus'' (Palearctic, Oriental, Australasian and Afrotropical), ''Cycloleppteron'' (Neotropical) and ''Lophoscelomyia'' (Oriental); and two groups, ''Arribalzagia'' (Neotropical) and ''Christya'' (Afrotropical). Reid and Knight (1961) modified this classification and consequently subdivided the subgenus ''Anopheles'' into two sections, ''Angusticorn'' and ''Laticorn'' and six series. The Arribalzagia and Christya Groups were considered to be series. The Laticorn Section includes the ''Arribalzagia'' (24 species), ''Christya'' and ''Myzorhynchus'' series. The ''Angusticorn'' section includes members of the ''Anopheles'', ''Cycloleppteron'' and ''Lophoscelomyia'' series.
All species known to carry human malaria lie within either the ''Myzorhynchus'' or the ''Anopheles'' series.
Life stages
Like all mosquitoes, anophelines go through four stages in their life cycles:
egg
An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...
,
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
,
pupa
A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their ...
, and
imago
In biology, the imago (Latin for "image") is the last stage an insect attains during its metamorphosis, its process of growth and development; it is also called the imaginal stage, the stage in which the insect attains maturity. It follows the f ...
. The first three stages are aquatic and together last 5–14 days, depending on the species and the ambient temperature. The adult stage is when the female ''Anopheles'' mosquito acts as
malaria
Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. S ...
vector. The adult females can live up to a month (or more in captivity), but most probably do not live more than two weeks in nature.
Eggs
![Anopheles egg 2](https://upload.wikimedia.org/wikipedia/commons/a/aa/Anopheles_egg_2.jpg)
Adult females lay 50–200 eggs per
oviposition
The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typical ...
. The eggs are quite small (about 0.5 × 0.2 mm). Eggs are laid singly and directly on water. They are unique in that they have floats on either side. Eggs are not resistant to drying and hatch within 2–3 days, although hatching may take up to 2–3 weeks in colder climates.
Larvae
![Anopheles Culex larvae feeding position-USDA](https://upload.wikimedia.org/wikipedia/commons/b/b0/Anopheles_Culex_larvae_feeding_position-USDA.jpg)
The mosquito larva has a well-developed head with mouth brushes used for feeding, a large
thorax
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...
and a nine-segment
abdomen
The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...
. It has no legs. In contrast to other mosquitoes, the ''Anopheles'' larva lacks a respiratory siphon, so it positions itself so that its body is parallel to the surface of the water.
In contrast, the feeding larva of a nonanopheline mosquito species attaches itself to the water surface with its posterior siphon, with its body pointing downwards.
Larvae breathe through
spiracle Spiracle or spiraculum may refer to:
* Spiracle (arthropods), opening in the exoskeletons of some arthropods
* Spiracle (vertebrates), openings on the surface of some vertebrates
* Spiraculum, a genus of land snails in family Cyclophoridae
Cycl ...
s located on the eighth abdominal segment, so must come to the surface frequently. The larvae spend most of their time feeding on
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
,
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
, and other microorganisms in the surface microlayer. They dive below the surface only when disturbed. Larvae swim either by jerky movements of the entire body or through
propulsion
Propulsion is the generation of force by any combination of pushing or pulling to modify the translational motion of an object, which is typically a rigid body (or an articulated rigid body) but may also concern a fluid. The term is derived from ...
with the mouth brushes.
Larvae develop through four stages, or
instar
An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ass ...
s, after which they
metamorphose into
pupae
A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their ...
. At the end of each instar, the larvae molt, shedding their exoskeletons, or skin, to allow for further growth.
First-stage larvae are about 1 mm in length; fourth-stage larvae are normally 5–8 mm in length.
The process from egg-laying to emergence of the adult is temperature dependent, with a minimum time of seven days.
The larvae occur in a wide range of habitats, but most species prefer clean, unpolluted water. Larvae of ''Anopheles'' mosquitoes have been found in freshwater or saltwater marshes, mangrove swamps, rice fields, grassy ditches, the edges of streams and rivers, and small, temporary rain pools. Many species prefer habitats with vegetation. Others prefer habitats with none. Some breed in open, sun-lit pools, while others are found only in shaded breeding sites in forests. A few species breed in tree holes or the leaf axils of some plants.
Pupae
The pupa (also known as the tumbler) is comma-shaped when viewed from the side. The head and
thorax
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...
are merged into a
cephalothorax
The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...
with the abdomen curving around underneath. As with the larvae, pupae must come to the surface frequently to breathe, which they do through a pair of respiratory trumpets on their cephalothoraces. After a few days as a pupa, the dorsal surface of the cephalothorax splits and the adult mosquito emerges.
The pupal stage lasts around 2–3 days in temperate areas.
Adults
![Anopheles Culex adult resting position-USDA](https://upload.wikimedia.org/wikipedia/commons/a/a0/Anopheles_Culex_adult_resting_position-USDA.jpg)
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 five days, but it can take 10–14 days in tropical conditions.
Like all mosquitoes, adult ''Anopheles'' species have slender bodies with three sections: head, thorax and abdomen.
The head is specialized for acquiring sensory information and for feeding. It contains the eyes and a pair of long, many-segmented
antennae. The antennae are important for detecting host odors, as well as odors of breeding sites where females lay eggs. The head also has an elongated, forward-projecting
proboscis
A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elong ...
used for feeding, and two
maxillary palps.
These palps also carry the receptors for
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
, a major attractant for the location of the mosquito's host.
The
thorax
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...
is specialized for locomotion. Three pairs of legs and a pair of wings are attached to the thorax.
The abdomen is specialized for food digestion and egg development. This segmented body part expands considerably when a female takes a blood meal. The blood is digested over time, serving as a source of
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
for the production of eggs, which gradually fill the
abdomen
The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...
.
''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. Adults can also be identified by their typical resting position: males and females rest with their abdomens sticking up in the air rather than parallel to the surface on which they are resting.
Adult mosquitoes usually mate within a few days after emerging from the pupal stage. In most species, the males form large
swarms, usually around dusk, and the females fly into the swarms to mate.
![Anopheles female Turkhud](https://upload.wikimedia.org/wikipedia/commons/3/39/Anopheles_female_Turkhud.png)
Males live for about a week, feeding on
nectar
Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists ...
and other sources of
sugar
Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...
. Males cannot feed on blood, as it appears to produce toxic effects and kills them within a few days, around the same lifespan as a water-only diet. Females will also feed on sugar sources for energy, but usually require a blood meal for the development of eggs. After obtaining a full blood meal, the female will rest for a few days while the blood is digested and eggs are developed. This process depends on the temperature, but usually takes 2–3 days in tropical conditions. Once the eggs are fully developed, the female lays them and resumes host-seeking.
The cycle repeats itself until the female dies. While females can live longer than a month in captivity, most do not live longer than one to two weeks in nature. Their lifespans depend on temperature, humidity, and their ability to successfully obtain a blood meal while avoiding host defenses.
In a study by the
London School of Hygiene & Tropical Medicine researchers found that female mosquitoes carrying malaria parasites are significantly more attracted to human breath and odours than uninfected mosquitoes. The research team infected laboratory-raised ''
Anopheles gambiae
The ''Anopheles gambiae'' complex consists of at least seven morphologically indistinguishable species of mosquitoes in the genus ''Anopheles''. The complex was recognised in the 1960s and includes the most important vectors of malaria in sub- ...
'' mosquitoes with ''
Plasmodium
''Plasmodium'' is a genus of unicellular eukaryotes that are obligate parasites of vertebrates and insects. The life cycles of ''Plasmodium'' species involve development in a blood-feeding insect host which then injects parasites into a vert ...
'' parasites, leaving a control group uninfected. Then tests were run on the two groups to record their attraction to human smells. Female mosquitoes are particularly drawn to foot odours, and one of the tests showed infected mosquitoes landing and biting a prospective host repeatedly. The team speculates that the parasite improves the mosquitoes' sense of smell. It may also reduce its risk aversion.
Habitat
Although malaria is nowadays limited to tropical areas, most notoriously the regions of sub-Saharan Africa, many ''Anopheles'' species live in colder latitudes (se
this mapfrom the CDC). Indeed, malaria outbreaks have, in the past, occurred in colder climates, for example during the construction of the
Rideau Canal
The Rideau Canal, also known unofficially as the Rideau Waterway, connects Canada's capital city of Ottawa, Ontario, to Lake Ontario and the Saint Lawrence River at Kingston. It is 202 kilometres long. The name ''Rideau'', French for "curtain", ...
in Canada during the 1820s.
[ Since then, the ''Plasmodium'' parasite (not the ''Anopheles'' mosquito) has been eliminated from first world countries.
The CDC warns, however, that "''Anopheles'' that can transmit malaria are found not only in malaria-endemic areas, but also in areas where malaria has been eliminated. The latter areas are thus constantly at risk of reintroduction of the disease.
]
Susceptibility to become a vectorous disease
Some species are poor vectors of malaria
Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. S ...
, as the parasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
s do not develop well (or at all) within them. There is also variation within species. In the laboratory, it is possible to select strains of ''A. gambiae'' that are refractory
In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase, ...
to infection by malaria
Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. S ...
parasites. These refractory strains have an immune
In biology, immunity is the capability of multicellular organisms to resist harmful microorganisms. Immunity involves both specific and nonspecific components. The nonspecific components act as barriers or eliminators of a wide range of pathogens ...
response that encapsulates and kills the parasites after they have invaded the mosquito's stomach wall. Scientists are studying the genetic mechanism for this response. Genetically modified mosquitoes refractory to malaria possibly could replace wild mosquitoes, thereby limiting or eliminating malaria transmission.
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 affecting a mosquito's facility to transmit malaria include its innate susceptibility to ''Plasmodium
''Plasmodium'' is a genus of unicellular eukaryotes that are obligate parasites of vertebrates and insects. The life cycles of ''Plasmodium'' species involve development in a blood-feeding insect host which then injects parasites into a vert ...
'', 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 insecticide
Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to b ...
s and the preferred feeding and resting location of adult mosquitoes.
On December 21, 2007, a study published in PLoS Pathogens
''PLOS Pathogens'' is a peer-reviewed open-access medical journal. All content in ''PLOS Pathogens'' is published under the Creative Commons "by-attribution" license.
''PLOS Pathogens'' began operation in September 2005. It was the fifth journal o ...
found the hemolytic C-type lectin
Lectins are carbohydrate-binding proteins that are highly specific for sugar groups that are part of other molecules, so cause agglutination of particular cells or precipitation of glycoconjugates and polysaccharides. Lectins have a role in rec ...
CEL-III from ''Cucumaria echinata'', a sea cucumber
Sea cucumbers are echinoderms from the class Holothuroidea (). They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of holothuria ...
found in the Bay of Bengal
The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...
, impaired the development of the malaria parasite when produced by transgenic ''A. stephensi''.[ This could potentially be used to control malaria by spreading genetically modified mosquitoes refractory to the parasites, although numerous scientific and ethical issues must be overcome before such a control strategy could be implemented.
]
Preferred sources for blood meals
One important behavioral factor is the degree to which an ''Anopheles'' species prefers to feed on humans (anthropophily
In parasitology, anthropophilia, from the Greek ἅνθρωπος (anthrōpos, "human being") and φιλία (philia, "friendship" or "love"), is a preference of a parasite
Parasitism is a close relationship between species, where one o ...
) or animals such as cattle or birds (zoophily). Anthropophilic ''Anopheles'' are more likely to transmit the malaria parasites from one person to another. Most ''Anopheles'' mosquitoes are not exclusively anthropophilic or zoophilic, including the primary malaria vector in the western United States, ''A. freeborni''. However, the primary malaria vectors in Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, ''A. gambiae'' and ''A. funestus'', are strongly anthropophilic and, consequently, are two of the most efficient malaria vectors in the world.
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 lifespans of mosquitoes in nature, but indirect estimates of daily survivorship have been made for several ''Anopheles'' species. Estimates of daily survivorship of ''A. gambiae'' in Tanzania
Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands and ...
ranged from 0.77 to 0.84, meaning at the end of one day, between 77% and 84% will have survived.
Assuming this survivorship is constant through the adult life of a mosquito, less than 10% of female ''A. gambiae'' would survive longer than a 14-day extrinsic incubation period. If daily survivorship increased to 0.9, over 20% of mosquitoes would survive longer than the same period. Control measures that rely on insecticide
Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to b ...
s (e.g. indoor residual spraying
Indoor residual spraying or IRS is the process of spraying the inside of dwellings with an insecticide to kill mosquitoes that spread malaria. A dilute solution of insecticide is sprayed on the inside walls of certain types of dwellings—those w ...
) may actually impact malaria transmission
Transmission may refer to:
Medicine, science and technology
* Power transmission
** Electric power transmission
** Propulsion transmission, technology allowing controlled application of power
*** Automatic transmission
*** Manual 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
In zoology, a crepuscular animal is one that is active primarily during the twilight period, being matutinal, vespertine, or both. This is distinguished from diurnal and nocturnal behavior, where an animal is active during the hours of daylig ...
(active at dusk or dawn) or nocturnal
Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.
Nocturnal creatures generally have highly developed sens ...
(active at night). Some feed indoors (endophagic), while others feed outdoors (exophagic). After feeding, some blood 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
Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to b ...
-treated bed nets or through improved housing construction to prevent mosquito entry (e.g. window screen
A window screen (also known as insect screen, bug screen, fly screen, flywire, wire mesh, or window net) is designed to cover the opening of a window. It is usually a mesh made of metal, fiberglass, fibreglass, plastic wire, or other pieces of ...
s). Endophilic mosquitoes are readily controlled by indoor spraying of residual insecticides. In contrast, exophagic/exophilic vectors are best controlled through source reduction (destruction of the breeding sites).
Gut flora
Because transmission of disease by the mosquito requires ingestion of blood, the gut flora may have a bearing on the success of infection of the mosquito host. This aspect of disease transmission has not been investigated until recently.[ The larval and pupal gut is largely colonized by photosynthetic cyanobacteria, while in the adult, ]Pseudomonadota
Pseudomonadota (synonym Proteobacteria) is a major phylum of Gram-negative bacteria. The renaming of phyla in 2021 remains controversial among microbiologists, many of whom continue to use the earlier names of long standing in the literature. The ...
and Bacteroidota
The phylum Bacteroidota (synonym Bacteroidetes) is composed of three large classes of Gram-negative, nonsporeforming, anaerobic or aerobic, and rod-shaped bacteria that are widely distributed in the environment, including in soil, sediments, and ...
predominate. Blood meals drastically reduce the diversity of organisms and favor enteric bacteria.
Insecticide resistance
Insecticide
Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to b ...
-based control measures (e.g. indoor spraying with insecticides, bed nets) are the principal ways to kill mosquitoes that bite indoors. However, after prolonged exposure to an insecticide over several generations, mosquito populations, like those of other insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...
s, may evolve resistance, a capacity to survive contact with an insecticide. Since mosquitoes can have many generations per year, high levels of resistance can evolve very quickly. Resistance of mosquitoes to some insecticides has been documented with just within a few years after the insecticides were introduced. Over 125 mosquito species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
have documented resistance to one or more insecticides. The evolution of resistance to insecticides used for indoor residual spraying was a major impediment during the Global Malaria Eradication Campaign
Global means of or referring to a globe and may also refer to:
Entertainment
* Global (Paul van Dyk album), ''Global'' (Paul van Dyk album), 2003
* Global (Bunji Garlin album), ''Global'' (Bunji Garlin album), 2007
* Global (Humanoid album), ''Gl ...
. Judicious use of insecticides for mosquito control can limit the evolution and spread of resistance. However, use of insecticides in agriculture has often been implicated as contributing to resistance in mosquito populations. Detection of evolving resistance in mosquito populations is possible, so control programs are well advised to conduct surveillance for this potential problem. In Malawi and other places, a shrub known as mpungabwi (''Ocimum americanum
''Ocimum americanum'', known as American basil, lime basil, or hoary basil, is a species of annual herb in the family Lamiaceae. Despite the misleading name, it is native to Africa, the Indian Subcontinent, China, and Southeast Asia. The specie ...
'') is used to repel mosquitoes.
Eradication
With substantial numbers of malaria cases affecting people around the globe, in tropical
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
and subtropical
The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Geographical z ...
regions, especially in sub-Saharan Africa
Sub-Saharan Africa is, geographically, the area and regions of the continent of Africa that lies south of the Sahara. These include West Africa, East Africa, Central Africa, and Southern Africa. Geopolitically, in addition to the List of sov ...
, where millions of children are killed by this infectious disease, eradication is back on the global health agenda.
Although malaria has existed since ancient times, its eradication was possible in Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
, the Caribbean
The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean Se ...
and parts of Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
and southern Central America during the first regional elimination campaigns in the late 1940s. However, the same results were not achieved in sub-Saharan Africa.
Though the World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
adopted a formal policy on the control and eradication of the malaria parasite since 1955, only recently, after the Gates Malaria Forum in October 2007, did key organizations start the debate on the pros and cons of redefining eradication as a goal to control malaria.
Clearly, the cost of preventing malaria is much less than treating the disease, in the long run. However, eradication of mosquitoes is not an easy task. For effective prevention of malaria, some conditions should be met, such as conducive conditions in the country, data collection about the disease, targeted technical approaches to the problem, very active and committed leadership, total governmental support, sufficient monetary resources, community involvement, and skilled technicians from different fields, as well as an adequate implementation.[
Currently, there are proposals to eradicate ''Anopheles gambiae,'' the main vector for malaria, with a CRISPR-Cas9 gene drive system. This system aims to eradicate the species through introducing a gene that would cause female sterility, thus causing the gene to be unable to replicate. It has been demonstrated in a study by Kyrou et al that such a gene drive system can suppress an entire caged ''An. gambiae'' population through targeting and deleting the '' dsx'' gene, which is vital for female fertility. By utilizing the conservation tendencies of selfish genes, Kyrou et al demonstrated full suppression of the population within 7–11 generations, typically less than a year. Of course, this has raised concerns with both the efficiency of a gene drive system as well as the ethical and ecological impact of such an eradication program. Therefore, there have been efforts to use the gene drive system to more efficiently introduce genes of ''Plasmodium'' resistance into the species, such as targeting and knocking out the ''FREP1'' gene in ''Anopheles gambiae.'' Such systems may generate less ecological impact, as the species are not removed from the ecosystem, though concerns regarding efficiency still linger.
Researchers in ]Burkina Faso
Burkina Faso (, ; , ff, 𞤄𞤵𞤪𞤳𞤭𞤲𞤢 𞤊𞤢𞤧𞤮, italic=no) is a landlocked country in West Africa with an area of , bordered by Mali to the northwest, Niger to the northeast, Benin to the southeast, Togo and Ghana to the ...
have created a strain of the fungus ''metarhizium pinghaense
''Metarhizium pinghaense'' is a species of entomopathogenic fungus in the family Clavicipitaceae. Some authorities have it as a synonym of ''Metarhizium anisopliae''. DNA studies show that it is a good species, with strong bootstrap support.
Re ...
'' genetically engineered to produce the venom of an Australian funnel-web spider
Funnel-web spider refers to many different species of spider, particularly those that spin a web in the shape of a funnel:
* spiders in the family Agelenidae, including
** '' Hololena curta''
* funnel-web tarantulas (suborder Mygalomorphae):
** ...
; exposure to the fungus caused populations of ''Anopheles'' mosquitoes to crash by 99% in a controlled trial.
A wide range of strategies is needed to achieve malaria eradication, starting from simple steps to complicated strategies which may not be possible to enforce with the current tools.
Although mosquito control is an important component of malaria control strategy, elimination of malaria in an area does not require the elimination of all ''Anopheles'' mosquitoes. For instance, in North America and Europe, although the vector ''Anopheles'' mosquitoes are still present, the parasite has been eliminated. Some socioeconomic improvements (e.g., houses with screened windows, air conditioning
Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
), once combined with vector reduction efforts and effective treatment, lead to the elimination of malaria without the complete elimination of the vectors. Some important measures in mosquito control to be followed are: discourage egg-laying, prevent development of eggs into larvae and adults, kill the adult mosquitoes, do not allow adult mosquitoes into places of human dwelling, prevent mosquitoes from biting human beings and deny them blood meals.[
Research in this sense continues, and a study has suggested sterile mosquitoes might be the answer to malaria elimination. This research suggests using the sterile insect technique, in which sexually sterile male insects are released to wipe out a pest population, could be a solution to the problem of malaria in Africa. This technique brings hope, as female mosquitoes only mate once during their lifetimes, and in doing so with sterile male mosquitoes, the insect population would decrease.][ This is another option to be considered by local and international authorities that may be combined with other methods and tools to achieve malaria eradication in sub-Saharan Africa.
]
Parasites
A number of parasites of this genus are known to exist, including microsporidia
Microsporidia are a group of spore-forming unicellular parasites. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore. They were once considered protozoans or prot ...
of the genera '' Amblyospora'', '' Crepidulospora'', '' Senoma'' and '' Parathelohania''.
Microsporidia infecting the aquatic stages of insects, a group that includes mosquitoes and black flies
A black fly or blackfly (sometimes called a buffalo gnat, turkey gnat, or white socks) is any member of the family Simuliidae of the Culicomorpha infraorder. It is related to the Ceratopogonidae, Chironomidae, and Thaumaleidae. Over 2,200 speci ...
, and copepods appear to form a distinct clade from those infecting terrestrial insects and fish. Two distinct life cycles are found in this group. In the first type, the parasite is transmitted by the oral route and is relatively species nonspecific. In the second, while again the oral route is the usual route of infection, the parasite is ingested within an already infected intermediate host. Infection of the insect larval form is frequently tissue-specific, and commonly involves the fat body. Vertical (transovarial) transmission is also known to occur.
Few phylogenetic studies of these parasites have been done, and their relationship to their mosquito hosts is still being determined. One study suggested ''Parathelohania'' is an early diverging genus within this group.[
The parasite '' Wolbachia'' bacteria have also been studied for use as control agents.][Mosquito Parasite Fights Infectious Disease : Discovery News](_blank)
News.discovery.com (2009-10-01). Retrieved on 2012-07-14.
Predators
The jumping spider ''Evarcha culicivora
''Evarcha culicivora'' is a species of jumping spider (family Salticidae) found only around Lake Victoria in Kenya and Uganda. At maturity, ''E. culicivora'' spiders have an average size of 5 mm for both males and females. The range in ...
'' indirectly feeds on vertebrate blood by preying on female ''Anopheles'' mosquitos. Interestingly, juvenile spiders choose the ''Anopheles'' over all other prey regardless of whether it actually is carrying blood.[Jackson, Robert R., and Fiona R. Cross. "Mosquito-terminator spiders and the meaning of predatory specialization." The Journal of Arachnology 43.2 (2015): 123–142.] Juvenile spiders have adopted an ''Anopheles''-specific prey-capture behavior, using the posture of ''Anopheles'' mosquitoes as a primary cue to identify them. ''Anopheles'' has a distinctive resting posture with its abdomen angled up. In this case, the spider takes a detour and approaches from behind the mosquito and under its abdomen, and then attacks from below.
See also
* Taxonomy of ''Anopheles''
* Tropical disease
Tropical diseases are Infectious disease, diseases that are prevalent in or unique to tropics, tropical and subtropics, subtropical regions. The diseases are less prevalent in temperate climates, due in part to the occurrence of a cold season, whic ...
References
External links for this search
''Anopheles'' Database
''Anopheles gambiae'' Genome and Related Data
CDC – National Center for Infectious Diseases, Division of Parasitic Diseases; '' Malaria
* ttp://www.wrbu.org/ Walter Reed Biosystematics Unit.– Links to the online mosquito catalog, keys for mosquito identification, images and information on medically important species and much more.
Malaria Atlas Project
''Anopheles gambiae'' taxonomy, facts and life cycle
on the University of Florida
The University of Florida (Florida or UF) is a public land-grant research university in Gainesville, Florida. It is a senior member of the State University System of Florida, traces its origins to 1853, and has operated continuously on its ...
/ Institute of Food and Agricultural Sciences
The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is a teaching, research and Extension scientific organization focused on agriculture and natural resources. It is a partnership of federal, state, and county governmen ...
''Featured Creatures'' website
* http://animaldiversity.ummz.umich.edu/site/accounts/classification/Anopheles.html
{{taxonbar, from=Q158597
Mosquito genera
Insect vectors of human pathogens
Malaria
Taxa named by Johann Wilhelm Meigen