Mosquitoes, the Culicidae, are a family of small Diptera consisting of 3,600 species. The word mosquito (formed by mosca and diminutive -ito)
The mosquito life cycle consists of four stages: egg, larva, pupa, and adult. Eggs are laid on the water surface; they hatch into Motility larvae that feed on aquatic algae and organic material. These larvae are important food sources for many freshwater animals, such as dragonfly nymphs, many fish, and some birds. Adult females of many species have mouthparts adapted to pierce the skin of a host and Hematophagy of a wide range of vertebrate hosts, and some , primarily other . Some species only produce eggs after a blood meal.
The mosquito's saliva is transferred to the host during the bite, and can cause an itchy rash. In addition, blood-feeding species can ingest pathogens while biting, and transmit them to other hosts. Those species include vectors of parasitic diseases such as malaria and filariasis, and arboviruses diseases such as yellow fever and dengue fever. By transmitting diseases, mosquitoes cause the deaths of over 725,000 people each year.
Description and life cycle
Like all flies, mosquitoes go through four stages in their life cycles: egg,
larva,
pupa, and
imago. The first three stages—egg, larva, and pupa—are largely aquatic,
the eggs usually being laid in stagnant water.
They hatch to become
, which feed, grow, and molt until they change into
. The adult mosquito emerges from the mature pupa as it floats at the water surface. Mosquitoes have adult lifespans ranging from as short as a week to around a month. Some species overwinter as adults in
diapause.
[Kosova, Jonida (2003) "Longevity Studies of Sindbis Virus Infected Aedes Albopictus" . All Volumes (2001–2008). Paper 94.]
Adult
Mosquitoes have one pair of wings, with distinct scales on the surface. Their wings are long and narrow, while the legs are long and thin. The body, usually grey or black, is slender, and typically 3–6 mm long. When at rest, mosquitoes hold their first pair of legs outwards, whereas the somewhat similar
Chironomidae midges hold these legs forwards.
mosquitoes can fly for up to four hours continuously at ,
traveling up to in a night. Males beat their wings between 450 and 600 times per second,
Indirect flight by muscles which vibrate the thorax.
Mosquitoes are mainly small flies; the largest are in the genus
Toxorhynchites, at up to in length and in wingspan.
Those in the genus
Aedes are much smaller, with a wingspan of .
Mosquitoes can develop from egg to adult in hot weather in as few as five days, but it may take up to a month.
File:Culex pipiens diagram en.svg|Anatomy of an adult female mosquito
File:Aedes aegypti E-A-Goeldi 1905.jpg|Adult yellow fever mosquito Aedes aegypti, typical of subfamily Culicinae. Male (left) has bushy antennae and longer palps than female (right)
Eggs
The eggs of most mosquitoes are laid in stagnant water, which may be a pond, a marsh, a temporary puddle, a water-filled hole in a tree, or the water-trapping leaf axils of a
Bromeliaceae. Some lay near the water's edge while others attach their eggs to aquatic plants. A few, like
Opifex fuscus, can breed in salt-marshes.
breeds in the pitchers of
, its larvae feeding on decaying insects that have drowned there.
[Crans, Wayne J.; Wyeomyia smithii (Coquillett) . Rutgers University, Center for Vector Biology.]
Oviposition, egg-laying, varies between species. Anopheles females fly over the water, touching down or dapping to place eggs on the surface one at a time; their eggs are roughly cigar-shaped and have floats down their sides. A female can lay 100–200 eggs in her lifetime.
Clutches of eggs of most mosquito species hatch simultaneously, but Aedes eggs in diapause hatch irregularly over an extended period.
File:Anopheles_egg_2_(cropped).jpg| Anopheles eggs with side floats
File:Mosquito egg SEM.jpg|Electron micrograph of a culicine egg
File:Gelege1 (cropped).jpg| Culex egg raft
Larva
The mosquito larva's head has prominent mouth brushes used for feeding, a large thorax with no legs, and a segmented abdomen. It breathes air through a siphon on its abdomen, so must come to the surface frequently. It spends most of its time feeding on
algae, bacteria, and other microbes in the water's surface layer. It dives below the surface when disturbed. It swims either by propelling itself with its mouth brushes, or by jerkily wriggling its body. It develops through several stages, or
, molting each time, after which it
metamorphosis into a
pupa.
larvae, except when very young, can withstand drying; they go into
diapause for several months if their pond dries out.
File:AnophelesLarvaPhoto CDCHarryWeinburgh publicdomain.jpg| Anopheles larva
File:Culex restuans larva diagram en.svg|Anatomy of a Culex larva
File:Culex sp larvae.png| Culex larvae plus one pupa
Pupa
The head and thorax of the
pupa are merged into a
cephalothorax, with the abdomen curving around beneath it. The pupa or "tumbler" can swim actively by flipping its abdomen. Like the larva, the pupa of most species must come to the surface frequently to breathe, which they do through a pair of respiratory trumpets on their cephalothoraxes. They do not feed; they pass much of their time hanging from the surface of the water by their respiratory trumpets. If alarmed, they swim downwards by flipping their abdomens in much the same way as the larvae. If undisturbed, they soon float up again. The adult emerges from the pupa at the surface of the water and flies off.
File:Underwater view of mosquito pupae in standing water.jpg|Mosquito pupae, shortly before the adults emerged. The head and thorax are fused into the cephalothorax.
Feeding by adults
Diet
Both male and female mosquitoes feed on
nectar source, aphid honeydew, and plant juices,
but in many species the females are also
Hematophagy Parasitism. In some of those species, a blood meal is essential for egg production; in others, it just enables the female to lay more eggs.
Both plant materials and blood are useful sources of energy in the form of sugars. Blood supplies more concentrated nutrients, such as
, but the main function of blood meals is to obtain proteins for egg production.
Mosquitoes like
Toxorhynchites reproduce autogenously, not needing blood meals. Disease vector mosquitoes like
Anopheles and
Aedes are
anautogenous, requiring blood to lay eggs. Many
Culex species are partially anautogenous, needing blood only for their second and subsequent clutches of eggs.
Host animals
Blood-sucking mosquitoes favour particular host species, though they are less selective when food is short. Different mosquito species favor
,
including
,
, and
. For example,
Culiseta melanura sucks the blood of
passerine birds, but as mosquito numbers rise they attack mammals including horses and humans, causing epidemics of Eastern equine encephalitis virus in North America.
Loss of blood from many bites can add up to a large volume, occasionally causing the death of
livestock as large as
cattle and
.
-transmitting mosquitoes seek out
and feed on their haemolymph,
impeding their development.
File:Chironius scurrulus (Yasuni) (cropped) with mosquitoes.jpg|Feeding on a snake
File:Mosquitoes vs. Frog (14555480700) (cropped).jpg|Feeding on a frog
File:JJeffreyApapaneMosquito.jpg|Feeding on a bird
Finding hosts
Most mosquito species are
crepuscular, feeding at dawn or dusk, and resting in a cool place through the heat of the day.
Some species, such as the Asian tiger mosquito, are known to fly and feed during daytime.
Female mosquitoes hunt for hosts by smelling substances such as
carbon dioxide (CO
2) and 1-octen-3-ol (mushroom alcohol, found in exhaled breath) produced from the host, and through visual recognition.
The
semiochemical that most strongly attracts
Culex quinquefasciatus is
nonanal.
Another attractant is
sulcatone.
A large part of the mosquito's sense of smell, or olfactory system, is devoted to sniffing out blood sources. Of 72 types of odor receptors on its antennae, at least 27 are tuned to detect chemicals found in perspiration.
In
Aedes, the search for a host takes place in two phases. First, the mosquito flies about until it detects a host's odorants; then it flies towards them, using the concentration of odorants as its guide.
Mosquitoes prefer to feed on people with type O blood, an abundance of skin bacteria, high body heat, and pregnant women.
Individuals' attractiveness to mosquitoes has a
heritable, genetically controlled component.
The multitude of characteristics in a host observed by the mosquito allows it to select a host to feed on. This occurs when a mosquito notes the presence of CO2, as it then activates odour and visual search behaviours that it otherwise would not use. In terms of a mosquito’s olfactory system, chemical analysis has revealed that people who are highly attractive to mosquitoes produce significantly more .
Contributing to a mosquito's ability to activate search behaviours, a mosquito's visual search system includes sensitivity to wavelengths from different colours. Mosquitoes are attracted to longer wavelengths, correlated to the colours of red and orange as seen by humans, and range through the spectrum of human skin tones. In addition, they have a strong attraction to dark, high-contrast objects, because of how longer wavelengths are perceived against a lighter-coloured background.
Mouthparts
Female mosquito mouthparts are highly adapted to piercing skin and sucking blood. Males only drink sugary fluids, and have less specialized mouthparts.
Externally, the most obvious feeding structure of the mosquito is the proboscis, composed of the labium, U-shaped in section like a rain gutter, which sheaths a bundle (fascicle) of six piercing mouthparts or stylets. These are two mandibles, two maxillae, the hypopharynx, and the labrum. The labium bends back into a bow when the mosquito begins to bite, staying in contact with the skin and guiding the stylets downwards. The extremely sharp tips of the labrum and maxillae are moved backwards and forwards to saw their way into the skin, with just one thousandth of the force that would be needed to penetrate the skin with a needle, resulting in a painless insertion.
File:Evolution of mosquito mouthparts.svg|Evolution of mosquito mouthparts, with grasshopper mouthparts (shown both in situ and separately) representing a more primitive condition. All the mouthparts except the labium are stylets, formed into a fascicle or bundle.
File:Feeding mosquito, mouthparts labelled.svg|Mouthparts of a female mosquito while feeding on blood, showing the flexible labium sheath supporting the piercing and sucking tube which penetrates the host's skin
Saliva
Mosquito saliva contains
that aid in sugar feeding,
and antimicrobial agents that control bacterial growth in the sugar meal.
For a mosquito to obtain a blood meal, it must circumvent its vertebrate host's physiological responses. Mosquito saliva blocks the host's hemostasis system, with proteins that reduce vascular constriction, blood clotting, and platelet aggregation, to ensure the blood keeps flowing.
Egg development and blood digestion
Females of many blood-feeding species need a blood meal to begin the process of egg development. A sufficiently large blood meal triggers a hormonal cascade that leads to egg development.
Upon completion of feeding, the mosquito withdraws her
proboscis, and as the gut fills up, the stomach lining secretes a peritrophic membrane that surrounds the blood. This keeps the blood separate from anything else in the stomach. Like many
Hemiptera that survive on dilute liquid diets, many adult mosquitoes excrete surplus liquid even when feeding. This permits females to accumulate a full meal of nutrient solids. The blood meal is digested over a period of several days.
Once blood is in the stomach, the midgut synthesizes
protease enzymes, primarily
trypsin assisted by
aminopeptidase, that hydrolyze the blood
into free
. These are used in the synthesis of
vitellogenin, which in turn is made into egg yolk protein.
Distribution
Cosmopolitan
Mosquitoes have a cosmopolitan distribution, occurring in every land region except Antarctica and a few islands with polar or
, such as
Iceland, which is essentially free of mosquitoes.
This absence is probably caused by Iceland's climate. Its weather is unpredictable, freezing but often warming suddenly in mid-winter, making mosquitoes emerge from pupae in diapause, and then freezing again before they can complete their life cycle.
Eggs of temperate zone mosquitoes are more tolerant of cold than the eggs of species indigenous to warmer regions.
Effect of climate change
For a mosquito to transmit disease, there must be favorable seasonal conditions,
primarily humidity, temperature, and precipitation.
El Niño affects the location and number of outbreaks in East Africa, Latin America, Southeast Asia and
India.
Climate change impacts the seasonal factors and in turn the dispersal of mosquitoes.
Climate models can use historic data to recreate past outbreaks and to predict the risk of vector-borne disease, based on an area's forecasted climate.
Mosquito-borne diseases have long been most prevalent in East Africa, Latin America, Southeast Asia, and
India. An emergence in Europe was observed early in the 21st century. It is predicted that by 2030, the climate of southern Great Britain will be suitable for transmission of
Plasmodium vivax malaria by
Anopheles mosquitoes for two months of the year, and that by 2080, the same will be true for southern Scotland.
, too, is spreading northwards with climate change. The vector, the Asian tiger mosquito
Aedes albopictus, has by 2023 established across southern Europe and as far north as much of northern France, Belgium, Holland, and both
Kent and West London in England.
Ecology
Predators and parasites
Mosquito larvae are among the commonest animals in ponds, and they form an important food source for freshwater
Predation. Among the many aquatic insects that catch mosquito larvae are
dragonfly and
damselfly nymphs,
, and
. Vertebrate predators include fish such as catfish and the
mosquitofish, amphibians including the
Scaphiopodidae and the giant tree frog, freshwater turtles such as the
red-eared slider, and birds such as ducks.
Emerging adults are consumed at the pond surface by predatory flies including Empididae and Dolichopodidae, and by . Flying adults are captured by dragonflies and damselflies, by birds such as swifts and , and by vertebrates including .
Mosquitoes are parasitised by Hydrachnidia mites, such as Glaucoma, such as Thelania, and fungi including species of Saprolegniaceae and Entomophthoraceae.
Pollination
Several flowers including members of the
Asteraceae,
Rosaceae and
Orchidaceae are
pollinated by mosquitoes, which visit to obtain sugar-rich
nectar. They are attracted to flowers by a range of semiochemicals such as alcohols, aldehydes, ketones, and terpenes. Mosquitoes have visited and pollinated flowers since the
Cretaceous period. It is possible that plant-sucking
Exaptation mosquitoes to blood-sucking.
Parasitism
Ecologically, blood-feeding mosquitoes are
, small animals that feed on larger animals without immediately killing them. Evolutionary biologists see this as a form of
parasitism; in Edward O. Wilson's phrase "Parasites ... are predators that eat prey in units of less than one."
Micropredation is one of six major evolutionarily stable strategies within parasitism. It is distinguished by leaving the host still able to reproduce, unlike the activity of parasitic castrators or
; and having multiple hosts, unlike conventional parasites.
[ ] From this perspective, mosquitoes are
, feeding on blood from the outside of their hosts, using their piercing mouthparts, rather than entering their bodies. Unlike some other ectoparasites such as
and
Louse, mosquitoes do not remain constantly on the body of the host, but visit only to feed.
Evolution
Fossil record
A 2023 study suggested that
Libanoculex found in
Lebanese amber, dating to the
Barremian age of the Early Cretaceous, around 125 million years ago was the oldest known mosquito.
However its identification as a mosquito is disputed, with other authors considering it to be a
Chaoboridae fly instead.
Three other unambiguous species of
Cretaceous mosquito are known.
Burmaculex antiquus and
Priscoculex burmanicus are known from
Burmese amber from Myanmar, which dates to the earliest part of the
Cenomanian age of the Late Cretaceous, around 99 million years ago.
, is known from
Canadian amber from Alberta, Canada, which dates to the
Campanian age of the Late Cretaceous, around 79 million years ago.
has been assigned to the
Anophelinae, indicating that the split between this subfamily and the
Culicinae took place over 99 million years ago.
Molecular estimates suggest that this split occurred 197.5 million years ago, during the Early
Jurassic, but that major diversification did not take place until the Cretaceous.
Taxonomy
Over 3,600 species of mosquitoes in 112
genera have been described. They are traditionally divided into two subfamilies, the Anophelinae and the
Culicinae, which carry different diseases. Roughly speaking, protozoal diseases like malaria are transmitted by anophelines, while viral diseases such as
yellow fever and
dengue fever are transmitted by culicines.
The name Culicidae was introduced by the German entomologist Johann Wilhelm Meigen in his seven-volume classification published in 1818–1838.
Phylogeny
External
Mosquitoes are members of a family of the
Fly: the Culicidae (from the
Latin culex,
Genitive case culicis, meaning "midge" or "gnat").
They are members of the infraorder
Culicomorpha and superfamily
Culicoidea. The phylogenetic tree is based on the FLYTREE project.
Internal
The two subfamilies of mosquitoes are
Anophelinae, containing three genera and approximately 430 species, and
Culicinae, which contains 11 tribes, 108 genera and 3,046 species. Kyanne Reidenbach and colleagues analysed mosquito
phylogenetics in 2009, using both nuclear DNA and morphology of 26 species. They note that Anophelinae is confirmed to be rather basal, but that the deeper parts of the tree are not well resolved.
Interactions with humans
Vectors of disease
Mosquitoes are vectors for many disease-causing
including
bacteria,
, and
parasites. Nearly 700 million people acquire a mosquito-borne illness each year, resulting in over 725,000 deaths.
Common mosquito-borne viral diseases include
yellow fever and
dengue fever transmitted mostly by
Aedes aegypti.
Parasitic diseases transmitted by mosquitoes include
malaria and lymphatic filariasis. The
Plasmodium parasites that cause malaria are carried by female
Anopheles mosquitoes. Lymphatic filariasis, the main cause of elephantiasis, is spread by a wide variety of mosquitoes.
A bacterial disease spread by
Culex and
Culiseta mosquitoes is
tularemia.
Control
Many measures have been tried for
mosquito control, including the elimination of breeding places, exclusion via
and
, biological control with parasites such as fungi
and nematodes,
or predators such as fish,
,
nymphs and adults, and some species of lizard and
gecko.
Another approach is to introduce large numbers of sterile males.
Genetic modification methods including cytoplasmic incompatibility, chromosomal translocations, sex distortion and gene replacement, solutions seen as inexpensive and not subject to vector resistance, have been explored.
[Webb, Jonathan (10 June 2014) GM lab mosquitoes may aid malaria fight . BBC.] Control of disease-carrying mosquitoes using
has been proposed.
Repellents
Insect repellents are applied on skin and give short-term protection against mosquito bites. The chemical
DEET repels some mosquitoes and other insects.
Some CDC-recommended repellents are
picaridin,
eucalyptus oil (PMD), and ethyl butylacetylaminopropionate (IR3535).
(from
Chrysanthemum species, particularly
C. cinerariifolium and
C. coccineum) is an effective plant-based repellent.
[Rachel Nuwer, Natural Mosquito Repellent's Powers Finally Decoded , Scientific American 325, 2, 23 (August 2021)] Electronic insect repellent devices that produce
intended to keep away insects (and mosquitoes) are marketed. No EPA or university study has shown that these devices prevent humans from being bitten by a mosquito.
Bites
Mosquito bites lead to a variety of skin reactions and more seriously to mosquito bite allergies.
Such
hypersensitivity to mosquito bites is an excessive reaction to mosquito saliva proteins.
Numerous species of mosquito can trigger such reactions, including
Aedes aegypti,
Aedes vexans,
Aedes albopictus,
Anopheles sinensis,
Culex pipiens,
,
Anopheles stephensi,
,
C. tritaeniorhynchus,
and
Ochlerotatus triseriatus.
Cross-reactivity between salivary proteins of different mosquitoes implies that allergic responses may be caused by virtually any mosquito species.
Treatment can be with
Antipruritic medications, including some taken orally, such as
diphenhydramine, or applied to the skin like
or
corticosteroids such as
hydrocortisone.
Aqueous ammonia (3.6%) also provides relief.
Both topical heat
and cold may be useful as treatments.
In human culture
Greek mythology
Ancient Greek beast fables including "The Elephant and the Mosquito" and "The Bull and the Mosquito", with the general moral that the large beast does not even notice the small one, derive ultimately from
Mesopotamia.
Origin myths
The peoples of
Siberia have
surrounding the mosquito. One
Ostiak myth tells of a man-eating giant,
Punegusse, who is killed by a hero but will not stay dead. The hero eventually burns the giant, but the ashes of the fire become mosquitoes that continue to plague mankind. Other myths from the
Yakuts, Goldes (
Nanai people), and Samoyed have the insect arising from the ashes or fragments of some giant creature or demon. Similar tales found in Native North American myth, with the mosquito arising from the ashes of a man-eater, suggest a common origin. The
Tatars of the
Altai Mountains had a variant of the same myth, involving the fragments of the dead giant,
Andalma-Muus, becoming mosquitoes and other insects.
Lafcadio Hearn tells that in Japan, mosquitoes are seen as reincarnations of the dead, condemned by the errors of their former lives to the condition of Jiki-ketsu-gaki, or "blood-drinking pretas".
Modern era
Winsor McCay's 1912 film
How a Mosquito Operates was one of the earliest works of animation. It has been described as far ahead of its time in technical quality.
It depicts a giant mosquito tormenting a sleeping man.
Twelve ships of the Royal Navy have borne the name HMS Mosquito or the archaic form of the name, HMS Musquito.[, "Mosquito" and "Musquito".]
The de Havilland Mosquito was a high-speed aircraft manufactured between 1940 and 1950, and used in many roles.
The Russian city of Berezniki annually celebrates its mosquitoes from the 17th of July to the 20th in a "most delicious girl" competition. In the competition, the girls stand for 20 minutes in their shorts and vests, and the one who receives the most bites wins.
Further reading
External links
