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Tuesday, September 3, 2024

Cannibalism

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Cannibalism
A slug, Arion vulgaris, eating a dead individual of the same species

Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is also well documented, both in ancient and in recent times.

The rate of cannibalism increases in nutritionally poor environments as individuals turn to members of their own species as an additional food source. Cannibalism regulates population numbers, whereby resources such as food, shelter and territory become more readily available with the decrease of potential competition. Although it may benefit the individual, it has been shown that the presence of cannibalism decreases the expected survival rate of the whole population and increases the risk of consuming a relative. Other negative effects may include the increased risk of pathogen transmission as the encounter rate of hosts increases. Cannibalism, however, does not—as once believed—occur only as a result of extreme food shortage or of artificial/unnatural conditions, but may also occur under natural conditions in a variety of species.

At the ecosystem level, cannibalism is most common in aquatic settings, with a cannibalism rate of up to 0.3% amongst fish. Cannibalism is not restricted to carnivorous species: it also occurs in herbivores and in detritivores. Sexual cannibalism normally involves the consumption of the male by the female individual before, during or after copulation. Other forms of cannibalism include size-structured cannibalism and intrauterine cannibalism. Behavioral, physiological and morphological adaptations have evolved to decrease the rate of cannibalism in individual species.

Benefits

In environments where food availability is constrained, individuals can receive extra nutrition and energy if they use members of their own species, also known as conspecifics, as an additional food source. This would, in turn, increase the survival rate of the cannibal and thus provide an evolutionary advantage in environments where food is scarce. For example, female Fletcher's frogs lay their eggs in ephemeral pools that lack food resources. Therefore, in order to survive, tadpoles within the same clutch are forced to consume each other and exploit their conspecifics as the only available source of nutrition. A study conducted on another amphibian, the wood frog, tadpoles showed that those that exhibited cannibalistic tendencies had faster growth rates and higher fitness levels than non-cannibals. An increase of size and growth would give them the added benefit of protection from potential predators such as other cannibals and give them an advantage when competing for resources.

The nutritional benefits of cannibalism may allow for the more efficient conversion of a conspecific diet into reusable resources than a fully herbaceous diet; as herbaceous diets may consist of excess elements which the animal has to expend energy to get rid of. This facilitates faster development; however, a trade-off may occur as there may be less time to ingest these acquired resources. Studies have shown that there is a noticeable size difference between animals fed on a high conspecific diet which were smaller compared to those fed on a low conspecific diet. Hence, individual fitness could only be increased if the balance between developmental rate and size is balanced out, with studies showing that this is achieved in low conspecific diets.

In some insects, cannibalism is used to control population. In confused flour beetles, population density is lowered by cannibalism when crowding occurs.

Cannibalism regulates population numbers and benefits the cannibalistic individual and its kin as resources such as extra shelter, territory and food are freed, thereby increasing the fitness of the cannibal by lowering crowding effects. However, this is only the case if the cannibal recognizes its own kin as this won't hinder any future chances of perpetuating its genes in future generations. The elimination of competition can also increase mating opportunities, allowing further spread of an individual's genes.

Costs

Animals which have diets consisting of predominantly conspecific prey expose themselves to a greater risk of injury and expend more energy foraging for suitable prey as compared to non-cannibalistic species.

Predators often target younger or more vulnerable prey. However, the time necessitated by such selective predation could result in a failure to meet the predator's self-set nutritional requirements. In addition, the consumption of conspecific prey may also involve the ingestion of defense compounds and hormones, which have the capacity to impact the developmental growth of the cannibal's offspring. Hence, predators normally partake in a cannibalistic diet in conditions where alternative food sources are absent or not as readily available.

Failure to recognize kin prey is also a disadvantage, provided cannibals target and consume younger individuals. For example, a male stickleback fish may often mistake their own "eggs" for their competitor's eggs, and hence would inadvertently eliminate some of its own genes from the available gene pool. Kin recognition has been observed in tadpoles of the spadefoot toad, whereby cannibalistic tadpoles of the same clutch tended to avoid consuming and harming siblings, while eating other non-siblings.

The act of cannibalism may also facilitate trophic disease transmission within a population, though cannibalistically spread pathogens and parasites generally employ alternative modes of infection.

Diseases transmitted through cannibalism

Cannibalism can potentially reduce the prevalence of parasites in the population by decreasing the number of susceptible hosts and indirectly killing the parasite in the host. It has been shown in some studies that the risk of encountering an infected victim increases when there is a higher cannibalism rate, though this risk drops as the number of available hosts decreases. However, this is only the case if the risk of disease transmission is low. Cannibalism is an ineffective method of disease spread as cannibalism in the animal kingdom is normally a one-on-one interaction, and the spread of disease requires group cannibalism; thereby it is rare for a disease to have evolved to rely solely on cannibalism to spread. Usually there are different means of transmission, such as with direct contact, maternal transmission, coprophagy, and necrophagy with different species. Infected individuals are more likely to be consumed than non-infected individuals, thus some research has suggested that the spread of disease may be a limiting factor to the prevalence of cannibalism in the population.

Some examples of diseases transmitted by cannibalism in mammals include the human disease Kuru which is a prion disease that degenerates the brain. This disease was prevalent in Papua New Guinea where tribes practiced endocannibalism in cannibalistic funeral rituals and consume the brains infected by these prions. It is a cerebellar dysfunctional disease which has symptoms including a broad-based gait and decreased motor activity control; however, the disease has a long incubation period and symptoms may not appear until years later.

Bovine spongiform encephalopathy, or mad cow disease is another prion disease which is usually caused by feeding contaminated bovine tissue to other cattle. It is a neurodegenerative disease and could be spread to humans if the individual were to consume contaminated beef. The spread of parasites such as nematodes may also be facilitated by cannibalism as eggs from these parasites are transferred more easily from one host to another.

Other forms of diseases include sarcocystis and iridovirus in reptiles and amphibians; granulosus virus, chagas disease, and microsporidia in insects; stained prawn disease, white pot syndrome, helminthes and tapeworms in crustaceans and fish.

Foraging dynamics

Cannibalism may become apparent when direct competition for limited resources forces individuals to use other conspecific individuals as an additional resource to maintain their metabolic rates. Hunger drives individuals to increase their foraging rates, which in turn decreases their attack threshold and tolerance to other conspecific individuals. As resources dwindle, individuals are forced to change their behaviour which may lead to animal migration, confrontation, or cannibalism.

Cannibalism rates increase with increasing population density as it becomes more advantageous to prey on conspecific organisms than to forage in the environment. This is because the encounter rate between predator and prey increases, making cannibalism more convenient and beneficial than foraging within the environment. Over time, the dynamics within the population change as those with cannibalistic tendencies may receive additional nutritional benefits and increase the size ratio of predator to prey. The presence of smaller prey, or prey which are at a vulnerable stage of their life cycle, increases the chances of cannibalism occurring due to the reduced risk of injury. A feedback loop occurs when increasing rates of cannibalism decreases population densities, leading to an increased abundance of alternative food sources; making it more beneficial to forage within the environment than for cannibalism to occur. When population numbers and foraging rates increase, the carrying capacity for that resource in the area may be reached, thus forcing individuals to look for other resources such as conspecific prey.

Sexual cannibalism

Sexual cannibalism is present largely in spiders and other invertebrates, including gastropods. This refers to the killing and consumption of conspecific sexual partners during courtship, and during or after copulation. Normally, it is the female which consumes the conspecific male organism, though there have been some reported cases of the male consuming the adult female, however, this has only been recorded under laboratory conditions. Sexual cannibalism has been recorded in the female redback spider, black widow spider, praying mantis, and scorpion, among others.

In most species of spiders, the consumption of the male individual occurs before copulation and the male fails to transfer his sperm into the female. This may be due to mistaken identity such as in the case of the orb weaving spider which holds little tolerance to any spider which is present in its web and may mistake the vibrations for those of a prey item. Other reasons for male consumption before mating may include female choice and the nutritional advantages of cannibalism. The size of the male spider may play a part in determining its reproductive success as smaller males are less likely to be consumed during pre-copulation; however, larger males may be able to prevent the smaller ones from gaining access to the female. There exists a conflict of interest between males and females, as females may be more inclined to turn to cannibalism as a source of nutritional intake while the male's interest is mostly focused on ensuring paternity of the future generations. It was found that cannibalistic females produced offspring with greater survival rates than non-cannibalistic females, as cannibals produced greater clutches and larger egg sizes. Hence, species such as the male dark fishing spider of the family Dolomedes self-sacrifice and spontaneously die during copulation to facilitate their own consumption by the female, thereby increasing the chance of survivorship of future offspring.

Sexual dimorphism has been theorised to have arisen from sexual selection as smaller males were captured more easily than larger males; however, it is also possible that sexual cannibalism only occurs due to the difference in size between male and females. Data comparing female and male spider body length shows that there is little support for the prior theory as there is not much correlation between body size and the presence of sexual cannibalism. Not all species of spiders which partake in sexual cannibalism exhibit size dimorphism.

The avoidance of sexual cannibalism is present in males of certain species to increase their rate of survival, whereby the male uses cautionary methods to lower the risk of his consumption. Male orb weaving spiders would often wait for females to moult or to finish eating before attempting to initiate mating, as the females are less likely to attack. Males which are vulnerable to post-copulation consumption may gather mating thread to generate a mechanical tension which they could use to spring away after insemination, while other spiders such as the crab spider may tangle the female's legs in webs to reduce the risk of the female capturing him. Male choice is common in mantids whereby males were observed to choose fatter females due to the reduced risk of attack and were more hesitant to approach starved females.

Size-structured cannibalism

Nematode of the order Mononchida eating another Mononchid

Size-structured cannibalism is cannibalism in which older, larger, more mature individuals consume smaller, younger conspecifics. In size-structured populations, (where populations are made of individuals of various sizes, ages, and maturities), cannibalism can be responsible for 8% (Belding's ground squirrel) to 95% (dragonfly larvae) of the total mortality, making it a significant and important factor for population and community dynamics.

Size-structured cannibalism has commonly been observed in the wild for a variety of taxa. Vertebrate examples include chimpanzees, where groups of adult males have been observed to attack and consume infants.

Filial cannibalism

Filial cannibalism is a specific type of size-structured cannibalism in which adults eat their own offspring. Although most often thought of as parents eating live young, filial cannibalism includes parental consumption of stillborn infants and miscarried fetuses as well as infertile and still-incubating eggs. Vertebrate examples include pigs, where cannibalistic piglet savaging occurs at a rate of about 0.3% and is considered to be an abnormal behavior. However, consumption by the sow of already dead piglets that were stillborn or accidentally crushed occurs at a much higher rate and is considered normal.

Filial cannibalism is particularly common in teleost fishes, appearing in at least seventeen different families of teleosts. Within this diverse group of fish, there have been many, variable explanations of the possible adaptive value of filial cannibalism. One of these is the energy-based hypothesis, which suggests that fish eat their offspring when they are low on energy as an investment in future reproductive success. This has been supported by experimental evidence, showing that male three-spined sticklebacks, male tessellated darters, and male sphinx blenny fish all consume or absorb their own eggs to maintain their physical conditions. In other words, when males of a fish species are low on energy, it might sometimes be beneficial for them to feed on their own offspring to survive and invest in future reproductive success.

Another hypothesis as to the adaptive value of filial cannibalism in teleosts is that it increases density-dependent egg survivorship. In other words, filial cannibalism simply increases overall reproductive success by helping the other eggs make it to maturity by thinning out the numbers. Possible explanations as to why this is so include increasing oxygen availability to the remaining eggs, the negative effects of accumulating embryo waste, and predation.

In some species of eusocial wasps, such as Polistes chinensis, the reproducing female will kill and feed younger larvae to her older brood. This occurs under food stressed conditions in order to ensure that the first generation of workers emerges without delay. Further evidence also suggests that occasionally filial cannibalism might occur as a by-product of cuckoldry in fish. Males consume broods, which may include their own offspring, when they believe a certain percentage of the brood contains genetic material that is not theirs.

It is not always the parent that cannibalizes the offspring; in some spiders, mothers have been observed to feed themselves to their brood as the ultimate provision from mother to children, known as matriphagy.

The dinosaur Coelophysis was once suspected to practice this form of cannibalism but this turned out to be wrong, although Deinonychus may have done so. Skeletal remains from subadults with missing parts are suspected of having been eaten by other Deinonychus, mainly full-grown adults.

Infanticide

Infanticide is the killing of a non-adult animal by an adult of the same species. Infanticide is often accompanied by cannibalism. It is often displayed in lions; a male lion encroaching on the territory of a rival pride will often kill any existing cubs fathered by other males; this brings the lionesses into heat more quickly, enabling the invading lion to sire his own young. This is an example of cannibalistic behaviour in a genetic context.

In many species of Lepidoptera, such as Cupido minimus and the Indianmeal moth, the first larvae to hatch will consume the other eggs or smaller larvae on the host plant, decreasing competition.

Intrauterine cannibalism

Intrauterine cannibalism is a behaviour in some carnivorous species, in which multiple embryos are created at impregnation, but only one or two are born. The larger or stronger ones consume their less-developed siblings as a source of nutrients.

In adelphophagy or embryophagy, the fetus eats sibling embryos, while in oophagy it feeds on eggs.

Adelphophagy occurs in some marine gastropods (calyptraeids, muricids, vermetids, and buccinids) and in some marine annelids (Boccardia proboscidia in Spionidae).

Intrauterine cannibalism is known to occur in lamnoid sharks such as the sand tiger shark, and in the fire salamander, as well as in some teleost fishes. The Carboniferous period chimaera, Delphyodontos dacriformes, is suspected of having practiced intrauterine cannibalism, also, due to the sharp teeth of the recently born (or possibly aborted) juveniles, and the presence of fecal matter in the juveniles' intestines.

Protection against cannibalism

Animals have evolved protection to prevent and deter potential predators such as those from their own kind. Many amphibian eggs are gelatinous and toxic to decrease edibility. Often, adults would lay their eggs in crevices, holes, or empty nesting sites to hide their eggs from potential conspecific predators which tend to ingest the eggs for an additional nutritional benefit or to get rid of genetic competition. In amphibians, the development of non-aquatic egg deposition has helped increase the survival rates of their young by the evolution of viviparity or direct development. In bees, worker policing occurs to prohibit worker reproduction, whereby workers cannibalize other worker laid eggs. Queen laid eggs have a different scent than worker laid eggs, allowing workers to differentiate between the two, allowing them to nurture and protect queen laid eggs rather than cannibalising them. Parental presence at nesting sites is also a common method of protection against infanticide committed by conspecific individuals, whereby the parent exhibits defensive displays to ward off potential predators. Parental investment in newborns are generally higher during their early stages of development whereby behaviours such as aggression, territorial behaviour, and pregnancy blocking become more apparent.

Morphological plasticity helps an individual account for different predation stresses, thereby increasing individual survival rates. Japanese brown frog tadpoles have been shown to exhibit morphological plasticity when they are in a high stress environment where cannibalism between tadpoles and more developed individuals were present. Shifting their morphology plays a key role in their survival, creating bulkier bodies when put into environments where more developed tadpoles were present, to make it difficult for the individuals to swallow them whole. Diet shifts between different stages of development have also evolved to decrease competition between each stage, thereby increasing the amount of food availability so that there is a decreased chance that the individuals will turn to cannibalism as an additional food source.

Mosquito

From Wikipedia, the free encyclopedia
Mosquito
Temporal range: 99–0 Ma Late Cretaceous (Cenomanian) – Recent
Aedes aegypti, vector of yellow fever
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Diptera
Superfamily: Culicoidea
Family: Culicidae
Meigen, 1818
Subfamilies
Diversity
112 genera

Mosquitoes, the Culicidae, are a family of small flies consisting of 3,600 species. The word mosquito (formed by mosca and diminutive -ito) is Spanish and Portuguese for little fly. Mosquitoes have a slender segmented body, one pair of wings, three pairs of long hair-like legs, and specialized, highly elongated, piercing-sucking mouthparts. All mosquitoes drink nectar from flowers; females of some species have in addition adapted to drink blood. The group diversified during the Cretaceous period. Evolutionary biologists view mosquitoes as micropredators, small animals that parasitise larger ones by drinking their blood without immediately killing them. Medical parasitologists view mosquitoes instead as vectors of disease, carrying protozoan parasites or bacterial or viral pathogens from one host to another.

The mosquito life cycle consists of four stages: egg, larva, pupa, and adult. Eggs are laid on the water surface; they hatch into motile 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 feed on blood of a wide range of vertebrate hosts, and some invertebrates, primarily other arthropods. 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 arboviral 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 adult. The first three stages—egg, larva, and pupa—are largely aquatic,[4] the eggs usually being laid in stagnant water. They hatch to become larvae, which feed, grow, and molt until they change into pupae. 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.

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 Chironomid midges hold these legs forwards. Anopheles mosquitoes can fly for up to four hours continuously at 1 to 2 km/h (0.62 to 1.24 mph), traveling up to 12 km (7.5 mi) in a night. Males beat their wings between 450 and 600 times per second, driven indirectly by muscles which vibrate the thorax. Mosquitoes are mainly small flies; the largest are in the genus Toxorhynchites, at up to 18 mm (0.71 in) in length and 24 mm (0.94 in) in wingspan. Those in the genus Aedes are much smaller, with a wingspan of 2.8 to 4.4 mm (0.11 to 0.17 in).

Mosquitoes can develop from egg to adult in hot weather in as few as five days, but it may take up to a month. At dawn or dusk, within days of pupating, males assemble in swarms, mating when females fly in. The female mates only once in her lifetime, attracted by the pheromones emitted by the male. As a species that need blood for the eggs to develop, the female finds a host and drinks a full meal of blood. She then rests for two or three days to digest the meal and allow her eggs to develop. She is then ready to lay the eggs and repeat the cycle of feeding and laying. Females can live for up to three weeks in the wild, depending on temperature, humidity, their ability to obtain a blood meal, and avoiding being killed by their vertebrate hosts.

 Anatomy of an adult female mosquito

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 bromeliad. 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. Wyeomyia smithii breeds in the pitchers of pitcher plants, its larvae feeding on decaying insects that have drowned there.

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. Aedes females drop their eggs singly, on damp mud or other surfaces near water; their eggs hatch only when they are flooded. Females in genera such as Culex, Culiseta, and Uranotaenia lay their eggs in floating rafts. Mansonia females in contrast lay their eggs in arrays, attached usually to the under-surfaces of waterlily pads.

Clutches of eggs of most mosquito species hatch simultaneously, but Aedes eggs in diapause hatch irregularly over an extended period.

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 instars, molting each time, after which it metamorphoses into a pupa. Aedes larvae, except when very young, can withstand drying; they go into diapause for several months if their pond dries out.

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.

Feeding by adults

Diet

Female Ochlerotatus notoscriptus feeding on blood from a human arm.

Both male and female mosquitoes feed on nectar, aphid honeydew, and plant juices, but in many species the females are also blood-sucking ectoparasites. 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 lipids, 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 amphibians, reptiles including snakes, birds, and mammals. 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 horses. Malaria-transmitting mosquitoes seek out caterpillars and feed on their haemolymph, impeding their development.

Finding hosts

Blood-feeding female mosquitoes find their hosts using multiple cues, including exhaled carbon dioxide, heat, and many different odorants.

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 (CO2) 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 that is observed by the mosquito allows it to select its host to feed on. This occurs when a mosquito notes the presence of CO2, as it then activates its odour and visual search behaviours, ones that otherwise would not be used. In terms of a mosquito’s olfactory system, chemical analysis has revealed that people who are highly attractive to mosquitoes produce significantly more carboxylic acids. A human's unique body odour indicates that the target is actually a human host rather than some other living warm-blooded animal (as the presence of CO2 shows). Body odour, composed of volatile organic compounds emitted from the skin of humans, is the most important cue used by mosquitoes. Variation in skin odour is caused by body weight, hormones, genetic factors, and metabolic or genetic disorders. Infections such as malaria can influence an individual’s body odour. People infected by malaria produce relatively large amounts of Plasmodium-induced aldehydes in the skin, creating large cues for mosquitoes as it increases the attractiveness of an odour blend, imitating a "healthy" human odour. Infected individuals produce larger amounts of aldehydes heptanal, octanal, and nonanal. These compounds are detected by mosquito antennae. Thus, people infected with malaria are more prone to mosquito biting.

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.

Scanning electron microscope image of the Labium tip of Culex mosquito

Different species of mosquitoes have evolved different methods of identifying target hosts. Study of a domestic form and an animal-biting form of the mosquito Aedes aegypti showed that the evolution of preference for human odour is linked to increases in the expression of the olfactory receptor AaegOr4. This recognises a compound present at high levels in human odour called sulcatone. However, the malaria mosquito Anopheles gambiae also has OR4 genes strongly activated by sulcatone, yet none of them are closely related to AaegOr4, suggesting that the two species have evolved to specialise in biting humans independently.

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.

Saliva

Mosquito saliva contains enzymes 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. It modulates the host's immune response via a mixture of proteins which lower angiogenesis and immunity; create inflammation; suppress tumor necrosis factor release from activated mast cells; suppress interleukin (IL)-2 and IFN-ฮณ production; suppress T cell populations; decrease expression of interferon−ฮฑ/ฮฒ, making virus infections more severe; increase natural killer T cells in the blood; and decrease cytokine production.

Egg development and blood digestion

An Anopheles stephensi female is engorged with blood and beginning to pass unwanted liquid fractions to make room in its gut for more of the solid nutrients.

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 proteins into free amino acids. 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 subpolar climates, 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. Many can tolerate subzero temperatures, while adults of some species can survive winter by sheltering in microhabitats such as buildings or hollow trees. In warm and humid tropical regions, some mosquito species are active for the entire year, but in temperate and cold regions they hibernate or enter diapause. Arctic or subarctic mosquitoes, like some other arctic midges in families such as Simuliidae and Ceratopogonidae may be active for only a few weeks annually as melt-water pools form on the permafrost. During that time, though, they emerge in huge numbers in some regions; a swarm may take up to 300 ml of blood per day from each animal in a caribou herd.

Effect of climate change

For a mosquito to transmit disease, there must be favorable seasonal conditions, primarily humidity, temperature, and precipitation. El Niรฑo 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. Dengue fever, 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 predators. Among the many aquatic insects that catch mosquito larvae are dragonfly and damselfly nymphs, whirligig beetles, and water striders. Vertebrate predators include fish such as catfish and the mosquitofish, amphibians including the spadefoot toad 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 spiders. Flying adults are captured by dragonflies and damselflies, by birds such as swifts and swallows, and by vertebrates including bats.

Mosquitoes are parasitised by hydrachnid mites, ciliates such as Glaucoma, microsporidians such as Thelania, and fungi including species of Saprolegniaceae and Entomophthoraceae.

Pollination

A mosquito visiting a marigold flower for nectar

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 exapted mosquitoes to blood-sucking.

Parasitism

Ecologically, blood-feeding mosquitoes are micropredators, 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 parasitoids; and having multiple hosts, unlike conventional parasites. From this perspective, mosquitoes are ectoparasites, feeding on blood from the outside of their hosts, using their piercing mouthparts, rather than entering their bodies. Unlike some other ectoparasites such as fleas and lice, mosquitoes do not remain constantly on the body of the host, but visit only to feed.

Evolution

Fossil record

Fossilized mosquito encased in amber
Culex malariager mosquito infected with the malarial parasite Plasmodium dominicana, in Dominican amber of Miocene age, 15–20 million years ago

The oldest insects that have been considered to be mosquitoes are Libanoculex intermedius found in Lebanese amber, dating to the Barremian age of the Early Cretaceous, around 125 million years ago. The mouthparts of male individuals of this species are similar to living female mosquitoes, indicating that they consumed blood, unlike living male mosquitoes. However, the affinity of Libanoculex as a mosquito is questioned in a 2024 study: it may be a chaoborid fly instead. Three other 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. Paleoculicis minutus, is known from Canadian amber from Alberta, Canada, which dates to the Campanian age of the Late Cretaceous, around 79 million years ago. P. burmanicus 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. Mosquito taxonomy was advanced in 1901 when the English entomologist Frederick Vincent Theobald published his 5-volume monograph on the Culicidae. He had been provided with mosquito specimens sent in to the British Museum (Natural History) from around the world, on the 1898 instruction of the Secretary of State for the Colonies, Joseph Chamberlain, who had written that "in view of the possible connection of Malaria with mosquitoes, it is desirable to obtain exact knowledge of the different species of mosquitoes and allied insects in the various tropical colonies. I will therefore ask you ... to have collections made of the winged insects in the Colony which bite men or animals."

Phylogeny

External

Mosquitoes are members of a family of true flies (Diptera): the Culicidae (from the Latin culex, genitive culicis, meaning "midge" or "gnat"). The phylogenetic tree is based on the FLYTREE project.

Diptera


Ptychopteromorpha (phantom and primitive crane-flies)


Culicomorpha

Chironomidae (non-biting midges)




Simulioidea (blackflies and biting midges)


Culicoidea

Dixidae (meniscus midges)




Corethrellidae (frog-biting midges)




Chaoboridae (phantom midges)



Culicidae










other midges and gnats



all other flies, inc. Brachycera



(true flies)  

Internal

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.

Culicidae

basal spp.



Anophelinae


Culicinae

other spp.




Aedini




other spp.



Sabethini







Interactions with humans

Anopheles albimanus feeding on a human arm. As mosquitoes are the only vectors of malaria, controlling them reduces its incidence.

Vectors of disease

Mosquitoes are vectors for many disease-causing microorganisms including bacteria, viruses, and protozoan 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

Mosquito nets can prevent people being bitten while they sleep.

Many measures have been tried for mosquito control, including the elimination of breeding places, exclusion via window screens and mosquito nets, biological control with parasites such as fungi and nematodes, or predators such as fish, copepods, dragonfly 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. Control of disease-carrying mosquitoes using gene drives has been proposed.

Repellents

Mosquito repellents (including a mosquito coil) in a Finnish store

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). Pyrethrum (from Chrysanthemum species, particularly C. cinerariifolium and C. coccineum) is an effective plant-based repellent. Electronic insect repellent devices that produce ultrasounds 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, A. vexans, A. albopictus, Anopheles sinensis, Culex pipiens, Aedes communis, Anopheles stephensi, C. quinquefasciatus, 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 anti-itch medications, including some taken orally, such as diphenhydramine, or applied to the skin like antihistamines 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

Arthur Rackham's illustration of the fable of "The Bull and the Mosquito", 1912

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 origin myths 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 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.

The de Havilland Mosquito was a high-speed aircraft manufactured between 1940 and 1950, and used in many roles.

Future of an expanding universe

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