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Mosquito vs Human: Swapping the roles

Mosquito vs Human: Swapping the roles


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Is there a known mosquito-specific lethal (for some relevant species of mosquitos) virus that you could safely (for the humans) put into the blood of living humans? Is it technically possible to engineer humans to produce such a virus?


Mosquito immune system mapped to help fight malaria

Scientists have created the first cell atlas of mosquito immune cells, to understand how mosquitoes fight malaria and other infections. Researchers from the Wellcome Sanger Institute, Umeå University, Sweden and the National Institutes of Health (NIH), USA, discovered new types of mosquito immune cells, including a rare cell type that could be involved in limiting malaria infection. They also identified molecular pathways implicated in controlling the malaria parasite.

Published today (27 August) in Science, the findings offer opportunities for uncovering novel ways to prevent mosquitoes from spreading the malaria parasite to humans and break the chain of malaria transmission. The atlas will also be a valuable resource for researchers trying to understand and control other mosquito-borne diseases such as Dengue or Zika.

Malaria is a life-threatening disease that affects more than 200 million people worldwide and caused an estimated 405,000 deaths in 2018 alone, the majority of which were children under five. It is caused by Plasmodium parasites, which are spread via the bites of female Anopheles mosquitoes. Breaking the chain of transmission from human to mosquito to human is key for reducing the burden of malaria.

The mosquito immune system controls how the insect can tolerate or transmit parasites or viruses, however little is known about the exact cell types involved. In this first in-depth study of mosquito immune cells, a team of researchers studied two types of mosquito: Anopheles gambiae, which transmits malaria, and Aedes aegypti, which carries the viruses that causes Dengue, Chikungunya and Zika infections.

Using cutting edge single cell techniques the researchers analysed more than 8,500 individual immune cells to see exactly which genes were switched on in each cell and identify specific molecular markers for each unique cell type. The team discovered there were at least twice as many types of immune cell than had previously been seen, and used the markers to find and quantify these cells in circulation, or on the gut and other parts of the mosquito. They were then able to follow how Anopheles mosquitoes and their immune cells reacted to infection with the Plasmodium parasite.

Dr Gianmarco Raddi, a first author on the paper from the Wellcome Sanger Institute, said: "We have carried out the first ever large scale survey of the mosquito immune system, and using single cell sequencing technology we found immune cell types and cell states that had never been seen before. We also looked at mosquitoes that were infected with the Plasmodium parasite and for the first time were able to study their immune response in molecular detail, and identify which cells and pathways were involved."

A previous study from the NIH team had shown that a process called 'immune priming' could limit the ability of mosquitoes to transmit malaria, by activating the mosquito immune system to successfully fight the parasite. In this study, the researchers discovered that one of the newly discovered immune cell types had high levels of a key molecule needed for immune priming, and could be involved in that process.

Dr Oliver Billker, joint senior author on the paper previously from the Wellcome Sanger Institute and now based at Molecular Infection Medicine Sweden, Umeå University, said: "We discovered a rare but important new cell type we called a Megacyte, which could be involved in immune priming, and which appears to switch on further immune responses to the Plasmodium parasite. This is the first time a specific mosquito cell type has been implicated in regulating the control of malaria infection, and is a really exciting discovery. We now need to carry out further studies to validate this and better understand these cells and their role."

The researchers showed that specific types of immune cell -- granulocytes -- increased in number in response to infection, and revealed that some of these could develop into other immune cells. They also discovered that immune cells in the mosquito's gut and other tissues are actively recruited into the circulation to fight infections after lying dormant on the mosquito fat body.

Dr Sarah Teichmann, an author from the Wellcome Sanger Institute, said: "The team has created the first mosquito immune cell atlas, to shed light on how mosquito immune systems fight infections. Mosquitos appear to have a sweet spot of immunity to parasites like malaria, with enough immunity to the infection that it doesn't kill the mosquito but not enough to remove the parasite. This atlas offers a vital resource for further research, which could reveal ways to modify the mosquito immune response to break the chain of disease transmission."


Genetic changes help mosquitoes survive pesticide attacks

For decades, chemical pesticides have been the most important way of controlling insects like the Anopheles mosquito species that spreads malaria to humans. Unfortunately, the bugs have fought back, evolving genetic shields to protect themselves and their offspring from future attacks.

The fascinating array of genetic changes that confer pesticide resistance in Anopheles mosquitoes is reviewed in an article published today in Trends in Parasitology. The paper is written by Colince Kamdem, a postdoctoral scholar, and two colleagues from the Department of Entomology at the University of California, Riverside. The findings highlight the interplay between human interventions, mosquito evolution, and disease outcomes, and will help scientists develop new strategies to overcome pesticide resistance.

In 2015, there were roughly 212 million malaria cases and an estimated 429,000 deaths due to malaria, according to the World Health Organization. While increased prevention and control measures have led to a 29 percent reduction in malaria mortality rates globally since 2010, the increase in pesticide resistant insects underscores the need for new strategies. "One of the main obstacles to malaria eradication is the enormous diversity and adaptive flexibility of the Anopheles mosquito species, therefore a better understanding of the genetic, behavioral, and ecological factors underlying its ability to evolve resistance is key to controlling this disease," Kamdem said.

In sub-Saharan Africa, multiple factors, including the widespread use of long-lasting insecticidal nets, indoor residual spraying, exposure to chemical pollutants, urbanization, and agricultural practices, are contributing to the selection of malaria mosquitoes that are highly resistant to several classes of insecticide.

Kamden's article highlights several ways that mosquitoes are adapting to insecticide exposure. Advantageous mutations in the insecticide target site are a major source of resistance, highlighting the direct impact of human interventions on the mosquito genome. Other mutations boost the activity of enzymes that degrade or sequester the insecticide before it reaches its target in the cell. In some cases, mosquitoes change their behaviors to avoid coming into contact with pesticides.

"These changes are occurring at the molecular, physiological and behavioral level, and multiple changes are often happening at the same time. With the accessibility of DNA sequencing we can now pinpoint these evolutionary changes at the genomic level," Kamdem said.

Kamdem said the high genetic diversity among mosquito species and their ability to swap genes makes it difficult to stop the development of insecticide-resistant groups. Gene drive systems that use genetic approaches to kill mosquitoes, prevent them from breeding, or stop them from transmitting the malaria-causing parasite are under development, but a concern is that mosquitoes could evolve resistance to these techniques, too. "The insights gained from the intensive use of insecticides and its impact on the mosquito genome will be critical for the successful implementation of gene editing systems as a new approach to controlling mosquito-borne diseases," Kamdem said. "Due to the emergence of mosquito-borne diseases such as Zika, several countries are implementing, or are preparing to deploy, vector control strategies on a large scale. One of the most pressing needs is to design evidence-based monitoring tools to fight back the inevitable resistance of mosquitoes."


The Food Web

Mosquito larvae are aquatic insects and, as such, play an important role in the aquatic food chain. According to Dr. Gilbert Waldbauer in "The Handy Bug Answer Book," Mosquito larvae are filter feeders that strain tiny organic particles such as unicellular algae from the water and convert them to the tissues of their own bodies, which are, in turn, eaten by fish. Mosquito larvae are, in essence, nutrient-packed snacks for fish and other aquatic animals.

In addition, while species of mosquitoes eat the carcasses of insects that drown in the water, the mosquito larvae feed on the waste products, making nutrients such as nitrogen available for the plant community to thrive. Thus, the elimination of those mosquitoes might affect plant growth in those areas.

A mosquito's role on the bottom of the food chain does not end at the larval stage. As adults, mosquitoes serve as equally nutritious meals for birds, bats, and spiders.

Mosquitoes seem to represent a considerable biomass of food for wildlife on the lower rungs of the food chain. Mosquito extinction, if it is achievable, could have an adverse effect on the ecosystem. However, many scientists suggest that the ecosystem could eventually rebound and another species could take its place in the system.


Contents

The oldest known mosquitoes are known from amber dating to the Late Cretaceous. Three species of Cretaceous mosquito are currently known, Burmaculex antiquus and Priscoculex burmanicus are known from Burmese amber from Myanmar, which dates to the earliest part of the Cenomanian stage of the Late Cretaceous, around 99 million years ago. [10] [11] Paleoculicis minutus, is known from Canadian amber from Alberta, Canada, which dates to the Campanian stage of the Late Cretaceous, around 79 million years ago. [12] Priscoculex burmanicus can be definitively assigned to Anophelinae, one of the two subfamilies of mosquitoes alongside Culicinae, indicating the split between these two subfamilies occurred over 99 million years ago. [11] Molecular estimates suggest that the split between the two subfamilies occurred 197.5 million years ago, during the Early Jurassic, but that major diversification did not take place until the Cretaceous. [13]

The mosquito Anopheles gambiae is currently undergoing speciation into the M(opti) and S(avanah) molecular forms. Consequently, some pesticides that work on the M form no longer work on the S form. [14] Over 3,500 species of the Culicidae have already been described. [15] They are generally divided into two subfamilies which in turn comprise some 43 genera. These figures are subject to continual change, as more species are discovered, and as DNA studies compel rearrangement of the taxonomy of the family. The two main subfamilies are the Anophelinae and Culicinae, with their genera as shown in the subsection below. [16] The distinction is of great practical importance because the two subfamilies tend to differ in their significance as vectors of different classes of diseases. Roughly speaking, arboviral diseases such as yellow fever and dengue fever tend to be transmitted by Culicine species, not necessarily in the genus Culex. Some transmit various species of avian malaria, but it is not clear that they ever transmit any form of human malaria. Some species do however transmit various forms of filariasis, much as many Simuliidae do.

Family Edit

Mosquitoes are members of a family of nematoceran flies: the Culicidae (from the Latin culex, genitive culicis, meaning "midge" or "gnat"). [17] Superficially, mosquitoes resemble crane flies (family Tipulidae) and chironomid flies (family Chironomidae).

Subfamilies Edit

Genera Edit

Mosquitoes have been classified into 112 genera, some of the more common of which appear below.

  • Aedeomyia
  • Aedes
  • Anopheles
  • Armigeres
  • Ayurakitia
  • Borachinda
  • Coquillettidia
  • Culex
  • Culiseta
  • Deinocerites
  • Eretmapodites
  • Ficalbia
  • Galindomyia
  • Haemagogus
  • Heizmannia
  • Hodgesia
  • Isostomyia
  • Johnbelkinia
  • Kimia
  • Limatus
  • Lutzia
  • Malaya
  • Mansonia
  • Maorigoeldia
  • Mimomyia
  • Onirion
  • Opifex
  • Orthopodomyia
  • Psorophora
  • Runchomyia
  • Sabethes
  • Shannoniana
  • Topomyia
  • Toxorhynchites
  • Trichoprosopon
  • Tripteroides
  • Udaya
  • Uranotaenia
  • Verrallina
  • Wyeomyia

Species Edit

Over 3,500 species of mosquitoes have thus far been described in the scientific literature. [18] [19]

As true flies, mosquitoes have one pair of wings, with distinct scales on the surface. Their wings are long and narrow, as are their long, thin legs. They have slender and dainty bodies of length typically 3–6 mm, with dark grey to black coloring. Some species harbor specific morphological patterns. When at rest they tend to hold their first pair of legs outward. They are similar in appearance to midges (Chironomidae), another ancient family of flies. Tokunagayusurika akamusi, for example, is a midge fly that look very much alike mosquitoes in that they also have slender and dainty bodies of similar colors, though larger in size. They also have only one pair of wings, but without scales on the surface. Another distinct feature to tell the two families of flies apart is the way they hold their first pair of legs - mosquitoes hold them outward, while midges hold them forward. [20]

Overview Edit

Like all flies, mosquitoes go through four stages in their life cycles: egg, larva, pupa, and adult or imago. The first three stages—egg, larva, and pupa—are largely aquatic. Each of the stages typically lasts 5 to 14 days, depending on the species and the ambient temperature, but there are important exceptions. [21] Mosquitoes living in regions where some seasons are freezing or waterless spend part of the year in diapause they delay their development, typically for months, and carry on with life only when there is enough water or warmth for their needs. For instance, Wyeomyia larvae typically get frozen into solid lumps of ice during winter and only complete their development in spring. The eggs of some species of Aedes remain unharmed in diapause if they dry out, and hatch later when they are covered by water.

Eggs hatch to become larvae, which grow until they are able to change into pupae. The adult mosquito emerges from the mature pupa as it floats at the water surface. Bloodsucking mosquitoes, depending on species, sex, and weather conditions, have potential adult lifespans ranging from as short as a week to as long as several months. Some species can overwinter as adults in diapause. [22] [23]

Breeding Edit

In most species, adult females lay their eggs in stagnant water: some lay near the water's edge while others attach their eggs to aquatic plants. Each species selects the situation of the water into which it lays its eggs and does so according to its own ecological adaptations. Some breed in lakes, some in temporary puddles. Some breed in marshes, some in salt-marshes. Among those that breed in salt water (such as Opifex fuscus), some are equally at home in fresh and salt water up to about one-third the concentration of seawater, whereas others must acclimatize themselves to the salinity. [24] Such differences are important because certain ecological preferences keep mosquitoes away from most humans, whereas other preferences bring them right into houses at night.

Some species of mosquitoes prefer to breed in phytotelmata (natural reservoirs on plants), such as rainwater accumulated in holes in tree trunks, or in the leaf-axils of bromeliads. Some specialize in the liquid in pitchers of particular species of pitcher plants, their larvae feeding on decaying insects that had drowned there or on the associated bacteria the genus Wyeomyia provides such examples — the harmless Wyeomyia smithii breeds only in the pitchers of Sarracenia purpurea. [25]

However, some of the species of mosquitoes that are adapted to breeding in phytotelmata are dangerous disease vectors. In nature, they might occupy anything from a hollow tree trunk to a cupped leaf. Such species typically take readily to breeding in artificial water containers. Such casual puddles are important breeding places for some of the most serious disease vectors, such as species of Aedes that transmit dengue and yellow fever. Some with such breeding habits are disproportionately important vectors because they are well-placed to pick up pathogens from humans and pass them on. In contrast, no matter how voracious, mosquitoes that breed and feed mainly in remote wetlands and salt marshes may well remain uninfected, and if they do happen to become infected with a relevant pathogen, might seldom encounter humans to infect, in turn.

Eggs and oviposition Edit

Mosquito habits of oviposition, the ways in which they lay their eggs, vary considerably between species, and the morphologies of the eggs vary accordingly. The simplest procedure is that followed by many species of Anopheles like many other gracile species of aquatic insects, females just fly over the water, bobbing up and down to the water surface and dropping eggs more or less singly. The bobbing behavior occurs among some other aquatic insects as well, for example mayflies and dragonflies it is sometimes called "dapping". The eggs of Anopheles species are roughly cigar-shaped and have floats down their sides. Females of many common species can lay 100–200 eggs during the course of the adult phase of their life cycles. Even with high egg and intergenerational mortality, over a period of several weeks, a single successful breeding pair can create a population of thousands.

Some other species, for example members of the genus Mansonia, lay their eggs in arrays, attached usually to the under-surfaces of waterlily pads. Their close relatives, the genus Coquillettidia, lay their eggs similarly, but not attached to plants. Instead, the eggs form layers called "rafts" that float on the water. This is a common mode of oviposition, and most species of Culex are known for the habit, which also occurs in some other genera, such as Culiseta and Uranotaenia. Anopheles eggs may on occasion cluster together on the water, too, but the clusters do not generally look much like compactly glued rafts of eggs.

In species that lay their eggs in rafts, rafts do not form adventitiously the female Culex settles carefully on still water with its hind legs crossed, and as it lays the eggs one by one, it twitches to arrange them into a head-down array that sticks together to form the raft. [26]

Aedes females generally drop their eggs singly, much as Anopheles do, but not as a rule into water. Instead, they lay their eggs on damp mud or other surfaces near the water's edge. Such an oviposition site commonly is the wall of a cavity such as a hollow stump or a container such as a bucket or a discarded vehicle tire. The eggs generally do not hatch until they are flooded, and they may have to withstand considerable desiccation before that happens. They are not resistant to desiccation straight after oviposition, but must develop to a suitable degree first. Once they have achieved that, however, they can enter diapause for several months if they dry out. Clutches of eggs of the majority of mosquito species hatch as soon as possible, and all the eggs in the clutch hatch at much the same time. In contrast, a batch of Aedes eggs in diapause tends to hatch irregularly over an extended period of time. This makes it much more difficult to control such species than those mosquitoes whose larvae can be killed all together as they hatch. Some Anopheles species do also behave in such a manner, though not to the same degree of sophistication. [27]

Larva Edit

The mosquito larva has a well-developed head with mouth brushes used for feeding, a large thorax with no legs, and a segmented abdomen.

Larvae breathe through spiracles located on their eighth abdominal segments, or through a siphon, so must come to the surface frequently. The larvae spend most of their time feeding on algae, bacteria, and other microbes in the surface microlayer.

Mosquito larvae have been investigated as prey of other Dipteran flies. Species such as Bezzia nobilis within the family Ceratopogonidae have been observed in experiments to prey upon mosquito larvae. [28] [29]

They dive below the surface when disturbed. Larvae swim either through propulsion with their mouth brushes, or by jerky movements of their entire bodies, giving them the common name of "wigglers" or "wrigglers".

Larvae develop through four stages, or instars, after which they metamorphose into pupae. At the end of each instar, the larvae molt, shedding their skins to allow for further growth.

Anopheles larva from southern Germany, about 8 mm long

Culex larva and pupa

Culex larvae plus one pupa

Pupa Edit

As seen in its lateral aspect, the mosquito pupa is comma-shaped. The head and thorax are merged into a cephalothorax, with the abdomen curving around underneath. The pupa can swim actively by flipping its abdomen, and it is commonly called a "tumbler" because of its swimming action. As with 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. However, pupae do not feed during this stage typically they pass their time hanging from the surface of the water by their respiratory trumpets. If alarmed, say by a passing shadow, they nimbly swim downwards by flipping their abdomens in much the same way as the larvae do. If undisturbed, they soon float up again.

After a few days or longer, depending on the temperature and other circumstances, the dorsal surface of its cephalothorax splits, and the adult mosquito emerges. The pupa is less active than the larva because it does not feed, whereas the larva feeds constantly. [26]

Adult Edit

The period of development from egg to adult varies among species and is strongly influenced by ambient temperature. Some species of mosquitoes can develop from egg to adult in as few as five days, but a more typical period of development in tropical conditions would be some 40 days or more for most species. The variation of the body size in adult mosquitoes depends on the density of the larval population and food supply within the breeding water.

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.

Males typically live for about 5–7 days, feeding on nectar and other sources of sugar. 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 two to three 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 and predators.

The length of the adult is typically between 3 mm and 6 mm. The smallest known mosquitoes are around 2 mm (0.1 in), and the largest around 19 mm (0.7 in). [30] Mosquitoes typically weigh around 5 mg. All mosquitoes have slender bodies with three segments: a head, a thorax and an abdomen.

The head is specialized for receiving sensory information and for feeding. It has 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. In all mosquito species, the antennae of the males in comparison to the females are noticeably bushier and contain auditory receptors to detect the characteristic whine of the females.

The compound eyes are distinctly separated from one another. Their larvae only possess a pit-eye ocellus. The compound eyes of adults develop in a separate region of the head. [31] New ommatidia are added in semicircular rows at the rear of the eye. During the first phase of growth, this leads to individual ommatidia being square, but later in development they become hexagonal. The hexagonal pattern will only become visible when the carapace of the stage with square eyes is molted. [31]

The head also has an elongated, forward-projecting, stinger-like proboscis used for feeding, and two sensory palps. The maxillary palps of the males are longer than their proboscises, whereas the females’ maxillary palps are much shorter. In typical bloodsucking species, the female has an elongated proboscis.

The thorax is specialized for locomotion. Three pairs of legs and a pair of wings are attached to the thorax. The insect wing is an outgrowth of the exoskeleton. The Anopheles mosquito can fly for up to four hours continuously at 1 to 2 km/h (0.6–1 mph), [32] traveling up to 12 km (7.5 mi) in a night. Males beat their wings between 450 and 600 times per second. [33]

The abdomen is specialized for food digestion and egg development the abdomen of a mosquito can hold three times its own weight in blood. [34] This segment expands considerably when a female takes a blood meal. The blood is digested over time, serving as a source of protein for the production of eggs, which gradually fill the abdomen.

Typically, both male and female mosquitoes feed on nectar, aphid honeydew, and plant juices, [35] but in many species the mouthparts of the females are adapted for piercing the skin of animal hosts and sucking their blood as ectoparasites. In many species, the female needs to obtain nutrients from a blood meal before it can produce eggs, whereas in many other species, obtaining nutrients from a blood meal enables the mosquito to lay more eggs. A mosquito has a variety of ways of finding nectar or its prey, including chemical, visual, and heat sensors. [36] [37] Both plant materials and blood are useful sources of energy in the form of sugars, and blood also supplies more concentrated nutrients, such as lipids, but the most important function of blood meals is to obtain proteins as materials for egg production. [38] [39]

Among humans, the feeding preferences of mosquitoes typically include: those with type O blood, heavy breathers, an abundance of skin bacteria, high body heat, and pregnant women. [40] [41] Individuals' attractiveness to mosquitoes also has a heritable, genetically-controlled component. [42]

When a female reproduces without such parasitic meals, it is said to practice autogenous reproduction, as in Toxorhynchites otherwise, the reproduction may be termed anautogenous, as occurs in mosquito species that serve as disease vectors, particularly Anopheles and some of the most important disease vectors in the genus Aedes. In contrast, some mosquitoes, for example, many Culex, are partially anautogenous: they do not need a blood meal for their first cycle of egg production, which they produce autogenously however, subsequent clutches of eggs are produced anautogenously, at which point their disease vectoring activity becomes operative. [43]

Female mosquitoes hunt their blood host by detecting organic 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. Mosquitoes prefer some people over others. The preferred victim's sweat smells more attractive than others' because of the proportions of the carbon dioxide, octenol, and other compounds that make up body odor. [44] The most powerful semiochemical that triggers the keen sense of smell of Culex quinquefasciatus is nonanal. [45] Another compound identified in human blood that attracts mosquitoes is sulcatone or 6-methyl-5-hepten-2-one, especially for Aedes aegypti mosquitoes with the odor receptor gene Or4. [46] 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. [47] In Aedes, the search for a host takes place in two phases. First, the mosquito exhibits a nonspecific searching behavior until the perception of a host's stimulants, then it follows a targeted approach. [48]

Most mosquito species are crepuscular (dawn or dusk) feeders. During the heat of the day, most mosquitoes rest in a cool place and wait for the evenings, although they may still bite if disturbed. [49] Some species, such as the Asian tiger mosquito, are known to fly and feed during daytime. [50]

Prior to and during blood feeding, blood-sucking mosquitoes inject saliva into the bodies of their source(s) of blood. This saliva serves as an anticoagulant without it the female mosquito's proboscis might become clogged with blood clots. The saliva also is the main route by which mosquito physiology offers passenger pathogens access to the hosts' bloodstream. The salivary glands are a major target to most pathogens, whence they find their way into the host via the saliva.

A mosquito bite often leaves an itchy weal, a raised bump, on the victim's skin, which is caused by histamines trying to fight off the protein left by the attacking insect. [51]

Mosquitoes of the genus Toxorhynchites never drink blood. [52] This genus includes the largest extant mosquitoes, the larvae of which prey on the larvae of other mosquitoes. These mosquito eaters have been used in the past as mosquito control agents, with varying success. [53]

Hosts of blood-feeding mosquito species Edit

Many, if not all, blood-sucking species of mosquitoes are fairly selective feeders that specialise in particular host species, though they often relax their selectivity when they experience severe competition for food, defensive activity on the part of the hosts, or starvation. Some species feed selectively on monkeys, while others prefer particular kinds of birds, but they become less selective as conditions become more difficult. For example, Culiseta melanura sucks the blood of passerine birds for preference, and such birds are typically the main reservoir of the Eastern equine encephalitis virus in North America. Early in the season while mosquito numbers are low, they concentrate on passerine hosts, but as mosquito numbers rise and the birds are forced to defend themselves more vigorously, the mosquitoes become less selective of hosts. Soon the mosquitoes begin attacking mammals more readily, thereby becoming the major vector of the virus, and causing epidemics of the disease, most conspicuously in humans and horses. [54]

Even more dramatically, in most of its range in North America, the main vector for the Western equine encephalitis virus is Culex tarsalis, because it is known to feed variously on mammals, birds, reptiles, and amphibians. Even fish may be attacked by some mosquito species if they expose themselves above water level, as mudskippers do. [54] [55]

In 1969 it was reported that some species of anautogenous mosquitoes would feed on the haemolymph of caterpillars. [56] Other observations include mosquitoes feeding on cicadas [57] and mantids. [58] In 2014, it was shown that malaria-transmitting mosquitoes actively seek out some species of caterpillars and feed on their haemolymph, [59] and do so to the caterpillar's apparent physical detriment. [60]

Mouthparts Edit

Mosquito mouthparts are very specialized, particularly those of the females, which in most species are adapted to piercing skin and then sucking blood. Apart from bloodsucking, the females generally also drink assorted fluids rich in dissolved sugar, such as nectar and honeydew, to obtain the energy they need. For this, their blood-sucking mouthparts are perfectly adequate. In contrast, male mosquitoes are not bloodsuckers they only drink sugary fluids. Accordingly, their mouthparts do not require the same degree of specialization as those of females. [61]

Externally, the most obvious feeding structure of the mosquito is the proboscis. More specifically, the visible part of the proboscis is the labium, which forms the sheath enclosing the rest of the mouthparts. When the mosquito first lands on a potential host, its mouthparts are enclosed entirely in this sheath, and it will touch the tip of the labium to the skin in various places. Sometimes, it will begin to bite almost straight away, while other times, it will prod around, apparently looking for a suitable place. Occasionally, it will wander for a considerable time, and eventually fly away without biting. Presumably, this probing is a search for a place with easily accessible blood vessels, but the exact mechanism is not known. It is known that there are two taste receptors at the tip of the labium which may well play a role. [62]

The female mosquito does not insert its labium into the skin it bends back into a bow when the mosquito begins to bite. The tip of the labium remains in contact with the skin of the victim, acting as a guide for the other mouthparts. In total, there are six mouthparts besides the labium: two mandibles, two maxillae, the hypopharynx, and the labrum.

The mandibles and the maxillae are used for piercing the skin. The mandibles are pointed, while the maxillae end in flat, toothed "blades". To force these into the skin, the mosquito moves its head backwards and forwards. On one movement, the maxillae are moved as far forward as possible. On the opposite movement, the mandibles are pushed deeper into the skin by levering against the maxillae. The maxillae do not slip back because the toothed blades grip the skin.

The hypopharynx and the labrum are both hollow. Saliva with anticoagulant is pumped down the hypopharynx to prevent clotting, and blood is drawn up the labrum.

To understand the mosquito mouthparts, it is helpful to draw a comparison with an insect that chews food, such as a dragonfly. A dragonfly has two mandibles, which are used for chewing, and two maxillae, which are used to hold the food in place as it is chewed. The labium forms the floor of the dragonfly's mouth, the labrum forms the top, while the hypopharynx is inside the mouth and is used in swallowing. Conceptually, then, the mosquito's proboscis is an adaptation of the mouthparts that occur in other insects. The labium still lies beneath the other mouthparts, but also enfolds them, and it has been extended into a proboscis. The maxillae still "grip" the "food" while the mandibles "bite" it. The top of the mouth, the labrum, has developed into a channeled blade the length of the proboscis, with a cross-section like an inverted "U". Finally, the hypopharynx has extended into a tube that can deliver saliva at the end of the proboscis. Its upper surface is somewhat flattened so, when the lower part of the hypopharynx is pressed against it, the labrum forms a closed tube for conveying blood from the victim. [63]

Saliva Edit

For the mosquito to obtain a blood meal, it must circumvent the vertebrate's physiological responses. The mosquito, as with all blood-feeding arthropods, has mechanisms to effectively block the hemostasis system with their saliva, which contains a mixture of secreted proteins. Mosquito saliva acts to reduce vascular constriction, blood clotting, platelet aggregation, angiogenesis and immunity, and creates inflammation. [64] Universally, hematophagous arthropod saliva contains at least one anti-clotting, one anti-platelet, and one vasodilatory substance. Mosquito saliva also contains enzymes that aid in sugar feeding, [65] and antimicrobial agents to control bacterial growth in the sugar meal. [66] The composition of mosquito saliva is relatively simple, as it usually contains fewer than 20 dominant proteins. [67] As of the early 2000s [update] , scientists still were unable to ascribe functions to more than half of the molecules found in arthropod saliva. [67] One promising application of components of mosquito saliva is the development of anti-clotting drugs, such as clotting inhibitors and capillary dilators, that could be useful for cardiovascular disease.

It is now well recognized that feeding ticks, sandflies, and, more recently, mosquitoes, have an ability to modulate the immune response of the animals (hosts) on which they feed. [64] The presence of this activity in vector saliva is a reflection of the inherent overlapping and interconnected nature of the host hemostatic and inflammatory/immunological responses and the intrinsic need to prevent these host defenses from disrupting successful feeding. The mechanism for mosquito saliva-induced alteration of the host immune response is unclear, but the data have become increasingly convincing that such an effect occurs. Early work described a factor in saliva that directly suppresses TNF-α release, but not antigen-induced histamine secretion, from activated mast cells. [68] Experiments by Cross et al. (1994) demonstrated that the inclusion of Ae. aegypti mosquito saliva into naïve cultures led to a suppression of interleukin (IL)-2 and IFN-γ production, while the cytokines IL-4 and IL-5 are unaffected. [69] Cellular proliferation in response to IL-2 is clearly reduced by prior treatment of cells with mosquito salivary gland extract. [69] Correspondingly, activated splenocytes isolated from mice fed upon by either Ae. aegypti or Cx. pipiens mosquitoes produce markedly higher levels of IL-4 and IL-10 concurrent with suppressed IFN-γ production. [70] Unexpectedly, this shift in cytokine expression is observed in splenocytes up to 10 days after mosquito exposure, suggesting natural feeding of mosquitoes can have a profound, enduring, and systemic effect on the immune response. [70]

T cell populations are decidedly susceptible to the suppressive effect of mosquito saliva, showing increased mortality and decreased division rates. [71] Parallel work by Wasserman et al. (2004) demonstrated that T and B cell proliferation was inhibited in a dose dependent manner with concentrations as low as 1/7 of the saliva in a single mosquito. [72] Depinay et al. (2005) observed a suppression of antibody-specific T cell responses mediated by mosquito saliva and dependent on mast cells and IL-10 expression. [73]

A 2006 study suggests mosquito saliva can also decrease expression of interferon−α/β during early mosquito-borne virus infection. [74] The contribution of type I interferons (IFN) in recovery from infection with viruses has been demonstrated in vivo by the therapeutic and prophylactic effects of administration of IFN inducers or IFN itself, [75] and different research suggests mosquito saliva exacerbates West Nile virus infection, [76] as well as other mosquito-transmitted viruses. [77]

Studies in humanized mice bearing a reconstituted human immune system have suggested potential impact of mosquito saliva in humans. Work published in 2018 from the Baylor College of Medicine using such humanized mice came to several conclusions, among them being that mosquito saliva led to an increase in natural killer T cells in peripheral blood to an overall decrease in ex vivo cytokine production by peripheral blood mononuclear cells (PBMCs) changes to proportions of subsets of PBMCs changes in the prevalence of T cell subtypes across organs and changes to circulating levels of cytokines. [78]

Egg development and blood digestion Edit

Most species of mosquito require a blood meal to begin the process of egg development. Females with poor larval nutrition may need to ingest sugar or a preliminary blood meal bring ovarian follicles to their resting stage. Once the follicles have reached the resting stage, digestion of a sufficiently large blood meal triggers a hormonal cascade that leads to egg development. [62] 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 membrane keeps the blood separate from anything else in the stomach. However, like certain other insects that survive on dilute, purely liquid diets, notably many of the Hemiptera, many adult mosquitoes must excrete unwanted aqueous fractions even as they feed. (See the photograph of a feeding Anopheles stephensi: Note that the excreted droplet patently is not whole blood, being far more dilute). As long as they are not disturbed, this permits mosquitoes to continue feeding until they have accumulated a full meal of nutrient solids. As a result, a mosquito replete with blood can continue to absorb sugar, even as the blood meal is slowly digested over a period of several days. [62] [79] Once blood is in the stomach, the midgut of the female synthesizes proteolytic enzymes that hydrolyze the blood proteins into free amino acids. These are used as building blocks for the synthesis of vitellogenin, which are the precursors for egg yolk protein. [62]

In the mosquito Anopheles stephensi, trypsin activity is restricted entirely to the posterior midgut lumen. No trypsin activity occurs before the blood meal, but activity increases continuously up to 30 hours after feeding, and subsequently returns to baseline levels by 60 hours. Aminopeptidase is active in the anterior and posterior midgut regions before and after feeding. In the whole midgut, activity rises from a baseline of approximately three enzyme units (EU) per midgut to a maximum of 12 EU at 30 hours after the blood meal, subsequently falling to baseline levels by 60 hours. A similar cycle of activity occurs in the posterior midgut and posterior midgut lumen, whereas aminopeptidase in the posterior midgut epithelium decreases in activity during digestion. Aminopeptidase in the anterior midgut is maintained at a constant, low level, showing no significant variation with time after feeding. Alpha-glucosidase is active in anterior and posterior midguts before and at all times after feeding. In whole midgut homogenates, alpha-glucosidase activity increases slowly up to 18 hours after the blood meal, then rises rapidly to a maximum at 30 hours after the blood meal, whereas the subsequent decline in activity is less predictable. All posterior midgut activity is restricted to the posterior midgut lumen. Depending on the time after feeding, greater than 25% of the total midgut activity of alpha-glucosidase is located in the anterior midgut. After blood meal ingestion, proteases are active only in the posterior midgut. Trypsin is the major primary hydrolytic protease and is secreted into the posterior midgut lumen without activation in the posterior midgut epithelium. Aminopeptidase activity is also luminal in the posterior midgut, but cellular aminopeptidases are required for peptide processing in both anterior and posterior midguts. Alpha-glucosidase activity is elevated in the posterior midgut after feeding in response to the blood meal, whereas activity in the anterior midgut is consistent with a nectar-processing role for this midgut region. [80]

Distribution Edit

Mosquitoes are cosmopolitan (world-wide): they are in every land region except Antarctica [62] and a few islands with polar or subpolar climates. Iceland is such an island, being essentially free of mosquitoes. [81]

The absence of mosquitoes in Iceland and similar regions is probably because of quirks of their climate, which differs in some respects from mainland regions. At the start of the uninterrupted continental winter of Greenland and the northern regions of Eurasia and America, the pupa enters diapause under the ice that covers sufficiently deep water. The imago emerges only after the ice breaks in late spring. In Iceland however, the weather is less predictable. In mid-winter it frequently warms up suddenly, causing the ice to break, but then to freeze again after a few days. By that time the mosquitoes will have emerged from their pupae, but the new freeze sets in before they can complete their life cycle. Any anautogenous adult mosquito would need a host to supply a blood meal before it could lay viable eggs it would need time to mate, mature the eggs and oviposit in suitable wetlands. These requirements would not be realistic in Iceland and in fact the absence of mosquitoes from such subpolar islands is in line with the islands' low biodiversity Iceland has fewer than 1,500 described species of insects, many of them probably accidentally introduced by human agency. In Iceland most ectoparasitic insects live in sheltered conditions or actually on mammals examples include lice, fleas and bedbugs, in whose living conditions freezing is no concern, and most of which were introduced inadvertently by humans. [81]

Some other aquatic Diptera, such as Simuliidae, do survive in Iceland, but their habits and adaptations differ from those of mosquitoes Simuliidae for example, though they, like mosquitoes, are bloodsuckers, generally inhabit stones under running water that does not readily freeze and which is totally unsuited to mosquitoes mosquitoes are generally not adapted to running water. [82] [83]

Eggs of species of mosquitoes from the temperate zones are more tolerant of cold than the eggs of species indigenous to warmer regions. [84] [85] Many even tolerate subzero temperatures. In addition, adults of some species can survive the winter by taking shelter in suitable microhabitats such as buildings or hollow trees. [86]

Pollination Edit

Several flowers are pollinated by mosquitoes, [87] including some members of the Asteraceae, Roseaceae and Orchidaceae. [88] [89] [90] [91]

Activity Edit

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 and may take up to 300 ml of blood per day from each animal in a caribou herd. [92]

Means of dispersal Edit

Worldwide introduction of various mosquito species over large distances into regions where they are not indigenous has occurred through human agencies, primarily on sea routes, in which the eggs, larvae, and pupae inhabiting water-filled used tires and cut flowers are transported. However, apart from sea transport, mosquitoes have been effectively carried by personal vehicles, delivery trucks, trains, and aircraft. Man-made areas such as storm water retention basins, or storm drains also provide sprawling sanctuaries. Sufficient quarantine measures have proven difficult to implement. In addition, outdoor pool areas make a perfect place for them to grow.

Climate and global distribution Edit

Seasonality Edit

In order for a mosquito to transmit a disease to the host there must be favorable conditions, referred to as transmission seasonality. [93] Seasonal factors that impact the prevalence of mosquitos and mosquito-borne diseases are primarily humidity, temperature, and precipitation. A positive correlation between malaria outbreaks and these climatic variables has been demonstrated in China [94] and El Niño has been shown to impact the location and number of outbreaks of mosquito-borne diseases observed in East Africa, Latin America, Southeast Asia and India. [95] Climate change impacts each of these seasonal factors and in turn impacts the dispersal of mosquitos.

Past and future patterns Edit

Climatology and the study of mosquito-borne disease have been developed only over the past 100 years however historical records of weather patterns and distinct symptoms associated with mosquito-borne diseases can be utilized to trace the prevalence of these diseases in relation to the climate over longer time periods. [93] Further, statistical models are being created to predict the impact of climate change on vector-borne diseases using these past records, and these models can be utilized in the field of public health in order to create interventions to reduce the impact of these predicted outcomes.

Two types of models are used to predict mosquito-borne disease spread in relation to climate: correlative models and mechanistic models. Correlative models focus primarily on vector distribution, and generally function in 3 steps. First, data is collected regarding geographical location of a target mosquito species. Next, a multivariate regression model establishes the conditions under which the target species can survive. Finally, the model determines the likelihood of the mosquito species to become established in a new location based on similar living conditions. The model can further predict future distributions based on environmental emissions data. Mechanistic models tend to be broader and include the pathogens and hosts in the analysis. These models have been used to recreate past outbreaks as well as predict the potential risk of a vector-borne disease based on an areas forecasted climate. [96]

Mosquito-borne diseases are currently most prevalent in East Africa, Latin America, Southeast Asia, and India however, emergence of vector-borne diseases in Europe have recently been observed. A weighted risk analysis demonstrated associations to climate for 49% of infectious diseases in Europe including all transmission routes. One statistical model predicts by 2030, the climate of southern Great Britain will be climatically suitable for malaria transmission Plasmodium vivax for 2 months of the year. By 2080 it is predicted that the same will be true for southern Scotland. [97] [98]

Mosquitoes can act as vectors for many disease-causing viruses and parasites. Infected mosquitoes carry these organisms from person to person without exhibiting symptoms themselves. [99] Mosquito-borne diseases include:

  • Viral diseases, such as yellow fever, dengue fever, and chikungunya, transmitted mostly by Aedes aegypti. Dengue fever is the most common cause of fever in travelers returning from the Caribbean, Central America, South America, and South Central Asia. This disease is spread through the bites of infected mosquitoes and cannot be spread person to person. Severe dengue can be fatal, but with good treatment, fewer than 1% of patients die from dengue. [100] Work published in 2012 from Baylor College of Medicine suggested that for some diseases, such as dengue fever, which can be transmitted via mosquitoes and by other means, the severity of the mosquito-transmitted disease could be greater. [101]
  • The parasitic diseases collectively called malaria, caused by various species of Plasmodium, carried by female mosquitoes of the genus Anopheles. (the main cause of elephantiasis) which can be spread by a wide variety of mosquito species. [102] is a significant concern in the United States but there are no reliable statistics on worldwide cases. [103]
  • Dengue viruses are a significant health risk globally. Severe cases of dengue often require hospitalization and can be life-threatening shortly after infection. Symptoms include a high fever, aches and pains, vomiting, and a rash. Warning signs of severe dengue infection include vomiting blood, bleeding from the gums or nose, and stomach tenderness/pain. [104][105]
  • Equine encephalitis viruses, such as Eastern equine encephalitis virus, Western equine encephalitis virus, and Venezuelan equine encephalitis virus, can be spread by mosquito vectors such as Aedes taeniorhynchus. , a bacterial disease caused by Francisella tularensis, is variously transmitted, including by biting flies. Culex and Culiseta are vectors of tularemia, as well as arbovirus infections such as West Nile virus. [106] , recently notorious, though rarely deadly. It causes fever, joint pain, rashes and conjunctivitis. The most serious consequence appears when the infected person is a pregnant woman, since during pregnancy this virus can originate a birth defect called microcephaly. , a mosquito-borne disease that is characterized by fever and headaches upon initial onset of infection, arises from mosquitos who feed on birds who are infected with the illness, and can result in death. The most common vector of this disease is Culex pipiens, also known as the common house mosquito. , a parasitic roundworm infection that affects dogs and other canids. Mosquitoes transmit larvae to the definitive host through bites. Adult heart worms infest the right heart and pulmonary artery, where they can cause serious complications including congestive heart failure.

Potential transmission of HIV was originally a public health concern, but practical considerations and detailed studies of epidemiological patterns suggest that any transmission of the HIV virus by mosquitoes is at worst extremely unlikely. [107]

Various species of mosquitoes are estimated to transmit various types of disease to more than 700 million people annually in Africa, South America, Central America, Mexico, Russia, and much of Asia, with millions of resultant deaths. At least two million people annually die of these diseases, and the morbidity rates are many times higher still.

Methods used to prevent the spread of disease, or to protect individuals in areas where disease is endemic, include:

    aimed at mosquito control or eradication
  • Disease prevention, using prophylactic drugs and developing vaccines
  • Prevention of mosquito bites, with insecticides, nets, and repellents

Since most such diseases are carried by "elderly" female mosquitoes, some scientists have suggested focusing on these to avoid the evolution of resistance. [108]

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 [109] [110] and nematodes, [111] or predators such as fish, [112] [113] [114] copepods, [115] dragonfly nymphs and adults, and some species of lizard and gecko. [116] Another approach is to introduce large numbers of sterile males. [117] Genetic methods including cytoplasmic incompatibility, chromosomal translocations, sex distortion and gene replacement, solutions seen as inexpensive and not subject to vector resistance, have been explored. [118]

According to an article in Nature discussing the idea of totally eradicating mosquitoes, "Ultimately, there seem to be few things that mosquitoes do that other organisms can’t do just as well—except perhaps for one. They are lethally efficient at sucking blood from one individual and mainlining it into another, providing an ideal route for the spread of pathogenic microbes." [92] The control of disease-carrying mosquitoes may in the future be possible using gene drives. [119] [120]

Repellents Edit

Insect repellents are applied on skin and give short-term protection against mosquito bites. The chemical DEET repels some mosquitoes and other insects. [121] Some CDC-recommended repellents are picaridin, eucalyptus oil (PMD) and ethyl butylacetylaminopropionate (IR3535). [122] Others are indalone, dimethyl phthalate, dimethyl carbate, and ethyl hexanediol.

There are also electronic insect repellent devices which produce ultrasounds that were developed to keep away insects (and mosquitoes). However, no scientific research based on the EPA's as well as the many universities' studies has ever provided evidence that these devices prevent a human from being bitten by a mosquito. [123] [124]

Mosquito bites lead to a variety of mild, serious, and, rarely, life-threatening allergic reactions. These include ordinary wheal and flare reactions and mosquito bite allergies (MBA). The MBA, also termed hypersensitivity to mosquito bites (HMB), are excessive reactions to mosquito bites that are not caused by any toxin or pathogen in the saliva injected by a mosquito at the time it takes its blood-meal. Rather, they are allergic hypersensitivity reactions caused by the non-toxic allergenic proteins contained in the mosquito's saliva. [125] Studies have shown or suggest that numerous species of mosquitoes can trigger ordinary reactions as well as MBA. These include Aedes aegypti, Aedes vexans, Aedes albopictus, Anopheles sinensis, Culex pipiens, [126] Aedes communis, Anopheles stephensi, [127] Culex quinquefasciatus, Ochlerotatus triseriatus, [128] and Culex tritaeniorhynchus. [129] Furthermore, there is considerable cross-reactivity between the salivary proteins of mosquitoes in the same family and, to a lesser extent, different families. It is therefore assumed that these allergic responses may be caused by virtually any mosquito species (or other biting insect). [130]

The mosquito bite allergies are informally classified as 1) the Skeeter syndrome, i.e. severe local skin reactions sometimes associated with low-grade fever 2) systemic reactions that range from high-grade fever, lymphadenopathy, abdominal pain, and/or diarrhea to, very rarely, life-threatening symptoms of anaphylaxis and 3) severe and often systemic reactions occurring in individuals that have an Epstein-Barr virus-associated lymphoproliferative disease, Epstein-Barr virus-negative lymphoid malignancy, [131] or another predisposing condition such as Eosinophilic cellulitis or chronic lymphocytic leukemia. [126]

Mechanism Edit

Visible, irritating bites are due to an immune response from the binding of IgG and IgE antibodies to antigens in the mosquito's saliva. Some of the sensitizing antigens are common to all mosquito species, whereas others are specific to certain species. There are both immediate hypersensitivity reactions (types I and III) and delayed hypersensitivity reactions (type IV) to mosquito bites. [132] Both reactions result in itching, redness and swelling. Immediate reactions develop within a few minutes of the bite and last for a few hours. Delayed reactions take around a day to develop, and last for up to a week.

Treatment Edit

Several anti-itch medications are commercially available, including those taken orally, such as diphenhydramine, or topically applied antihistamines and, for more severe cases, corticosteroids, such as hydrocortisone and triamcinolone. Aqueous ammonia (3.6%) has also been shown to provide relief. [133]

Both topical heat [134] and cool [135] may be useful to treat mosquito bites.

Greek mythology Edit

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. [136]

Origin myths Edit

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 mosquitos 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 similar myth, thought to be of Native North American origin, involving the fragments of the dead giant, Andalma-Muus, becoming mosquitos and other insects. [137]

Modern era Edit

Winsor McCay's 1912 film How a Mosquito Operates was one of the earliest works of animation, far ahead of its time in technical quality. It depicts a giant mosquito tormenting a sleeping man. [138]

The de Havilland Mosquito was a high-speed aircraft manufactured between 1940 and 1950, and used in many roles. [139]


Thawing triggers hatch

During two recent field seasons in Greenland, Culler found that with the Arctic already warming twice as fast as the rest of the globe, ponds and lakes on the tundra are melting up to several weeks sooner. When that happens mosquitoes take wing earlier.

“It was really when the pond thawed that triggered the hatch,” Culler says. “That’s not unexpected. Lots of biology is triggered by these melting events.”

But she also found that warming allowed the insects to develop faster, which had a huge impact on survival. Mosquitoes are most vulnerable in their early life stages, when they are easily gobbled up by diving pond beetles. Even though these beetles, too, are growing faster and eating more, mosquitoes still managed to make it to their adult stage in greater numbers.

“The faster they go through these life stages, the better off they are,” Culler says. “If you’re only exposed for 20 days instead of 24, that’s good for you. That’s four days you don’t have to worry about being eaten.”

Arctic mosquitoes typically emerge all at once in massive swarms. (That’s one reason they are jokingly called “Alaska’s state bird.”) It can be hard to overstate the scale. One of Culler’s colleagues in Greenland was assaulted by more than 100 mosquitoes at once. And the bugs in that region were mild for the Arctic. “You can be completely covered in a matter of seconds,” Culler says.

But what is mostly an annoyance for humans can threaten entire populations of other animals. When these insects attack caribou or reindeer en masse, the mammals run to snowy or icy areas or a windy ridge to escape the onslaught. The more time they spend fleeing swarming insects, the less time they spend eating. Previous studies have shown caribou and reindeer populations drop when insect harassment goes up, and many of those populations are already in decline.

Some Alaskans jokingly refer to the mosquito as “Alaska’s state bird.”

Plus, the earlier ponds melt, the more closely aligned the emergence of mosquitoes is with the birth of caribou calves. A mosquito’s ability to reproduce depends on the adult female finding blood to slurp. Because the birthing period limits the the caribou herd’s ability to flee, that provides female mosquitoes with an even greater supply of mammal blood.


Biology

Schistosomiasis (Bilharziasis) is caused by some species of blood trematodes (flukes) in the genus Schistosoma. The three main species infecting humans are Schistosoma haematobium, S. japonicum, and S. mansoni. Three other species, more localized geographically, are S. mekongi, S. intercalatum, and S. guineensis (previously considered synonymous with S. intercalatum). There have also been a few reports of hybrid schistosomes of cattle origin (S. haematobium, x S. bovis, x S. curassoni, x S. mattheei) infecting humans. Unlike other trematodes, which are hermaphroditic, Schistosoma spp. are dioecous (individuals of separate sexes).

In addition, other species of schistosomes, which parasitize birds and mammals, can cause cercarial dermatitis in humans but this is clinically distinct from schistosomiasis.

Life Cycle

Schistosoma eggs are eliminated with feces or urine, depending on species . Under appropriate conditions the eggs hatch and release miracidia , which swim and penetrate specific snail intermediate hosts . The stages in the snail include two generations of sporocysts and the production of cercariae . Upon release from the snail, the infective cercariae swim, penetrate the skin of the human host , and shed their forked tails, becoming schistosomulae . The schistosomulae migrate via venous circulation to lungs, then to the heart, and then develop in the liver, exiting the liver via the portal vein system when mature, . Male and female adult worms copulate and reside in the mesenteric venules, the location of which varies by species (with some exceptions) . For instance, S. japonicum is more frequently found in the superior mesenteric veins draining the small intestine , and S. mansoni occurs more often in the inferior mesenteric veins draining the large intestine . However, both species can occupy either location and are capable of moving between sites. S. intercalatum and S. guineensis also inhabit the inferior mesenteric plexus but lower in the bowel than S. mansoni. S. haematobium most often inhabitsin the vesicular and pelvic venous plexus of the bladder , but it can also be found in the rectal venules. The females (size ranges from 7&ndash28 mm, depending on species) deposit eggs in the small venules of the portal and perivesical systems. The eggs are moved progressively toward the lumen of the intestine (S. mansoni,S. japonicum, S. mekongi, S. intercalatum/guineensis) and of the bladder and ureters (S. haematobium), and are eliminated with feces or urine, respectively .

Hosts

Various animals such as cattle, dogs, cats, rodents, pigs, horses, and goats, serve as reservoirs for S. japonicum, and dogs for S. mekongi. S. mansoni is also frequently recovered from wild primates in endemic areas but is considered primarily a human parasite and not a zoonosis.

Intermediate hosts are snails of the genera Biomphalaria, (S. mansoni), Oncomelania (S. japonicum), Bulinus (S. haematobium, S. intercalatum, S. guineensis). The only known intermediate host for S. mekongi is Neotricula aperta.

Geographic Distribution

Schistosoma mansoni is found primarily across sub-Saharan Africa and some South American countries (Brazil, Venezuela, Suriname) and the Caribbean, with sporadic reports in the Arabian Peninsula.

S. haematobium is found in Africa and pockets of the Middle East.

S. japonicum is found in China, the Philippines, and Sulawesi. Despite its name, it has long been eliminated from Japan.

The other, less common human-infecting species have relatively restricted geographic ranges. S. mekongi occurs focally in parts of Cambodia and Laos. S. intercalatum has only been found in the Democratic Republic of the Congo S. guineensis is found in West Africa. Instances of infections with hybrid/introgressed Schistosoma (S. haematobium x S. bovis, x S. curassoni, x S. mattheei) have occurred in Corsica, France, and some West African countries.

Clinical Presentation

Symptoms of schistosomiasis are not caused by the worms themselves but by the body&rsquos reaction to the eggs. Many infections are asymptomatic. A local cutaneous hypersensitivity reaction following skin penetration by cercariae may occur and appears as small, itchy maculopapular lesions. Acute schistosomiasis (Katayama fever) is a systemic hypersensitivity reaction that may occur weeks after the initial infection, especially by S. mansoni and S. japonicum. Manifestations include systemic symptoms/signs including fever, cough, abdominal pain, diarrhea, hepatosplenomegaly, and eosinophilia.

Occasionally, Schistosoma infections may lead to central nervous system lesions. Cerebral granulomatous disease may be caused by ectopic S. japonicum eggs in the brain, and granulomatous lesions around ectopic eggs in the spinal cord may occur in S. mansoni and S. haematobium infections. Continuing infection may cause granulomatous reactions and fibrosis in the affected organs (e.g., liver and spleen) with associated signs/symptoms.

Pathology associated with S. mansoni and S. japonicum schistosomiasis includes various hepatic complications from inflammation and granulomatous reactions, and occasional embolic egg granulomas in brain or spinal cord. Pathology of S. haematobium schistosomiasis includes hematuria, scarring, calcification, squamous cell carcinoma, and occasional embolic egg granulomas in brain or spinal cord.


Horrifying Alaskan Mosquito Swarm Engulfs Scientists Who Record 'God-Awful' Phenomenon (VIDEO)

Relatively nonlethal, mosquitoes are the reigning champions in the "Most Annoying Bug" category. But researchers working in the Alaskan tundra know that mosquito swarms are anything but benign.

Jesse Krause, a Ph.D. student at the University of California, Davis, knows firsthand the horrors of the swarm. Krause recently spent 78 days working at the Toolik Field Station on Alaska's North Slope, where the mosquitoes were "pretty god-awful," according to the Alaska Dispatch.

Visiting the region to study the effects of climate change on bird migrations, Krause told the Dispatch that this swarm (see video, above) was the worst he'd seen in four summers.

Mosquito "swarms" occur across Alaska in the spring and summer when the hungry insects hatch. Seasonal swarm strength is dictated by the weather, and conditions this year may have been particularly favorable for the state's insects, according to Alaska-based radio station KTNA.

North Slope mosquitoes are notoriously aggressive and large, according to The Seattle Times. The region's "skeeters," as they are commonly called, have been known to drive the direction of caribou herds and feed on animals as diverse as rabbits and frogs. (Krause told the Dispatch that the bugs are so ruthless, he once saw a pair of mosquitoes feeding from a horsefly.)

In videos and photos taken by Krause and his colleagues, the vast number of mosquitoes is compounded by the sheer size of each insect. On Facebook, friends of the researcher noted the images were so terrifying, they appeared photoshopped.

"Those are not edited. Does it scare you more, now?" Krause told one commenter.

GrindTV Outdoor spoke with the operations manager of Toolik Field Station, Mike Ables, who noted that the swarm can be disconcerting for unwitting tourists who have to stop to, say, change a flat tire.

“They’ll have to put up with them for 40 minutes until they get their tire changed,” Ables said. “It’s not going to kill them, but they’re just going to have to endure them.”

Krause and his colleagues tried to prevent bites by dressing up in long sleeves, pants and mesh helmets and covering themselves in bug spray, according to the Dispatch. Complete coverage is key, as the bloodsuckers will “crawl up your sleeves." The mesh over their faces serves a dual purpose: to protect from bites and "to filter the air."

Not that there aren't some fun moments within the swarm, too.

"We have some electric fly swatters up here. It is very satisfying to use them," Krause said on Facebook. "Although it is an exercise in futility based on the number [of] mosquitoes. We were wondering if the electric swatter would short out when all the mosquitoes become imbedded [sic] in the wire mesh."

The Alaska Public Lands website notes that with around 35 species, "the mosquito is the unofficial state bird for a reason!" When they're at their bloodsucking-best in June, the site recommends bug repellent and light-colored clothing. Topical antihistamines or aloe vera may help relieve the itch if these precautions prove unsuccessful.


Mosquito-Borne Pathogens

Lee and colleagues (2013) agree that climate change affects not only survival rates of the vector but also development and transmission rates for the vector-borne diseases. This finding is consistent with the data for dengue virus and the mosquito that carries it. Higher temperatures shorten the incubation period for the virus as well as breeding and development of the mosquito, increasing dengue transmission (Colon-Gonzalez et al., 2013).

A study by Singh, Shukla, and Chandra (2005) added another variable to this complex issue, human population density. Simply put, as the mosquito population increases, mosquitoes will infect more humans. The more humans that are infected, the more chance mosquitoes have to become infected. In other words, the denser the human population, the more likely mosquito-borne pathogens will spread. These include the following deadly diseases.

Malaria

Malaria, a blood-borne pathogen Plasmodium falciparum transmitted by Anopheles mosquitoes, kills more people than any other disease in the world (Reiter, 2001). Malaria is endemic to poor, tropical countries (Ehiri et al., 2004). A study by Yacoub, Kotit, and Yacoub (2011) found that, of the over 247 million people infected with malaria in 2008, 1 million died. One-third of the world's population lives in an area where malaria can be found. Recent cases of malaria have been found in Europe most have been traced to visitors to sub-Saharan Africa or immigrants fleeing war in an endemic area (Askling et al., 2012).

Dengue Fever

The most common viral disease in the world spread by mosquitoes is dengue fever. Research by Bouzid and colleagues (2014) demonstrated that warmer weather would extend the range of mosquitoes into previously unaffected areas.

Both Aedes aegypti and A. albopictus are now spreading dengue fever. Aedes is well adapted to urban settings, is diurnal, prefers peridomestic settings, and can reproduce in almost any container that holds water. This scenario is more likely in wealthier countries because A. albopictus prefers the urban garden setting, biting during the day (Lambrecht et al., 2010).

Four viruses cause dengue, and though very closely related, these four serotypes do not confer immunity for each other (Bambrick et al., 2009). Dengue has been called breakbone fever because it causes severe pain in the muscles, joints, and head. It also causes nausea, skin rash, and vomiting. Many people who are infected with more than one serotype may suffer from dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). Fatality for DHF/DSS is about 50 percent as the blood vessels become permeable and the patient bleeds out (Reiter, 2001).

The geographic range, as well as incidence, has increased in the last fifty years. Infection is now possible in 50 percent of the world population (Reiter, 2001 Yacoub et al., 2011). Figure 1 shows how dengue fever has increased over the last 65 years.

Cases of Dengue fever reported to WHO in the last 65 years (World Health Organization, 2012).

Cases of Dengue fever reported to WHO in the last 65 years (World Health Organization, 2012).

Yellow Fever

The tropical disease yellow fever came to the United States from Africa aboard slave ships in their water supply. Besides finding a new host, the disease infected at least 14 species of Aedes mosquitoes. The disease can be fatal (20 to 50 percent of the time), and other symptoms include high fever and spontaneous bleeding (Reiter, 2001).

A. aegypti is the most common vector and is associated with human habitation, and readily breeds in any container holding water. In the United States, its range currently extends as far north as North Carolina. As with the malaria parasite, higher temperatures cause the pathogen to reproduce more quickly (Martens et al., 1995).

Chikungunya

Chikungunya, its name from an African dialect and meaning “that which bends up,” was first recorded in Asia and Africa in 1779. However, because most all the victims were poor, little attention was paid until 2005, when Chikungunya invaded the French Island of Réunion. With this outbreak came epidemiological changes in the disease. The first change was a switch in its primary host from Aedes aegypti to A. albopictus. This is significant because A. albopictus has a very quick life cycle, is anthropophilic, and with climate change is rapidly spreading throughout the world. Increased virulence was the second change that transformed Chikungunya from an extremely painful but nonlethal disease to one that cripples and kills. New symptoms include kidney failure, thrombocytopenia (and subsequently, bleed outs), meningoencephalitis, and direct infection from mother to child. Of the recovered patients, 93.7 percent of them reported chronic arthritis leading to severe disability (Meason & Paterson, 2014).

West Nile Virus

According to Hahn and colleagues (2015), West Nile is the most ubiquitous mosquito-borne virus in the United States. It was first observed in 1999 in New York, quickly spread through the country, and reached the Pacific Coast by 2003. A study by Hahn et al. (2015) found a direct correlation between the number of cases and the climate. This study analyzed both the temperature and precipitation in each area of the country from 2004 through 2014. Interestingly, low precipitation was loosely correlated with a rise in West Nile, and an article by Meason and Paterson (2014) suggests that people are likely to save more water during a drought in places that would make great breeding spots for mosquitoes.

Counties in seven of ten regions in the United States that experienced higher than normal average temperature increases also experienced higher than normal cases of West Nile disease. The study also found that warmer winter temperature predicted a higher disease rate the following summer (Hahn et al., 2015). A higher infection rate agreed with earlier research by Wimberly, Lamsal, Giacomo and Chuang (2014) that found warmer spring and summer caused accelerated larval emergence, development, and mating, increasing the abundance of mosquitoes. A higher temperature also accelerates viral replication.

Zika Virus

The latest virus to use mosquitoes as a vector is Zika. Currently, the fallout from this disease links Guillain-Barré Syndrome (GBS), microcephaly, and possibly blindness (CDC, 2016c). The virus is named after the Zika Forest of Uganda where it was first discovered in 1947. Few human cases had been observed until 2007, when the vacation destination of Yap Island in the southwest Pacific Ocean had over 8,000 cases in three months. Because no one died and symptoms of fever, joint pain, eye inflammation, and rash resolved quickly, few were concerned (Cha & Sun, 2016). Research by Grard and colleagues (2007) found that the change of vector from Aedes aegypti to A. albopictus facilitated the spread and increased the virulence of Zika. Research by Harvey (2016) shows that climate change could increase the rate of infection by Zika due to the increase in the mosquito population.

As early as 2013, a connection between GBS and Zika was demonstrated (Oehler et al., 2014). GBS is an autoimmune disorder in which the immune system attacks motor neurons (CDC, 2016d). Zika, which arrived in Brazil in May of 2015, has resulted in a six-fold increase of GBS. In one hospital where 94 patients were treated, 50 of them died (Barchfield & Aleman, 2016).

Early in 2016, the Pan American Health Organization (PAHO) and World Health Organization (WHO) stated that an “increase of congenital anomalies, Guillain-Barré syndrome, and other neurological and autoimmune syndromes were found in areas where Zika virus is circulating” (Sun, 2016). One of those congenital anomalies is microcephaly, a rare condition in which brain development is retarded, and the baby is born with an abnormally small head. Symptoms include delayed or inhibited develop of motor skills. The virus may also cause blindness (Ventura et al., 2016).

Summary

In 1939, Guy Callender, a British engineer, made the connection between burning fossil fuels and global warming (Fleming, 2014). He could not have foreseen the ramifications of his prediction. It is not only the weather that has been affected by climate change. Subtle changes have already begun in mosquito populations: temperature increases, the mosquito population increases, their range increases, and ultimately, the number of people infected with mosquito-borne illnesses increases.


What Would Happen If We Eliminated The World's Mosquitoes?

Mosquitoes: Can we get rid of them, and what would happen if we did? originally appeared on Quora: the place to gain and share knowledge, empowering people to learn from others and better understand the world.

Answer by Matan Shelomi, Entomology, Biology, Evolution, on Quora:

It's strange to hear people so eager to cause an extinction for once rather than prevent it, right? This hatred is not just because mosquitoes are annoying. Mosquitoes are arguably the deadliest animal in the world to humans, and I'm including other humans. They spread, or vector, diseases like malaria, yellow fever, dengue, chikungunya, West Nile Virus, and Zika virus, which together cause more deaths each year than war and homicide combined. Eliminating these diseases would save millions of lives, and eliminate much suffering and disability as well. Without the mosquitoes, these diseases would cease to exist … but why is that?

Do we need to kill all the mosquitoes?

No, because not all are bad. Mosquitoes are a fly in the family Culicidae, and there are over 3500 species of them! The females lay eggs usually in still water, anything from a shallow pond to a flowerpot or birdbath or puddle. The larvae live in the water, eating microbes and small particles or algae. They pupate in the water, and the adult mosquito eventually emerges from the water surface and flies off.

What do adult mosquitoes eat? Most are vegetarian. They drink flower nectar, plant sap, and fruit juices, and never drink blood. Killing these species is not necessary: in fact, it’s counterproductive. The more than 90 species of one such harmless genus, Toxorhynchites, also known as the “elephant mosquito” because of their great size, are an ally to our cause: their larvae eat other mosquito larvae! Since they are helpful, we should make sure any strategies we use to kill bad mosquitoes will leave these gentle giants alone.

Of the mosquitoes that do suck blood, only a few (200 or so) feed on humans. Others only feed from birds or lizards or smaller mammals, and many of those that do bite humans would prefer feeding on something else. Of those that can feed on humans, not all carry human diseases, and even in the species that do, not all strains are efficient vectors. Also, different species carry certain diseases. For example, Plasmodium, the protozoan parasite that causes malaria, is spread almost exclusively by mosquitoes in the genus Anopheles. Of the about 460 species of Anopheles mosquito, only a hundred or so can actually carry the five or so species of Plasmodium that infect humans [out of over 200 species of Plasmodium that infect other animals]. Of this hundred, only three or four dozen are good enough vectors to pose a risk to humans, and only a handful of these actually prefer humans as a blood source, and only five carry Plasmodium falciparum, the one species of malaria responsible for the worst symptoms and most deaths. Of these, the worst is Anopheles gambiae, although this is technically a species complex of at least seven different species… but that's another story. In summary, if you want to destroy malaria, there are only a few species that matter the most, and focusing on An. gambiae is the priority. Killing this one species [complex] alone would save millions.

A few other genera carry other disease agents, namely arboviruses (short for arthropod-borne viruses). Many species in the genus Aedes, but especially Aedes aegypti and Ae. albopictus, vector arboviruses such as dengue virus, yellow fever virus, Zika virus, chikungunya virus, West Nile Virus, La Crosse virus, and some animal viruses such as Western equine encephalomyelitis virus. Many of these viruses are also spread by species in the genus Culex, which also spreads bird malaria, and the genus Culiseta, which rarely bites humans, and Ochlerotatus [there is controversy over this genus name that I won't get into here]. The genus Haemagogus spreads yellow fever and some rarer viruses called Mayaro and Ilheus viruses. The genus Mansonsia can spread some arboviruses, but are more important for spreading roundworms that cause filiariasis in Asia and the Pacific. The other genera also have roundworm-vectoring species, responsible for the spread of heartworm in dogs and other animals and lymphatic filiariasis and elephantitis in humans.

Why are some species better vectors than others? The answer is because mosquitoes don’t just carry diseases: they get sick from them. When the mosquito swallows infected blood, its own midgut gets infected. The pathogens replicate in the midgut and burst out into the body cavity, where they eventually infect the salivary glands. The whole process takes up to two weeks depending on the disease. When mosquitoes bite their next victim, the pathogen is injected with the saliva. This is one reason why HIV, the virus that causes AIDS, is not vectored by mosquitoes: it cannot infect the mosquito midgut and just gets digested away. Different mosquito species may be immune to certain pathogens, have resistant midguts or resistant salivary glands, or may simply die of natural causes before the pathogen can complete its replication cycle and reach the salivary glands. Infected mosquitoes do sometimes have shorter life spans, so evolution keeps the diseases in check: they cannot kill the mosquito before they've finished incubating and have been injected into a new host.

In summary, we don't need to kill all the mosquitoes. Just the vector species.

What do mosquitoes do for the world?

Do mosquitoes serve a purpose other than spreading disease? More importantly, do the vector species have a role that makes them worth keeping around?

Let’s start with the larvae. Living in the water and eating detritus, they do keep the water somewhat clean, but so do lots of other organisms that aren't disease vectors. So mosquito larvae don’t eat anything important… except for the Toxorhynchites larvae that eat other mosquito larvae, and we’ve already agreed that we’ll be sparing this genus from genocide.

What eats the larvae? Other aquatic larvae do, such as dragonfly and damselfly nymphs, as well as some turtles and large tadpoles and fish. The most famous predators of mosquito larvae are Gambusia affinis and Gambusia holbrooki, better known as mosquitofish. Native to the USA, they are commonly introduced to ponds and pools as a mosquito control, with some governments giving them out for free, with the assumption that they will eat the mosquito larvae rather than anything else. This worked wonders in some parts of the world, especially near the Russian city of Sochi, formerly a malaria hotspot a statue of the fish was erected there in gratitude in 2010.

However, the assumption is incorrect, and the common name a misnomer. G. holbrooki actually prefers plankton, algae, and detritus [the same foods as larval mosquitoes], and mostly switches to invertebrates like mosquito larvae when it really has no choice. G. affinis is a better predator, capable of eating half to one-and-a-half times their own body weight in mosquitoes every day. However, they cannot live on mosquitoes alone, but actually suffer malnourishment and stunted growth, and must eat other foods too like plankton and other insects. Despite their name, they only eat mosquitoes as a small part of their normal diet. Worse, they are extremely aggressive towards other fish, which themselves are often just as effective at eating mosquitoes. In Australia, mosquitofish deliberately introduced in the 1920’s and 30’s bullied or outcompeted native fish and frogs and reduced their numbers to such an extent that mosquito numbers actually went up, because there were fewer predators overall. That the fish and frogs and native insects being killed or eaten by the mosquitofish were themselves important species now threatened by extinction meant introducing the mosquitofish would have been a bad idea even if they did fight mosquitoes. Sochi was spared this disaster because they didn’t have many native fauna to be threatened by the mosquitofish to begin with. The possibility exists that introducing another fish, like a catfish or even goldfish, would have worked there just as well. Clearly, Gambusia is not a reliable ally in the global mosquito extinction campaign, but on the other hand we need not worry about losing fish if the mosquito larvae die off, since no fish [or other animal] depends on them exclusively.

What about adult mosquitoes? They’re food for an even greater diversity of creatures, from fish and frogs to salamanders and lizards to venus fly traps and birds and bats, not to mention other insects… but not, by the way, the "mosquito-hawk." That's a name given to crane flies, which not only don't eat mosquitoes but also don't eat anything at all: the adults have short lifespans and don't bother feeding. The insects that do eat adult mosquitoes include dragonflies and damselflies, with the benefit that their aquatic nymphs also eat the aquatic mosquito larvae and pupae. They are the mosquitoes’ lifelong nemesis.

Could these natural predators be used to eradicate mosquitoes, and would eradicating mosquitoes harm these predators? No and no. Again, the mosquito is not the only animal eaten by any of these creatures. A great example is the Purple Martin (Progne subis), a rather handsome, insectivorous, American bird commonly promoted as a viable biocontrol against mosquitoes, but possibly overhyped. Multiple studies have looked at its feeding habits, and found that mosquitoes are not a big part of its diet, that their feeding ranges and times do not overlap with when and where vector mosquitoes are active, and that Purple Martin releases have not had big effects on local mosquito populations [though some contradictory studies exist]. Also, like Gambusia, the Purple Martin can make the situation worse because it eats other predatory insects like dragonflies, as well as other insects across the harmful/helpful spectrum from beetles to bees. Dragonflies themselves will also happily eat honeybees and butterflies in addition to mosquitoes, gnats, midges, and flies. The same applies for bats, where mosquitoes may make up less than 1% of their diet. Can you blame these predators? Mosquitoes are tiny, barely a mouthful, while a fat beetle or chubby moth is much more nutritious snack.

What if these alternative food sources did not exist? Is there any part of the world where mosquitoes are a dominant insect? Yes: the arctic. While most insects prefer warm weather, and the tropics have the greatest insect diversity overall, the arctic tundra actually has the biggest mosquito problems in the world, because the land there is a perfect incubator for mosquitoes. The soil is near frozen all winter, but in the summer it thaws, making entire fields one gigantic breeding ground for mosquitoes. Mosquito swarms reach biblical proportions in these regions, forming thick, dark clouds of insects. Scientists believe the mosquitoes are a critical part of the diet of birds in these regions… but others disagree, claiming native midges (related flies from the family Chironomidae) are actually a bigger part of the native birds’ diets and would fill the gap left by mosquitoes. Thus the birds of the arctic are the most likely and perhaps only creatures that could lose a major food source without mosquitoes. Fortunately, the dominant mosquito species in the arctic are Aedes impiger and Aedes nigripes, neither of which vectors human diseases. So if our goal is to fight vector species, we could leave the arctic alone.

What about pollination? Are any plants mosquito-pollinated? Yes, many, but most of these are pollinated by other insects as well, such as goldenrod. A few plants do exist that are preferentially mosquito pollinated, meaning other insects can pollinate them but mosquitoes are the most common and most efficient. All are orchids, namely cold-temperature ones. An example is Platanthera obtusata, the blunt-leaved orchid found across the Arctic, pollinated by mostly female Aedes mosquitoes as well as a few moths. It attracts mosquitoes by giving off a faint scent, detectable by mosquitoes but not our own noses, that is very similar to human body odor. The related Platanthera flava is also pollinated by Aedes primarily and small moths secondarily. Other Platanthera species are pollinated by mosquitoes secondarily and other insects primarily, or are mostly self-pollinating and rarely require insect help, and a few other orchid species have similar cases. Loss of some of these orchids is thus a risk of loss of mosquitoes. However, none of the orchids are important to the ecosystem itself, nor are they important to humans: the world will live on without them. That’s not to say the rather large problem of orchid extinctions isn’t serious, but the problem of insect-vectored disease is arguably worse.

What are the risks of eradicating mosquitoes?

As you noticed, there are no keystone species in mosquitoes. No ecosystem depends on any mosquito to the point that it would collapse if they were to disappear. An exception may be the Arctic, but the species there are non-vectors and thus can be left alone.

Granted, we are making assumptions here. We certainly do not know all the myriad ways all mosquitoes interact with all life forms in their environment, and there may be something we are overlooking. Non-target extinction isn’t the only problem: there’s also the possibility that the gap (technically an ecological niche) left behind by mosquitoes will be filled by something even more annoying, though likely non-vectoring. The worst scenario is one vector mosquito species will replace another, and the most likely scenario is mosquitoes will be replaced by midges. They also have aquatic larvae and the females of some also blood-feed, some on humans. The combination of fewer mosquito competitors and possibly fewer predators of mosquitoes could mean an explosion of midge populations. On the other hand, the predators now reliant on mosquitoes may eat more midges instead, causing the populations to reach a stable equilibrium after a while. Are midges dangerous? Those in the family Chironomidae do not bite, but those in the family Ceratopogonidae do, and not only can their bites be itchy for as long as week, a few do vector human and animal diseases [though not human malaria or yellow fever as far as we know].

Another surprising way mosquitoes can affect the ecosystem comes, again, from the arctic. Mosquitoes control the migrations of woodland caribou (Rangifer tarandus caribou). Their massive herds in Canada are always on the move to find food, but in the summer they travel a lot more, covering greater distances and moving to higher ground, sometimes avoiding the best feeding sites, because they are trying to avoid the gigantic swarms of mosquitoes that plague the Arctic regions in the summer! All the time spent running and not eating means they build up less fat that they would need for the cold winters, which can often mean death. Killing off these mosquitoes would change the historic caribou historical migration routes, with unpredictable consequences. On the other hand, caribou populations today are a fraction of what they once were, down to several thousands from several hundreds of thousands due primarily to human habitat destruction, so more caribou would be a good thing. The caribou are clearly are bothered by mosquitoes, losing up to a liter of blood a week during the worst outbreaks, so if asked I’m sure they’d vote for eliminating mosquitoes, and given their population size and herd mentalities they’d likely come out to vote in large numbers.

Truly worst-case scenarios are unlikely, considering that we’ve eradicated many malaria mosquitoes from parts of Europe and North America without trouble, but they are still possible, so any extinction or extirpation [a local extinction from a smaller area, not the entire planet] has unforeseen risks. The question is: are the risks of maybe altering an ecosystem worth human life, and how much? We are not arguing over whether or not to save the panda, but to eliminate the greatest killers humanity has ever known. Given that arboviruses and malaria currently are killing or affecting millions, to not eradicate the vector mosquitoes responsible could only be justified if the expected environmental effects would be similarly damaging. We cannot poison an entire rainforest to fight yellow fever, because millions of people depend on that rainforest for food, medicine, wood, employment, clean water, and clean air: the cure would be worse than the disease [literally] and affect more people. On the other hand, say we eliminate Aedes aegypti and a salamander species and an orchid are eliminated along with it: that is a trade we can live with, and by “we” I mean the millions who will no longer die from yellow fever. The other extinctions will be a tragedy, yes, but the loss of yellow fever will be a triumph worthy of the Nobel Peace Prize. Compared to the losses of the dodo and the Tasmanian tiger, which came with no benefit to society and are thus completely unfortunate, the benefits of the loss of Ae. aegypti or An. gambiae would outweigh even the most pessimistic estimates of costs.

How could we kill all the world's vector mosquitoes?

Because tampering with ecosystems is so tricky, it is important not to use methods that are too broad. It’s hard enough to predict the effects of killing one species: imagine having to factor in the loss of any species accidentally killed in the process… assuming we can even predict them all! So pesticides are out: they have non-target effects, and, besides, they won't work on a global scale. Aerial sprays won't hit the mosquitoes that like to bite indoors, and putting oils or insecticides in breeding sites won't catch the many, many tiny breeding sites in peoples' properties: everything from a tree hollow to a bit of rainwater sitting in a discarded plastic bag is a potential mosquito breeding site. That's why public participation is important in mosquito control: everyone must do their part to clear the breeding sites in their backyards. Alas, if even one is missed, the mosquitoes will return.

No, if we are going to eradicate mosquitoes worldwide, we need a method that is species specific, unstoppable, and inescapable. Something guaranteed, by way of design, to affect only the target organism, and to be impossible to adapt to or evolve resistance against. We need autocide, where the species is unwittingly responsible for its own death. Is such a thing even possible?

It is, and it has been done. The New World screw-worm fly (Cochliomyia hominivorax), also known as the screw-worm, is a parasitic fly whose maggots infest the healthy tissue of warm-blooded mammals. This includes humans, but the bigger problem is cattle, where the worms cause death within ten days. In the 1950’s, losses in the USA due to screw-worm were over US$200million a year. Something needed to be done, but pesticides were not working. Scientists studied the screw-worm intensively, including a $250000 study partly on the sex-lives of screw worms that was widely decried by US senators as wasteful spending of taxpayer funding. They would later eat their words with an American-grown steak and a glass of milk. It turns out that female screw-worms are monogamous, only mating once in their lifetime. Scientists Edward Knipling and Raymond Bushland reasoned that if a female screw-worm mates with a sterile male, her eggs will never hatch, and since males mate repeatedly, one sterile male can not-impregnate multiple females. Thus, if one floods an ecosystem with a large enough number of sterile males [which have no effect on cattle, because males don't drink blood or lay eggs], they will out-mate the healthy males and the number of fertile matings is reduced, instantly reducing the size of the next generation. This process is repeated constantly until eventually every female mates with a sterile male, at which point the population is wiped out… forever.

This sterile insect technique (SIT) was tested with screw-worms in the 1950’s using X-rays [later gamma rays and other techniques] to sterilize flies mass-reared on ground meat in the lab, irradiating them at the pupal stage just enough to sterilize males without making them too weak to compete with normal males. Long story short, it worked. By releasing large numbers of sterile male flies over several weeks at a time, SIT successfully eliminated the screw-worm from the USA, then Mexico, working southwards until all of North and Central America was cleared of the flies. When screw-worm was accidentally imported to Libya in 1988, sterile males were eventually brought in on December 1990 and eradicated the screw-worm in less than a year. Sterile screw-worm males are still released in Panama periodically, forming a biological wall against any females from the South. The results saved the US cattle industry alone over $20billion and counting, winning its authors the 1992 World Food Prize and being declared “the greatest entomological achievement of (the 20th) century.”

The principles of SIT make sense for safely eliminating vector species, since there are no other effects on the environment other than those caused by the loss of the species itself, and it only works on a single species at a time: SIT against Aedes aegypti won’t have an impact on Aedes impiger, let alone other genera of mosquitoes, let alone other insects, let alone mammals or people. Many mosquito females are also monogamous, so SIT could work in theory. Plus, since only the vegetarian male insects are released, one can unleash billions of these mosquitoes in an area and there won’t be a single extra insect bite. SIT has been successfully used to eradicate tsetse fly (Glossina spp., the vector of African Sleeping Sickness) in parts of Africa, and several have tried it against mosquitoes… but many failed. Efforts to eliminate Anopheles quadrimaculatus in Florida, USA over nearly a year had no effect, because the sterile males simply could not compete with the normal ones and were not chosen by mates. This happened again for Culex tarsalis in California. The problem is the radiation can weaken mosquitoes and/or lower their lifespans, so they fail to attract females. Not all insects respond well to irradiation, which limits the subjects SIT can work with.

An alternative strategy is cytoplasmic incompatability, which sounds more complex than it is. Instead of radiation the mosquitoes are infected with a bacteria called Wolbachia that lives inside insect cells, including egg and sperm cells. When Wolbachia-infected sperm combine with uninfected eggs, the egg dies. Guaranteed. Culex quinquefasciatus was successfully eliminated from the city of Okpo in Burma in 1967 in 9-weeks with this method. However, this technique won’t work if the wild mosquitoes alsoare infected with Wolbachia: if both egg and sperm are infected with the same strain, or even if the egg is infected and the sperm not, the embryo lives and becomes a new male or female whose eggs will also be immune. It also doesn’t solve the problem that rearing at large densities in a facility is itself stressful: studies with Anopheles gambiae showed those reared at higher densities were less like to win mates than those reared at lower or natural densities. Large numbers of mosquitoes need to be produced cheaply, but if one cuts too many costs they won’t be effective competitors for wild males and will fail to mate.

There’s another problem: since we don’t want to release blood-sucking female mosquitoes, sterile or otherwise, we need a good way to eliminate females in the lab from the irradiated pool before they are released. Unfortunately, the sex ratio for mosquitoes is 50/50, so a way of separating males and females is needed. The ones used at first could not be more primitive: Male and female mosquito pupae are slightly different colors and sizes, so someone manually or a machine with a strainer had to sort them and ensure only males get sent to be irradiated and released. Unfortunately, this does not work for Anopheline mosquitoes, because the pupa sizes overlap. Even before this point, though, money has been lost. Both males and females require the same resources in lab, so inevitably no more than half the insects raised in an SIT program will ever be released, making everything twice as expensive as it should be. Since a huge number of sterile males is needed to have any effect, these high costs are a problem for a global extermination program.

Is there some way to ensure only males are produced, or a way to kill off unnecessary females earlier? Yes, using genetic sexing strains (GSS), an old technique in which a dominant selectable marker—a gene that makes its possessor able to survive an otherwise lethal challenge— is attached to the male sex chromosome. A successful example is the aptly named MACHO: a strain of An. albimanus with an insecticide-resistance gene attached to the male chromosome (mosquitoes mostly have an XY sex-determination system like humans do, where only males have a Y-chromosome). Treating a batch of MACHO eggs with insecticide will kill 99.9% of all females, allowing a million mosquitoes per day to be released when it was used to control mosquitoes in El Salvador in the late ‘70’s. In case you are wondering, the eradication almost worked, until the mosquito immigrated back in from another country. Whatever technique we choose, it would need to be global, and in any case GSS doesn’t solve the problem that irradiation can make many mosquitoes weak competitors.

The latest advance skips irradiation all together. It is called RIDL, short for Release of Insects carrying Dominant Lethals, invented by entomologist Luke Alphey. In RIDL, the males are not irradiated, meaning they are just as healthy and competitive for mates as wild males, but also they will produce viable eggs. So instead they carry a lethal gene that causes their larval offspring to die before reaching blood-sucking adulthood. The current form of RIDL involves a gene called tTAV (tetracycline repressible activator variant), which makes a nontoxic protein that clogs up the insect’s cell machinery so no other genes are activated, causing death. The system only works in the mosquitoes’ own cells, and the protein is degraded when eaten, so there is zero effect to animals that eat the modified mosquitoes or their larvae: It is a completely nontoxic system. “But wait, how do these mosquitoes survive to adulthood in the lab?,” you ask. The answer is Tetracycline, a common antibiotic that is also the antidote to tTAV. In the rearing facility they are fed this antidote so they can live to adulthood, but in the wild they and their offspring have no hope. RIDL is currently being used to fight mosquitoes in the southern US and South America, where they have already caused massive declines in dengue mosquitoes, and are now being deployed to stop the Zika epidemic in Brazil.

A new technique, currently developed for the Mediterranean fruit fly but perhaps one day available for vector mosquitoes, is a female-specific RIDL. In this system, males carry a gene for a protein that, in absence of the antidote, only kills females. In this system, females mated with the modified males will produce perfectly viable eggs, but the female offspring die as larvae, and only the male offspring will survive into adulthood. These males still carry the modified gene, and go on to mate with the now smaller population of females, etc. In this scenario, one need only release the males once to start a chain reaction that works through the population, reducing it with every generation.

RIDL is an amazing strategy, with no harmful effects on the environment or on non-target organisms, and it even saves humans from having to work with radiation. Alas, it involves genetic modification, which means the mosquitoes are technically a GMO, which means the usual suspects are out in force trying to stop them, some spreading rather creative lies, and the media is often unable or uninterested in sorting fact and fiction. Most stories worry about the mosquitoes flying and biting local people. Some articles claim the mosquitoes vaccinate humans against diseases, which would be amazing if it was true, but it isn’t. Others claim the mosquitoes will mutate you if they bite you, which is equally ridiculous. Some are even claiming that microcephaly isn’t caused by Zika virus but by the released mosquitoes, calling it “loose gene syndrome." Never mind that such a condition does not exist and is biologically impossible the fact that these people are willing to deny the very real problem of Zika-induced microcephaly in order to scare people off GMOs and better sell their overpriced organic produce in stores is a truly nasty appropriation of real human suffering. Fortunately, you now know the one important fact that thoroughly contradicts almost every mistake and lie ever written about insect releases: male mosquitoes don’t bite people. They don't drink blood, but actually avoid humans, and since only male mosquitoes are ever released, the idea that a released insect can harm a human is pure fiction.

Will these techniques mean we can get rid of pesticides and insecticides forever? Not quite yet. Remember that SIT and RIDL require the released males to outnumber the native males. No matter how efficiently we can rear sterile or modified males, if the wild populations are too high then these techniques will never be practical. Instead, we would need pesticides to bring down the wild populations first, to a threshold at which SIT or RIDL will work. In addition, if we want to rid the entire planet of these species, the releases would need to cover their entire ranges, which could be a massive amount of space. Still, progress is good, and even if we don’t eliminate all the vector mosquitoes in the world, we have already made a massive dent in the death toll of mosquito-vectored disease worldwide.

But wait, there's more! There is one technique that can eliminate the pathogen without harming the vector or the environment in any way, and does not require releasing or raising insects. First, let me introduce you to Chagas disease, caused by the protozoan Trypanosoma cruzi which is vectored by kissing bugs in the subfamily Triatominae, the most serious vectors being Triatoma infestans and Rhodnius prolixus. They are called “kissing bugs” because they like to bite near the mouth to suck blood. They also have the filthy habit of defecating right after they eat, and when humans scratch the bite they scrape the parasite-infested poop into the wound, infecting themselves. Charming, and also deadly, as Chagas disease can cause symptoms such as an enlarged heart. SIT has been tried in these species, but the new technique is called paratransgenesis. Rather than genetically modify the insect to make a protein (transgenesis), one modifies a symbiotic microbe that lives inside the insect instead. In the case of Rhodnius prolixus, all individuals have a symbiotic bacteria, Rhodococcus rhodnii, that makes vitamins for them that are otherwise absent in their blood-based diet. Genetically modifying bacteria is easy, so scientists created transgenic symbionts that produce proteins toxic to the Trypanosome. If you feed Rhodnius some modified Rhodococcus, the insect now became immune to Trypanosoma cruzi, unable to vector it anymore. The bacteria can be produced in large numbers easily, bypassing a problem with insect release. Best of all, the infected adult kissing bugs pass the bacteria on to their offspring: young triatomines often eat the feces of the adults, inoculating themselves with the Rhodococcus bacteria. [In case you are wondering, the bacteria can’t survive in our bloodstream, so they can neither harm us nor help us.] The system is quite promising, involving spreading Rhodnius poop infected with modified Rhodococcus everywhere Trypanosoma is a problem, with the end result that only the parasite dies out, while the insect is left alive, and the ecosystem is not affected at all. Paratransgenesis could be applied elsewhere, and scientists are working on developing it for other species, such using a modified fungus to make Anopheline mosquitoes immune to malaria.

You now have a clear idea of the many issues that go into whether or not a species should be eliminated, and whether or not that is even practical. If you have such a question for another insect, like fleas or roaches, maybe you can answer the question yourself! Ask yourself: Which species from the group are the real problem? What do they do in the world? Are males and females both a problem? Is SIT practical? Is there an alternative solution to the disease? If questions like these interest you, consider a career in medical entomology, epidemiology, genetics, or [of course] medicine, and maybe that Nobel Prize I mentioned will be yours.

What should we do in the meantime?

Global extermination of vector mosquitoes, whether or not it is doable and whether or not it is a good idea, is a long way off. Until then, the best strategies are to do local extirpations. If you have a pond, add goldfish, koi fish, or guppies—not necessarily mosquitofish—to eat the larvae. Insecticides are another, less ideal option, as they will kill beneficial insects too, but in emergencies they can be used as many are nontoxic to humans. That includes the ones being used in Brazil right now to fight Zika… and, no, they are not responsible for microcephaly. That claim has also been thoroughly disproven, despite what conspiracy theorists say.

For container breeding mosquitoes, remove the containers or drain them often. Keep an eye out for anything that can catch rainwater, from animal feeding bowls and flowerpots to old tires and plastic bags or tarps. The mosquitoes from these containers will bite you first, so you're doing yourself a favor in addition to the public health! Most importantly, protect yourself. Use insect repellents on your skin or clothes, and sleep under a bed net if you’re really deep in a disease endemic zone. Bed nets are most important for children, as they will suffer the hardest from diseases like malaria.

For more information on what you can do, find your local vector control or mosquito abatement district website or specialist and see what they recommend for your region.

For more on mosquito- and other insect-vectored diseases check the websites of the Center for Disease Control ( CDC - Malaria , Zika Virus | CDC ), or the US National Institute of Allergy and Infectious Diseases ( Malaria , Zika Virus ).


Aedes japonicus (Theobald)

Other: Upper and lower head hairs are arranged in a straight line.

GEOGRAPHIC DISTRIBUTION: The first North American specimens of Aedes japonicus were adults recovered from light trap collections in Ocean County, NJ and Suffolk County, NY in September 1998. The larvae were first discovered in automatic horse watering devices in Ocean County, NJ the following spring. Presently, breeding populations of Ae. japonicus are known in 18 of NJ's 21 counties. At the end of 2003, Ae. japonicus had been collected from 19 states in the USA (CT, DE, GA, MA, ME, MD, NC, NH, NJ, NY, OH, PA, RI, SC, TN, VA, VT, WA, and WV) and Quebec, Canada.

SEASONAL DISTRIBUTION: Present all season long. The earliest recorded larval collection was made on March 6, 2002 in Bergen County, NJ. The latest larval collection was made on 07 January 2003 in Somerset County, NJ. In central New Jersey, the adults have been collected with gravid traps from early April through late November.

LARVAL HABITAT: The larvae of Ae. japonicus are typically found in small-volume containers of relatively clean, clear water. They are most often recovered from artificial containers, including bird baths, buckets, plastic milk jugs, wheelbarrows, animal watering containers, and tires. They have also been collected from natural containers such as treeholes in Sussex County, and rockpools in Hunterdon, Sussex, and Warren Counties. Within their native range, they are occasionally collected from ground water, and Bergen County has collected Ae. japonicus larvae from standing water in tire ruts. It has also been collected from cement catch basins in Warren County, NJ and New York.

COMMON ASSOCIATE SPECIES: Aedes japonicus larvae have been found in container habitats with: Aedes albopictus, Anopheles barberi, An. punctipennis, An. quadrimaculatus, Ae. atropalpus, Ae. hendersoni, Ae. triseriatus, Culex pipiens, Cx. quinquefasciatus, Cx. restuans, Cx. salinarius, Cx. territans, Culiseta melanura, Cs. incidens, Orthopodomyia signifera and Toxorhynchites rutilus septentrionalis. More than likely, the larvae of Ae. japonicus will eventually be found with other container breeding mosquito species as its range continues to expand in North America.

LARVAL IDENTIFICATION: There are two major characters which separate Aedes japonicus larvae from all other North American mosquitoes: its highly spiculated anal saddle, and the upper and lower head hairs which are multiple (tufts) and arranged in a straight line.

Aedes japonicus larvae are relatively easy to separate from associated container species. The Culex species are easily recognized and can be separated in the dipper by their longer air tubes.

Aedes atropalpus most closely resembles Ae. japonicus in general body shape, and, using the standard North American mosquito identification keys, Ae. japonicus will be misidentified as Ae. atropalpus based on their detached pecten teeth and the tuft inserted within the pecten row. Fortunately, these two species are easily separated under the microscope by their head hairs and the difference in spiculation on the anal saddle as described above.

Aedes triseriatus larvae have a darker coloration, a characteristic serpentine motion and an elongate body shape which are useful in screening field collections but should not be relied upon for separation of early instars. There are several useful characteristics to quickly isolate the Ae. japonicus larvae from field populations of Ae. triseriatus. Aedes triseriatus has much smaller gills and the ventral pair is considerably shorter than the dorsal pair. The anal gills of Ae. japonicus are much longer than the saddle and are equal in size. Be aware, however, that gills frequently break off in preserved specimens. As a result, gill characteristics are most useful when observing living specimens. Aedes triseriatus has a single row of comb scales that are arranged in an extremely irregular fashion, while the comb scales of Ae. japonicus are arranged in a patch. The upper and lower head hairs of Ae. triseriatus are single and arranged in a box-like formation, while in Ae. japonicus they are all multiple and aligned in row. The lateral hairs on the saddle are useful because they can be observed in living specimens without special orientation. The lateral hairs are very long in Ae. japonicus and 5-7 branched in Ae. triseriatus.

IMPORTANCE: We do not yet know what the impact of Ae. japonicus will be in New Jersey. It does not seem to be an aggressive human-biting mosquito like New Jersey's other exotic mosquito, Aedes albopictus. Laboratory studies have show that Ae. japonicus is a very efficient vector of West Nile virus, but its actual role in the natural transmission of this virus has yet to be determined. It is worth noting, however, that several pools of Ae. japonicus were positive for West Nile virus during the 2000, 2001, and 2002 surveillance seasons. This may indicate that Aedes japonicus could provide an important link between people and West Nile virus in the United States.


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