How long does a mosquito take to land on a host, bite, and fly off?

How long does a mosquito take to land on a host, bite, and fly off?

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How long does a mosquito take to land on a host, start its bite, end its bite and then fly off?

And what about different species?

I am most interested in human hosts.

References to web sites or books would be appreciated.

I cannot find this even after extensive trawling of Google.

That's an interesting question and not easy to answer. I haven't found data for humans but from experiments with mice. They analysed how the mosquito actually bites, probes for the blood vessels (not all bites are successful) and finally sucks bloods. In their research they observed feeding times between 150 and 329 seconds, depending on the size of the blood vessel. The mean feeding time was 240 seconds. It also depends on the age of the mosquito, older mosquitos suck longer. To this comes the time for probing (mean time 142 seconds) and the time before the mosquito starts probing after it landed (mean time 6.5 seconds). This totals to about 389 seconds (or roughly 6.5 minutes) total time after landing. This data can be found in table 1 of reference 2.

This is pretty interesting, they also show videos of the mosquito probing the skin for a blood vessel. You can find a pretty nice summary in the first reference and the original paper in the second:

  1. Here's What Happens Inside You When a Mosquito Bites
  2. Visualizing Non Infectious and Infectious Anopheles gambiae Blood Feedings in Naive and Saliva-Immunized Mice.

Gillett studied the feeding behavior of Aedes africanus and Aedes aegypti, the abstract says that

They showed that while the period between salivary injection and the onset of irritation was the same in both species (ca. 3 min)

It seems to me that the abstract does not say whether the hosts were humans or not. Unfortunately I am not able to get the full paper.

GILLETT, J. D. Natural selection and feeding speed in a blood-sucking insect. Proceedings of the Royal Society of London B: Biological Sciences, 1967, 167.1008: 316-329.

Insects and Ticks > Mosquitoes

This is an Aedes albopictus female mosquito obtaining a blood meal from a human host. Photo by: James Gathany

Mosquitoes are well known as annoying biting pests and vectors of disease-causing agents to humans and other animals. Numerous information sources discuss mosquito biology, mosquito-borne diseases, methods of personal protection, and approaches to mosquito control. Still, many people lack understanding of the biology and public health importance of mosquitoes. You are encouraged to learn more about the biology of mosquitoes in Indiana. This will enable you to make more informed decisions about health risks and whether to attempt mosquito control.

Why Are Mosquitoes In My House?

Picture this: You’re relaxing on your couch or in bed, reading a book or watching TV, when you hear the telltale, annoying, high-pitched whine of a mosquito—or, worse, you start smacking at your skin because you feel the tiny sting of a bite in progress. If an evening spent safely indoors leads to multiple red, itchy welts on your skin, you might find yourself wondering, “Why are mosquitoes in my house?”

The answer is relatively straightforward: Mosquitoes gravitate toward dark, warm, moist places where they have access to water, and this can include laundry rooms and bathrooms inside our homes. Anytime you enter or exit your home, especially on a warm, humid night, you’re giving mosquitoes an opportunity to slip through the open door into your house. Unfortunately, if these pests take up residence inside your home, getting rid of your unwelcome visitors may take some know-how and vigilance.

3) Pupa Stage

The mosquito pupae (also known as tumbler) doesn’t eat or do anything. They simply swim around in the water all day.

They have short and curved bodies with a large head on one end and flippers on the other end to help them swim. They live near the water surface and inhale oxygen through their little tubes (also known as trumpets).

When disturbed, the pupae will decent downwards to the deeper depth and slowly rise back to the water surface. Like the mosquito larvae, the purpae is also vulnerable to predators birds and fishes. Human acts can also post a risk to them (i.e. a layer of floating substance like oil in the water can kill them as they are unable to get to the water surface for oxygen).

It takes about 3 to 4 days for the mosquito pupal to grow and develop into the adult mosquito depending on the temperature of the water which it grows in. It is during this stage where the pupal uses air pressure to split open the cocoon and emerge as an adult mozzie.

Side note: Both the larvae and pupae cannot survive for long without water, hence should a water source dried up before they grew into adult mosquitoes, they will die.

11 Ways to Prevent Mosquito Bites That Actually Work, According to Entomologists

Stocking up on the right repellent is only the first step in preventing a painfully itchy bite.

This article was medically reviewed by Shonda Hawkins, M.S.N., a nurse practitioner and member of the Prevention Medical Review Board.

It&rsquos backyard barbecue season&mdashbut you&rsquore not the only one planning a feast. The mosquitoes are out and ready to chow down. But before you fill another shopping bag with citronella candles, it&rsquos important to understand your adversary.

When a mosquito lands on your skin, it will feed on your blood&mdashbut once it leaves, the proteins in its saliva stay behind. Your immune system sees this is a threat and pumps out histamine (the same response it has to allergens) to attack these proteins. The result? Those unbearably itchy, red welts you remember scratching at as a kid. Luckily, there are ways to get rid of a mosquito bite quickly, and the itching should go away within two to three days.

But it&rsquos not just bites you need to worry about&mdashthe aftermath can be unpleasant, too. Mosquitoes can carry all sorts of intense diseases, like the West Nile or Zika viruses, or even chikungunya and malaria (which are risks if you travel to certain countries). That&rsquos why preventing mosquito bites in the first place should be a priority during the warmer months.

Entomologists know how these insects operate, which is why we consulted several for the dos and don&rsquots of repelling these pesky pests.

Almost any breeze&mdashanything above 1 MPH&mdashmakes it very difficult for mosquitoes to fly, says Jonathan Day, Ph.D., a mosquito expert and professor of medical entomology at the University of Florida. If you can pick a breezy spot for your summer outing, that can help prevent mosquito bites.

Plug-in fans are also a great deterrent, he adds. Just keep the flow of air directed at the lower half of your body mosquitoes tend to fly very close to the ground to avoid wind, so directing the fan&rsquos force downward will block their approach.

Natural wind or a fan will work much more in your favor than those fancy, ultrasonic devices and apps marketed as mosquito repellants&mdashsome of which claim to mimic the sound of dragonflies. &ldquoThey don&rsquot work at all,&rdquo Day says.

Just like you, mosquitoes crave a meal during certain times of day, says Howard Russell, M.S., an entomologist at Michigan State University. And for these critters, it&rsquos often around dusk and dawn.

That&rsquos because the wind typically dissipates as the sun rises and sets, which brings mosquitoes out to feed, Day explains. If you can try to stay inside during these times when the weather is warm, you&rsquoll be able to prevent more than a few mosquito bites.

DEET has a bad reputation, but adverse reactions to it are rare&mdashand tend to occur only when people swallow or snort the stuff. When used as directed, it&rsquos extremely effective, since it blocks a mosquito&rsquos CO2 receoptors, Day says. Still, he&rsquos quick to add: &ldquoMost people don&rsquot understand how to apply it properly.&rdquo (Fun fact: DEET makes a great tick repellent, too.)

First, you should not spray DEET on your body and clothes like it&rsquos perfume, he stresses. Instead, squirt a little onto your hands and rub it onto your ankles, elbows, wrists, forehead, and all the other places where your skin is thin&mdashand where mosquitoes love to feed.

Also important: Day says a product&rsquos DEET concentration determines how long it will last&mdashnot how well it will work. If you&rsquoll be outside for 90 minutes or less, he says a product with 7 to 10% DEET will do the job, and you can always reapply to extend its efficacy (do not go higher than 30%). DEET in lotion or wipe form is also just as effective as a spray and removes the risk of inhaling it.

Finally, don&rsquot waste your money on wearable DEET items, like wristbands or anklets&mdashthey don&rsquot actually prevent mosquito bites, says Day.

If you just can&rsquot with DEET, there are other options that are recommended by the Centers for Disease Control and Prevention (CDC) for use in repelling mosquitoes, including:

While all of the above have been found to be effective like DEET, picaridin is the next best choice. &ldquoThis is something that was developed for the military just like DEET was,&rdquo says Roberto M. Pereira, Ph.D., an entomologist and research scientist at the University of Florida. &ldquoIt works really well.&rdquo

If you&rsquore at the store and you&rsquore not sure if a repellent has these ingredients, &ldquoyour safest bet is to look for Environmental Protection Agency approval on the product&rsquos label,&rdquo Nancy Troyano, Ph.D., a board-certified entomologist and Director of Operations Education and Training for Western Exterminator Company. If it does, it should be effective and safe. (You can also search products registered with the EPA here.)

This can be easier said than done in the summer, but mosquitoes are drawn in by pheromones released in your sweat, says Pereira.

This can vary from person to person. &ldquoSome people, like me, attract mosquitoes regardless of what they drink, eat, or wear,&rdquo says Russell. Still, the more you can do to take it easy on the sweating&mdashespecially during peak mosquito hours&mdashthe better.

Mosquitoes can&rsquot penetrate clothing that has a very tight weave, Day says. While cotton and linen typically aren&rsquot great armor against mosquito bites, Day says many synthetic fibers&mdashparticularly high-tech athletic apparel&mdashtend to be woven tightly enough to keep bugs out. Any garment that offers sun protection will also have a tight enough weave to prevent mosquito bites, especially when you opt for long sleeves and pants.

Mosquitoes also use their vision to search for food sources during the daylight hours. Since they fly very close to the ground, they tend to find targets by looking for things that contrast with the horizon, Day says. &ldquoDark colors stand out, but light colors are less attractive to them,&rdquo he adds. Of course, make sure you protect any exposed areas with a repellent if you&rsquore going to be spending time outdoors for a long period of time.

Day says carbon dioxide (CO2) is the primary thing mosquitoes search for to identify food sources. And when your heart rate is elevated, your body produces more CO2. From exercise to drinking alcohol to eating spicy foods, anything that cranks up your metabolic rate will increase your CO2 production&mdashand make you irresistible to mosquitoes, Day says. Unfortunately, being overweight or pregnant can also up your CO2 output, he adds.

If you&rsquore outdoors and you know your heart rate will be spiking, make sure you wear protective clothing or apply a repellent to keep bug bites at bay.

There are different types of mosquitoes, and the &ldquomosquitoes that we worry about in urban areas are usually ones that are being produced in your own backyard,&rdquo Pereira says. Aedes mosquitoes, which transmit Zika virus and chikungunya, can easily breed in small containers of water like a birdbath or even water sitting around your plants. &ldquoThey can breed in your own yard, and you wouldn&rsquot necessarily know it,&rdquo Pereira says.

Do your best to clear out any standing water to lower the odds that you&rsquoll have lots of mosquitoes hanging around your place ready to bite.

This shouldn&rsquot be your only mosquito-combating strategy, but Pereira says that certain plants may help discourage mosquitoes from hovering near your house. Those include things like citronella, lavender, lemongrass, marigolds, and basil. &ldquoIf you had enough, it could make a difference in terms of mosquitoes inside your property,&rdquo he says.

Just keep realistic expectations about what these can and can&rsquot do, Troyano says. While they may help tamp down on the number of mosquitoes around your place, &ldquoeven planted in large quantities, the potency of these plants would not be enough to keep mosquitoes out of your yard entirely,&rdquo she says.

The same goes for citronella candles and oils. While they&rsquore natural insect repellents, Day says they only work if their scent or smoke gets between you and the mosquito. So if you&rsquore lighting tiki torches that sit a few feet off the ground, they won&rsquot do much to prevent mosquito bites, he says.

If you live in an area where the mosquitoes are unbearable, it might be worth hiring a professional to come and treat your yard with insecticide, Russell says. This can do a pretty good job of ensuring they won&rsquot come anywhere near your place.

As for mosquito traps? They&rsquove been souped up with fancy features to attract mosquitoes with special lights, heats, or scents. &ldquoThere&rsquos no doubt that traps can&mdashunder the right environmental conditions&mdashcapture of a lot of mosquitoes,&rdquo Day says. Realistically, though, you can&rsquot catch &lsquoem all. &ldquoOver the last 30 years, there have been many traps marketed as being able to clear a one-acre or five-acre lot,&rdquo Day says, &ldquoand it has never been my experience, even with very efficient traps, that they can rid a whole area of mosquitoes.&rdquo

A trap in the middle of your backyard will kill mosquitoes that fly close enough to sense its lures, sure, he says, but countless more will come flying into your yard to fill the space they leave behind. Mosquitoes are also adept at telling the difference between a trap and a living, breathing host&mdasha.k.a. you.

This can be tough, but it&rsquos definitely worth a try if mosquitoes are terrible in your area. &ldquoAny scented perfume, lotion, or soap could potentially attract mosquitoes,&rdquo Troyano says. &ldquoIf you want to reduce your attractiveness to mosquitoes, avoid scented products in general.&rdquo

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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]

Mosquito Life Cycle Facts

The length of the mosquito life cycle varies between species and is dependent upon environmental conditions such as temperature and moisture. However, the life cycle of all mosquitoes is comprised of the egg, larval, pupal, and adult stages.

Male mosquitoes feed on plant nectar alone, while females extract the blood of hosts in order to develop and nourish eggs. Most mosquitoes lay their eggs directly into water. Others lay their eggs near bodies of water but not within them.

Life Cycle Stages

How Long Do Mosquitoes Live?
The length of the mosquito life cycle and lifespan varies between species and is dependent upon environmental conditions such as temperature and moisture. However, the life cycle of all mosquitoes is comprised of the egg, larval, pupal, and adult stages.

Male mosquitoes feed on plant nectar alone, while females extract the blood of hosts in order to develop and nourish eggs. Most mosquitoes lay their eggs directly into water. Others lay their eggs near bodies of water but not within them.

Eggs will hatch into larvae within 24 to 48 hours. Larvae soon grow to become approximately 5 mm in length. Most larvae breathe through air tubes. Larger larvae can be seen floating just above the surface of infested waters. Larvae and pupae usually cannot survive without water. If a water source evaporates before the larvae and pupae within it transform into adult mosquitoes, those young often will die.

Within seven to ten days, larvae enter the pupal stage. Pupae are also visible upon the surface of the breeding site. After a mosquito is fully developed, it will emerge as an adult from its pupal case. At this time, the new adult stands upon the water and dries its wings to prepare for flight. Adult female mosquitoes will then seek an animal on which to feed. Females are capable of flying for miles if necessary and can lay over 100 eggs at a time.

Encounters & Concerns

Where will a homeowner encounter the eggs, larvae, and pupae life cycle stages? Encounters with potential mosquito developmental sources can be places where you might not expect. Almost any source of water found on a homeowner’s property can support these developmental stages, and unless a homeowner is diligent to inspect their property, adults are going to be a problem.

Adult mosquitoes creating problems on your property may have come from a water source miles away, but also may have come from a water source located near your home. For example, two areas of concern that might not occur to homeowners are stopped up gutters that hold water and corrugated plastic downspout extensions that direct water away from the house.

Mosquitoes are notorious for their involvement in disease transmission, creating annoyances, interfering with outdoor recreation activities, and even ruining a good night sleep. Another concern related to bites is the possibility of secondary infections of mosquito bites that are scratched and become infected with bacteria.Eggs will hatch into larvae within 24 to 48 hours. Larvae soon grow to become approximately 5 mm in length. Most larvae breathe through air tubes. Larger larvae can be seen floating just above the surface of infested waters. Larvae and pupae usually cannot survive without water. If a water source evaporates before the larvae and pupae within it transform into adult mosquitoes, those young often will die.

Within seven to ten days, larvae enter the pupal stage. Pupae are also visible upon the surface of the breeding site. After a mosquito is fully developed, it will emerge as an adult from its pupal case. At this time, the new adult stands upon the water and dries its wings to prepare for flight. Adult female mosquitoes will then seek an animal on which to feed. Females are capable of flying for miles if necessary and can lay over 100 eggs at a time.

Encounters & Concerns

Where will a homeowner encounter the eggs, larvae, and pupae life cycle stages? Encounters with potential mosquito developmental sources can be places where you might not expect. Almost any source of water found on a homeowner’s property can support these developmental stages, and unless a homeowner is diligent to inspect their property, adults are going to be a problem.

Adult mosquitoes creating problems on your property may have come from a water source miles away, but also may have come from a water source located near your home. For example, two areas of concern that might not occur to homeowners are stopped up gutters that hold water and corrugated plastic downspout extensions that direct water away from the house.

Mosquitoes are notorious for their involvement in disease transmission, creating annoyances, interfering with outdoor recreation activities, and even ruining a good night sleep. Another concern related to bites is the possibility of secondary infections of mosquito bites that are scratched and become infected with bacteria.

An Aedes aegypti mosquito with an abnormally large blood meal (left) next to typical engorged mosquito (right) for comparison. (Photo by Perran Ross, Ph.D.

By Perran Ross, Ph.D.

An urban legend says that if you tense your muscle when a mosquito bites you and feeds on your blood, it can swell up and explode. With mosquitoes often cited as the most hated creature on the planet, the idea of being able to make them burst at will is perhaps an appealing one to many. But, having spent the better part of a decade feeding mosquitoes on my own arms for research, I can confidently say that it’s a myth. There is, however, a way to make mosquitoes actually burst all it takes is a steady hand and some forceps.

The first ever exploding mosquitoes can be attributed to Robert Gwadz, Ph.D., in a discovery that was made through basic laboratory research over 50 years ago. He found that making an incision in the ventral nerve cord of a mosquito cuts off the signal to stop feeding, giving it an unquenchable thirst for blood. Mosquitoes that have undergone this procedure can drink in excess of four times their weight and may eventually burst. This led Gwadz to a hypothesis that blood ingestion is regulated by abdominal stretch receptors that prevent mosquitoes from (quite literally) drinking themselves to death.

Severing or crushing the ventral nerve cord of a mosquito at the point shown by the green arrow leads to an unregulated intake of blood. (Image by Perran Ross, Ph.D.)

Although this research is fundamental to our understanding of blood feeding behavior in mosquitoes, the results have rarely been repeated. So, while running my own experiments involving blood-feeding mosquitoes, I attempted to replicate these findings using a simple procedure.

Female Aedes aegypti mosquitoes (only females feed on blood) were immobilized by placing them in the fridge for an hour. Then, under a dissecting microscope, I used a pair of forceps to pin the mosquito down on its side and a second pair to pinch the abdomen (pictured above), crushing the ventral nerve cord. The next day, I let the mosquitoes feed on my arm, as we do routinely in our laboratory. And then the magic happened.

Warning: Graphic content. Mosquitoes undergoing a simple operation are unable to sense when they are full, drinking blood until they burst. (Video by Perran Ross, Ph.D.)

The video above—which, be warned, may not be suitable for those squeamish at the sight of blood—shows some of the more dramatic results of the operation. Mosquitoes drank far beyond their fair share of blood and were rendered unable to fly or even walk. Others went even further, drinking so much that they eventually burst. Often, they would continue to feed long after their abdomen ruptured, unaware that what was going in was coming straight out the other end.

Although the results are dramatic, performing surgery on individual mosquitoes is not a practical way to control mosquito populations or reduce the incidence of mosquito-borne diseases. But this knowledge of mosquito biology and their blood-feeding mechanisms could have many unexpected applications and inspire future research. For instance, one group of researchers is exploring how mosquitoes discern between plant nectar and blood. And the discovery that diet drugs can suppress mosquito appetite came from simple curiosity. Although we probably don’t want blood from exploding mosquitoes raining down from the skies, sometimes it takes an absurd question for an important scientific breakthrough.


Name and systematics Edit

In 1894, a British-Australian entomologist, Frederick A. Askew Skuse, was the first to scientifically describe the Asian tiger mosquito, which he named Culex albopictus (lat. culex "gnat", "midge" and albopictus "white-painted"). [6] [7] Later, the species was assigned to the genus Aedes (gr. άηδής , "unpleasant") [8] and referred to as Aedes albopictus. [9] Like the yellow fever mosquito, it belongs to the subgenus Stegomyia (Gr. στέγος , "covered, roofed", referring to the scales that completely cover the dorsal surface in this subgenus, and μυία , "fly") within the genus Aedes. [10] In 2004, scientists explored higher-level relationships and proposed a new classification within the genus Aedes and Stegomyia was elevated to the genus level, making Aedes albopictus now Stegomyia albopicta. This is, however, a controversial matter, and the use of Stegomyia albopicta versus Aedes albopictus is continually debated. [11] [12] [13]

Characteristics Edit

The adult Asian tiger mosquito is less than 10 mm (0.39 in) long from end to end with a striking white and black pattern. [6] [14] [15] The variation of the body size in adult mosquitoes depends on the density of the larval population and food supply within the breeding water. Since these circumstances are seldom optimal, the average body size of adult mosquitoes is considerably smaller than 10 mm. For example, the average length of the abdomen was calculated to be 2.63 mm (0.104 in), the wings 2.7 mm (0.11 in), and the proboscis 1.88 mm (0.074 in). [16]

The males are roughly 20% smaller than the females, but they are morphologically very similar. However, as 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, almost inaudible to humans, of the female. The maxillary palps of the males are also longer than their proboscis, whereas the females' maxillary palps are much shorter. (This is typical for the males of the Culicinae.) In addition, the tarsus of the hind legs of the males is more silvery. Tarsomere IV is roughly 75% silver in the males whereas the females' is only about 60% silver.

The other characteristics do not differentiate between sexes. A single silvery-white line of tight scales begins between the eyes and continues down the dorsal side of the thorax. This characteristic marking is the easiest and surest way to identify the Asian tiger mosquito.

The proboscis is dark colored, the upper surface of the end segment of the palps is covered in silvery scales, and the labium does not feature a light line on its underside. The compound eyes are distinctly separated from one another. The scute, the dorsal portion of an insect's thoracic segment, is black alongside the characteristic white midline. On the side of the thorax, the scutellum, and the abdomen are numerous spots covered in white-silvery scales.

Such white-silvery scales can also be found on the tarsus, particularly on the hind legs that are commonly suspended in the air. The bases of tarsomeres I through IV have a ring of white scales, creating the appearance of white and black rings. On the fore legs and middle legs, only the first three tarsomeres have the ring of white scales, whereas tarsomere V on the hind legs is completely white. The femur of each leg is also black with white scales on the end of the "knee". The femora of the middle legs do not feature a silver line on the base of the upper side, whereas, the femora on the hind legs have short white lines on base of the upper side. The tibiae are black on the base and have no white scales.

The terga on segments II through VI of the abdomen are dark and have an almost triangular silvery-white marking on the base that is not aligned with the silvery bands of scales on the ventral side of the abdomen. The triangular marking and the silvery band are only aligned on abdominal segment VII. The transparent wings have white spots on the base of the costae. With older mosquito specimens, the scales could be partially worn off, making these characteristics not stand out as much. [14] [16]

As with other members of the mosquito family, the female is equipped with an elongated proboscis that she uses to collect blood to feed her eggs. The Asian tiger mosquito has a rapid bite and an agility that allows it to escape most attempts by people to swat it. By contrast, the male member of the species primarily feeds on nectar and does not bite.

The female lays her eggs near water, not directly into it as other mosquitoes do, but typically near a stagnant pool. However, any open container containing water will suffice for larvae development, even with less than an ounce (30mL) of water. It can also breed in running water, so stagnant pools of water are not its only breeding sites. It is more likely to lay eggs in water sources near flowers than in water sources without flowers. It has a short flight range (less than 200 m (220 yd)), so breeding sites are likely to be close to where this mosquito is found. [17] [18]

Other mosquito species may be visually confused with the tiger mosquito. Comparison with approved pictures is the best way to determine the species with certainty. [19] Behavioral cues like almost-silent flight and difficulty in catching combined with knowledge of the range of local endemic mosquitoes may also aid this process.

Similar species Edit

Some mosquitoes in North America, such as Ochlerotatus canadensis, have a similar leg pattern. In North and South America, Ae. albopictus can be distinguished from Aedes taeniorhynchus since only Ae. albopictus has back markings.

In Europe, the mosquito Culiseta annulata, which is very common, but does not occur in high densities, can be mistaken for an Asian tiger mosquito because of its black-and-white-ringed legs. However, this species is missing the distinctive white line that runs from the middle of its head and down the thorax. It is also considerably larger than Ae. albopictus, is not black and white, but rather beige and grey striped, and has wings with noticeable veins and four dark, indistinct spots. The Tree Hole mosquito or Aedes geniculatus - a native to Europe and North Africa- has also been mistaken for Ae. albopictus. This is because the Tree Hole mosquito has very white scales on a very similar body. [20]

In the eastern Mediterranean area, Ae. albopictus species can be mistaken for Aedes cretinus, which also belongs to the subgenus Stegomyia and uses similar breeding waters. Aedes cretinus also has a white stripe on the scute, but it ends shortly before the abdomen, and also has two additional stripes to the left and right of the middle stripe. So far Aedes cretinus is only located in Cyprus, Greece, Macedonia, Georgia and Turkey. [21]

In Asia, the Asian tiger mosquito can be mistaken for other members of the subgenus Stegomyia, particularly the yellow fever mosquito Aedes aegypti (the most prevalent species in the tropics and subtropics), because both species display a similar black and white pattern. It can be hard to distinguish Ae. albopictus from the closely related Aedes scutellaris (India, Indonesia, Papua New Guinea, and the Philippines), Aedes pseudoalbopictus (India, Indonesia, Malaysia, Myanmar, Nepal, Taiwan, Thailand, and Vietnam) and Aedes seatoi (Thailand). [14] [22]

Diet and host location Edit

Like other mosquito species, only the females require a blood meal to develop their eggs. Apart from that, they feed on nectar and other sweet plant juices just as the males do. In regards to host location, carbon dioxide and organic substances produced from the host, humidity, and optical recognition play important roles.

The search for a host takes place in two phases. First, the mosquito exhibits a nonspecific searching behavior until it perceives host stimulants, whereupon it secondly takes a targeted approach. [23] For catching tiger mosquitoes with special traps, carbon dioxide and a combination of chemicals that naturally occur in human skin (fatty acids, ammonia, and lactic acid) are the most attractive. [24]

The Asian tiger mosquito particularly bites in forests during the day, so has been known as the forest day mosquito. Depending upon region and biotype, activity peaks differ, but for the most part, they rest during the morning and night hours. They search for their hosts inside and outside of human dwellings, but are particularly active outside. The size of the blood meal depends upon the size of the mosquito, but it is usually around 2 μl. Their bites are not necessarily painful, but they are more noticeable than those from other kinds of mosquitoes. Tiger mosquitoes generally tend to bite a human host more than once if they are able to. [23] [25]

Ae. albopictus also bites other mammals besides humans, as well as birds. [23] [25] The females are always on the search for a host and are persistent but cautious when it comes to their blood meal and host location. Their blood meal is often broken off before enough blood has been ingested for the development of their eggs, so Asian tiger mosquitoes bite multiple hosts during their development cycle of the egg, making them particularly efficient at transmitting diseases. The mannerism of biting diverse host species enables the Asian tiger mosquito to be a potential bridge vector for certain pathogens that can jump species boundaries, for example the West Nile virus.

Natural enemies Edit

Primarily, other mosquito larvae, flatworms, swimming beetles, fungi, ciliates, paramecia, protozoans which act as parasites, predatory copepods, and spiders are natural enemies of the larval stage of Asian tiger mosquitoes.

Toxorhynchites larvae, a mosquito genus that does not suck blood, feeds upon other mosquito larvae and are often found with tiger mosquito larvae. Flatworms and small swimming beetles are considered natural predators. [25]

Fungi from the genus Coelomomyces (order Blastocladiales) develop inside the visceral cavity of mosquito larvae. The species Coelomomyces stegomyiae was first found on the Asian tiger mosquito. [25]

Paramecia, or ciliates, can also affect Ae. albopictus larvae, and the first detected species was Lambornella stegomyiae (Hymenostomatida: Tetrahymenidae). [25] The virulence, mortality rate, and subsequent possibilities of Lambornella being implemented as a biological remedy to control Ae. albopictus, however, has conflicting views. [26] [27]

Sporozoans of the genus Ascogregarina (Lecudinidae) infect the larval stage of mosquitoes. The species Ascogregarina taiwanensis was found in Asian tiger mosquitoes. [25] When the adult mosquitoes emerge from their pupal case, they leave the infectious intermediary stage of parasites in the water and close off the infection cycle. Infected adults are generally smaller than non-infected adults and have an insignificantly higher mortality rate therefore, food supply and larval density apparently play a role. In competitive situations, an infection with sporozoans can also reduce the biological fitness of other uninfected mosquitoes. However, the use of the parasites as an effective biological remedy to control mosquito populations is implausible because the host must reach the adult stage for the transmission of the parasites. [28]

Though they do not commonly occur in the natural habitats of Asian tiger mosquitoes, predatory copepods from the family Cyclopidae seem to willingly feed on them given the opportunity. [25] Relatives of different genera could therefore present a possibility in the control of tiger mosquitoes. [29]

Predators of adult Ae. albopictus in Malaysia include various spider species. Up to 90% of the gathered spiders from rubber plantations and a cemetery fed upon Asian tiger mosquitoes. Whether the spiders would have an effect on the mosquito population is still unclear. Tiger mosquitoes were abundantly present despite the existence of the spiders. [30]

Climatic adaptations Edit

The Asian tiger mosquito originally came from Southeast Asia. In 1966, parts of Asia and the island worlds of India and the Pacific Ocean were denoted as the area of circulation for the Asian tiger mosquito. [31] Ae. albopictus as a native to tropical and subtropical regions with warm and humid climate, is active all year long however, it has been adapting successfully to cooler, temperate regions, where they hibernate over winter. Eggs from strains in the temperate zones are more tolerant to the cold than ones from warmer regions. [32] [33] The species can even tolerate snow and temperatures under freezing. Adult tiger mosquitoes can survive throughout winter in suitable microhabitats. [34]

Invasive species Edit

Since the mid 1960s, the tiger mosquito has spread to Europe, the Americas, the Caribbean, Africa, and the Middle East. As of 2008 Ae. albopictus was one of the 100 world's worst invasive species according to the Global Invasive Species Database. [35]

As of 2006, Ae. albopictus was not native to Australia and New Zealand. [36] [37] The species was introduced there multiple times, but has yet to establish itself. This is due to the well-organized entomological surveillance programs in the harbors and airports of these countries. Nevertheless, as of 2006 it has become domestic on the islands in the Torres Strait between Queensland, Australia, and New Guinea. [38]

In Europe, Asian tiger mosquitos first emerged in Albania in 1979, introduced through a shipment of goods from China. In 1990–1991, they were most likely brought to Italy in used tires from Georgia (USA), and since then have spread throughout the entire mainland of Italy, as well as parts of Sicily and Sardinia. Since 1999, they have established themselves on the mainland of France, primarily southern France. In 2002, they were also discovered in a vacation town on the island of Corsica, but did not completely establish themselves there until 2005. In Belgium, they were detected in 2000 and 2013, [39] in 2001 in Montenegro, 2003 in Canton Ticino in southern Switzerland, and Greece, 2004 in Spain and Croatia, 2005 in the Netherlands and Slovenia, and 2006 in Bosnia and Herzegovina. [1] In the fall of 2007, the first tiger mosquito eggs were discovered in Rastatt (Baden-Wuerttemberg, Germany). [40] Shortly before, they were found in the northern Alps of Switzerland in Canton Aargau. [41] since 2010, it has also been sighted increasingly in Malta during summer. [ citation needed ] In September 2016, Public Health England found eggs, though no mosquitos, in a lorry park at Folkestone service station on the M20, near Westenhanger, which is 6 miles West of the Eurotunnel. [42]

In the United States, this species invaded the Southern United States in the 1980s and rapidly spread northward into novel climate compared to its native range. [43] It was initially found in 1983 in Memphis, Tennessee. [44] then at the Port of Houston in a 1985 shipment of used tires, [45] and spread across the South up the East Coast to become prevalent in the Northeast. [46] It was not discovered in Southern California until 2001, then eradicated for over a decade however, by 2011, it was again being found in Los Angeles County traps, then over the next two years expanded its range to Kern County and San Diego County. [47] [48] [49] As of 2013 [update] , North American land favoring the environmental conditions of the Asian tiger mosquito was expected to more than triple in size in the coming 20 years, especially in urban areas. [50] As of 2017 [update] Aedes albopictus mosquitoes have been identified in 1,368 counties in 40 U.S states. [51] [52] A 2019 study in Nature Microbiology that modeled expansion of Aedes albopictus due to climate change, urbanization, and human movement found that the species would likely continue to spread throughout the coming decades. [53]

In Latin America, the Asian tiger mosquito was first discovered 1986 in Brazil [54] and in 1988 in Argentina and Mexico, [55] as well. Other parts of Latin America where the Asian tiger mosquito was discovered are the Dominican Republic in 1993, Bolivia, Cuba, Honduras, and Guatemala in 1995, El Salvador in 1996, Paraguay in 1999, Panama in 2002, and Uruguay and Nicaragua in 2003. [56]

In Africa, the species was first detected in 1990 in South Africa. [57] In Nigeria, it has been domestic since at least 1991. [58] It spread to Cameroon in 1999/2000, [59] to the Bioko Island of Equatorial Guinea in 2001, [60] and to Gabon in 2006. [61]

In the Middle East, the species was detected in Lebanon in 2003 and in Syria in 2005 the first record in Israel was published in 2003. [62]

Competition with established species Edit

Ae. albopictus can outcompete and even eradicate other species with similar breeding habitats from the very start of its dispersal to other regions and biotopes. [63] In Kolkata, for example, it was observed in the 1960s that egg depositing containers were being settled by the Asian tiger mosquito in city districts where the malaria mosquito (genus Anopheles) and yellow fever mosquito (Aedes aegypti) had both been eliminated by the application of DDT. [64] This may be because primarily the inner walls of the houses were treated with DDT to kill the mosquitoes resting there and fight the malaria mosquito. The yellow fever mosquito also lingers particularly in the inside of buildings and would have been also affected. The Asian tiger mosquito rests in the vicinity of human dwellings would therefore have an advantage over the other two species. In other cases where the yellow fever mosquito was repressed by the Asian tiger mosquito, for instance in Florida, this explanation does not fit. [65] [66] Other hypotheses include competition in the larval breeding waters, differences in metabolism and reproductive biology, or a major susceptibility to sporozoans (Apicomplexa). [67]

Another species which was suppressed by the migrating Ae. albopictus was Ae. guamensis in Guam. [68]

The Asian tiger mosquito is similar, in terms of its close socialization with humans, to the common house mosquito (Culex pipiens). Among other differences in their biology, Culex pipiens prefers larger breeding waters and is more tolerant to cold. In this respect, no significant competition or suppression between the two species likely occurs. [67]

A possible competition among mosquito species that all lay their eggs in knotholes and other similar places (Ae. cretinus, Ae. geniculatus, and Anopheles plumbeus) has yet to be observed.

In Europe, the Asian tiger mosquito apparently covers an extensive new niche. This means that no native, long-established species conflict with the dispersal of Ae. albopictus.

For humans Edit

Ae. albopictus is known to transmit pathogens and viruses, such as the yellow fever virus, dengue fever, Chikungunya fever, [2] and Usutu virus. [69] There is some evidence supporting the role of Ae. albopictus in the transmission of Zika virus, which is primarily transmitted by the related Ae. aegypti. [5]

The Asian tiger mosquito was responsible for the Chikungunya epidemic on the French Island La Réunion in 2005–2006. By September 2006, an estimated 266,000 people were infected with the virus, and 248 fatalities occurred on the island. [70] The Asian tiger mosquito was also the transmitter of the virus in the first and only outbreak of Chikungunya fever on the European continent. This outbreak occurred in the Italian province of Ravenna in the summer of 2007, and infected over 200 people. [71] [72] Evidently, mutated strains of the Chikungunya virus are being directly transmitted through Ae. albopictus particularly well and in such a way that another dispersal of the disease in regions with the Asian tiger mosquito is feared. [73]

On the basis of experimental evidence and probability estimates, the likelihood of mechanical or biological transmission of HIV by insects is virtually nonexistent. [74]

For animals Edit

The tiger mosquito is relevant to veterinary medicine. For example, tiger mosquitoes are transmitters of Dirofilaria immitis, a parasitic roundworm that causes heartworm in dogs and cats. [75]

For arthropods Edit

Wolbachia infection are the most common infection in arthropods today, and over 40% of arthropods have contracted it. [76] Wolbachia can be transmitted from parent to offspring or between breeding individuals. Wolbachia is easily transmitted within the Ae. albopictus mosquito due to the effects it has on fecundity in females. [77] Once female Asian tiger mosquitos have contracted the infection, they produce more eggs, give birth more frequently, and live longer than uninfected females. In this way, Wolbachia provides a fitness advantage to the infected females and prevents uninfected females from reproducing. This allows control of the spread of diseases that many species carry by suppressing reproduction of the individuals with the harmful disease, but without the Wolbachia infection. Wolbachia can also be used to transfer certain genes into the population to further control the spread of diseases. [78]

Cytoplasmic incompatibility Edit

In the natural environment, Wolbachia and the Asian tiger mosquito are in a symbiotic relationship, so both species benefit from each other and can evolve together. The relationship between Wolbachia and its host might not have always been mutualistic, as Drosophila populations once experienced decreased fecundity in infected females, suggesting that Wolbachia evolved over time so that infected individuals would actually reproduce much more. [79] The mechanism by which Wolbachia is inherited through maternal heredity is called cytoplasmic incompatibility. [77] This changes the gamete cells of males and females, making some individuals unable to mate with each other. Although little is known about why cytoplasmic incompatibility exists, Wolbachia infection creates a fitness advantage for infected females, as they can mate with either infected or uninfected males. Despite this, infected males cannot reproduce with uninfected females. Therefore, over time, a population exposed to Wolbachia transitions from a few infected individuals to all individuals becoming infected, as the males that cannot reproduce successfully do not contribute to future generations. This is called population replacement, where the population's overall genotype is replaced by a new genotype. This shows how populations of Asian tiger mosquitoes can vary in number of Wolbachia-infected individuals, based on how often the infection is transmitted. [80] Due to Wolbachia's ability to transmit from one host to the next, it can change the average genotype of a population, potentially reducing the population's gene flow with other nearby populations.

Unidirectional cytoplasmic incompatibility Edit

This type of cytoplasmic incompatibility where an infected male cannot reproduce successfully with an uninfected female is called unidirectional cytoplasmic incompatibility. It occurs because Wolbachia modifies the paternal chromosomes during sperm development, leading to complications for these offspring during embryonic development. [81]

Bidirectional cytoplasmic incompatibility Edit

Also, bidirectional cytoplasmic incompatibility occurs when an infected male carrying one strain of Wolbachia reproduces with an infected female carrying a different strain of Wolbachia. This also results in failed reproduction. Bidirectional cytoplasmic incompatibility also has evolutionary implications for populations of Ae. albopictus and other vectors of the infection. [82] This is because bidirectional cytoplasmic incompatibility in Wolbachia creates unviable offspring, reducing gene flow between two populations, which can eventually lead to speciation.

Ae. albopictus is very difficult to suppress or to control due to its remarkable ability to adapt to various environments, its close contact with humans, and its reproductive biology.

The containment of infestations is generally effected by public health services through area-wide integrated control plans, which aim to reduce the nuisance perceived by populations and the risks of viraemic transmission. Such plans consist of different activities that include entomological surveillance, larvicide treatments in public and private areas, information campaigns, and treatments against adult mosquitoes in the zones affected by suspected cases of transmissible viroses. [83]

Efficient monitoring or surveillance is essential to prevent the spread and establishment of this species. In addition to the monitoring of ports, warehouses with imported plants, and stockpiles of tires, rest areas on highways and train stations should be monitored with appropriate methods. [84]

The control of Asian tiger mosquitoes begins with destroying the places where they lay their eggs, which are never far from where people are being bitten, since they are weak fliers, with only about a 180-m (650-ft) lifetime flying radius. Puddles that last more than three days, sagging or plugged roof gutters, old tires holding water, litter, and any other possible containers or pools of standing water should be drained or removed. Bird baths, inlets to sewers and drainage systems holding stagnant water, flower pots, standing flower vases, knotholes, and other crevices that can collect water should be filled with sand or fine gravel to prevent mosquitoes from laying their eggs in them.

Any standing water in pools, catchment basins, etc., that cannot be drained, or dumped, can be periodically treated with properly labeled insecticides or Bacillus thuringiensis israelensis (Bti), often formed into doughnut-shaped "mosquito dunks". Bti produces toxins which are effective in killing larvae of mosquitoes and certain other dipterans, while having almost no effect on other organisms. Bti preparations are readily available at farm, garden, and pool suppliers.

Flowing water will not be a breeding spot, and water that contains minnows is not usually a problem, because the fish eat the mosquito larvae. Dragonflies are also an excellent method of control. Dragonfly larvae eat mosquito larvae in the water, and adults snatch adult mosquitoes as they fly.

In any case, an efficient surveillance is essential to monitor the presence of tiger mosquitoes and the effect of control programs. Ovitraps are normally used for the monitoring of Ae. albopictus. They are black water containers with floating Styrofoam blocks or small wooden paddles that are in contact with the surface of the water. Female tiger mosquitoes lay their eggs on these surfaces. Through the identification of these eggs or of the larvae that hatch from these eggs in the laboratory, the presence and abundance of mosquito species can be estimated. Versions of these traps with an adhesive film (sticky traps) that catch the egg-depositing mosquitoes make the analysis much easier and quicker, but are more complicated in terms of handling. [85] [86] The results of ovitraps are often variable and depend on the availability of alternative egg-depositing waters. Due to this, it is best to use them in large numbers and in conjunction with other monitoring methods.

To date, few effective traps for adult Asian tiger mosquitoes are available. Those traps that catch other species of mosquitoes do not catch tiger mosquitoes efficiently. A form of an ovitrap called a lethal ovitrap mimics the breeding site for Ae. albopictus just like the monitoring tool, but it has the added benefit of containing chemicals that are toxic to the mosquitoes when they enter, but do not harm humans. These traps have had success in some countries to control Aedes mosquito populations. [87] A new trap type has now been shown to catch significant numbers of Ae. albopictus. [88] [89] This device, with the help of a ventilator, produces an upward air current of ammonia, fatty acids, and lactic acids that takes a similar form and smell of a human body. With the addition of carbon dioxide, the efficacy of the trap is increased. This means a suitable tool is available for trapping adult tiger mosquitoes, and for example, examining the existence of viruses in the trapped mosquitoes. Previously, the mosquitoes had to be collected from volunteers to be studied, which is ethically questionable, especially during epidemics. Recent research also indicates this trap type may also have a use as a control tool in a study in Cesena, Italy, the number of biting tiger mosquitoes was reduced in places where traps were installed. [90]

An amino acid substitution mutation - F1534C - is overwhelmingly the most common voltage-gated sodium channel in A. albopictus in Singapore. [91] This channel being the target of pyrethroids, [91] this is suspected to be a knockdown resistance (kdr) mutation, [91] and that that is the reason for its prevalence. [91]

Although the Wolbachia infection is prevalent in arthropod species, especially the Asian tiger mosquito, it is a useful mechanism for inhibiting the spread of dengue. [92] Ae. aegypti individuals, a close relative of Ae. albopictus, with an artificial Wolbachia infection, cannot transmit dengue, an infectious virus, but they can pass on the Wolbachia infection to other populations. This could lead to many more discoveries in disease control for Ae. albopictus and other mosquito species. [92] In addition, due to the cytoplasmic incompatibility caused by Wolbachia, the artificial infection of males can serve as a biological control as they are unable to reproduce successfully with uninfected females (unidirectional CI). [81] When artificially infected males are unable to reproduce, the population size can be controlled, thereby reducing the transmission of the harmful disease of interest. Artificial infection of males is achieved by the removal of cytoplasm from infected oocytes, which is then transferred into embryos prior to the blastoderm stage.

How mosquitoes find you to bite you

Photo credit: iStock

Are you dousing your skin with bug repellents and lighting citronella candles to keep mosquitoes away? These efforts may keep them at bay for a while, but no solution is perfect because mosquitoes have evolved to use a triple threat of visual, olfactory, and thermal cues to home in on their human targets, a new Caltech study suggests.

The study appears in the July 17 online version of the journal Current Biology.

When an adult female mosquito needs a blood meal to feed her young, she searches for a host — often a human. Many insects, mosquitoes included, are attracted by the odor of the carbon dioxide (CO2) gas that humans and other animals naturally exhale. However, mosquitoes can also pick up other cues that signal a human is nearby. They use their vision to spot a host and thermal sensory information to detect body heat.

To find a human host, mosquitoes face the challenging task of integrating sensory cues that are separated in space and time. This sensory integration happens as a result of their multi-pronged strategy, which begins with tracking a plume of CO2 upwind. Research from the Dickinson lab indicates that mosquitoes also respond to CO2 by exploring visual features they otherwise ignore. This behavior guides them towards potential hosts, where they use cues such as heat to locate a landing site. Image credit: Lance Hayashida/Caltech

Mosquitoes combine this information to map out the path to their next meal.

To find out how and when the mosquitoes use each type of sensory information, the researchers released hungry, mated female mosquitoes into a wind tunnel in which different sensory cues could be independently controlled. The researchers injected a high-concentration CO2 plume into the tunnel, mimicking the signal created by the breath of a human. In series of experiments, they found that the insects were attracted by the CO2, which is an indicator of a nearby host, and would also spend a lot of time hovering near high-contrast objects control experiments – think: a person. In another set of experiments, to test thermal factors, the researchers found that mosquitoes are attracted to warmth.

Read more about how the researchers got their results here

Information gathered from all of these experiments enabled the researchers to create a model of how the mosquito finds its host over different distances. They hypothesize that from 10 to 50 meters away, a mosquito smells a host’s CO2 plume. As it flies closer—to within 5 to 15 meters—it begins to see the host. Then, guided by visual cues that draw it even closer, the mosquito can sense the host’s body heat. This occurs at a distance of less than a meter.

Michael Dickinson, professor of bioengineering at the California Institute of Technology, is the principal investigator of the study. Dickinson said:

Our experiments suggest that female mosquitoes do this in a rather elegant way when searching for food. They only pay attention to visual features after they detect an odor that indicates the presence of a host nearby. This helps ensure that they don’t waste their time investigating false targets like rocks and vegetation. Our next challenge is to uncover the circuits in the brain that allow an odor to so profoundly change the way they respond to a visual image.

The study paints a bleak picture for those hoping to avoid mosquito bites. At the end of the paper, the authors note:

Even if it were possible to hold one’s breath indefinitely, another human breathing nearby, or several meters upwind, would create a CO2 plume that could lead mosquitoes close enough to you that they may lock on to your visual signature. The strongest defense is therefore to become invisible, or at least visually camouflaged. Even in this case, however, mosquitoes could still locate you by tracking the heat signature of your body . . . The independent and iterative nature of the sensory-motor reflexes renders mosquitoes’ host seeking strategy annoyingly robust.

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Bottom line: According to a Caltech study, mosquitoes use a triple threat of visual, olfactory, and thermal cues to home in on their human targets.