I walk by a home that has been professionally sprayed outside for mosquitoes, advertising the vendor who did so. I have not quite reached that point at my townhome, but I might. I will confess that I do like to leave a bit of water in my bird bath — even though I know it will attract mosquitoes. I just like watching the birds drink and bathe in the water. I know that in the heat of the summer the Town of Addison will send out trucks all over town to spray for mosquitoes. The West Nile virus that is spread by mosquitoes is very serious in Texas; I have known of a couple of people who have died from it. The media will broadcast warnings not to go outside at dusk and to always wear long pants and long-sleeved shirts when you are outside. Long before the COVID-19 outbreak, it was important to stay inside in the hot summer to avoid mosquitoes. Let’s learn more about these pesky pests.
Mosquitoes are members of a group of about 3,500 species of small flies within the family Culicidae, from the Latin “culex” meaning "gnat.” The word "mosquito" — formed by “mosca” and diminutive “-ito” is Spanish and Portuguese for "little fly." Mosquitoes have a slender segmented body, one pair of wings, one pair of halteres — club-shaped organs that provide information about body rotations during flight, three pairs of long hair-like legs and elongated mouthparts.
The mosquito life cycle consists of egg, larva, pupa and adult stages. Eggs are laid on the water surface; they hatch into motile larvae that feed on aquatic algae and organic material. The adult females of most species have tube-like mouthparts called a proboscis that can pierce the skin of a host and feed on blood, which contains protein and iron needed to produce eggs. Thousands of mosquito species feed on the blood of various hosts — vertebrates, including mammals, birds, reptiles, amphibians and some fish; along with some invertebrates, primarily other arthropods. This loss of blood is seldom of any importance to the host.
The mosquito's saliva is transferred to the host during the bite and can cause an itchy rash. In addition, many species can ingest pathogens while biting and transmit them to future hosts. In this way, mosquitoes are important vectors of diseases such as malaria, yellow fever, Chikungunya, West Nile, dengue fever, filariasis, Zika and other arboviruses. By transmitting diseases, mosquitoes cause the deaths of more people than any other animal taxon: over 700,000 each year. It has been claimed that almost half of the people who have ever lived have died of mosquito-vectored disease, but this claim is disputed, with more conservative estimates placing the death toll closer to 5% of all humans.
Fossil record and evolution
The oldest known mosquito with an anatomy similar to modern species, Paleoculicis minutus, was found in 79-million-year-old Canadian amber from the Cretaceous geological period. The photo shows: 1.-Entire male specimen; 2.-Scales on wing veins; 3.-Portion of head showing pedicel, compound eyes and clypeus; 4.-Terminal tarsal segments and claws on foreleg, arrow shows spur on smaller posterior claw.
An older species with more primitive features, Burmaculex antiquus, was found in Burmese amber that is around 99 million years old. Despite no fossils being found earlier than the Cretaceous, recent studies suggest that the earliest divergence of mosquitoes between the lineages leading to Anopheliae and Culicinae occurred 226 million years ago. In 2019 a species of the same age as Burmaculex was also described from the Burmese amber, Priscoculex burmanicus, however it was recognized as belonging to the modern subfamily Anophelinae, suggesting that the split between the two subfamilies must predate this time. Two mosquito fossils have been found that show very little morphological change in modern mosquitoes against their counterpart from 46 million years ago. These fossils are also the oldest ever found to have blood preserved within their abdomens.
Morphology
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 or 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.
Life cycle overview
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. 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.
Breeding
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, 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. 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 or 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.
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 pathgoers 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
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 or slender 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.
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.
Larva
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, a species of biting midges, within the family Ceratopogonidae have been observed in experiments to prey upon mosquito larvae.
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.
Pupa
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 the pupa’s 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.
Adult
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 or 0.1 inch, and the largest around 19 mm or 0.7 inch. 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. 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.
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 0.6–1 mph, traveling up to 7.5 miles in a night. Males beat their wings between 450 and 600 times per second.
The abdomen is specialized for food digestion and egg development; the abdomen of a mosquito can hold three times its own weight in blood. 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.
Feeding by adults
Typically, both male and female mosquitoes feed on nectar, aphid honeydew and plant juices, 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. 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.
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. Individuals' attractiveness to mosquitoes also has a heritable, genetically controlled component.
Female mosquitoes hunt their blood host by detecting organic substances such as carbon dioxide 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. 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.
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.
Hosts of blood-feeding mosquito species
Many, if not all, blood-sucking species of mosquitoes are fairly selective feeders that specialize 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.
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.
In 1969 it was reported that some species of anautogenous mosquitoes would feed on the haemolymph of caterpillars. Other observations include mosquitoes feeding on cicadas and mantids. In 2014, it was shown that malaria-transmitting mosquitoes actively seek out some species of caterpillars and feed on their haemolymph and do so to the caterpillar's apparent physical detriment.
Control
Many measures have been tried for mosquito control, including the elimination of breeding places, exclusion via window screens and mosquito nets, biological control with parasites such as fungi and nematodes or predators such as fish, copepods, dragonfly nymphs and adults and some species of lizard and gecko. Another approach is to introduce large numbers of sterile males. Genetic methods including cytoplasmic incompatibility, chromosomal translocations, sex distortion and gene replacement — solutions seen as inexpensive and not subject to vector resistance — have been explored.
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." The control of disease-carrying mosquitoes may in the future be possible using gene drives.
Insect repellents are applied on skin and give short-term protection against mosquito bites. The chemical DEET repels some mosquitoes and other insects. Some CDC-recommended repellents are picaridin, eucalyptus oil or PMD and ethyl butylacetylaminopropionate. 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 many universities' studies has ever provided evidence that these devices prevent a human from being bitten by a mosquito.
In human culture
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.
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 or Nanai people and Samoyed have the insect arising from the ashes or fragments of some giant creature or demon. Similar tales are found in Native North American myth, with the mosquito arising from the ashes of a man-eater, suggest a common origin. The Tatars of the Altai Mountains had a similar myth, thought to be of Native North American origin, involving the fragments of the dead giant Andalma-Muus becoming mosquitos and other insects.
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.
The de Havilland DH.98 Mosquito is a British twin-engined, shoulder-winged multirole combat aircraft, introduced during the Second World War. Unusual in that its frame was constructed mostly of wood, it was nicknamed the "Wooden Wonder" or "Mossie." Lord Beaverbrook, Minister of Aircraft Production, nicknamed it "Freeman's Folly," alluding to Air Chief Marshal Sir Wilfrid Freeman, who defended Geoffrey de Havilland and his design concept against orders to scrap the project. In 1941, it was one of the fastest operational aircraft in the world.
Originally conceived as an unarmed fast bomber, the Mosquito's use evolved during the war into many roles, including low- to medium-altitude daytime tactical bomber, high-altitude night bomber, pathfinder, day or night fighter, fighter-bomber, intruder, maritime strike and photo-reconnaissance aircraft. It was also used by the British Overseas Airways Corp. as a fast transport to carry small, high-value cargo to and from neutral countries through enemy-controlled airspace. The crew of two, pilot and navigator, sat side by side. A single passenger could ride in the aircraft's bomb bay when necessary.
The Mosquito FBVI was often flown in special raids, such as Operation Jericho — an attack on Amiens Prison in early 1944 and precision attacks against military intelligence, security and police facilities, such as Gestapo headquarters. On January 30, 1943, the 10th anniversary of the Nazis' seizure of power, a morning Mosquito attack knocked out the main Berlin broadcasting station while Hermann Göring was speaking, taking his speech off the air.
The Mosquito flew with the Royal Air Force and other air forces in the European, Mediterranean and Italian theatres. The Mosquito was also operated by the RAF in the Southeast Asian theatre and by the Royal Australian Air Force based in the Halmaheras and Borneo during the Pacific War. During the 1950s, the RAF replaced the Mosquito with the jet-powered English Electric Canberra.
“The Mosquito Coast” is a 1986 American drama film directed by Peter Weir and starring Harrison Ford, Helen Mirren, Andre Gregory and River Phoenix. It is based on the 1981 novel of the same name by Paul Theroux. The film tells the story of a family that leaves the United States and tries to find a happier and simpler life in the jungles of Central America. However, their jungle paradise quickly turns into a dystopia as their stubborn father's behavior becomes increasingly erratic and aggressive. It was shot in the cities of Cartersville and Rome in Georgia, in addition to Baltimore, Maryland and Belize.
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