Aedes albopictus (synonym Stegomyia albopicta), from the mosquito (Culicidae) family, also known as the (Asian) tiger mosquito or forest mosquito, is a mosquito native to the tropical and subtropical areas of Southeast Asia. In the past few centuries, however, this species has spread to many countries through the transport of goods and international travel.[2] It is characterized by the white bands on its legs and body.
This mosquito has become a significant pest in many communities because it closely associates with humans (rather than living in wetlands), and typically flies and feeds in the daytime in addition to at dusk and dawn. The insect is called a tiger mosquito for its striped appearance, which resembles that of the tiger. Ae. albopictus is an epidemiologically important vector for the transmission of many viral pathogens, including the yellow fever virus, dengue fever, and Chikungunya fever,[3] as well as several filarial nematodes such as Dirofilaria immitis.[4] Aedes albopictus is capable of hosting the Zika virus[5][6] and is considered a potential vector for Zika transmission among humans.
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").[7][8] Later, the species was assigned to the genus Aedes (gr. άηδής, "unpleasant")[9] and referred to as Aedes albopictus.[10] 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.[11] 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.[12][13][14]
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.[7][15][16] 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).[17]
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.[citation needed]
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.[citation needed]
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.[citation needed]
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 forelegs 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.[citation needed]
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.[15][17]
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 one US fl oz (30 ml) 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.[18][19]
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.[20] 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.
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.[21]
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, North Macedonia, Georgia and Turkey.[22]
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).[15][23]
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.[citation needed]
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.[24] 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.[25]
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 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.[24][26]
Ae. albopictus also bites other mammals besides humans, as well as birds.[24][26] 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.[citation needed]
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.[citation needed]
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.[26]
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.[26]
Paramecia, or ciliates, can also affect Ae. albopictus larvae, and the first detected species was Lambornella stegomyiae (Hymenostomatida: Tetrahymenidae).[26] The virulence, mortality rate, and subsequent possibilities of Lambornella being implemented as a biological remedy to control Ae. albopictus, however, has conflicting views.[27][28]
Sporozoans of the genus Ascogregarina (Lecudinidae) infect the larval stage of mosquitoes. The species Ascogregarina taiwanensis was found in Asian tiger mosquitoes.[26] 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.[29]
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.[26] Relatives of different genera could therefore present a possibility in the control of tiger mosquitoes.[30]
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.[31]
The Asian tiger mosquito originally came from Southeast Asia. In 1966, parts of Asia and the island of India and the Pacific Ocean were denoted as the area of circulation for the Asian tiger mosquito.[32] 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.[33][34] The species can even tolerate snow and temperatures under freezing. Adult tiger mosquitoes can survive throughout winter in suitable microhabitats.[35]
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.[36]
As of 2006, Ae. albopictus was not native to Australia and New Zealand.[37][38] 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.[39]
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,[40] in 2001 in Montenegro, 2003 in Canton Ticino in southern Switzerland, and Greece, 2004 in Spain and Croatia, 2005 in the Netherlands and Slovenia, 2006 in Bosnia and Herzegovina[2] and 2022 in Cyprus.[41] In the fall of 2007, the first tiger mosquito eggs were discovered in Rastatt (Baden-Wuerttemberg, Germany).[42] Shortly before, they were found in the northern Alps of Switzerland in Canton Aargau.[43] 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