The tiger mosquito (Aedes albopictus) is a species of Asian origin first reported in Italy in 1990. Currently, it is widespread throughout the national territory and in many European countries. Its distribution on a continental scale is due to the passive transport of eggs (e.g., trade in used tires), while on a regional scale, dispersal is also facilitated by the passive transport of adults (e.g., cars, public transport). Although of tropical origin, this mosquito is able to survive the harsh winter seasons of Northern Italy thanks to its ability to produce eggs resistant to low temperatures (diapausing eggs) and desiccation. In Trentino, it was first reported in Rovereto in 1996, progressively colonizing all valleys below 600-700 m a.s.l. Even today, the spread of the tiger mosquito has not stopped, and ongoing climate changes are favoring its expansion by creating new areas favorable to its establishment especially at higher altitudes.

Morphology

The tiger mosquito is a small insect (5-8 mm), with a typical black coloration and white transverse bands on the legs and body. Furthermore, it features a characteristic metallic white stripe on the thorax.

Habitat and behaviour

The tiger mosquito proliferates in highly anthropized environments and is active with mild outdoor temperatures, usually from May to October. At our latitudes, the population peak is between late August and the first half of September. The female lays eggs inside various types of artificial containers, such as pots, saucers, buckets, bins, gullies, used tires, and any object capable of holding water; natural sites such as holes in trees or in the ground can also serve as breeding sites for larval development. The search for a blood meal occurs during daylight hours, and it preferentially bites humans, mainly outdoors but occasionally entering indoors. It is not a strong flyer (less than 200 meters from the emergence site, although some specimens can cover greater distances), so the search for a blood meal generally takes place near the hatching area.

Transmitted pathogens

The high presence of the insect combined with its exceptional aggressiveness in seeking a blood meal often forces victims to abandon outdoor activities to seek refuge indoors. The presence of the tiger mosquito therefore constitutes a serious social problem both for the high degree of nuisance caused to humans by its ectoparasitic activity and because it can represent a danger as a vector of exotic arboviruses. It should be remembered that this species is a potential vector of numerous viruses, including Dengue, Chikungunya, West Nile, and Zika. Furthermore, in Italy, the tiger mosquito has been found naturally infected with Dirofilaria repens and Dirofilaria immitis, agents of animal helminthiasis accidentally transmissible to humans.

The korean bush mosquito (Aedes koreicus) was found for the first time in 2011 in the Belluno area. Reported in Trentino since 2013, it is currently found throughout Valsugana, Adige Valley, Valle dei Laghi, Val di Cembra and Valli Giudicarie. Its distribution range is continuously expanding, especially towards the South and West. Originating from Asia, its continental distribution is due to the passive transport of eggs (e.g., trade in used tires), while on a regional scale, dispersal is also facilitated by the passive transport of adults (e.g., cars, public transport). The korean bush mosquito can survive the winter thanks to its ability to produce eggs resistant to low temperatures (diapausing eggs) and desiccation. Thanks to its tolerance for low temperatures, it manages to colonize hilly and mountainous areas above 800 m a.s.l. (not reached by the tiger mosquito); the highest breeding site where it has been found in Trentino is at 1500 m a.s.l.

Morphology

The korean bush mosquito is similar to the tiger mosquito but is larger (8-10 mm) and dark brown in color with pale-white transverse bands on the body and legs. The pattern on the thorax consists of 5 pale-white lines.

Habitat and behaviour

The korean bush mosquito proliferates mainly in urban and suburban contexts. The seasonal activity period is longer than that of the tiger mosquito because it tolerates lower temperatures. Adults of Ae. koreicus can indeed be found starting from March/April until late November. At our latitudes, the population peak is between late August and the first half of September. The female lays eggs inside various types of artificial containers, such as pots, saucers, buckets, bins, gullies, used tires, and any object capable of holding water; natural sites such as holes in trees or in the ground can also serve as breeding sites. It rarely shares a breeding site with the tiger mosquito. The search for a blood meal occurs during daylight hours, biting humans in urban environments but also wild animals in rural environments.

Transmitted pathogens

Very little is known about the potential of Ae. koreicus as a pathogen vector. In the past, it seems to have been involved in the spread of Japanese encephalitis in its area of origin (Southeast Asia). More recently, it has been shown to be a competent vector of Dirofilaria immitis. Recent studies also indicate it as a potential vector of the Chikungunya virus.

The Asian bush mosquito (Aedes japonicus japonicus) is an invasive species native to Northeast Asia. In Europe, it was first reported in 2000 in Normandy (France) and is currently distributed discontinuously with populations detected in Germany, Austria, Switzerland, Belgium, Slovenia, Croatia, Hungary, and the Netherlands. Recently, some specimens were found in Friuli Venezia Giulia and Veneto. In Trentino, it was found for the first time in 2021 in some municipalities of Primiero. The Asian bush mosquito can survive the winter thanks to its ability to produce eggs resistant to low temperatures (diapausing eggs) and desiccation. Thanks to the tolerance of adults to low temperatures, it manages to colonize hilly and mountainous areas.

Morphology

The Asian bush mosquito is very similar to the Korean mosquito and is practically indistinguishable to the naked eye (size 8-10 mm, dark brown colour with pale-white transverse bands on the body and legs. Pattern on the thorax consisting of 5 pale-white lines). What distinguishes it from the Korean mosquito is the colouring of the last two tarsi (segments) of the third pair of legs (rear) which in Ae. j. japonicus are completely dark.

Habitat and behaviour

The Asian bush mosquito proliferates mainly in wooded areas in urban, suburban, and rural contexts. The seasonal activity period is longer than that of the tiger mosquito (similar to Ae. koreicus) because it tolerates lower temperatures. The female lays eggs inside various types of artificial containers, such as pots, saucers, buckets, bins, gullies, used tires, and any object capable of holding water; natural sites such as holes in trees can also serve as breeding sites. The search for a blood meal occurs during daylight hours, biting both humans and wild animals.

Transmitted pathogens

Ae. j. japonicus is a potential vector of pathogens of medical importance, including West Nile virus (WNv), Japanese encephalitis, and La Crosse virus. Laboratory tests have demonstrated its ability to transmit Chikungunya, Dengue, and Rift Valley fever viruses.

The common house mosquito (Culex pipiens), unlike alien mosquitoes, is a species that has always been present in the Trentino territory (autochthonous species) and is ubiquitous up to hilly altitudes. It has two biotypes that are morphologically identical to each other but with different host preferences. The biotype Culex pipiens pipiens primarily prefers birds, while Culex pipiens molestus primarily prefers humans.

Morphology

The common house mosquito has a light brown body with faint whitish streaks on the abdomen. The legs, however, are a uniform dark brown color. Its size (6-8 mm) is slightly larger than that of the tiger mosquito.

Habitat and behaviour

The common house mosquito proliferates mainly in urban and suburban contexts. It exploits breeding sites with water with a high organic load, also favoring those of larger dimensions compared to those chosen by the tiger mosquito. Not infrequently, breeding sites are infested by both Cx. pipiens and Ae. albopicutus, which then enter into competition, with the tiger mosquito having surpassed the common house mosquito in abundance over the years, especially in urban areas. The common house mosquito is active mainly at night and prefers closed environments for the search of a blood meal and to survive the winter (as an adult), taking refuge where temperatures are never harsh. After surviving the winter, Culex pipiens females become active again at the beginning of spring (April) and the population reaches its peak in July.

Transmitted pathogens

The common house mosquito plays a primary role in the transmission of at least three viruses with medical and veterinary relevance: West Nile virus (WNv), USUTU virus, and Sindbis virus. The most important from a medical/veterinary point of view is WNv, which, despite circulating mainly among birds, can accidentally be transmitted to humans and horses. USUTU and Sindbis also circulate mainly among wild birds and are accidentally transmitted to humans, but their medical relevance is lower than WNv.

Anopheles plumbeus is a mosquito species widespread throughout Europe and Italy. Recent studies indicate that its presence in Trentino is scarce but distributed over much of the territory. The altitudinal distribution range is very wide, ranging from the valley floor up to 1200 m a.s.l. It is able to survive the winter at the egg stage or at most as a larva, taking refuge at the bottom of the breeding site when the surface is frozen.

Morphology

The characteristic that distinguishes the genus Anopheles from other mosquito genera is that the females have palps (appendages at the sides of the proboscis) of the same length as the proboscis. The body is of medium-small size and a uniform lead color.

Habitat and behaviour

The main breeding sites for this insect consist of natural cavities in trees and rocks in wooded areas or at the forest/urban edge. Recently, An. plumbeus larvae have also been found in septic tanks, gullies, tires, and cemetery vases, thus demonstrating the ability to settle even in a typically urban context. Adults appear from late spring until late September. The search for a blood meal occurs during the night hours, biting humans in urban environments but also wild animals in rural environments.

Transmitted pathogens

An. plumbeus is considered a potential vector of the malaria parasite, in particular Plasmodium vivax and Plasmodium falciparum. West Nile virus (WNv) can also be transmitted by this insect.

The castor bean tick (Ixodes ricinus) is an arthropod of health interest, widely distributed in Europe and Italy. In Trentino, it is found up to mountain altitudes. In recent years, attention to this insect has increased significantly due to numerous cases of disease transmitted to humans by this vector. This tick is able to survive harsh winter seasons thanks to the ability of the various developmental stages to take refuge in the undergrowth (deciduous forests) waiting to re-emerge the following spring. Due to climate change, its range is gradually expanding towards increasingly higher altitudes. A limiting factor for the spread of I. ricinus is its low resistance to desiccation. Indeed, it is found where the relative humidity is very high (70-80%) and the vegetation is lush.

Morphology

Ixodes ricinus belongs to the order of arachnids (the same as spiders) and as such has 4 pairs of legs (the larval stage has 3 pairs). It is a relatively small tick, with the adult female (6-7 mm) being larger than the male. Dorsally, adults have a black sclerotized plate which partially covers the back in females and entirely in males. In the female, the exposed part of the abdomen is red. Nymphs are much smaller than adults (2 mm) and they also have a sclerotized plate on the back that only partially covers the abdomen.

Habitat and behaviour

The ideal habitat for the castor bean tick consists of wooded environments (deciduous forests) with a high rate of humidity and undergrowth rich in leaves and shrubs. It is not uncommon to find it in city parks, transported by domestic dogs. Generally, Ixodes ricinus has two density peaks, a main one in spring and a secondary one in autumn although it can be found active all year round. The female lays eggs on the ground from which the larvae will hatch. After the blood meal, it molts into a nymph and subsequently, after another blood meal, it molts into an adult. The entire cycle can last up to 3 years. The search for a blood meal occurs by questing, and the size of the host depends on the stage the tick is in.

Transmitted pathogens

Ixodes ricinus can transmit pathogens of medical importance including tick-borne encephalitis virus (TBE) and the bacterium Borrelia burgdorferi s.l., the etiological agent of lyme borreliosis. The stage most involved in the transmission of pathogens to humans are the nymphs due to their small size which makes it difficult to spot and remove them from the skin, thus increasing the probability of transmission.