Culicidae

Mosquitoes are important blood-feeding insects around the world. They are vectors of several human diseases, including malaria, yellow fever, encephalitis, dengue, and filari-asis. Adults are 3-9 mm long with scales on their body and wings, and they have a long, slender proboscis. Females of most species take a blood meal, while males and the females of other species feed only on nectar and other plant juices. Larval stages are aquatic and occur in a variety of habitats, including standing or still water in natural sites and artificial containers. Larvae of most species feed on algae, but a few are predaceous.

Pest species in urban and rural areas belong to four genera: Azdes, Anopheles, Culex, and Psorophora. Adult males and females of Anopheles are distinguished by their long maxillary palps, and in the resting position, the body of adult Anopheles is at a 30-45° angle to the surface. Adults of the other genera have short palps, and in the resting position, their body is nearly parallel to the surface. The tip of the abdomen of female Aedes is usually pointed, and the thorax has white markings; in Culex the tip of the abdomen is usually blunt, and the thorax has no white marks. Psorophora species are 6-9 mm long and have long, erect scales on the hind tibia. Larvae of Anopheles lack a breathing tube at the end of the abdomen; while feeding they lie parallel to the water surface. Anopheles larvae are usually found in marshes and other places where there is considerable vegetation. Larvae of other genera have a breathing tube, and they hang down from the water surface. Aedes and Psorophora larvae are usually in woodland pools and salt marshes; Culex larvae are usually in artificial containers.

Mosquito-borne encephalitis viruses have become a major health concern in urban and suburban areas in many regions of the world. Encephalitis is caused by bacterial and viral agents. The resulting inflammation of the brain can result in high fever, seizures, prolonged illness, and sometimes death. The viruses carried by mosquitoes that cause encephalitis in people are essentially animal diseases. They are occasionally transmitted to people, but are usually circulated by blood-feeding mosquitoes in bird and small-animal populations. The most common strains of encephalitis affecting urban populations include: West Nile virus (WNV), which occurs throughout Europe, parts of Africa and Asia, and the USA; Japanese encephalitis, which occurs throughout Asia to India; Murray Valley and Kupiin virus, which occurs in Australia; and Rocio encephalitis and Venezuelan equine encephalitis, which occur in South America. There are several of these diseases in the USA, including eastern (EEE) and western (WEE) equine encephalitis, and St. Louis (SLE) and LaCrosse encephalitis.

Mosquitoes in several genera are vectors for encephalitides; many are bird-feeding species that occasionally bite humans. The most common vectors are species that have successfully adapted to urban habitats or secondary habitats near urban areas. EEE may be transmitted to humans by Aedes sollicitans, Ae. vexans, and Coquillettidia perturbans; WEE is primarily transmitted by Culex tarsalis.SLEis transmitted by several urban Culex species, including Cx. tarsalis, Cx. quinqufasciatus, and Cx. nigri-palpus. LaCrosse encephalitis is transmitted by the tree hole mosquito, Ae. triseritatus. WNV has been isolated from more than 40 mosquito species: the most common are Culex species, including the common house mosquito, Cx. pipiens, and Cx. univittatus, Cx. modestus, Cx. quinqufasciatus, and Cx. vishnui.

Female mosquitoes may fly from their breeding site in search of a blood meal, but males usually remain close to the breeding site. Female flight range varies with species, time of year, wind direction, and other factors. Most adult mosquitoes disperse only 100-200 m from their emergence site. Aedes aegypti fly 25-100 m and Anopheles species fly about 2 km. Wind above 6.4 km/h permits only downwind movement, and velocities above 9.7 km/h inhibit flight of most adults. Dispersal records for Aedes mosquitoes include: Ae. nigromaculatus, 45 km downwind; Ae. sollicitans, 177 km away from the seacoast and at sea off the Atlantic Coast; Ae. dorsalis, 61 km downwind; Ae. taeniorhynchus 40 km downwind.

Aedes

Most of the adults have distinct patterns on the thorax and abdomen formed by yellow, white, or silvery scales, and the legs often have white rings. Adults of most species bite during the day or early evening. Biting occurs outdoors and adults usually rest outdoors before and after feeding. Eggs are laid singly on a wet substrate, but they are resistant to drying and can withstand desiccation for months and, in some species, for several years. Winter is spent in the egg stage, and hatching occurs with spring flooding. Marshes and ground pools are breeding sites for many species, but some of the important disease vectors utilize household or domestic containers in peridomestic habitats. Several floodwater and salt marsh Aedes are serious pests in urban and rural areas around the world, including Ae. taeniorhynchus, Ae. sollicitans, and Ae. dorsalis. Larvae of many species live in clean drinking water. Ae. aegypti breeds in pots and water-storage jars located inside or outside houses. Ae. albopictus, which is a vector for dengue in southern Asia, breeds in natural and domestic containers, such as cooking pots and used vehicle tires. Spread of the Asian tiger mosquito, Ae. albopictus,to the USA and parts ofEurope is linked to commercial distribution of used tires. In northern Europe (Lithuania), the most common Aedes biting humans in urban areas are: Ae. communis, Ae. cantans, Ae. punctor,andAe. cataphylla. Aedes species such as Ae. sierrensis and Ae. triseriatus most often breed in water-filled tree hole cavities.

Aedes are vectors of yellow fever, dengue, and encephalitis viruses. The arbovirus causingyellow fever occurs in Africa and tropical areas of the Americas, and the major mosquito vector is Ae. aegypti.Several Aedes species vector filarial worms, including Ae. togoi in China, Ae. polynesiensis and Ae. pseudoscutellaris in the Polynesian region, and Ae. niveus in Thailand.

Aedes aegypti (Fig. 7.1d) Adults are about 6 mm long and the body is black with white markings. The thorax has several longitudinal silvery-white lines, resembling a lyre; the legs are black and with white bands. This is the common yellow fever mosquito, and itis widely distributed throughout tropical and subtropical regions. It does not usually occur in areas where night temperatures are 20 °Cor less. This day-biting mosquito is adapted to living in the urban environment, and is often found breeding and feeding around and in buildings. Females lay eggs on wet surfaces adjacent to the water line. Eggs withstand desiccation, and can remain dry but viable for months. When flooded, some eggs hatch immediately while others delay a few days, thus hatching is spread over days or weeks. Larval development depends on temperature, and ranges from 7 days to about 7 months. There are two or three generations per year.

The nominal species Aedes aegypti exists in several subspecies forms, which are characterized by morphological and behavior differences. The African subspecies Ae. aegyptiformosus has black abdominal tergites, and it rests and feeds outdoors in nonurban areas. The species with primarily peridomestic and domestic habits are Ae. aegypti aegypti, which has white scales on the abdomen and breeds in domestic water-storage pots outside of houses, and Ae. aegypti queenslandensis, which breeds in water-storage pots inside houses.

This species is believed to have migrated from West Africa to the New World in the fifteenth through seventeenth centuries aboard slave ships. It may have first invaded Portugal and Spain before reaching the western hemisphere on European ships. The evolution of domestic traits in this originally feral species was crucial for enabling Ae. aegypti to occupy and reproduce in water-storage jars in the holds of these sailing vessels. Yellow fever was absent from urban settlements in the western hemisphere until the arrival of Ae. aegypti, which is the only known vector of urban epidemics of this disease. The firstdocu-mented epidemic of yellow fever in this region occurred in the Yucatan in 1648, although it may have appeared in Haiti in 1495. In the seventeenth through the nineteenth centuries, yellow fever occurred in seaports on the Atlantic coast, as far north as Philadelphia and New York. The yellow fever virus may have been reintroduced to the New World periodically by passengers, especially slaves, on ships coming from West Africa.

Aedesalbopictus Adults are about 5.5 mm long and the body is black with white markings. The thorax has a broad, silvery white band in the center, and the legs are banded with white. Full-grown larvae are about 8 mm long and yellowish white to gray; the head is yellowish white and slightly longer than broad, and has few markings. Eggs are deposited in batches containing 42-88 eggs per blood meal; in natural habitats females produce 0.2-2.1 batches; the highestnumber of eggs produced after a single blood meal is 147. Fecundity is 300-345 eggs, butas many as 950 have been recorded. Hatching is in 6-7 days at 30 °C and abouti0 days at 21 °C. Mortality is nearly 100% when eggs less than 12 h old are dried, but only 60%for eggs 16 hold. After 3 months at25 °Cand 70-75% RH egg survival is about 50%; 78-99% of Ae. albopictus eggs from temperate Asia and USA survive exposure to —10 °C for 24 h. Maximum longevity of an egg is 243 days. Larval development is about 19 days at 14 °C and the pupal period is about 4 days at 15 °C; at 25 °C larval development is 8 days and the pupal period is 1 day. In the laboratory at 25 °C and adequate food, larval development is 5-10 days. Development is prolonged when food amount is suboptimal: 58 days for males and 24 days for females. Females live 4-8 weeks in the laboratory at 25 °Cand30% of RH females may live 3-6 months. Time from

Anopheles Aedes Culex Wings
Figure 7.3 Diptera: Culicidae. (a) Aedes sollicitans; (b) Anopheles punctipennis; (c) Aedes vexans; (d) Culex pipiens.

emergence to first blood meal at 25 °C is about 2.5 days for a population from Japan, time is 3.5-4.5 days when reared at high larval densities. Females become receptive to mating 48-72 h after emergence.

Adults fly close to the ground and do not fly in strong winds, and wind-aided dispersal is limited. Dispersal is 90-183 m from breeding sites, and maximum dispersal is about 434 m. The potential for dispersal is greatest for females from high-density larval rearing sites. It is a day-biting mosquito, and there may be an early-morning and late-afternoon peak in biting. Females usually bite at ground level, and prefer to feed around the ankles and knees. The native range of this species is the oriental region and India, but also extends to Mauritius, Seychelles, and Madagascar. Based on presence of diapause in established populations, the North American Ae. albopictus apparently originated in temperate Japan. The Ae. albopictus biotype occurring in southeastern Brazil has no diapause, and it probably originated from a tropical site. In Guatemala, it breeds in small water containers in urban and suburban sites of the Caribbean harbor cities of Puerto Barrios and Puerto de Santo Tom4s de Castilla. Ae. albopictus is a vector of dengue fever in epidemics in Southeast Asia, southern China, and Japan. It is capable of transmitting Japanese B encephalitis, and is susceptible to infection with Getah virus, a virus affecting horses.

Ae. japonicus is a related species, and is known primarily from Japan and Korea. It has also spread in used tires to other parts of the world, including eastern USA. In the last 20 years, widespread distribution of the Asian tiger mosquito has been facilitated primarily by shipments of used tires and casings.

Aedes sollicitans (Fig. 7.3a) Adults are 5.5-6 mm long and brown to dark brown; the thorax is golden brown, and the pleura silvery white. The proboscis and tarsi are white-banded; abdominal segments have yellowish-white bands at the base, and a yellowish-white longitudinal stripe medially. Full-grown larvae are 8-9 mm long and yellowish white to gray; the head is yellowish white, 1.5 times as broad as long; the thorax is wider than long. Eggs are deposited in three batches containing 14-115 eggs; there is a 4-7-day interval between batches, and a blood meal is required for each batch. Eggs hatch in a range of salinity, including concentration of salt up to 25% greater than seawater. Larval development is in water temperatures 10-39 ° C. Females live 25-35 days in a laboratory. Breeding is in coastal marshes and salt pools where marsh grasses grow, but infrequent in marshes that are submerged for 25 days or more each month. Inland sites for this mosquito include habitats retaining or inundated with saltwater, such as from natural salt deposits, oil well, mines, and swimmingpools. Apercentage of emerging females disperse from the breeding site, and mass dispersal flights occur. Long-distance dispersal often brings females 13-17 km and as far as 166 km (at sea) from breeding sites. Urban areas that are a long distance from A. sollicitans breeding sites can be affected by this mosquito. However, this species usually remains outdoors, and does not enter a building to bite. Itis a blood-feeder on any animal; females take a blood meal on the second day after emergence, and feed twice before oviposition. This species feeds during the day and night, and records of severe and intense attack by large numbers are well known. This species is distributed in the coastal marshes of eastern and southeastern USA, and in salt pools of all eastern states.

Aedes vexans (Fig. 7.3c; Fig. 7.4c) Adults are 4-5.5 mm long, brown, with golden-brown scales scattered on the thorax. The proboscis is dark brown to blackish brown toward the tip. The abdomen is dark brown with yellowish white bands at the base of segments; the band is constricted medially and laterally. Wings are dark brown. Full-grown larvae are 6-8.5 mm long, yellowish brown to gray throughout; the head has dis-

Figure 7.4 Diptera. Culicidae larvae. (a) Psorophora ciliata; (b) Culex pipiens; (c) Aedes uexans.

tinct, symmetrical ventral markings. Eggs are deposited singly on the surface of water and they sink to the bottom, or eggs may be laid in moist soil at the edge of pools (subject to inundation in the spring). Overwintering is in the egg stage, and prolonged freezing or drying has little detrimental effect on egg viability; eggs may survive 1-2 years. Hatching is erratic or uneven. It may be induced by submergence in the spring or summer, depending on water temperature, an interval of drying prior to submergence, and embryo development time. Larval habitats are fresh water over a layer of decaying vegetation, and free of filamentous algae; flooded meadows or urban grassy areas are suitable. Development is 7-25 days at 22 °C, 5-21 days at 27 °C, and 4-6 days at 32 °C; development is prevented at 0-10° C. The pupal stage lasts 3-9 days at 15-22 °C, and 1-3 days at 27-37 °C; there is 50% pupal mortality at 40 °C. Larvae are frequently found in small pools and in large concentrations, such as 500+ in 0.6 liters, but this does not adversely affect development. This is a migratory species that disperses individually or in mass movements in which both males and females fly from the breeding site. Mass dispersals have created clouds ofmosquitoes moving towards the glowing skyline ofsuburban lights. Females are capable ofmoving 24-48 km from the breeding site, and wind seems to have little or no influence on the direction offlight. This species breeds in woodland pools and in temporary pools in urban areas. It breeds throughout the year, but is usually more abundant in late summer, when it may be the dominant species in some areas. It readily moves indoors to bite. This is one of the most abundant and widely distributed mosquitoes: it occurs in the Nearctic and Palearcticregions south of55 °Nlatitude, African west coast, and the oriental region, south and east to Samoa (170 °Wlongitude). It is a common pest in urban and suburban areas.

Anopheles

Adults have spotted wings and the arrangement of blocks of dark and pale scales on the wings provides characters for species identification. The dorsal and ventral surface of the abdomen is nearly or entirely without scales. In males and females, the palps are about as long as the proboscis, and in males the palps are enlarged apically. Anopheles species are major vectors of malaria around the world. The genus is distributed nearly worldwide, except for Micronesia (but they are on Guam) and Polynesia. Adults of most species are crepuscular or nocturnal, but the time and location for seeking a blood meal vary. An. albimanus, which is a malaria vector in Central and South America, bites mainly outdoors (exophagic) from sunset to about 21:00 h. The An. gambiae species, which are vectors in Africa, bite mainly after 23:00 h and mostly indoors (endophagic). Before and after feeding some Anopheles will rest indoors (endophilic); others will rest outdoors (exophilic) on vegetation or in natural cavities.

Anophelinemosquitoes overwinterasfertilizedfemales, and in spring they oviposit and die. Breeding is generally continuous throughout the warm months. Eggs are laid singly but in batches of 100 or more; fecundity is 400-500 eggs. Eggs float freely on the water surface and accumulate around floating objects or the shoreline. Hatching occurs in 1-3 days. Larvae do not have a long breathing siphon, and remain parallel with the water surface. They feed by moving their mouthparts back and forth to sweep the undersurface of the water. The respiratory siphons of the pupae are also short. The adults are not strong flyers and dispersal is usually accomplished by short flights in low vegetation. The flight of these mosquitoes produces a low-pitched hum that is almost inaudible unless they are close to the ear. The adults usually bite at night, inside or outside houses.

Pest status of these mosquitoes is based on their nuisance biting and their ability to vector disease. There are more than 400 described species of Anopheles worldwide, and about 40 are known to vector malaria. There are 12 epidemiological zones ofmalaria-North, Central, and South America, Mediterranean, North Eurasian, Afro-Arabian, Afrotropical, Indo-Iranian, Indo-Chinese, Malaysian, Chinese, Australasian -

and each has one or more Anopheles species as vectors of the disease. An. quadrimaculatus is a common vector of malaria in North America. Certain species of Anopheles transmit filarial worms ofWuchereria bancrofti, Brugia malayi, and B. timori, all of which cause filariasis in humans. The mosquitoes involved in disease transmission differ according to region, but many of the principal malaria vectors are also involved. O'nyong nyong, an arbovirus that occurs in Africa, is spread by species of the An. gambiae complex and An.funestrus.

Urban habitats are utilized as breeding sites by several Anopheles species. An. plumbeus is widely distributed in northern Europe, south to Sicily and east to the Caucasus. It breeds in tree holes in natural habitats; in the urban environment it breeds in flowerpots and household containers. An. maculipen-nis is the dominant species in permanent water bodies in towns in Lithuania. The adults feed during the day and night, and are commonly found in urban greenspace and undisturbed areas. An. claviger is distributed from Europe to northern Africa and east through southern Russia. In temperate regions it breeds in woodland ditches and pools, but in southern regions it commonly breeds in underground cisterns and wells. Adults usually feed outdoors, but in the UK it enters houses to bite in spring. An. algeriensis is widely distributed in Europe and south to northern Africa; it typically breeds in marshy areas but will invade houses to bite humans.

There are several Anopheles species complexes, composed of various forms with differing morphological, physiological, and behavioral characteristics. In addition to the complexes presented here, there is the An. punctulatus complex in tropical Australasia (New Guinea, Solomon Islands), An. culici-facies complex (four species), An. dirus complex (eight species), An. leucophyrus complex (22 species), An. maculatus (four species) of the oriental region, the An. marshal complex (four African species), and the An. gambiae complex (six species).

Anopheles maculipennis complex This species complex is distributed across Europe and North America, in some regions member species are vectors of malaria, and it is called the European malaria mosquito (complex). This group ofmosquitoes was the first species complex to be delimited; now there are at least 15 species considered within the complex. At first they were distinguished using egg morphology and wing characteristics; larval salivary gland chromosomes are currently used. An. maculipennis is distributed in Europe, except the UK, Northern Scandinavia, Greece, and Italy; An. messeaehas nearly the same distribution, butincludes the UK and excludes Spain. An. labranchiae atroparvus occurs in Europe, from Spain east to the Caspian; An. labranchia labranchiae occurs along the shore of the western Mediterranean; An. sacharovi occurs in the eastern Mediterranean, and the Middle East to the Caspian; An. subalpi-nus occurs in the Pyrenees, Alps, and Balkan mountains, and the Elburz mountains of Iran; An. melanoon occurs in Corsica, Albania, and southern Italy.

Adults are about 6 mm long and brown. They have blackspotted wings, and a brown patch at the apex of the wing fringe. The palp is entirely black. Eggs for most species are laid in freshwater in ditches, pools, and the margins of rivers. Eggs of An. atroparvus, An. labranchiae, and An. sacharovi are laid in brackish water, each with its optimum degree of salinity and temperature. Eggs are dropped randomly over the water surface. They are deposited in batches, and fecundity is about nine batches per female. A single batch may contain 86-197 eggs, and the largest number of eggs in one batch may be 312. Hatching occurs in 2-3 days, but is temperature-dependent and can extend to 7 days (An. sacharovi). Some of the species in the complex are resistant to drying and cold temperatures. Development varies in duration according to the time of year and abundance of food; it is complete in 27-31 days at 13-15 °C, 15-20 days at 19-21 °C, and 10-14 days at 22-24 °C. The pupal period is variable; 2 days is the shortest time, and the minimum critical temperature is about 10 °C. Larvae do not tolerate freezing and will die at 0 °C for 6 h, and lastinstar larvae dies when submerged for 30 min (An. sacharovi) or 4 h (An. labranchiae). Adults overwinter and become active and begin laying eggs in spring. There are two or three generations per year. Females may be active and feed during the day or night and enter quarters occupied by humans or domestic animals. Hibernation sites may be selected on the basis of temperature, humidity, and proximity to animals; in Siberia, An. messeae selects dark cold cellars where temperature varies from 3 to 7 °C. Dispersal flights are for mating, feeding, ovipositing, and hibernation. In Netherlands, premating flights of An. atroparvus may be 14 km to leeward, and feeding flights may be 2.5-2.9 km.

Anophelespunctipennis(Fig.7.3b) Adults are4-5.5 mmlong, but there is considerable variability in size. The head is dark brown with yellowish-white scales at the margins of the eyes. Wings have black scales on the veins, and a yellowish-white spot and three small spots on the outer third of the wing. Legs have white spots on the tips of the femora and tibia. Full-grown larvae are 6-6.5 mm long, gray to brownish gray; there is a longitudinal white stripe on the dorsum. Eggs are laid singly on the water surface and usually occur together in groups of 3-20

eggs; this species may produce morphologically different eggs in the winter and summer. Eggs mature in batches of about 200, and fecundity is about 2000 eggs. Hatching is irregular, but occurs in 2-6 days at 20-25 °C. Adults feed outdoors at night. Larvae are in weedy ponds, springs, streams, and shallow pools; they may be in flowing water. Development takes 12-14 days during warm months; in winter it is 18-25 days. The pupal period is 2-4 days, but is extended to 6 days at 8-13° C. Adults feed during the early evening and usually outdoors, but will feed in the shade during the day. Adults overwinter in protected locations, and are active during winter. This species is generally distributed in North America, from southern Canada to Mexico and from coast to coast; it has the greatest range of any Anopheles in the Nearctic region. Adults attack humans and animals outdoors, but do not usually enter buildings. Breeding may be continuous in southern regions; in the north adults overwinter in protected locations, such as in culverts and outbuildings in urban areas, and in hollow trees and tree holes in natural habitats.

Anopheles pseudopunctipennis Adults have distinct white patches on the wings, and a dark-gray abdomen. There are yellowish-white spots on the legs, and white rings at the base of the palpi. This species breeds in sunlighthabitats with algae, including pools, puddles, and along the edges of streams. It feeds indoors and outdoors on humans and domestic animals; it typically rests outdoors. Itis distributed in Central and South America, from Argentina to southern USA. An. albimanus is a related species and an important malaria vector in this region.

Anopheles quadrimaculatus complex In North America the An. quadrimaculatus complex is represented by An. quadrimaculatus, which is widely distributed east of a line from southern Ontario to eastern Texas; An. freeborni occurs west of the Rocky Mountains, An. earlei occurs in southern Canada and northern USA, An. occidentalis is restricted to the coast ofCalifornia and British Columbia, and A. aztecus occurs in the interior ofMexico.

Adults are about 5.5 mm long and light brown. The median thoracic stripe is yellowish brown and somewhat indistinct. Wings have brown scales, and four distinct patches ofbrown scales, which distinguish it from other Anopheles. Full-grown larvae are about 9 mm long; the head is rounded and longer than wide; the thorax is about as long as wide. The abdomen has six pairs of fan-lift tufts of setae on segments 2-7. Eggs are laid singly around emergent vegetation; hatching depends on temperature and the optimum is 33 °C, at which hatching is in about 24 h. Larvae do not generally occur in large bodies of water, but prefer small pools with emergent vegetation. In lakes or other large bodies of water they are usually limited to the vegetated margins. Emergent vegetation, leaves, sticks, and other material on the water surface provide suitable conditions for the larvae. Developmentis affected by temperature, depth of the water, and food. The minimum temperature for development is about 7 °C and the lowest lethal temperature is about 35 °C. Larvae complete development in 8-10 days at 27 °C; the pupal period is 37-40 h at 28 °C. Larvae may survive 1-2 days in moist soil above the water line. Adults often rest in dark or shaded locations, including outbuildings and cellars. This species overwinters as an adult, and is active and flies during winter warm spells. It bites humans and domestic animals indoors and outdoors, and rests in either. Adults generally remain close to their breeding site during summer. In the southern part of its range, brood peaks may be 20-30 days apart, and there are 8-10 annual broods with the first appearing about 30 days after the last frost, and the last brood late in the year. In spring and fall females disperse long distances, as much as 20 km, to locate breeding sites (spring) or suitable overwintering sites (fall).

Culex

Adult thorax, legs, and wings are uniformly covered with brown scales, but some white scales may be present on the abdomen. These mosquitoes are generally distributed in urban environments around the world, but they are not common or absent in extreme northern parts of temperate zones. Most species breed in ground pools, puddles, and agricultural fields; some utilize domestic containers in urban areas. Cx. pipiens fatigans (= Cx. quinquefasciatus) is a vector of filariasis, and breeds in waters polluted with organic debris, such as household refuse and excreta. This species is associated with urbanization, and towns with poor or inadequate drainage and sanitation support large populations. Culex mosquitoes are night biters, and they commonly rest indoors before and after biting.

Culex pervigilans This species breeds throughout the year, and hibernates in the larval or adult stage. Eggs are laid in both fresh and partly saline water. The anal papillae are large in fresh water and small in saline water. This is the most prevalent species in New Zealand.

Culex pipiens complex (Fig. 7.3d; Fig. 7.4b) This is the common house mosquito and it is a large species-group consisting of several urban pests: Cx. p. pallens, Cx. p. pipiens, Cx. p. fatigans (= Cx. p. quinquefasciatus), and Cx. p. molestus. Each species has adapted to a particular habitat or ecological zone. Cx. p. molestus and Cx. p. fatigans only occur in urban environments, while Cx. p. pipiens can live in both agricultural and urban environments and is the world's third most commonly distributed mosquito (Aedes aegypti and A. vexans are more cosmopolitan, but less abundant). Cx. p. fatigans evolved in tropical zones; and Cx. p. pallens evolved in temperate zones; larvae of both live in highly polluted urban habitats. Cx. p. pipiens extends across Europe and Asia between 30 and 60 °N latitude, and extends up the coast of Norway as far as the Arctic Circle. In the Nearctic region this form occurs between 30 and 55 °N latitude. Itranges into eastern Africa, South Africa, and Dakar. Cx. p. molestus is distributed nearly worldwide (North America, Europe, northern Asia, Mediterranean, Africa, and east coastal Australia). Cx. p. pallens occurs in the islands of the Pacific and Japan, and coastal California. Cx. p.fatigens is nearly circumtropical.

Adults are 4-5.5 mm long and brown, with yellow scales around the eyes; the thorax and legs are brown. The abdomen is blackish brown and with yellowish bands, and the apical segment may be yellowish brown. Full-grown larvae are 7-8 mm long; the anal siphon is pale brown and about four times as long as broad, and tapered on the terminal half. Eggs are laid in masses or rafts on the water surface; they are a single layer of erect eggs placed side by side. Oviposition is often in domestic and discarded containers and ground pools. For Cx. p. molestus, oviposition is in dark sites where the water is foul, as in cesspits and sumps. Hatching varies according to temperature, but over an optimum range of 21-35 °C hatching occurs in 36-26 h. Water temperatures near 0 °C are usually lethal, but Cx. p. pipiens may survive a few days at 2-5 °C. Larvae live in a variety ofurban habitats, including street drains, gutters, domestic containers, cess pits, and drains. Temperature affects larval development, and generally no development occurs at 5 °C and 34 °C. Development takes 60 days at 10 °C, 45 days at 15 °C, and 10 days at 25 °C. The pupal period is 2-3 days; in Egypt the pupal period is 76 hat 20 °C, 53 hat 24.7 ° C, and 26-36 hat30-33 °C.

Larval habitats are variable according to locality, season of the year, and population. In the northern part of its range, larvae are in ground water pools and artificial containers. In southern and warmer parts of its range larvae are primarily in containers. Cx. p. molestus seem to prefer dark and confined locations. Cx. p. pipiens along the seaboard of northeastern USA are in polluted ground water; along the southeastern seaboard the preferred sites are protected places, such as street drains, catch basins, and other pools of foul water. In western USA (California) they are found in foul water in street drains, gutters, and domestic containers; water with algae is preferred. In Europe and Africa foul water in containers in shaded and unshaded sites are infested. Clear water of ditches, pools, ponds, and recently flooded depressions contain larvae in Norway and Denmark. Larvae ingest almost anything organic, including diatoms, filamentous algae, algal cysts, flagellates, bacteria, and other organic matter. Growth does not occur when the diet is dead organic matter.

Culiseta

Adults in this genus are large and the tarsi lack pulvilli. Wings of several species have one or two dark spots. Eggs are generally produced in rafts on the water or leaf surface. Culiseta eggs do not withstand desiccation, but those of Cs. morsitans may remain viable for 6 months on damp surfaces. Larval habitats are usually pools with submerged vegetation, butinEurope, Cs. longiareolata occurs inrockpools and in domestic habitats, such as wells. These are often considered as winter mosquitoes, with many species found from September through May or June. In coastal areas, some species develop throughout the year. Most of these species are distributed in temperate regions, and some, including Cs. alaskaensis, Cs. incidens, and Cs. silvestris, occur in northern or subarctic areas. Species in temperate regions usually overwinter as larvae or hibernating adults. Overwintering adults of the European species Cs. annulata periodically take blood meals.

Mansonia

Adults are recognized by the speckled pattern of pale and dark scales on their wings, and their pale-banded legs. The species here are primarily found in wet tropical regions, but some range to temperate latitudes, such as Tasmania to the south and Sweden to the north. The larval stage is long and the number of generations per year is usually limited to two or three in the tropics and one in temperate regions. Larvae penetrate the roots ofsubmerged plants with their siphon to tap air cells. A variety of plants is used, but water lettuce, Pista stratoites, is the most common and preferred by some Mansonia species.

Urban environments may provide limited breeding sites for Mansonia species, but the adults are strong flyers and may travel several kilometers from the breeding site in search ofa blood meal. M. perturbans is distributed in North America south to the Gulf Coast, and in Europe from the UK and Sweden south to the Middle East. Females readily enter houses at night, and it is a consistentpestwherever itoccurs. M. uniformis is distributed from West Africa eastward through the Indian subcontinent to Japan and the Australian region. Females will typically travel far for a blood meal, and enter houses soonafter dark. M. indubitans is distributed in northern South America, from Brazil to Peru; while it is a forest mosquito in the Amazon Valley, it readily invades houses in Peru. M. africana commonly occurs indoors after dark in Central Africa.

Mansonia pertubans Adults are 5.5-6.5 mm long and dark brown; the thorax is dark brown, and with numerous yellowish scales. The proboscis has a median white band; legs have white bands on base oftarsi; the abdomen has indistinct, narrow white bands at the base of segments. Full-grown larvae are 6-7.5 mm long, yellowish white with a tinge of green. Larvae remain below the surface in the debris at the bottom, or attached to plant roots, and are rarely at the water surface. In the UK, larvae attach to the roots of Acorus, Ranunculus, Gly-ceria, and Typha. The Norwegian form is found exclusively with Sparganium. In the USA, a variety of plants provide suitable attachment, including species of Typha, Limnobium, Pistia, and Saggitaria. Attachment is often for a long time, but larvae often relocate. Air may be obtained at the surface, from dissolved oxygen in the water, or from air cells in submerged plants; satisfactory development requires submerged plants. Pupae generally remain submerged and attached to plant roots; they are at the surface prior to adult emergence. Eggs are laid in rafts on the water surface; the number of eggs per raft is about 195, but may be as many as 308 eggs. Hatching occurs in 6-7 days in the field, and 6 days in the laboratory at 20 °C. Development takes 83-117 days, while the pupal period takes about 5 days. There is one generation per year, and the majority of larvae complete development during the first season. Other larvae overwinter and complete development in the spring of the second year. Adults are active and feed during the day and night, and readily enter houses to feed; the greatest activity is atdusk. Both sexes fly long distances, and have been recorded 17 km from breeding sites. This species is distributed in North America, from southern Canada to the Gulf of Mexico. In Europe it occurs from Sweden to the UK, and extends to the Middle East.

Psorophora

These are primarily Neotropical mosquitoes, but several species, including Psorophora columbiae, P. discolor, P.ferox, and P. ciliata, occur in North America. The adults are large, ranging from 6 to 9 mm long. Larvae of some species are predaceous, feeding on other mosquito larvae and other animals in temporary pools. Eggs are deposited singly on wet substrates, and they can withstand months of desiccation, then hatch when flooded (thus their name floodwater mosquitoes), which often gives rise to enormous numbers of adults. Breeding sites are flooded pastures and sometimes rice fields. Larvae of some species are predators. Adults bite during the day and night.

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