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Report: Harmful Species of Mosquitoes –A Worldwide Focus

The following report gives a detailed insight into the harmful species of mosquitoesworldwide, and the problems that they cause.

ContentsPage

0. Summary 21. Background 32. General life-cycle 43. Sub family 1 –

Anopheline mosquitoes 73.1 Background 73.2 Life cycle 73.3 Activity 83.4 Medical importance 83.4.1 - Biting Nuisance & Diseases 84. Sub family 2 –

Culicine mosquitoes 134.1 Background 134.2 Culex mosquitoes 134.3 Aedes mosquitoes 144.4 Haemogogus mosquitoes 154.5 Sabethes mosquitoes 154.6 Mansonia mosquitoes 164.7 Coqullettidia mosquitoes 164.8 Psorophora mosquitoes 174.9 Medical importance 174.9.1 - Biting nuisance & Diseases 175. Mosquito common names 216. Sources 23

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Summary:

There are nearly 3500 species of mosquito worldwide. This report summarises thepresent state of knowledge regarding the principle mosquito disease vectors,indicating where problems occur, and when mosquitoes are most likely to attack. Theprinciple diseases transmitted by named genera of mosquito are:

• Malaria (Anopheles)• Filariasis (Anopheles, Mansonia, Culex, Coquillettidia)• Dengue (Aedes)• Yellow fever (Aedes, Haemogogus, Sabethes)• Other arboviruses (Anopheles, Culex, Aedes, Psorophora)

It is generally the case, though not without exception, that adult Anophelesmosquitoes bite at dusk, dawn, or during the night, Culex species bite at night, andAedes bite during the day, or early evening. Mansonia mosquitoes bite at night orduring the day depending on species. A table of mosquito common names is given insection 5 on page 21.

Table of Key words:

Anthropophagic Species that prefer to feed on human blood sources

Cephalothorax Combination of the head and thorax in the Pupal stage

Crepuscular Species that are active at dusk and dawn

Desiccation Without water

Endophagic Mosquito species that enter houses to feed

Endophilic Species that seek shelter in-doors to digest their blood meal

Exophagic Species that bite their hosts outside of the house

Exophilic Species that seek shelter out-doors to digest their blood meal

Gonotrophic Cycle Pattern of feeding, egg maturation and oviposition

Gravid The female mosquito's state when ready to lay eggs

Instars Stages of larval development

Oviposition Egg laying

SiphonFor species that do not take atmospheric air - allowing them to take air fromroots or stems of aquatic plants

Spermatoza Male reproductive fluid

Spermotheca Female reproductive system

SpiraclesAir intake for some species during larval development - situated on thetenth abdomen

Sylvatic CycleForest cycle that maintains a reservoir of infection within the animalpopulation

The Rural CycleMosquitoes being infected via animals and thereafter transmitted thedisease to humans

The Urban CycleMosquitoes being infected by biting infected humans and then transferringthe disease to other non-infected humans

Zoophagic Species that prefer to feed on animal blood sources

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Harmful Mosquitoes Worldwide:

1. Background

There are nearly 3,500 species of mosquito known to science. These are found in 38genera, all in the family Culicidae, within the order Diptera. The family is divided into 3subfamilies:

• Toxorhynchitinae• Anophelinae (anophelines)• Culicinae (culicines)

Mosquitoes enjoy a near global distribution, occurring in the tropics and temperateregions, and northwards into the Arctic Circle. They are only absent from a few islandsand from Antarctica. They occur at elevations of 5,500 metres/16,700 feet, and downmines to depths of 1,250 metres/4,000 feet below sea level. They even occur on theLondon underground system where there is some evidence of speciation during thelast 100 years.

In terms of pest status and disease vectors, the most important species belong to thegenera: Aedes, Culex, Anopheles, Psorophora, Mansonia, Sabethes, andHaemagogus. With the exception of the Anopheles (Anophelinae) all thesemosquitoes occur within the subfamily Culicinae.

Anopheles species transmit malaria and are also vectors of filariasis and somearboviruses. Some Culex species transmit filariasis and some arboviruses. Aedesspecies include important vectors of yellow fever, dengue, encephalitis virus, andother arboviruses. They may also, in some areas, vector filariasis. Sabethes andHaemagogus mosquitoes vector yellow fever and some other arboviruses in Southand Central America, whilst the Psorophora contain some pest species in North andSouth America. Some mosquitoes in other genera are implicated as vectors ofarboviruses, and other mosquitoes (whilst not vectoring disease) can be seriousbiting nuisances.

2. General life cycle

2.1 Mating and egg maturation

Mosquitoes normally mate shortly after adult emergence. The male passesspermatozoa into the spermatheca of the female. Usually this serves to fertilize allthe eggs laid by the female during her lifetime, so only one mating and inseminationis required. In most cases, the female must feed on blood to obtain the necessarymaterials to develop eggs in the ovaries. A few species are able to develop a firstbatch of eggs without a blood meal but this is the exception. Speed of digestion of themeal is temperature dependent. In most tropical species this only takes 2-3 days, butin colder, temperate countries, may last up to 14 days.

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Only female mosquitoes take a blood meal. Males feed on nectar and other naturallyoccurring sugary materials and do not therefore transmit disease.

Following a blood meal the abdomen of the mosquito swells up and is bright red incolour, becoming dark red a few hours later. As blood is digested, the colour of theabdomen changes. As the white eggs in the ovaries enlarge so the abdomenbecomes whitish at the back and dark red at the front. When all the blood is digestedthe abdomen becomes dilated and whitish with fully formed eggs. The female is saidto be gravid, and searches for an appropriate place to lay her eggs. After oviposition(egg-laying), the female mosquito feeds again and begins to mature another batch ofeggs. This pattern of feeding, egg maturation, and oviposition occurs several timesduring the lifetime of a female mosquito and is known as the gonotrophic cycle.

2.2 Egg laying and development

The female mosquito will lay 30-300 eggs at any one oviposition, depending onspecies. Eggs are blackish or brown and up to 1mm long. Eggs are elongate or ovoidin many Culicinae. In the Anophelinae, eggs are boat-shaped, and eggs of theMansonia are drawn out into a terminal filament. It is common, for example in manyspecies of Anopheles and Culex, for mosquitoes to lay their eggs directly on the watersurface. In Anopheles, the eggs are laid individually and float on the water. In Culexeggs are laid vertically in rows and are held together by surface tension, forming anegg raft, which floats on the water surface. Mansonia lay their eggs in sticky masses,glued to the underside of floating plants. Mosquito eggs from these species cannotsurvive desiccation and soon die if they become dry. In tropical regions eggs hatch in2-3 days. In cooler climates egg hatch may be 2 weeks or longer.

Some mosquitoes, for example those in the genera Aedes, Psorophora andHaemogogus, deposit eggs just above the water line on damp substrates includingleaf litter, mud, clay water storage pots, and tree holes. Eggs from these genera cansurvive desiccation (to be without water), particularly those of Aedes and Psorophora.These eggs may remain dry for years but still be viable when submerged in water.

2.3 Larval Development

Unlike other aquatic insects, mosquito larvae are legless and have a bulbous thoraxthat is wider than the head and the abdomen. There are four active larval instars(stages). Mosquito larvae require water in which to develop and are unable towithstand desiccation.

The larvae have well developed heads with a pair of antennae and compound eyes.Most species have prominent mouthbrushes, which serve to sweep water, containingfood particles, into the mouth. The thorax is roundish with hairs that are usuallyconspicuous and long. The abdomen is in 10 segments, 9 of which are visible.

Most mosquito larvae, with the exception of Mansonia and Coquillettidia species, needto come to the water surface in order to breathe.

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Air is taken in through two spiracles situated dorsally on the tenth abdominalsegment, or at the end of a single dark coloured and heavily sclerotised tube calledthe siphon, depending on species. Those species that do not take atmospheric airhave a specialised siphon that allows them to take oxygen from the roots or stems ofaquatic plants.

The larvae feed on protozoa, yeasts, bacteria, and other microorganisms found in thewater. Some species are bottom feeders, some feed at the surface. Some speciesare carnivorous or cannibalistic. In tropical countries, development from hatching topupation can take anything from 5-14 days. In temperate species larval developmentmay last weeks or months. Some temperate species overwinter as larvae.

Larval habitats include freshwater swamps, ricefields, marshes, small pools,puddles, tree holes, tin cans, snail shells, and motor vehicle tyres. Some species likeshade, whilst others like sunlight. Some cannot tolerate organic debris, whereasothers breed prolifically in water contaminated with excreta. Some mosquitoes breedin brackish or salt water.

2.4 Pupal Biology

Mosquito pupae are aquatic and are comma-shaped. The head and thorax combineto form the cephalothorax, which has a pair of dorsal respiratory trumpets. Theabdomen is 10-segmented. Some of the structures of the adult mosquito can be seenthrough the cephalothorax, including compound eyes, folded wings, legs, andproboscis. The pupae do not feed, spending most of their time at the water surfacetaking in air.

Pupae of the Mansonia and Coquillettidia differ in that they have modified breathingtrumpets allowing them to obtain oxygen by piercing aquatic vegetation. Their pupaetherefore remain submerged. In the tropics the pupal period lasts 2-3 days. In cooler,temperate, regions development may last 9-12 days, or longer. At the end of thisperiod, the skin on the dorsal surface of the cephalothorax splits and the adultmosquito emerges.

2.5 The Adult Mosquito

Females of most species need a blood meal in order to develop their eggs. Feedingusually occurs after mating. Some species feed on human beings in preference toother blood sources and are described as anthropophagic. Others prefer to feed onanimals and are described as zoophagic. “Females are attracted to their host bybody odour, carbon dioxide and heat – the very attractants used by the Dragonflysystem”. Vision is not considered to play a major role in host orientation but themovement or silhouette of the host attracts some species.

Some species feed at any time of day or night. Others are mainly nocturnal or diurnalin their feeding habit. Some species of mosquito frequently enter houses in order tofeed and are described as endophagic. Others usually bite their host outside thehouse and are described as exophagic.

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After feeding, mosquitoes seek out shelter where they can digest their blood meal andmature eggs. Some species seek out shelter within the house and are described asendophilic. Others seek shelter outside the house and are called exophilic. As anexample, female adult Aedes (which vectors yellow fever) is generally anthropophagic,exophagic, and exophilic. It is important to note, however, that few mosquito speciesare entirely bound by these classifications, with most showing various degrees ofthese behaviours. Some species may even show different behaviours in differentseasons. It is, nevertheless, useful to understand the behaviour of different species ofmosquitoes, as this information may be useful in “planning control strategies.”

It is thought that most mosquitoes only disperse a few hundred metres from theiremergence sites, and it is unusual for dispersion of greater than 2 km to occur. Thereare records of mosquitoes being found up to 100 km from their breeding site, but thisis usually due to wind-assisted dispersal. Mosquitoes can be transported over longdistances in aeroplanes, sometimes resulting in outbreaks of so-called ‘airportmalaria’.

In the tropics, life expectancy of an adult female mosquito is probably about 1-2weeks, whereas average life expectancy in temperate countries is 3-4 weeks. Someadults must live longer than this as otherwise they would not be vectors of diseasessuch as malaria. Male mosquitoes usually live less time than females.

3. Sub family 1 – Anopheline Mosquitoes (Anophelinae)

3.1 Background

There are 3 genera in the subfamily Anophelinae, but only the genus Anopheles is ofany medical importance. Anopheles mosquitoes are distributed worldwide, withrepresentatives in tropical and temperate regions. There are over 400 species.Although some Anopheles mosquitoes transmit filariasis and arboviruses of minormedical importance, they are best known as vectors of malaria.

Figure 1. Anopheles sp. mosquito

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3.2 Life-cycle

Following mating and blood feeding, Anopheles lay 50-200 small blackish or brownboat-shaped eggs on the surface of the water. Air-filled floats on the eggs help to keepthem floating on the water surface. Eggs, which cannot withstand desiccation, hatchin 2-3 days in the tropics, and 2-3 weeks in colder climates.

There are 4 larval instars. The larvae are filter feeders, remaining at the water surfaceas much as possible, and feeding on microorganisms, while breathing through theirspiracles. Shadows or vibrations easily disturb the larvae, which respond byswimming to the bottom of the water. Anopheles larvae are found in a variety ofhabitats, including fresh and salt-water marshes, grassy ditches, edges of streamsand rivers, ponds, puddles, hoofprints, wells, old tins, and water-filled tree holes.Some species like shade, others prefer sunlight. Some like the presence of aquaticvegetation, whereas others do not. Anopheles usually prefer clean and unpollutedwater. The larval period lasts some 7 days in the tropics, and up to 4 weeks in coolerclimates. In temperate areas, Anopheles may overwinter as larvae thus living severalmonths at this stage. Pupae float at the water surface, but swim to the bottom whendisturbed. The pupal period lasts 2-3 days in the tropics, and up to 2 weekselsewhere.

3.3 Activity

Most adult Anopheles are crepuscular (active at dawn and dusk) or nocturnal. Thismeans that blood feeding and oviposition will occur in the evening, night, or earlymorning.

3.4 Medical importance

3.4.1 Biting nuisance and Diseases

Anopheles mosquitoes may constitute a biting nuisance even where they are notdisease vectors. However, it is usually the culicine mosquitoes that cause bitingproblems.

3.4.2 Malaria

It is only the mosquitoes of the genus Anopheles that transmit the 4 parasites(Plasmodium falciparum, P. vivax, P. malariae, P. ovale) that cause human malaria.Only about 70 species of Anopheles are malaria vectors, and some 40 of these areconsidered to be important. The most important vectors in the 12 malariaepidemiological zones are listed in table 1.

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Table 1. Primary malaria vectors by epidemiological zone (after Service, 1996)

Zone VectorsNorth America (inc. N Mexico) An. freeborni, An. quadrimaculatusCentral America An. albimanus, An. aquasalis, An. darlingiSouth America An. albimanus, An. albitarsis, An.

aquasalis, An. darlingi, An. nuneztovari,An. pseudopunctipennis, An.punctimacula

North Eurasian An. atroparvus,Mediterranean An. atroparvus, An. labranchiae, An.

superpictusAfro-Arabian An. arabiensis, An. funestus, An. gambiaeIndo-Iranian An. culicifacies, An. fluviatilisIndo-Chinese hills An. dirus, An. fluviatilisMalaysia An. aconitus, An. balabacensis, An.

campestris, An. dirus, An. donaldi, An.flavirostris, An. letifer, An. leucosphyrus,An. maculatus, An. minimus, An.nigerrimus, An. subpictus, An. sundaicus

Chinese An. anthropophagus, An. sinensisAustralian An. farauti, An. koliensis, An. punctulatus

The following represents notes on the most important malaria vectors:

• An. aconitus: Found in ricefields, swamps, irrigation ditches, pools, streams withvegetation. Sunlit habitats preferred. Adults will feed indoors and outdoors onhumans, also commonly on animals. After feeding, adults rest indoors or outdoors

• An. albimanus: Found in fresh or brackish water, including puddles, pools,marshes, ponds, lagoons, especially those with floating or grassy vegetation.Prefers sunlit habitats. Adults feed on humans and on animals, both indoors andoutdoors. Rest mainly outdoors.

• An. albitarsis: Larvae usually in sunlit ponds, marshes, large pools, withfilamentous algae. Bites humans and animals. Feeds outdoors and indoors.Usually rests outdoors.

• An. anthropophagus: Occurs in shaded pools and ponds. Sometimes found inricefields. Bites humans indoors. Rests mainly indoors.

• An. aquasalis: Found in tidal salt-water marshes, lagoons, salt water rivers,estuaries. Rarely found in fresh water. Likes sunlit and shaded areas. Biteshumans and animals indoors and outdoors. Rests mainly outdoors.

• An. arabiensis: Likes ricefields and temporary waters such as pools, hoofprints,puddles. Only found in sunlit habitats. Bites humans indoors and outdoors. Restsindoors and outdoors.

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• An. atroparvus: Occurs in sunlit and exposed pools and ditches. Fresh or brackishwater. Also in ricefields. Adults bite humans and animals. Normally rest in stables,cow sheds, piggeries.

• An. balabacensis: Found in muddy, shaded forest pools, vehicle ruts, hoofprints,sometimes in deep wells. Bites humans and cattle. Feeds and rests outside.Restricted in distribution to Sabah, Java, Borneo, and some Philippine islands.

• An. bellator: Larvae found in water in leaf axils of bromeliads. Adults bite humansday and night, and may enter houses to feed. Rest mainly outdoors. Found inTrinidad, Venezuela, Guyana, Surinam, Brazil.

• An. campestris: Prefers deep, shaded water including ditches and wells. Larvaesometimes found in brackish water. Bites humans and animals inside andoutside. Often rests indoors.

• An. culicifacies: Found in irrigation ditches, pools, wells, stream edges, marshes,ricefields, and in brackish water on occasion. Prefers domestic animals, but willbite humans inside and outside. Mainly rests indoors.

• An. darlingi: Occurs in fresh water marshes, swamps, lakes, lagoons, ricefields,ponds, pools, and stream edges, especially with vegetation. Feeds principally onhumans indoors, rests indoors.

• An. dirus: Hoofprints at edge of or in forests, shaded pools. Adults bite humansand animals, usually outdoors, and stay outdoors following feeding. Distributedfrom western India to South-east Asia.

• An. donaldi: Shaded habitats such as forest pools and tree-covered swamps.Often associated with vegetation and ricefields. Bites domestic livestock but willalso feed on humans inside or outside. Rests principally outdoors.

• An. farauti: Usually occurs in semipermanent waters including ponds, swamps,lagoons, puddles, hoofprints. Water can be fresh, slightly brackish, or polluted, andin sunlight or shade. Adults bite animals and humans indoors and outdoors,resting mainly outdoors.

• An. flavirostris: Found in flowing water including springs and irrigation ditches. Alsofound in ricefields. Preference for shaded parts of sunlit habitats. Feeds mainly onhumans, but also on animals. Feeds inside or outside, rests mainly outside.

• An. fluviatilis: Flowing waters including hill streams, irrigation ditches. Preferssunlight. Bites humans and domestic animals. Feeds and rests indoors andoutdoors.

• An. freeborni: Larvae found in ditches, pools, seepages, mainly with floating oremergent vegetation or filamentous algae. Also found in ricefields. Preferssunlight, bites animals and humans inside and outside. Rests indoors oroutdoors.

• An. funestus: Occurs in permanent waters, especially with vegetation. Habitatsinclude marshes, river edges, ditches and rice fields. Prefers shade. Mainly biteshumans, but also domestic animals. Feeds inside and outside. Mainly restsindoors.

• An. gambiae: This is a complex of 6 morphologically very similar species (An.gambiae, An. arabiensis, An. melas, An. merus, An. quadriannulatus, An.bwambae). An. gambiae is the most anthropophagic species in the complex andthe main malaria vector. Larvae are found in sunlit pools, puddles, ricefields. Biteshumans and animals indoors and outdoors. Rests mainly indoors. An. melasbreeds in coastal salt waters including mangrove swamps, and only occurs inwest Africa.

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• An. merus is mainly found in coastal salt water in East and South Africa. Adults ofboth species bite humans, resting indoors and outdoors. An. quadriannulatus isfound in parts of eastern and southern Africa, feeding mainly on cattle. An.bwambae breeds in warm mineral springs in Uganda, transmitting malaria locally.

• An. koliensis: Found in marshy pools, irrigation ditches and pools at edge of foreststreams. Prefers sunlight. Adults bite humans and, on occasion, animals. Mainlyrests indoors.

• An. labranchiae: Habitats include brackish waters in coastal marshes, ricefields,and freshwater marshes. Prefers sunlight. Bites humans and animals indoorsand outdoors. Rests mainly in animal shelters or houses.

• An. letifer: Found in acidic stagnant pools, swamps, and ponds, especially oncoastal plains. Prefers shade. Bites animals and humans, mainly outside. Restsoutside.

• An. leucosphyrus: Occurs in clear seepage pools in forests. Adults bite humansinside and outside. Rests outdoors.

• An. maculatus: Habitats include seepage waters, edges of ponds, swamps rich invegetation. Prefers sunlight. Bites humans and animals, mainly outdoors. Restsoutdoors.

• An. minimus: Flowing water including springs, irrigation ditches, ricefields. Prefersshaded areas. Feeds mainly on humans, sometimes on animals. Feeds andrests mainly indoors.

• An. nigerrimus: Larvae occur in deep ponds, marshes rich in vegetation, ricefields,irrigation ditches. Prefers sunlight. Bites humans and animals. Feeds and restsmainly outdoors.

• An. nuneztovari: Muddy waters such as found in vehicle tracks, hoofprints, andsmall ponds. Prefers sunlight. Mainly feeds on animals, but also attacks humans.Feeds and rests outside.

• An. pharoensis: Occurs in marshes and ponds, especially with grassy and floatingvegetation in abundance. Also found in ricefields. Bites humans and animals,inside and outside. rests outside after feeding.

• An. pseudopunctipennis: Found in pools, puddles, edges of streams. Especiallylikes habitats with algae, prefers sunlight. Feeds indoors and outdoors onhumans and animals. Rests outdoors.

• An. punctimacula: Swamps, small pools, grassy pools at edge of streams. Biteshumans and animals indoors and outdoors. Rests inside or outside after feeding.

• An. punctulatus: Larvae found in temporary and often muddy pools, puddles,hoofprints and ditches. Bites humans in preference to animals. Rests indoors oroutdoors.

• An. quadrimaculatus: Habitats include ponds and marshes, especially wherevegetation or filamentous algae present. Also found in ricefields. Bites humansand animals, indoors or outdoors. Rests inside or outside.

• An. sacharovi: Fresh or brackish marsh waters, pools, ponds, especially wherevegetation present. Prefers sunlight. Bites humans and animals inside or outside.Usually rests indoors.

• An. sergentii: Habitats include ricefields, ditches, and slow-flowing streams.Prefers sunlight or partial shade. Bites humans or animals indoors or outdoors.Rests in houses and caves.

• An. sinensis: Mainly found in ricefields. Adults bite humans and cattle. Feedsindoors or outdoors. Rests mainly outdoors.

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• An. stephensi: Can be important malaria vector locally. Main vector of malaria inIndian subcontinent. Larvae breed in fresh, brackish, or polluted water, and can befound in man-made habitats including, water tanks, wells, gutters, and containers.Adults bite humans indoors and outdoors. Rest mainly indoors. Wide distribution.

• An. subpictus: Found in muddy pools, gutters, and brackish water. Bites mainlyanimals, but also humans. Feeds and rests indoors and outdoors.

• An. sundaicus: Occurs in brackish waters including lagoons and marshes,especially in presence of putrifying algae and vegetation. Mainly a coastal species,but also found in freshwater inland pools in Sumatra and Java. Prefers sunlight.Bites humans and animals indoors and outdoors. Rests mainly indoors.

• An. superpictus: Found in flowing waters including torrents of shallow water inrocky streams and pools in rivers. Prefers sunlight. Bites humans and animalsinside and outside. Rests mainly indoors, but also in caves.

3.4.3 Filariasis

Some species of Anopheles transmit filarial worms (Wuchereria bancrofti, Brugiamalayi, Brugia timori), which cause filariasis in humans. The vector species are givenin table 2 below (see page 19 within section on Culicine mosquitoes).

W. bancrofti is the causative agent of filariasis in people living in Central and SouthAmerica, Africa and Asia, as well as in some subtropical countries in the Middle East.In these areas bancroftian filariasis is mainly an urban disease. B malayi on the otherhand is more of a rural disease, with a distribution restricted to Asian countries(including southern India, West Malaysia, Viet Nam, Indonesia, Thailand, China, NewGuinea, Philippines, and Korea). Both diseases occur in two forms, nocturnal periodicand nocturnal sub-periodic filariasis. Anophelines (and some culicines - see table 2,page 19) are the vectors of the nocturnal periodic form. The anophelines that vectorfilariasis vary from area to area, but are often the same as those transmitting malaria.Vectors of nocturnally periodic W. bancrofti, for example, include An. aconitus, An.anthropohagus, An. aquasalis, An. nigerrimus and An. vagus. There are no animalreservoirs of this disease. Nocturnal periodic B. malayi is vectored by suchanophelines as An. anthropophagus, An. donaldi and An. sinensis. There are noknown important animal reservoirs of this disease.

Brugia timori is known only from the islands of Timor, Flores, Alor, and Roti, in or nearIndonesia, and is transmitted by An. barbirostris and possibly by other anophelines.There are no known animal reservoirs.

3.4.4 Arboviruses

Over 500 arthropod-borne-viruses (arboviruses) have been catalogued, of which 100are transmitted by mosquitoes and infect human beings. In 1959-1960 a majorepidemic of the painful disease O’nyong nyong (joint-breaker) occurred in East andCentral Africa. It was subsequently discovered that the disease was being spread bythe An. gambiae complex and by An. funestus.

Subsequently there is evidence for about 20 other arboviruses that infect humans,transmitted by Anopheles mosquitoes.

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4. Sub family 2 – Culicine Mosquitoes (Culicinae)

4.1 Background

This subfamily contains 34 genera of mosquitoes. The most important medically are:

• Culex• Aedes• Psorophora• Mansonia• Haemagogus• Sabethes

Culex, Aedes and Mansonia mosquitoes are found in temperate and tropical regions,whilst Psorophora species are found in North, Central, and Southern America, andHaemagogus and Sabethes are restricted to Central and South America.

Some species of Aedes are vectors of yellow fever in Africa. Aedes, Haemagogus andSabethes are vectors of yellow fever in Central and South America. Aedes speciesalso transmit dengue. All the genera of culicine mosquitoes listed here can transmit avariety of other arboviruses. Some species of Mansonia, Culex and Aedes are vectorsof filariasis. Psorophora mosquitoes are mainly pest insects.

4.2 Culex Mosquitoes

4.2.1 Description

Culex mosquitoes are found worldwide except in the extreme northern parts of thetemperate regions. Eggs are usually brown and are long and cylindrical. They are laidupright on the water surface, placed together to form rafts of up to 300 eggs. Larvaeusually have a long, narrow siphon, although it may be short and fat. Adults aregenerally recognised by their lack of ornamentation, with the thorax, legs and wing-veins often covered with brown scales. The abdomen is often covered with blackish orbrown scales.

Figure 2. Emerging Culex sp. mosquito

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4.2.2 Biology

Culex species usually breed in pools, puddles, ditches, borrow pits, and ricefields.Some lay their eggs in artificial habitats, including tins, bottles, and storage tanks. Themost important species is Culex quinquefasciatus which transmits filariasis. Thisspecies breeds in polluted water containing rotting vegetation, excreta, and householdrefuse. Larvae of C. quinquefasciatus often occur in partially blocked drains, septictanks, and in village pots. The species is associated with urbanisation, particularlyareas with poor sanitation and drainage.

Culex tritaeniorhynchus transmits Japanese encephalitis, breeding in ricefields andgrassy pools. They are also found in fish ponds where manure has been added insouthern Asia.

C. quinquefasciatus and many other species of Culex bite humans and other hosts atnight.

4.3 Aedes Mosquitoes

4.3.1 Description

Distribution is worldwide including into Arctic areas, where they can be seriousnuisance pests to humans and to livestock. Eggs are usually black, ovoid in shape,and laid singly. Eggs are deposited on damp substrates just above the water line, forexample on damp mud, or on damp walls of clay pots. Eggs can withstanddesiccation, sometimes for many months. This, combined with the ability for the eggsto hatch in instalments, can create problems in control programmes. Larvae usuallyhave a short barrel-shaped siphon. Adults often have conspicuous patterns on thethorax. Black, white, yellow, or silvery scales form these. The legs may have black andwhite rings.

Figure 3. Aedes sp. mosquito

4.3.2 Biology

Many species breed in artificial or natural container-habitats including tree-holes,rock-pools, tin cans, pots, and water-storage jars. Larvae are usually found in cleanwater intended for drinking. The life cycle can be completed in as little as 7 days in thetropics, but usually lasts 10-12 days. In temperate species the life cycle may takeweeks or months to complete. Adults of most Aedes species bite mainly during theday or early evening. Biting usually occurs outside (exophagic), and the insectsusually rest outside (exophilic).

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4.4 Haemagogus Mosquitoes

4.4.1 Description & Biology

Haemagogus mosquitoes are only found in Central and Southern America. Eggs areusually black, ovoid, and laid singly in tree-holes and other container-habitats. Adultsare very colourful and are easy to recognise from the presence of bright metallic blue,red, green, or golden coloured scales, which cover the dorsal part of the thorax.

Eggs are able to withstand desiccation. Larvae are usually found in tree-holes butalso in bamboo stumps, rock-pools, split coconut shells, and domestic containers.They are forest mosquitoes, spending most of their time in treetops where they bitemonkeys. In tree-felling operations, however, or during the dry season, they maydescend to the forest floor where they will bite humans. The following species areinvolved in transmitting yellow fever:

• H. spegazzinii• H. equinus• H. leucocelaenus• H. janthinomys• H. capricornii

4.5 Sabethes Mosquitoes

4.5.1 Description and Biology

Sabethes are only found in Central and Southern America. Eggs are believed to belaid singly, and to be incapable of desiccation. In the adult, the dorsal surface of thethorax is covered with iridescent blue, green, and red scales. They can be difficult todistinguish from Haemogogus mosquitoes.

Larvae are found in bamboo stumps and in tree-holes. Some species occur in leafaxils of bromeliads and of other plants. They are basically forest mosquitoes, bitingduring the day. Like Haemogogus they may descend to ground level and bite humanbeings. Sabethes chloropterus is thought to be a vector of yellow fever.

4.6 Mansonia Mosquitoes

4.6.1 Description and Biology

Mansonia mosquitoes occur mainly in wet tropical areas, with a few species intemperate zones. Eggs are black or dark brown and are cylindrical, with a tube-likeextension apically that is darker than the rest of the egg. Eggs are laid in stickycompact masses. They are often laid as a rosette, which is glued to the underside offloating vegetation. Larvae are easily recognised as they have specialised siphons,which are adapted to pierce aquatic plants. Adults typically have legs, palps, wingsand body covered with a mixture of dark and pale scales, giving the insect a dustyappearance. Wings appear as though they have been sprinkled with salt and pepper.

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Figure 4. Mansonia sp. mosquito

Eggs are glued to the underside of plants and hatch out after a few days. They are notable to withstand desiccation. Larval habitat will have vegetation. Larvae thus occur inpermanent collections of water including swamps, ponds, and irrigation canals.Larvae and pupae will not detach themselves from the plant and rise to the surface ofthe water unless disturbed. The fact that larvae may be some way below the watersurface means that conventional forms of insecticidal mosquito control are difficult toapply.

Adults usually bite at night but a few species feed by day. Most species rest outside,but some do so inside. Main medical importance is as vectors of filariasis.

4.7 Coquillettidia Mosquitoes

Mainly tropical but with a few temperate species. Related to the Mansonia Mosquitoes,but differ in that eggs are formed in rafts that float on water. As with the Mansonia,these mosquitoes have siphons which are inserted into plants for respiration. Adultshave narrow scales on the wings, and several species are bright yellow. This genusis of minor medical importance, although Cq. crassipes can transmit nocturnalsubperiodic B. malayi in Malaysia.

4.8 Psorophora Mosquitoes

Only found in the Americas, from Canada to South America. Eggs similar to Aedesand able to withstand desiccation. Psorophora mosquitoes breed in flooded pasturesand rice fields and the larvae of some species are predators. The species cantransmit some arboviruses, including Venezuelan equine encephalomyelitis, howevertheir main importance is as vicious biters.

4.9 Medical importance

4.9.1 Biting Nuisance and Diseases

Mosquitoes can cause considerable biting nuisance and in some areas of the worldlarge amounts of money are spent on mosquito control for this reason.

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It is interesting to note that in North America more money is spent on controllingnuisance culicine mosquitoes, than is spent in most tropical countries whereculicines transmit disease. Large swarms of Aedes mosquitoes attack human beingsin northern temperate and subarctic areas of Asia, Europe, and America. An exampleof the sort of damage that this can cause is shown in Figure 5.

Figure 5. Damage resulting from nuisance mosquito attack in Scandinavia

4.9.2 Yellow Fever

The yellow fever arbovirus occurs in Africa, and in tropical regions of the Americas.Yellow fever is a zoonosis, principally associated with monkeys, which can undercertain conditions be transmitted to humans.

In Africa the disease occurs in cercopithecis monkeys in forests, and is vectoredmainly by Aedes africanus. This forest-dwelling mosquito breeds in tree-holes andbites in the forest canopy soon after sunset. This sylvatic (forest) cycle maintains adisease reservoir in the monkey population. The monkeys themselves only rarely diefrom the disease. However, some affected monkeys descend from the trees and stealbananas from farms. In this habitat they can be bitten by other mosquito species suchas Aedes bromeliae. This is a day-biting species which breeds in leaf axils ofbananas and other plants, and bites the host at forest edges. If the monkeys areinfected with yellow fever, the mosquito becomes infected, and can pass on thedisease to other monkeys and to human beings. This transmission cycle is referredto as the rural cycle. Infected humans then return to their villages where they can bebitten by other mosquitoes, including Aedes aegypti. The Aedes aegypti can in turnbecome infected and then transmit yellow fever to other humans - this is the urbancycle of yellow fever transmission.

In Southern and Central America, yellow fever is also principally a disease of forestmonkeys, and is transmitted among them by various species of Haemogogusmosquito, and by Sabethes chloropterus, and species of Aedes. These are all tree-hole breeding, arboreal mosquitoes. In the New World, the monkeys are moreaffected by the disease, and often become sick and die.

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When humans enter the jungle, they come into contact with the vector mosquitoes,which may bite them. If the mosquitoes are infected then they can transmit thedisease. Yellow fever is then spread between humans in villages and towns by Aedesaegypti.

Symptoms of Yellow fever include, fever, chills, headaches, flu like symptoms,lethargy, nausea, vomiting and jaundice

4.9.3 Dengue

Dengue is caused by a number of different viruses (dengue types 1,2,3 and 4) and iswidely distributed throughout the tropics, including Southeast Asia, the Pacific, theIndian subcontinent, Africa, the USA, Central America, northern parts of SouthAmerica, and the Caribbean. There is a more severe form called denguehaemorrhagic fever, which causes infant mortality, which has appeared in South EastAsia, India, and the Americas. Dengue is the most important mosquito vectored viraldisease.

Dengue and haemorrhagic dengue are transmitted by Aedes aegypti, with sometransmission by Aedes scutellaris in Southeast Asia. Both species breed in container-habitats such as water pots and tyres. Aedes scutellaris is thought to be a denguevector in the Pacific islands. There are not any known animal reservoirs, althoughthere is transmission of dengue among monkeys in Malaysia, by Aedes niveus.

Symptoms of Dengue include high fever, severe headache, pain behind the eyes,muscle and joint pains, and rash.

4.9.4 Encephalitis Viruses

A number of other mosquito-borne arboviruses infect people in various parts of theworld. These include the following zoonoses:

• Ross River virus (Australia)• Chikungunya (Africa and Asia)• Sindbis (Africa, Asia and Australia)• Rift Valley fever (Africa)The most important arboviruses are the following encephalitis ones:

1) Japanese encephalitis. In Japan, China, Malaysia, Korea, and elsewhere in south-east Asia and India. Animal hosts include birds and pigs. Transmission to birds,humans, and pigs is by Culex tritaeniorhynchus which breeds in ricefields, whilstCulex gelidus is believed to maintain pig-to-pig transmission in south-east Asia, andCulex vishnui is a vector in India.

2) St Louis encephalitis. Southern Canada, USA, Central and South America. In theeastern USA this is a mainly urban disease transmitted by Culex quinquefasciatusand Culex molestus. In rural areas Culex tarsalis is a vector. Animal hosts arechickens and peridomestic wild birds.

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3) Eastern Equine Encephalomyelitis. Canada, eastern USA, South America.Principally an infection of birds, but affects humans and horses. Transmitted tohumans and horses by various Aedes species, including Aedes sollicitans and Aedesvexans.

4) Western Equine Encephalomyelitis. Western USA, South America down to Uruguay.Arboviral infection of birds, transmitted to humans and horses by various Culexspecies including Culex tarsalis (which breeds in ricefields) and by Culisetamelanura.

5) Venezuelan Equine Encephalomyelitis. Southern USA, Central America, northernparts of South America. Often fatal in horses. Transmitted by species of Aedes, Culexand Psorophora.

Symptoms of encephalitis include high fever, stiff neck, headache, confusion,sleepiness.

4.9.5 Filariasis

Table 2 summarises the main mosquito vectors of filariaisis (Service, 1996).Filariasis occurs in two forms, the nocturnal periodic form, in which microfilariae are inthe peripheral blood at night only, is transmitted by night biting mosquitoes includingAnopheles, Mansonia and Culex quinqefasciatus. In the day the microfiliariae are inblood vessels supplying the lungs and cannot be taken up by mosquitoes. Insubperiodic forms of W. bancrofti and B. malayi microfilariae are present in theperipheral blood during the day and the night.

Table 2. Summary of main mosquito vectors of filariaisis

Species and formof filariasis

Geographicdistribution

Vectors Zoonoticreservoir

Wucheria bancroftiNocturnal periodic Tropics (not Polynesia) Anopheles app

including many malariavectors

None

Tropics (not Polynesia),New Guinea, China,Philippines

Mansonia uniformisAedes togoiAedes poicilius

None

Diurnal subperiodic Polynesis, Fiji, NewCaledonia

Aedes polynesiensisAedespseudoscutellarisAedes vigilax

None

Nocturnal subperiodic Thailand Aedes niveus group NoneBrugia malayiNocturnal periodic(open swamps)

Asia, from India toJapan

Anopheles sppincluding malariavectors

May exist

Asia, from India toJapan

Mansonia annulifera,Ma. uniformis, Ma.annulata, Cq.crassipes, Aedes togoi

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China, Korea, Japan Aedes togoiNocturnal subperiodic(swampy forest)

Malaysia, Indonesia,Thailand, Philippines

Mansonia dives, Ma.bonneae, Ma.annulata, Ma. uniformis

Monkeys, cats.pangolins

Brugia timoriNocturnal periodic Timor, Flores, Rotor,

Alor islands in/nearIndonesia

Anopheles barbirostris None

4.9.5.1 Bancroftian filariasis

Occurs through much of tropics and in subtropical countries in the Middle East.Essentially an urban disease with no animal reservoirs. The nocturnal periodic formis transmitted by Anopheles mosquitoes, and by Culex quinquefasciatus which iswidespread in the tropics. The diurnal subperiodic form found in Polynesia, isprincipally transmitted by the day biting Aedes polynesiensis, which mainly feeds andrests outside. Nocturnal subperiodic filariasis is found in Thailand and is transmittedby Aedes niveus mosquitoes. Adults bite and rest outdoors.

4.9.5.2 Brugian filariasis

The nocturnal periodic form is considered as a mainly rural disease and istransmitted mainly by night-biting Mansonia mosquitoes, and also by someAnopheles mosquitoes. Adults bite and rest mainly outdoors. The nocturnalsubperiodic form is transmitted by Mansonia mosquitoes, and by Coquillettidiacrassipes in Malaysia. Adults bite mainly at night, but also in the daytime.

5. Common names for Mosquito Species:

Table 3. List of mosquito common names:Species Language Common nameAedes spp German Muecken, Stechmuecken;

Wiesenmücken; Waldmcken;Uberschwemmungsmücken

Hungarian csipö szúnyogok, tócsaszúnyogokEnglish field mosquito; (s Afr) bush

mosquitoesRussian kusaki

Aedes aboriginis English northwest coast mosquitoAedes aegypti English Yellow fever mosquito,

(Australia) dengue mosquitoGerman Gelbfiebermuecke,

DenguefiebermueckeFrench moustique de la fièvre jaune;

(Canada) maringouinHungarian sárgalázterjesztö szúnyog; sárgaláz-

szúnyogRussian sheltolichoradotchnyj [yellow-

fever] komarAedes albopictus English Asian tiger mosquito; forest day

mosquito; Japanese tigermosquito

Aedes alternans English Scotch grey, Hexham grey

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Aedes australis English saltwater mosquitoAedes campestris English snowpool mosquitoAedes camptorhynchus English southern saltmarsh mosquitoAedes cantator English brown saltmarsh mosquitoAedes casplus German Wiestenstechmücke;

Wiesenmück, RheinschnakeHungarian aranyio szunyog

Aedes communis English common snow mosquito; woodgnat

Aedes dorsalis English brown saltmarsh mosquito;flood-water mosquito

Aedes flavescens German Wiesenstechmücke;Rheinschnake

Hungarian sarga szunyogAedes maculatus German Waldstechmücke; Waldmücke

Hungarian erdei szunyogAedes notoscriptus English domestic container mosquitoAedes punctipennis English spottedwing mosquitoAedes quadrimaculatus English common malaria mosquitoAedes sierrensis English western treehole mosquitoAedes sollicitans English saltmarsh mosquitoAedes squamiger English California saltmarsh mosquitoAedes sticticus English floodwater mosquito

German AuwaldmückeHungarian oldalfoltos szunyog

Aedes taeniorhynchus English black saltmarsh mosquito

Species Language Common nameAedes vexans German Wiesentechmücke;

Wiesenmücke; RheinschnakeEnglish vexatious mosquito; flood-water

mosquito; vexans mosquito;rainpool mosquito; freshwatermarsh mosquito

Hungarian gyotro szunyogAedes vigilax English saltmarsh mosquitoAedes vittiger English grey-striped mosquitoAnopheles annulipes English common Australian anophelineAnopheles bancrofti English black Australian anophelineAnopheles maculipennis English malaria mosquitoAnopheles farauti English Australian malaria mosquitoCoquillettidia xanthogaster English Golden mosquitoCulex annulisrostris English common banded mosquitoCulex pipiens German gemeine Haumücke; gemeine

Stechmücke; Hausstechmücke;Hausmücke

English common gnat; (n Am) northernhouse mosquito; housemosquito; common mosquito;house gnat; common gnat; (US)common rain-barrel mosquito

French mostique domestique commun;cousin commun; (Canada)maringouin domestique;maringouin

Hungarian dalos szunyogSpanish mosquito comun; (c Am)

zanendo

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Culex quinquefasciatus English brown house mosquito;southern house mosquito

Culex restuans English whitedotted mosquitoCulex sitiens English saltmarsh culexCulex tarsalis English encephalitis mosquitoCulicidae (plural) German Stechmuecken, (local, not usual

at all:) Gelsen, Moskitos,Rheinschnaken, Schnaken,Fliegen, Muecken,Stechschnaken

French moustiques; (local:) cousins;(Canada) maringouins

English moquitoes and gnatsHungarian szúnyogfélék; igazi szúnyogokSpanish culicidos; mosquitos; (local:)

cinifesCuliseta melanura English swamp mosquitoDeinocerites cancer English crabhole mosquitoMansonia perturbans English irritating mosquito; Manson

mosquitoPsorophora ciliata English shaggylegged gallinipper; giant

mosquitoWyeomyia smithii English pitcherplant mosquito

6. Sources

Much of the information in this report is taken from Service, M W (1996) MedicalEntomology for Students, Chapman & Hall, London. Information has beensupplemented from internal Insect Investigations Ltd resources, and from variousinternet based scientific libraries. Common names have been compiled frompersonal contacts (including scientists in the USA, Australia, New Zealand, Germany,and Hungary), from Gozmany L (1979) Vocabularium Nominum Animalium EuropaeSeptem Linguis Redactum, Akademiai Kiado, Budapest, and from Naumann I (1993)CSIRO Handbook of Australian Insect Names (6th Edition), Melbourne, CSIROPublications.

Report produced for Brandenburg UK Limited by Insect Investigations Ltd:Dr Peter McEwen, Research Director, Insect Investigations Ltd, School of Biosciences, CardiffUniversity, PO Box 915, Cardiff, CF1 3TL, UK. May 2000.