Document

Insecta : Nematocera, Brachycera By Assist. Lecturer Maytham A. Alwan

4/13/2015

Suborder: Nematocera • Family: Culicidae (mosquito) • The Culicidae are the mosquitoes, small slender flies with long legs. Although their bites are a severe nuisance to man and animals they are principally important as vectors of malaria (Plasmodium spp.), filarial nematodes and viruses. • Hosts: • A wide variety of mammals, including man; reptiles and birds. • Species: • This family contains over 3000 species belonging to 34 genera, the most important of which are Anopheles, Culex and Aedes.

Mosquito • General morphology • Mosquitoes vary from 2.0 to l0.0 mm in length and have slender bodies, prominent eyes and long legs . • The mouthparts consist of a conspicuous, forwardprojecting, elongated proboscis adapted for piercing and sucking. Individual elements comprise a long U shaped fleshy labium containing paired maxillae, mandibles and a hypopharynx which carries a salivary duct which delivers anticoagulant into the host's tissues. The labrum forms the roof of the proboscis and all the elements, with the exception of the labium, enter the skin during feeding by the females, forming a tube through which blood is sucked. In the nonparasitic males the maxillae and mandibles are reduced or absent. The maxillary palps of different species are variable in length and morphology. Both sexes have long filamentous segmented antennae, pilose in females and plumose in males.

Mosquito

Culicidae: Mosquitoes

Larvae and pupa of mosquito

pupa of mosquito

Pupa of mosquitoes

labium

General life cycle • After a blood meal the gravid female lays up to 300 eggs on the surface of water in the case of Culex in groups forming egg-rafts. The eggs are dark-coloured, elongate or ovoid, and in the genus Anopheles, boat-shaped, and cannot survive desiccation. Hatching is temperature-dependent and occurs after several days to weeks, but in some temperate species eggs may overwinter. All four larval instars are aquatic feeding on organic material. Most larvae take in air through a pair of spiracles on the penultimate abdominal segment, but in Culex spp. these are situated at the end of a small tube called the respiratory siphon . Maturation of larvae can extend from one week to several months and several species overwinter as larvae in temperate areas. Larval habitats in small temporary collections of water or extensive areas such as marshes, but they are usually absent from large tracts of uninterrupted water, such as lakes, and from fast-flowing streams or rivers.

Life cycle

• All mosquito pupae are aquatic, motile and commashaped with a distinct cephalothorax which bears a pair of respiratory trumpets. The tegument of the cephalothorax is transparent and the eyes, legs and other structures of the developing adult are readily visible. The tapering abdominal segments have short hairs and terminally there is a pair of oval, paddle-like extensions which enable the pupa to move up and down in the water. Generally the pupal stage is short, being only a few days in the tropics and several weeks or longer in temperate regions, the adult emerging through a dorsal split in the pupal tegument. Adults usually fly only up to a few hundred metres from their breeding sites, but may be dispersed long distances by winds. Although the life-span of adult flies is generally short some species can overwinter by hibernating.

Mosquito • Pathogenic significance • Most species of mosquitoes are nocturnal feeders and may cause considerable annoyance by biting, their long mouthparts allowing them to bite man even through clothing. More importantly, species of Anopheles, Culex and Aedes transmit both the dog heartworm, Dirofilaria immitis, and one form of avian malaria caused by Plasmodium. Mosquitoes are also important in the transmission of the arboviruses (arthropodborne) causing Eastern, Western and Venezuelan encephalitis in horses and other arbovirus diseases of man and animals.

• The only known vectors of human malaria belong to the genus Anopheles while yellow fever is transmitted by Aedes spp. All three genera transmit the human filarial nematodes Wuchereria and Brugia.

Control 1. The various measures used against larvae include the removal or reduction of available breeding sites by drainage or other means which make these sites unsuitable for larval development. 2. Biological control has been attempted by, for example, introducing predatory fish into marshy areas and rice fields. 3. Probably the most widely used measures against mosquito larvae are those which involve the repeated application to breeding sites of toxic chemicals, mineral oils or insecticides.

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4. Essential water sources can be rendered unsuitable as breeding sites by spreading inert polystyrene beads to cover the surface of the water Insecticides with a residual action are effective against the adult stages, particularly if applied indoors, and these have been widely used to control the Anopheles vectors of malaria in man. Organophosphorous compounds and carbamates are recommended for this purpose. 5. Although synthetic pyrethroids have been available for some time as short-acting space sprays. Flyscreens, nets and repellents are available for the protection of man.

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Family: PSYCHODIDAE • The flies of this family are called the 'sandflies' and Phlebotomus is the only genus of any veterinary importance. These flies are important as vectors of Leishmania. Phlebotomus • Hosts:

• Many mammals, reptiles, birds and man. • Species: • There are over 600 species of phlebotomine sandflies.

Phlebotomus • Morphology • These small flies, up to 5.0 mm long, are characterized by their hairy appearance, their large black eyes and long stilt-like legs. The wings, which, unlike those of other biting flies, are lanceolate in outline, are also covered in hairs and are held erect over the body at rest. • As in many other nematoceran flies the mouthparts are of short to medium length, hang downwards, and are adapted for piercing and sucking. In both sexes the very long antennae of up to 16 segments bear many short hairs. 4/13/2015

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Sandfly: Phlebotomus

Sand fly: Phlebotomus

Sand fly: Life cycle • Up to 100 ovoid, 0.3-0.4 mm long, brown or black eggs may be laid at each oviposition in small cracks or holes in the ground, the floors of animal houses or in leaf litter. Although not laid in water the eggs need moist conditions for survival, as do the larvae and pupae. Under optimal conditions the eggs can hatch in 1-2 weeks, but this may be prolonged in cold weather. The larvae, which resemble small caterpillars, scavenge on organic matter.

Sand fly: Life cycle There are four larval instars, maturation taking three weeks to several months depending on species, temperature and food availability and in temperate regions these flies overwinter as mature larvae. The major characteristics of the mature larvae, which are 4.0-6.0 mm long, are a black head and a segmented greyish body covered in bristles. The adults emerge from pupation after 1-2 weeks. The whole life cycle takes 30-100 days, or even longer in cool weather.

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Sand fly • Pathogenic significance • In common with many other small biting flies, only the females suck blood. They prefer to feed at night, resting in shaded areas during the day. Since they are capable of only limited flight, nuisance due to biting may be confined to certain areas near the breeding sites. • There is some seasonality in activity, the numbers of flies increasing during the rainy season in the tropics whereas they are only present during the summer months in temperate zones. phlebotomine sandflies are important as the sole known vectors of Leishmania tropica and L. donovani, which cause cutaneous and visceral leishmaniasis in man, dogs being important reservoir hosts in some regions.

Control • The adults are, however, susceptible to most insecticides and where there have been spraying campaigns to control the mosquito vectors of malaria these have effectively controlled Phlebotomus. Man has protected himself from the bites of these flies by using residual house-sprays, repellents and very fine mesh fly screens. 4/13/2015

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Suborder: Brachycera • Family: Tabanidae

• These large robust flies are commonly known throughout the world as horseflies, although they will attack and feed on a wide variety of large animals and man. The pain caused by their bites leads to interrupted feeding, and as a consequence, flies may feed on a succession of hosts and are therefore important in the mechanical transmission of pathogens such as trypanosomes. • There are many genera of tabanids, but only three are of veterinary significance, namely Tabanus, Haematopota and Chrysops.

Tabanus • Hosts: • Generally large domestic or wild animals and man, but small mammals and birds may also be attacked. • Species: There are over 3000 species of tabanids.

•

Morphology

• These are medium to large biting flies, up to 2.5cm in length, with wing spans of up to 6.5cm. They are generally dark coloured, but may have various stripes or patches of colour on the abdomen or thorax and even the large eyes, which are dichoptic in the female and holoptic in the male, may be coloured.

Tabanus • The coloration of the wings is useful in differentiating the three major genera. the characteristics of short, stout, three-segmented antennae which, unlike large cyclorrhaphan flies, have no arista . • The mouthparts, which are adapted for slashing/ sponging, are short and strong and always point downwards. 4/13/2015

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Tabanus

labium

mandibles hypopharynx

maxillae

Haematopota

Tabanus

Chrysops

Life cycle • After a blood meal the female lays batches of several hundred creamy-white or greyish cigar-shaped eggs, 1.02.5 mm long, on the underside of vegetation or on stones, generally in muddy or marshy areas. The eggs hatch in 1-2 weeks and the cylindrical, poorly differentiated larvae drop into the mud or water. They are sluggish and feed either by scavenging on decaying organic matter or by predation on small arthropods including other tabanid larvae. Optimally, larval development takes three months, but if hibernation occurs, may extend for up to three years. Mature larvae pupate partially buried in mud or soil and the adult fly emerges after 1-3 weeks. The whole life cycle takes a minimum of 4-5 months or longer if larval development is prolonged.

Tabanus • Pathogenic significance • These powerful flies may disperse many kilometres from their breeding areas and are most active during hot, sunny days. The adult females locate their prey mainly by sight and their bites are deep and painful. They feed every 3-4 days causing a great deal of annoyance, and because their feeding is often disturbed, are efficient mechanical vectors of the organisms responsible for diseases such as anthrax, pasteurellosis, trypanosomosis, anaplasmosis and the human filarial disease, loaiasis.

Control • This poses a special problem since breeding places are both diffuse and difficult to detect. For general fly control insecticidal sprays with a residual effect are used in animal houses and on the animals themselves. There is also the possibility of using dark panels with sticky adhesive as traps and there are a number of electrocution grids which may prove useful in animal houses. 4/13/2015

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