Transcript 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.
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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.
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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.
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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.
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