Order: Diptera (‘two-winged’)
Characteristics:
Adults: Globular head, a large part of the
surface of which is taken up by the compound
eyes; a pair of antennae, which are about three
times as long as the head, are somewhat hairy
in the female and quite bushy in the male; this
difference provides a ready means of
distinguishing between the sexes with the naked
eye. Also on the head a pair of palps, one on
each side of the proboscis; in the female they
are smooth, in the male they have tufts of
bristles. Mouthparts form a long thin projecting
proboscis which in the female are designed for
piercing; there is a single pair of membranous
wings which bear tiny scales along the veins as
well as a fringe of scales along the hind margin.
The wing venation is also typical with 6
longitudinal veins of which the second, fourth
and fifth are forked; tarsi are 5-segmented.
Larvae:
Entirely aquatic. They have a well developed
head followed by a swollen unsegmented
thorax; abdomen is segmented and there is a
pair of spiracles on the last but one segment
through which they breathe at the water's
surface. Tufts of bristles arise from many of the
body segments.
Pupae:
Comma-shaped with a curved tail which ends in
a pair of paddles; head is equipped with a pair
of respiratory trumpets through which the pupa
breathes. The fused head and thorax show
traces of the wings and long legs of the adult
which are developing inside.
Family: Culicidae (mosquitoes)
Metamorphosis is complete with egg, larval,
pupal and adult stages. There are about 3000
species of mosquitoes in the world.
Sub-Family: Anophelinae
Genus: Anopheles spp.
Characteristics:
Wings speckled with dark and pale-coloured
scales; there are no scales on the abdomen;
female palps almost as long as the proboscis,
the male palps are usually clubbed. When
resting the abdomen is held at an angle from
the surface on which the mosquito is standing,
forming a straight line with the proboscis (e.g.
Anopheles gambiae).
Sub-Family: Culicinae
Characteristics:
Female palps are short and the abdomen is
covered in scales. The resting stance is parallel
to the surface.
Genus: Culex spp.
Characteristics:
Vary in size but all have a blunt tipped
abdomen and usually lack distinctive markings
on the body or wings (e.g. Culex quinquefasciatus).
Genus: Aedes spp.
Characteristics:
Medium to large; most have pointed abdomen
and well separated eyes; usually distinctly
marked by patches of dark and light scales;
often general appearance of black with silver
markings (e.g. Aedes aegypti).
Genus: Mansonia spp.
Characteristics:
Medium sized and heavily covered in scales
which are of mixed colours giving a ‘salt and
pepper’ appearance. Larvae are rarely seen since
they remain submerged and pierce plant tissues
with their breathing siphons to obtain oxygen
(e.g. Mansonia uniformis).
Note: There are several other Genera of
mosquitoes some of which are implicated in
disease transmission but others are of no risk to
humans. Space does not allow consideration of
all the other Genera here.
Distribution
Mosquitoes are ubiquitous insects, they can be
found in nearly every type of climatic region of
the world from the arctic regions to the tropics,
surviving severe winters or dry seasons
depending on the region. Depending on species
they can be found breeding in all types of
water; from heavily polluted, to clean; from
small collections of water in tin cans, to pools or
streams; such is their adaptability. Their
distribution is increased and aided by transport
systems such as boats and aircraft and nonindigenous
species have been introduced to new
territories in this way, even infected mosquitoes
have been transported to temperate climates,
thereby transmitting tropical diseases.
Significance
Primarily a seasonal biting nuisance in cooler
climates but in the tropics they can also be
major vectors of disease. They can transmit
many diseases to both humans and animals,
e.g. malaria, filariasis, yellow fever, encephalitis,
and dengue fever. Only a few species of
mosquitoes are implicated as vectors of human
diseases. It is those which utilise humans as
Mosquitoes
Examples of human disease transmission by mosquitoes
Genus Diseases
Anopheles spp. malaria, filariasis, various viruses e.g. Anopheles gambiae
Aedes spp. yellow fever, dengue fever, encephalitis, various viruses e.g. Aedes aegypti
Culex spp. filariasis, encephalitis, various viruses e.g. Culex quinquefasciatus
Mansonia spp. filariasis, various viruses e.g. Mansonia uniformis.
Mosquito. Aedes spp.
6.5mm wingspan
Glossary of terms
Diapause: A period of suspended development
or growth.
Instars: Any stage in an insects life cycle,
especially between moults.
Palps: Sensory organs associated with the
mouthparts.
Spiracle: External opening of the trachea;
breathing pore.
Tarsus (Tarsi): Apical section of leg (the foot).
Vector: An animal which transmits parasites.
Advice
Aventis has an extensive range of products
specifically formulated for the control of flying
and crawling insect pests.
Further information on all Aventis
Environmental Science professional pest control
products is available from:
Aventis Environmental Science
Fyfield Road, Ongar, Essex, CM5 0HW
United Kingdom
Tel: +44 1277 301116
Fax: +44 1277 301119
The greatest care has been taken to ensure the
accuracy of the information contained in this Fact
Sheet. In no circumstance, however, will Aventis
Environmental Science be liable in respect of any error
or omission.
© Copyright Aventis 2000
their primary host and are also willing to enter
houses in their pursuit of a blood meal which
are the most important. Some species do not
feed on humans at all but utilise other
mammals, birds or even reptiles as their hosts.
Statistics show that 270 million people are
infected with malaria alone and of those up to
two million will die annually. It is this that
makes the mosquito the most dangerous
creature in the world.
Life-Cycle
The mosquito mates within 48 hours of
emergence from the pupa. The female only
mates once in her lifetime, because she is able
to store the sperm in sacs within her body and
fertilise subsequent batches of eggs herself.
Most mosquitoes feed from sunset onwards,
both sexes feed on nectar or fruits for
sustenance but the female usually requires the
high protein content of blood to produce eggs
and soon after mating she will go in search of a
blood meal. The female has powerful sensory
organs which are able to detect body smell,
carbon dioxide, warmth and moisture
emanating from the host, she follows these
stimuli upwind until she locates the host. Adults
can fly several kilometres in search of food but
can disperse further when carried by the wind.
The female pierces the host's skin with her
mouthparts and locates a blood vessel from
which to suck blood. She takes approximately
her own bodyweight in blood at each feed.
While feeding, saliva which contains an anticoagulant
passes into the wound to stop clotting
and keep the blood flowing. It is the host body's
allergic reaction to this which causes the
irritating marks left behind.
Whilst the infected mosquito feeds, disease
causing parasites are able to enter the host’s
body via the saliva or mouthparts of the
infected mosquitoes. Conversely an uninfected
mosquito becomes infected when it feeds on a
person carrying infective forms of the parasite.
These develop within the mosquito until the
insect becomes infective and can transmit the
parasites to new hosts. The relationships
between parasite, mosquito and host have
evolved over many years and are often highly
specific to the species involved.
The blood meal stimulates egg production and
provides the nutrients required for the eggs to
develop. They are fertilised from stored sperm
just before they are laid, between 30-350 eggs
are laid in each batch, depending on the
species. They are spindle-shaped averaging
1.5mm in length and are laid either on surfaces
surrounding the water’s edge or in small floating
rafts of eggs glued together or laid singly and
scattered over the surface of the water,
depending on the species.
Eggs hatch after several days and the first stage
larva swims free. The larva feeds by the action
of mouth brushes which cause a current of
water to flow past the mouth bringing with it
organic particles. They will also browse on algae
or plants. Culicine larvae obtain their food at
various depths but the Anopheline larvae feed
only on substances floating on the surface of
the water. Culicine larvae hang from the surface
of the water by their breathing siphon in
contrast to Anopheline larvae which lay
horizontal to the surface. The larvae pass
through 4 developmental stages or instars, at
the end of each instar the larva sheds its skin or
moults.
When the 4th instar larva sheds its skin it
becomes a pupa. The pupa does not feed but
remains at the water's surface. When disturbed
they dive with a jerking motion returning to the
surface passively.
The adult mosquito develops within the pupa.
When it is fully developed the pupal skin splits
along the dorsal surface and the adult emerges.
Within a short time when the cuticle has
hardened and the wings expanded, it will fly off.
The adult's life expectancy is not usually more
than a few weeks unless it is in diapause.
During its life however the female may lay
several batches of eggs each containing several
hundred eggs.
The length of the complete life cycle is very
dependent on temperature and can range from
10 days to 6 months or longer in those species
which overwinter as larvae.
Control
Control measures can be directed against the
larvae or adults.
Larvae
Larval habitats may be minimised especially in
urban environments by sealing drains and
soakaways, reeradicating receptacles containing
water such as old tins or tyres etc. In other
situations physical methods such as ensuring
drainage channels run freely or draining
standing water from building sites, earthworks
etc. will contribute to reducing the problem.
Where these physical measures are not possible
larvicides may be applied regularly to the water
to kill the larval stages before they pupate.
Adults
Adult mosquitoes may be killed indoors using
an aerosol, or the biting nuisance may be
minimised by the use of repellents, treated bed
nets, vaporisers eg mosquito coils, mats etc.
Vector control programmes may use surface
sprays with residual activity applied inside
houses. Alternatively, the use of space sprays eg
Ultra Low Volume (ULV) aerosols or fogs will
rapidly reduce adult populations indoors or
outside.
Mosquito. Anopheles spp.
7.5mm wingspan
