The mosquito vectors: Aedes aegypti and A. albopictus Paul R. Earl Facultad de Ciencias Biol - PowerPoint PPT Presentation

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The mosquito vectors: Aedes aegypti and A. albopictus Paul R. Earl Facultad de Ciencias Biol

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Title: The mosquito vectors: Aedes aegypti and A. albopictus Paul R. Earl Facultad de Ciencias Biol


1
The mosquito vectors Aedes aegypti and
A. albopictusPaul R. EarlFacultad de
Ciencias BiológicasUniversidad Autónoma de Nuevo
LeónSan Nicolás, NL, Mexico pearl_at_dsi.uanl.mx
2
Distribution. Aedes aegypti, the
yellow fever mosquito, that transmits dengue and
other viruses has worldwide distribution, and
within the last 2 decades A. albopictus, the
Asian tiger mosquito, has gained the Americas
like culex-carried West Nile fever also has.
Prevention and control of disease may depend upon
the level of mosquito infestation, control and
vigilance of the vector. See also M. J. Nelson
(PAHO, 1986).
3
The world distribution of Aedes aegypti
4
By 1965, A. aegypti was eradicated by DDT from
17/49 countries and political units of the
Americas. However due to lack of determination
before 1980, this household mosquito was
reestablished even in coastal Brazil and in
Bolivia where it had not been a problem for 27
years. Ecuador and Panama have been determined to
control reinfestations. Fortunately, a world ban
on DDT has recently been defeated.
5
Aedes aegypti adult male
6
Aedes albopictus adult male
7
The life cycle The eggs are about 1 mm
long, cigarshaped and smooth. They are fertilized
at the moment of oviposition and deposited singly
on the container wall just above the water level.
Embryonic development can take 2-3 days,
sometimes 5. The eggs can then withstand being
dry for perhaps a year. They will hatch promptly
upon flooding. Eggs can be transported great
distances and for long times in old car tires,
soft drink containers, etc.
8
Life cycle of Aedes Aegypti
9
The larva. The larvas like the pupas are
entirely aquatic. The larvas spend their time
using fanshaped mouth brushes to feed on bacteria
and organic matter found in the containers. An
example is a vase holding flowers.
10
The pupa. Pupas swim but do not
feed. The larval form changes to the adult
insect, and changes in form are called
metamorphosis. Pupas last 2-3 days. Aedes spp.
pupas have short trumpets and a single hair at
the tip of each swimming paddle. Strong setae
(see Figure) occur on the underside of the
corners of the 2-6th abdominal segments of Aedes
aegypti, not on other members of Aedes.
11
The adult and emergence. The adult rests on the
container wall a few hours after emergence from
the pupal case. The males rotate the male
terminalia 180?. Adult Aedes and other Culcicinae
have shorter palps than Anopheles. They are dark
with white bands. They rest parallel to surfaces.
The male has long feathered antenas as in other
culcicines and better developed palps.
12
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13
Mating. Males are attracted by
the sound of the females wings. Mating often
occurs in flight or on surfaces like walls
usually before females have fed. The male clasps
the females abdomen with his terminalia and
inserts his aedeagus into the genital chamber.
The bursa copulatrix of the female fills with
sperm that pass into the spermathecae where they
are stored. One insemination will fertilize all
the eggs a female will have in her lifetime.
Males are not attracted by this sound once a
female has fed since the wing beat is faster.
14
Feeding. Females feed on any
vertebrate host, but prefer humans. They fly
upwind following odors. The first step can be to
enter a house. Blood feeding and oviposition
occur mostly in the morning and in the late
afternoon.
15
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16
Gonadotropic cycle. If a female takes a
complete blood meal of 2-3 mg blood, she will
produce a batch of about 100 eggs in about 3
days. Stomach distention triggers ovarian
development. Thus, smaller blood meals produce
fewer eggs, and refeeding is encouraged, i. e.,
repeated biting by the same female occurs. The
ovaries have tracheas that are air tubules. These
branch into finer tracheoles. In parous females,
a folicular relic appears on each ovariole. In
this way, histological technique help experts to
judge the age of the population. Older
populations having taken many blood meals have a
greater potential for disease transmission.
17
Flight range.Although females usually
do not fly futher than 50 m, they can easily fly
100-200 m, and can travel 3 km in search for a
site to oviposit in. Recall transport by cars,
trucks, aircraft and even hurricanes. However, as
domesticated A. aegypti is block-bound, distant
dispersals likely will not affect local civic
conditions.
18
Resting behavior. Mosquitoes seek a dark quiet
place to rest such as under beds or in a closet.
They are in the house, rather than in the garden.
Most resting is on walls. This is one reason why
fumigants are effective.
19
Longevity. These mosquitoes can live for
months, yet usually survive only a few weeks.
Half of them could die in the first week, and 95
in the first month.
20
Containers including tires. Streams and ponds are
improbable oviposition sites for Aedes aegypti.
It is a container breeder. Females prefer to
deposit eggs just above the water level.
Universally, automobile and truck tires are the
main source of these mosquitoes.
21
Aedes Aegypti most common breeding places
22
Surveillance. Determine the
distributions and densities of populations, and
control program effects. Sampling includes
larval, adult and standard and sticky ovitrap
surveys. Control is usually by spray treatments
conducted by thermal foggers, mistblowers and
aerosol generators. They can be hand-carried or
used by backpack. Of course, they can be truck or
aircraft mounted. Thermophos (Abate) is a popular
larvicide.
23
Education. Sanitary (Public Health,
PH) education leading to low mosquito populations
by cleanup campaigns and the like, by public
action, is a necessary step. The public deserves
to know the risks it is under and how to reduce
them. The common schoolchild audience is the
answer to much of the propoganda problem? What is
the real problem?
24
Financing disease control depends on political
will. Partially, this will depends on better
educated populations that are attaining a higher
culture that allows them to demand a better
standard of living such as attaining piped water.
The better integrated clean communities do not
have the large mosquito populations that
container communities do.
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