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1. The mosquito vectors:
Aedes aegypti and
A. albopictus
Paul R. Earl
Facultad de Ciencias Biológicas
Universidad Autónoma de Nuevo León
San Nicolás, NL, Mexico
pearl@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).
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.
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.
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.
13. Mating.
Males are attracted by the sound of the
female’s wings. Mating often occurs in
flight or on surfaces like walls usually
before females have fed. The male clasps
the female’s 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.
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.
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.
