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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.
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The mosquito vectors: Aedes aegypti and A. albopictusPaul R. EarlFacultad de Ciencias BiológicasUniversidad Autónoma de Nuevo LeónSan Nicolás, NL, Mexico pearl@dsi.uanl.mx
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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?
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.
