The mosquito vectors:Aedes aegypti andA. albopictusPaul R. EarlFacultad de Ciencias BiológicasUniversidad Autónoma de Nuevo LeónSan Nicolás, NL, Mexicopearl@dsi.uanl.mx
Distribution.Aedes aegypti, the yellow fevermosquito, that transmits dengue andother viruses has worldwidedistribution, and within the last 2decades A. albopictus, the Asian tigermosquito, has gained the Americaslike culex-carried West Nile fever alsohas. Prevention and control of diseasemay depend upon the level ofmosquito infestation, control andvigilance of the vector. See also M. J.Nelson (PAHO, 1986).
The world distribution of Aedes aegypti
By 1965, A. aegypti was eradicated byDDT from 17/49 countries and politicalunits of the Americas. However due tolack of determination before 1980, thishousehold mosquito was reestablishedeven in coastal Brazil and in Boliviawhere it had not been a problem for 27years. Ecuador and Panama have beendetermined to control reinfestations.Fortunately, a world ban on DDT hasrecently been defeated.
Aedes aegypti adult male
Aedes albopictus adult male
The life cycle:The eggs are about 1 mm long,cigarshaped and smooth. They arefertilized at the moment of oviposition anddeposited singly on the container wall justabove the water level.Embryonic development can take 2-3 days,sometimes 5. The eggs can then withstandbeing dry for perhaps a year. They willhatch promptly upon flooding. Eggs can betransported great distances and for longtimes in old car tires, soft drink containers,etc.
Life cycleof AedesAegypti
The larva.The larvas like the pupas areentirely aquatic. The larvas spendtheir time using fanshaped mouthbrushes to feed on bacteria andorganic matter found in thecontainers. An example is a vaseholding flowers.
The pupa.Pupas swim but do not feed. Thelarval form changes to the adultinsect, and changes in form are calledmetamorphosis. Pupas last 2-3 days.Aedes spp. pupas have shorttrumpets and a single hair at the tipof each swimming paddle. Strongsetae (see Figure) occur on theunderside of the corners of the 2-6thabdominal segments of Aedesaegypti, not on other members ofAedes.
The adult and emergence.The adult rests on the container walla few hours after emergence fromthe pupal case. The males rotate themale terminalia 180. Adult Aedesand other Culcicinae have shorterpalps than Anopheles. They are darkwith white bands. They rest parallelto surfaces. The male has longfeathered antenas as in otherculcicines and better developedpalps.
Mating. Males are attracted by the sound of thefemale’s wings. Mating often occurs inflight or on surfaces like walls usuallybefore females have fed. The male claspsthe female’s abdomen with his terminaliaand inserts his aedeagus into the genitalchamber. The bursa copulatrix of thefemale fills with sperm that pass into thespermathecae where they are stored. Oneinsemination will fertilize all the eggs afemale will have in her lifetime. Males arenot attracted by this sound once a femalehas fed since the wing beat is faster.
Feeding.Females feed on anyvertebrate host, but preferhumans. They fly upwindfollowing odors. The first stepcan be to enter a house.Blood feeding and ovipositionoccur mostly in the morningand in the late afternoon.
Gonadotropic cycle.If a female takes a complete blood meal of 2-3mg blood, she will produce a batch of about100 eggs in about 3 days. Stomach distentiontriggers ovarian development. Thus, smallerblood meals produce fewer eggs, and refeedingis encouraged, i. e., repeated biting by the samefemale occurs.The ovaries have tracheas that are air tubules.These branch into finer tracheoles. In parousfemales, a folicular relic appears on eachovariole. In this way, histological techniquehelp experts to judge the age of the population.Older populations having taken many bloodmeals have a greater potential for diseasetransmission.
Flight range.Although females usually do not flyfuther than 50 m, they can easily fly100-200 m, and can travel 3 km insearch for a site to oviposit in.Recall transport by cars, trucks,aircraft and even hurricanes.However, as domesticated A. aegyptiis block-bound, distant dispersalslikely will not affect local civicconditions.
Resting behavior. Mosquitoes seek a darkquiet place to rest such asunder beds or in a closet.They are in the house, ratherthan in the garden. Mostresting is on walls. This isone reason why fumigantsare effective.
Longevity. These mosquitoes can livefor months, yet usuallysurvive only a few weeks.Half of them could die inthe first week, and 95 %in the first month.
Containers including tires.Streams and ponds areimprobable oviposition sites forAedes aegypti. It is a containerbreeder. Females prefer todeposit eggs just above thewater level.Universally, automobile andtruck tires are the main sourceof these mosquitoes.
Aedes Aegypti: most common breeding places
Surveillance. Determine the distributions anddensities of populations, and controlprogram effects. Sampling includeslarval, adult and standard and stickyovitrap surveys.Control is usually by spray treatmentsconducted by thermal foggers,mistblowers and aerosol generators.They can be hand-carried or used bybackpack. Of course, they can be truck oraircraft mounted. Thermophos (Abate) isa popular larvicide.
Education.Sanitary (Public Health, PH)education leading to low mosquitopopulations by cleanup campaignsand the like, by public action, is anecessary step. The publicdeserves to know the risks it isunder and how to reduce them.The common schoolchild audienceis the answer to much of thepropoganda problem? What is thereal problem?
Financing disease control dependson political will. Partially, this willdepends on better educatedpopulations that are attaining ahigher culture that allows them todemand a better standard of livingsuch as attaining piped water. Thebetter integrated cleancommunities do not have the largemosquito populations thatcontainer communities do.