Aedes Aegypti (Click to select text)

Aedes Aegypti The mosquito that has attracted the most attention is the mosquito Aedes aegypti. It belongs to the family Culcidae, consisting of about 2,500 species (Encyclopedia Britanica 1999), along with other genera of mosquitoes such as Anopheles, Culex, Orthopodomyia, and the Toxorynchites, to name a few (Womack 1993, E.B. 1999). This mosquito has been known best for transmitting yellow fever and human dengue throughout the tropic and subtropic of the Americas (Womack, M 1993). This mosquito along with others are looked upon as pests and nuisances in modern day society because of their attraction to moisture, lactic acid, carbon dioxide, body heat and movement (E.B. 1999) but we can not confuse the Aedes aegypti with any other mosquito for it has a very distinct look to it as well as a specific habitat. It has many related species and it’s geographic distribution is extremely wide and varied. The Aedes aegypti, with regard to both sexes, are generally similar in coloration (Womack 1993). The female adult is noticed by it’s small dark figure that is colored by white markings and banded legs. Its proboscis or snout is mostly black with regard to the white palp tips (Russel 1996). The dorsal pattern of white scales on the scutum is in the shape of a ‘lyre’ with two central based stripes that contrast with the dark scales present on the insect (Womack 1993, Russel 1996). Its wings are dark scaled and femur and hind legs are pale scaled for about three-quarters, and dark scaled for about two-thirds (Russel 1996). The first through the fourth segments of the hind tarsi are characterized by white rings and the fifth segment is all white. Adults can be found in abundance in towns and cities near human dwelling places., living in trees, herbaceous plants, dim closets, cabinets or even old automobile tires (Womack 1993, Juliano 1998). The species feeds mostly during the day increasing its feeding rate two hours after sunrise and several hours before sunset ( Womack 1993, Geographical Magazine 1998), while it is not rare for females to feed under artificial light at night. The above feeding habits of the Aedes aegypti contributes to the species’ life span which is dependent on nutrition, temperature and humidity (Womack 1993) as well as its ability to avoid predators such as reptiles or even sometimes other types of mosquitoes (E.B. 1999). The male mosquito can only live a short time ranging from a few days to a couple weeks whereas the female can live up to a month which allows her to reproduce longer (Womack 1993). They lay their eggs in artificial containers on damp surfaces such as jars, urns, cans or anything that can contain rain water (Womack 1993, Juliano 1998). The eggs hatch when they become flooded by deoxygenated water, except during winter(Womack 1993, Juliano 1998) and after which can only survive in temperatures above ten degrees or below 44 degrees Celsius (Womack 1993). The larvae feed on aquatic microbiota which develops inside the artificial containers in which the eggs are laid (Womack 1993). In the pupal stage they are free swimming and active and breathe by means of tubes on the thorax (E.B. 1999). The limitations of availability of habitat has greatly affected the geographic distribution of the species. They have a “cosmopolitan range extending from 40 degrees N to 40 degrees S latitude.” says Womack (1993). It is found throughout the world in tropic and subtropic regions (Womack 1993). The species has been distributed throughout New England staying close to the marshes and damp areas and away from dry and cold climates. It is not only the dry and cold climates that threaten the Aedes aegypti but one of its associated species as well. The Aedes albopictus is an Asian mosquito that was introduced to North America in the 1980s (Hawley 1988, OMeara et al. 1992,1993,1995, Juliano 1998). It has spread throughout the north and now threatens declines in the Aedes aegypti because of its “positive population growth at higher combined density and lower per capita resource availability” (Juliano 1998). The A. albopictus is a successful invader because of its generalized habitat, its adaptation to many climates, ability to live in human dominated areas, as well as its food requirements and its desiccation resistant eggs (Hawley 1988, Focks et al. 1994, Juliano 1998). The “primary determinant of success” says Juliano (1998) “was survivorship to adulthood.” The Aedes aegypti only survived well in it’s environment when it was raised alone at a low density with a high resource availability (Juliano 1998). Competition for these resources among larvae is what seems to sufficient in accounting the near replacement of the A. aegypti with the A. albopictus. It is a species that lives to survive, feed and reproduce and although this may not seem difficult, Juliano has shown us that Darwin’s theory of evolution and natural selection is one that prevails in all species of organisms and in this battle the A. aegypti is losing to a fellow, more adapted mosquito the A. abopictus. Some other related species of the A. aegypti are the A. notoscriptus (Russel 1996), the A. triseriatus, A. atropalupus, Othopodomyia signifera, Toxorhynchites rutilis, Culex nigripalpus, Culex quinquefasciaus, Culex resuans, and Culex salinarius (Womack 1993). The A. aegytpi is a species best known for infecting people with such diseases as yellow fever and human dengue. Its life cycle is very simple compared to many other organisms. The female feeds on a blood diet to mature her eggs (E.B. 1999), and she lays them in a damp artificial container. The time for development of these eggs to mosquitoes is anywhere from four to ten days depending on the water temperature and the food supply (Womack 1993). Soon after the organism passes through the pupal stage they mate and start the cycle over again.