An Introduction to Medical Entomology
For educational purposes.
Please CLICK on underlined links to view:
[Also See: <Culicidae Key>]
Nematocera = "long antennae."
Culicidae. -- <Habits>; <Adults> & <Juveniles> -- The mosquitoes are identifiable by having scales present as patches on their wings. Only the female mosquito is capable of sucking blood. The eggs are laid in water and the pupae are capable of locomotion. Details on the subfamilies Anophelinae and Culicinae follow:
Anophelinae-- Anopheles spp.
The wings are spotted with definite patches of scales. Their feeding position is at a 45-degree angle with the surface. The aquatic larvae feed horizontal with the water film due to short terminal spiracles (See Photo). Members of the genus are the sole vectors of malaria. They have long palpi and the eggs are laid singly.
The wings are not spotted and mostly entirely clear. The feeding position angle is primarily horizontal with the surface. The aquatic larvae have developed an elongated siphon and feed hanging down from the water surface at an angle. Members of the genus include the common pest mosquitoes, which carry many viruses such as Yellow Fever, Dengue, Encephalomyelitis and the Filarial Worm. They have short palpi and the eggs are laid in masses.
There is disagreement about the number of genera in the subfamily, but Service (2008) listed 38 genera, assigning some to subgenus status. Of primary medical importance are Culex, Aedes, Haemagogus, Sabethes and Mansonia, with Coquillettidia and Psorophora of lesser importance. Culex, Aedes and Coquillettidia are found both in tropical and temperate climates while Psorophora are found only in the Americas with a wide distribution over many climates. Sabethes and Haemagogus are found only in Central and South America with Mansonia occurs in tropical portions only.
Service (2008) noted that members of the Aedes genus are vectors of Yellow Fever in Africa, while Aedes, Haemagogus and Sabethes are vectors of Yellow Fever in South and Central America. Some Aedes vector Dengue Fever, and all Culicinae may vector other arboviruses. Some Culex, Aedes and Mansonia are also vectors of Filariasis caused by Wuchereria bancrofti and Brugia malayi. Although some Psorophora vector arboviruses, most species are mainly annoying pests. Coquillettdia crassipes vectors Brugian Filariasis.
Culex spp. Biology
Many different aquatic habitats are chosen for oviposition onto rafts that float on the water. The Culex species tend to choose shallow habitats such as ditches, ricefields and temporary puddles, with even small containers and tree holes being adequate. Culex quinquefasciatus, the vector of Bancroftian Filariasis chooses polluted aquatic habitats containing rotting organic debris. Service (2008) noted that the larvae of this species also occur in ditches, blocked drains, septic tanks, etc. containing polluted water, and that it has adapted well to urbanization. The adults are especially active after sundown.
Other species of Culex, such as Cx. quinquefasciatus, bite during nighttime and may rest indoors as well as outside of dwellings.
Aedes spp. Biology
Many Aedes species in warm climatic areas choose restricted containers to oviposit, such as tree holes, small pools, tires, barrels, cans, etc. Service (2008) noted that Aedes aegypti breeds in water-storage containers both inside and outside of dwellings. The larvae require uncontaminated water for development. Aedes africanus, a vector of Yellow Fever, breeds in tree holes and bamboo while Aedes bromeliae also a vector of Yellow Fever, chooses leaf axils of banana, pineapple, etc. The vector of Dengue, Aedes albopictus, prefers natural and container habitats. Vectors of Filariasis, Aedes polynesiensis and Ae. pseudoscutellaris, develop in coconut shells or tree holes and bamboo. Aedes togoi, also a vector of Filariasis, prefers pools of fresh water among rocks.
Other Aedes species in colder climatic areas prefer pools formed from melting snow and marshlands.
Aedes mosquitoes are able to complete their development in only 7-12 days, depending on temperature. They are usually active in daytime and rest outdoors.
Haemagogus spp. Biology
Mosquitoes of the Haemagogus genus are restricted to South and Central America. Their eggs tolerate desiccation, and oviposition and larval development are primarily in tree holes and bamboo, but also in rock pools, coconut shells and occasionally in containers. But they are typically forest dwellers. The adults are active during the day feeding on simians in tree tops. However, they may descend to the ground during lumbering operations to attack humans. Several species, such as Haemagogus spegazzinii, Hg. leucocelaenus and Hg. janthinomys are vectors of Yellow Fever (Service 2008).
Sabethes spp. Biology
Sabethes mosquitoes are also restricted to South and Central America. Oviposition is in tree holes, bamboo and bromeliads, etc. They are also forest dwellers, which are active during daytime primarily in tree canopies. However, they will also descend when forced to by logging operations. Sabethes chloropterus is a vector of Yellow Fever.
Mansonia spp. Biology
Most species of Mansonia occur in tropical climates, with only a few being found in temperate regions. Oviposition is on the undersurface of vegetation where the eggs are glued. The eggs can tolerate desiccation. The larvae develop in permanent water that contains vegetation such as marshes and swamps. Irrigation canals with vegetation are also suitable.
The larvae and pupae remain attached to plants but will leave if disturbed, but they are difficult to detect. Most adults are active at night, with a few species also active during the day. Service (2008) reported that the medical concern is for Mansonia vectors of Filariasis, and rarely of some mild arboviruses.
Coquillettidia spp. Biology
Mosquitoes of the Coquillettidia genus are of minor medical importance in the tropics but only occasionally in temperate climates. Their eggs are formed onto rafts that float like the Culex species. The larvae are similar to Mansonia. Coquillettidia crassipes is a vector of Filariasis.
Psorophora spp. Biology
Psorophora mosquitoes, which range throughout the Americas, are also of minor medical importance. Like Aedes their eggs tolerate desiccation. Oviposition is in rice fields and flooded pastures. There are a few vectors of arboviruses, such as Venezuelan Equine Encephalitis, and Yellow Fever. Their importance is mainly as vicious biters (e.g. Psorophora ciliata, Ps. columbiae, Ps. cyanescens, Ps. ferox #1 & #2)
= = = = = = = = = = = = = = = = = = = =
Bock, G. R. & G. Cardew. 1996. Olfaction in Mosquito-Host Interactions. Chichester: Wiley Publ., England
Carpenter & Lacasse. 1955. Mosquitoes of North America.
Clark, G. G. 1994. Prevention of tropical diseases: status of new and emerging vector control strategies. Proc. Symp. Vector Control, Amer. J. Trop.
Med. & Hyg. 50(6): 1-159.
Clements, A. N. 1992. The Biology of Mosquitoes. Vol. 1: Development, Nutrition & Reproduction, Chapman & Hall, London.
Curtis, C. F. 1989. Appropriate Technology in Vector Control. CRC Press, Boca Raton, Florida.
Foster, W. A. & E. D. Walker. 2002. Mosquitoes (Culicidae). IN: Med. & Veterinary Ent.. Acad. Press, Amsterdam. pp. 203-62.
Matheson, R. 1950. Medical Entomology. Comstock Publ. Co, Inc. 610 p.
Service, M. 2008. Medical Entomology For Students. Cambridge Univ. Press. 289 p
Legner, E. F. 1995. Biological control of Diptera of medical and veterinary importance. J. Vector Ecology 20(1): 59-120.
Legner, E. F.. 2000. Biological control of aquatic Diptera. p. 847-870. Contributions to a Manual of Palaearctic Diptera, Vol. 1, Sci.
Herald, Budapest. 978 p.
Pates, H. & C. Curtis. 2005. Mosquito behavior and vector control. Ann. Rev. Ent. 50: 53-70.
Spielman, A. & M. d'Antonio. 2001. Mosquito: a Natural History of Our Most Persistent and Deadly Foe. Faber & Faber, London.