Culex

For other uses, see Culex (disambiguation).
Culex
Culex sp. male
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Diptera
Family: Culicidae
Subfamily: Culicinae
Genus: Culex
Linnaeus, 1758
Diversity
Over 1000 species
Anatomy of a Culex larva
Anatomy of a Culex adult

Culex is a genus of mosquitoes, several species of which serve as vectors of one or more important diseases of birds, humans and other animals. The diseases they vector include arbovirus infections, West Nile virus, filariasis, Japanese encephalitis, St. Louis encephalitis, and avian malaria. They occur worldwide except for the extreme northern parts of the temperate zone, and are the most common form of mosquito encountered in some major US cities such as Los Angeles.

Etymology

In naming this genus, Carl Linnaeus appropriated the non-specific Latin term for a midge or gnat: culex.[1]

Description

Depending on the species, the adult Culex mosquito may measure from 4–10 mm (0.2–0.4 in). The adult morphology is typical of flies in the suborder Nematocera with the head, thorax, and abdomen clearly defined and the two fore wings held horizontally over the abdomen when at rest. As in all Diptera capable of flight, the second pair of wings are reduced and modified into tiny, inconspicuous halteres.

Formal identification is important in mosquito control, but it is demanding and requires careful measurements of bodily proportions and noting the presence of absence of various bristles or other bodily features.[2]

In the field informal identification is more often important, and the first question as a rule is whether the mosquito is anopheline or culicine. Given a specimen in good condition, one of the first things to notice is the length of the maxillary palps. Especially in the female, palps as long as the proboscis are characteristic of anopheline mosquitoes. Culicine females have short palps. Anopheline mosquitoes tend to have dappled or spotted wings, while Culicine wings tend to be clear. Anopheline mosquitoes tend to sit with their heads low and their rear ends raised high, especially when feeding, while Culicine females keep their bodies horizontal.

Anopheline larvae tend to float horizontal at the surface of the water when not in motion, whereas culicine larvae float with head low and only the siphon at the tail held at the surface.

Lifecycle

The developmental cycle of most species takes about two weeks in warm weather. The metamorphosis is typical of holometabolism in an insect: The female lays eggs in rafts of as many as 300 on the water's surface. Suitable habitats for egg-laying are small bodies of standing fresh water: puddles, pools, ditches, tin cans, buckets, bottles, and water storage tanks (tree boles are suitable for only a few species). The tiny cigar-shaped dark brown eggs adhere to each other through adhesion forces, not any kind of cement, and are easily separated. Eggs hatch only in the presence of water and the larvae are obligately aquatic, linear in form, and maintain their position and mostly-vertical attitude in water by movements of their bristly mouthparts. To swim, they lash the body back and forth through the water.[3][4]

During the larval stage, the insect lives submerged in water and feeds on particles of organic matter, microscopic organisms or plant material; after several instars it then develops into a pupa. Unlike the larva, the pupa is comma-shaped. It does not feed, but can swim in rapid jerking motions to avoid potential predators. It must remain in regular contact with the surface in order to breathe, but it must not become desiccated. After 24-48 hours the pupa ruptures and the adult emerges from the shed exoskeleton.

Vector role

Diseases borne by one or more species of Culex mosquitoes vary in their dependence on the species of vector. Some are rarely and only incidentally transmitted by Culex species, but Culex and closely related genera of culicine mosquitoes readily support perennial epidemics of certain major diseases if they become established in a particular region.

Nonanal has been identified as a compound that attracts Culex mosquitoes, perhaps pheromonally.[6][7][8] Nonanal acts synergistically with carbon dioxide.[9]

Diversity

Main article: List of Culex species
Culex malariager in amber

Culex is a diverse genus. It comprises over twenty subgenera that include a total of well over a thousand species. Descriptions of additional species are frequent.

References

  1. ↑ "culex". dictionary.com. Retrieved 2011-07-06.
  2. ↑ Harbach, Ralph. "Culex Mosquito Taxonomic Inventory".
  3. ↑ "Mosquito Ecology and Surveillance Laboratory". Retrieved 7 August 2014.
  4. ↑ Mike Service (21 February 2008). Medical Entomology for Students. Cambridge University. pp. 53–54. ISBN 978-0-521-70928-6.
  5. ↑ "Brazilian experts investigate if 'common mosquito' is transmitting zika virus". March 27, 2016. Retrieved 2016-03-07.
  6. ↑ "UC Davis Researchers Identify Dominant Chemical That Attracts Mosquitoes to Humans". University of California, Davis. October 26, 2009. Retrieved 2011-07-06.
  7. ↑ Syed, Z.; Leal, W. S. (2009). "Acute olfactory response of Culex mosquitoes to a human- and bird-derived attractant". Proceedings of the National Academy of Sciences. 106 (44): 18803–8. doi:10.1073/pnas.0906932106. PMC 2767364Freely accessible. PMID 19858490.
  8. ↑ Hill, Sharon R.; Hansson, Bill S.; Ignell, Rickard (January 15, 2009). "Characterization of Antennal Trichoid Sensilla from Female Southern House Mosquito, Culex quinquefasciatus Say". Chemical Senses. Oxford University Press. 34 (3): 231–252. doi:10.1093/chemse/bjn080. PMID 19153252.
  9. ↑ "Scientists Identify Key Smell that Attracts Mosquitoes to Humans". U.S. News & World Report. October 28, 2009. Retrieved 2011-07-06.
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