Culex mosquitoes are widely distributed in tropical and temperate parts of the world. Approximately 770 species of Culex mosquitoes have been described, several of which serve as vectors of agents that cause disease in birds, humans, and other animals. West Nile virus, Japanese encephalitis, St. Louis encephalitis, filariasis and avian malaria can all be transmitted by Culex species[1, 2, 3].

Biology
Like all mosquitoes, Culex go through four stages in their life cycle: egg, larva, pupa, and adult. Culex eggs are laid upright in distinct rafts on the surface of the water. Rafts can contain up to 300 eggs. Culex larvae have a siphon tube at their posterior end, through which they breathe, and they filter feed on microorganisms at the water surface or scrape biofilms from underwater rocks and vegetation[4].

Habitat
The larval habitats of Culex mosquitoes include pools, puddles, ditches, borrow pits, rice fields, pit latrines and treeholes. Culex quinquefasciatus tends to lay eggs in anaerobic waters, which means their larvae are under less risk from aquatic predators[4]. They are also associated with turbid waters, while Cx. tritaeniorhynchus larvae are often found in rice fields, grassy pools and fish ponds[5].

Distribution
Culex species are widely distributed around the world but are absent from extreme northern parts of temperate zones. Culex quinquefasciatus is present mainly across tropical and subtropical regions, while Cx. pipiens pipiens is present across more temperate regions, including parts of North and South America, the Middle East, Africa and Asia. There is some overlap in the distribution of this species with Cx. quinquefasciatus in North America[6].

Biting Behaviours
Adult Culex mosquitoes feed on a range of hosts, including humans and domestic animals, and birds. Feeding on birds has important implications for the transmission of West Nile virus, as avians can act as reservoir hosts[7,8].

Different species within the genus show different feeding and resting habits. Culex pipiens f. molestus are endophilic (rest indoors), while Cx. pipiens pipiens is an exophilic species (rest outdoors). Members of the Cx. vishnui subgroup are known to rest and feed outside[9].

 

References

  1. Turell MJ. Members of the Culex pipiens Complex as Vectors of Viruses1. Journal of the American Mosquito Control Association. 2012 Dec;28(4s):123
    https://bioone.org/journals/Journal-of-the-American-Mosquito-Control-Association/volume-28/issue-4s/8756-971X-28.4.123/Members-of-the-span-classgenus-speciesCulex-pipiens-span-Complex-as/10.2987/8756-971X-28.4.123.short

  2. Mak JW. Epidemiology of lymphatic filariasis. InCiba Found Symp 1987 Apr 22 (Vol. 127, No. 1, pp. 5-14).
    https://doi.org/10.1002/9780470513446.ch2

  3. Kimura M, Darbro JM, Harrington LC. Avian malaria parasites share congeneric mosquito vectors. Journal of Parasitology. 2010 Feb;96(1):144-52.
    https://bioone.org/journals/Journal-of-Parasitology/volume-96/issue-1/GE-2060.1/Avian-Malaria-Parasites-Share-Congeneric-Mosquito-Vectors/10.1645/GE-2060.1.short

  4. Roberts D. Mosquito larvae change their feeding behavior in response to kairomones from some predators. Journal of medical entomology. 2014 Mar 1;51(2):368-74.
    https://academic.oup.com/jme/article-abstract/51/2/368/882256

  5. Service, M. Medical entomology for students. 5th edition. Cambridge University Press, Cambridge. Pages 55-57; 2012.

  6. Farajollahi A, Fonseca DM, Kramer LD, Kilpatrick AM. “Bird biting” mosquitoes and human disease: a review of the role of Culex pipiens complex mosquitoes in epidemiology. Infection, genetics and evolution. 2011 Oct 1;11(7):1577-85.
    https://www.sciencedirect.com/science/article/pii/S1567134811002929

  7. Julian EG, Bradley JB, Jose AF, Maria AL, Wilberth AC, Luis FF, Elsy RP, Carlos BB, Jose PM, Victor SS, Ildefonso FS. Host-feeding preference of the mosquito, Culex quinquefasciatus, in Yucatan State, Mexico. Journal of insect Science. 2010 Jan 1;10(1):32.

  8. Brugman VA, Hernández-Triana LM, Medlock JM, Fooks AR, Carpenter S, Johnson N. The role of Culex pipiens L.(Diptera: Culicidae) in virus transmission in Europe. International journal of environmental research and public health. 2018 Feb;15(2):389.
    https://www.mdpi.com/1660-4601/15/2/389

  9. Das BP, Lal S, Saxena VK. Outdoor resting preference of Culex tritaeniorhynchus, the vector of Japanese encephalitis in Warangal and Karim Nagar districts, Andhra Pradesh. Journal of vector borne diseases. 2004;41(1/2):32.
    http://mrcindia.org/journal/issues/411032.pdf