Culex restuans

Short description: Species of fly

Culex restuans

An adult male Cx. restuans resting on a flowering plant
Scientific classification
Kingdom:  | Animalia
Phylum:  | Arthropoda
Class:  | Insecta
Order:  | Diptera
Family:  | Culicidae
Genus:  | Culex
Subgenus:  | Culex
Species:  |

C. restuans

Binomial name
Culex restuans

Theobald, 1901

Culex restuans is a species of mosquito known to occur in Canada, the United States, Mexico, Guatemala, Honduras, and the Bahamas.[1][2] It is a disease vector for St. Louis encephalitis and West Nile virus.[3] In 2013 West Nile Virus positive specimens were collected in Southern California.[4][5]

## Contents

* 1 Taxonomy
* 2 Description
* 2.1 Adults
* 2.2 Larvae
* 3 Natural History
* 3.1 Life cycle, habitat, and oviposition behavior
* 3.2 Diet
* 4 Control Methods
* 5 References

## Taxonomy

Culex restuans is a mosquito, falling within the family Culicidae. It is a member of the tribe Culicini and the genus Culex. It is considered part of the Pipiens group and the Restuans species complex.[6]

## Description

### Adults

Culex restuans is a medium-sized brown mosquito, with adult female wing length ranging from 4 to 4.4mm.[7] It is occasionally called the "white-dotted mosquito", referring to two white dots sometimes found on the dorsal scutum.[8] This, however, is not a reliable character for identification because scales that constitute these spots can fall off and some adult mosquitoes eclose without these spots.[9] Without these distinctive white dots, this species looks very similar to another medically important Culex mosquito, Cx pipiens.[9]

A paper published in 2020 addresses the lack of reliable distinguishing characters between Cx. pipiens and restuans in reputable keys, and identified five characters that reliably distinguished these two species in their data set collected from Minnesota and Wisconsin.[10] The coloration and number of erect scales on the dorsal area of the head, number of setae on the upper thoracic proepisternum, coloration of prepostnotal setae, coloration of setae found on the mid-lobe of the scutellum, and coloration of wing remigial setae were all found to be reliable characters for distinguishing these two species in their data set.[10] More research needs to be done on Cx. pipiens and restuans populations throughout the United States before these characters can confidently be incorporated into a larger taxonomic key.[10]

### Larvae

Diagram of Culex restuans larval morphology.

Like other mosquito larvae, Cx restuans larvae are aquatic and swim by wiggling, which is why they are commonly referred to as "wigglers."[11] They are worm-like in appearance, with distinct brush-like mouthparts, a round thorax, abdominal segments with distinct lateral tufts of setae, and a siphon at the end of their abdomen which they use to breathe.[12] Cx restuans larvae can be recognized from other species of Culex from at least three long, individual setae on their siphon that are irregularly placed; siphon setae of other Culex species are found in groups or tufts.[13]

## Natural History

### Life cycle, habitat, and oviposition behavior

Like other dipterans, Cx. restuans is a holometabolous insect with egg, larval, pupal, and adult life stages. Gravid, blood-fed females lay egg rafts which float in standing water.[14] The quality of water does not matter much; larvae have been found in water that ranges from clean to polluted.[14] They go through four larval instars before pupating and then eclosing into adults; this process can take a minimum of 10 days in water with plenty of organic matter.[14]

Immature Cx. restuans are commonly found in small containers, with one notable example being discarded vehicle tires.[15] These are significant in regards to vector dynamics because of their usual proximity to human habitat and their ability to assist in expansion of mosquito range.[15]

Females have been found to decrease oviposition in containers with preexisting larvae of the same species and are more likely to lay eggs in nutrient-rich water sources, suggesting that females make oviposition-related decisions based on the future competition of their offspring.[16]

### Diet

Female Cx. restuans adults opportunistically feed mainly on birds, but will occasionally feed on mammals; this allows them to act as an enzootic vector in the West Nile virus transmission cycle.[17] Whether or not these mosquitoes bite humans is a controversial topic -- some say they bite humans often, but some say they are bird-feeders and rarely bite humans.[7][14]

The diet of Cx. restuans larvae remains largely unknown, but in the laboratory they are commonly fed on a diet that consists of ingredients like fish food, rabbit pellets, and liver powder.[18]

## Control Methods

For the control of medically important mosquito species like Cx. restuans in the United States, synthetic pyrethroids and organophosphates are the most commonly used adulticides; insect growth regulators like methoprene and bacteria such as Bacillus thuringiensis israelensis (Bti) and Lysinibacillus sphaericus are commonly used larvicides.[19][20][21]

Insecticide resistance in Cx. restuans populations is a prevalent problem facing vector control programs.[20] The Northeast Regional Center for Vector-Borne Disease reports widespread trends of low- and moderate-level insecticide resistance to methoprene in Culex spp. populations in the northeast United States.[20] Instances of moderate and high level resistance to pyrethroids have increased in recent years.[20]

Entomophthoraceae family, fungus Species Erynia conica infects (and kills) mosquitos Aedes aegypti and Culex restuans. Attempts are being made to use it as a biological control for the insect.[22]

## References

1. ↑ Strickman, D.; Darsie, R. F. Jr. (1988). "The previously undetected presence of Culex restuans (Diptera: Culicidae) in Central america, with notes on identification". Mosquito Systematics 20 (1): 21–27.
2. ↑ "Culex restuans Theobald, 1901 | Walter Reed Biosystematics Unit (WRBU)". https://www.wrbu.si.edu/vectorspecies/mosquitoes/restuans.
3. ↑ "Culex restuans" (in en). The Walter Reed Biosystematics Unit. http://www.wrbu.org/mqID/mq_medspc/AD/CXres_hab.html. Retrieved 2018-11-24.
4. ↑ Sandhu TS, Williams GW, Haynes BW, Dhillon MS. Population dynamics of blood-fed female mosquitoes and comparative efficacy of resting boxes in collecting them from the northwestern part of Riverside County, California. J Global Infect Dis [serial online] 2013 [cited 2013 Oct 22];5:15-8.
5. ↑ Sandhu TS, Williams GA, Haynes BW, Dhillon MS. Evaluation of arboviral activity at Northwest Mosquito and Vector Control District, Riverside County, California during 2008. Proc and Papers of the Mosq and Vector Control Assoc of Calif, vol 77, 2009. p. 108-15.
6. ↑ Harbach, Ralph E. (2011-10-01). "Classification within the cosmopolitan genus Culex (Diptera: Culicidae): The foundation for molecular systematics and phylogenetic research". Acta Tropica 120 (1): 1–14. doi:10.1016/j.actatropica.2011.06.005. ISSN 0001-706X. PMID 21741350. https://www.sciencedirect.com/science/article/pii/S0001706X11001884.
7. ↑ 7.0 7.1 Carpenter, Stanley J.; Casse, Walter J. La (1955) (in en). Mosquitoes of North America (north of Mexico). University of California Press. https://books.google.com/books?id=ngaod22BkUcC&q=restuans&pg=PA1.
8. ↑ "Species Culex restuans - White-dotted Mosquito". https://bugguide.net/node/view/60334.
9. ↑ 9.0 9.1 Harrington, Laura C.; Poulson, Rebecca L. (2008-01-01). "Considerations for Accurate Identification of Adult Culex restuans (Diptera: Culicidae) in Field Studies" (in en). Journal of Medical Entomology 45 (1): 1–8. doi:10.1093/jmedent/45.1.1. ISSN 0022-2585. PMID 18283935. https://academic.oup.com/jme/article-lookup/doi/10.1093/jmedent/45.1.1.
10. ↑ 10.0 10.1 10.2 Ferreira-de-Freitas, Lílian; Thrun, Nicholas B; Tucker, Bradley J; Melidosian, Lauren; Bartholomay, Lyric C (2020-11-01). "An Evaluation of Characters for the Separation of Two Culex Species (Diptera: Culicidae) Based on Material From the Upper Midwest". Journal of Insect Science 20 (6). doi:10.1093/jisesa/ieaa119. ISSN 1536-2442. PMID 33147340. PMC 7641446. https://doi.org/10.1093/jisesa/ieaa119.
11. ↑ CDC (2022-07-12). "Culex Mosquito Life Cycle | CDC" (in en-us). https://www.cdc.gov/mosquitoes/about/life-cycles/culex.html.
12. ↑ Carpenter, Stanley J.; Casse, Walter J. La (1955) (in en). Mosquitoes of North America (north of Mexico). University of California Press. https://books.google.com/books?id=ngaod22BkUcC&q=restuans&pg=PA1.
13. ↑ Andreadis, T. G.; Thomas, M. C.; Shepard, J. J. (2005). Identification Guide to the Mosquitoes of Connecticut. Connecticut Agricultural Experiment Station.
14. ↑ 14.0 14.1 14.2 14.3 "Mosquito Biology: Rutgers Center for Vector Biology". https://vectorbio.rutgers.edu/outreach/species/rest.htm.
15. ↑ 15.0 15.1 Yee, Donald A. (2008-07-01). "Tires as Habitats for Mosquitoes: A Review of Studies Within the Eastern United States: Table 1". Journal of Medical Entomology 45 (4): 581–593. doi:10.1093/jmedent/45.4.581. ISSN 0022-2585. https://doi.org/10.1093/jmedent/45.4.581.
16. ↑ Reiskind, Michael H.; Wilson, Mark L. (2004-03-01). "Culex restuans (Diptera: Culicidae) Oviposition Behavior Determined by Larval Habitat Quality and Quantity in Southeastern Michigan" (in en). Journal of Medical Entomology 41 (2): 179–186. doi:10.1603/0022-2585-41.2.179. ISSN 0022-2585. https://academic.oup.com/jme/article-lookup/doi/10.1603/0022-2585-41.2.179.
17. ↑ Apperson, Charles S.; Harrison, Bruce A.; Unnasch, Thomas R.; Hassan, Hassan K.; Irby, William S.; Savage, Harry M.; Aspen, Stephen E.; Watson, D. Wesley et al. (2002-09-01). "Host-Feeding Habits of Culex and Other Mosquitoes (Diptera: Culicidae) in the Borough of Queens in New York City, with Characters and Techniques for Identification of Culex Mosquitoes" (in en). Journal of Medical Entomology 39 (5): 777–785. doi:10.1603/0022-2585-39.5.777. ISSN 0022-2585. https://academic.oup.com/jme/article-lookup/doi/10.1603/0022-2585-39.5.777.
18. ↑ Kimura, Mari (2008). Understanding avian Plasmodium distribution: the role of vector and host (PhD thesis). Cornell University. Retrieved 2023-11-10.
19. ↑ CDC (2023-05-01). "Adulticides | CDC" (in en-us). https://www.cdc.gov/mosquitoes/mosquito-control/community/adulticides.html.
20. ↑ 20.0 20.1 20.2 20.3 Diseases, Northeast Regional Center for Excellence in Vector-Borne (2023-10-26). "Pesticide Resistance Monitoring Program" (in en-US). https://storymaps.arcgis.com/stories/dffd054adc84449aa801ad2396761f9d.
21. ↑ CDC (2020-08-24). "Larvicides | CDC" (in en-us). https://www.cdc.gov/mosquitoes/mosquito-control/community/larvicides.html.
22. ↑ Cuebas-Incle, E. L. (December 1992). "Infection of adult mosquitoes by the entomopathogenic fungus Erynia conica (Entomophthorales: Entomophthoraceae)". J Am Mosq Control Assoc 8 (4): 367–71. PMID 1474381.

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