Genus Culex Linnaeus, 1758

Type species: 

Culex pipiens Linnaeus, 1758.

Classification: 

Subfamily Culicinae, tribe Culicini. Culex is a large and important genus of mosquitoes. It includes 769 species. Seven species are without subgeneric placement; the remainder are divided between 26 subgenera (number of species in parentheses): Acalleomyia (1), Acallyntrum (8), Aedinus (4), Afroculex (1), Allimanta (1), Anoedioporpa (12), Barraudius (4), Belkinomyia (1), Carrollia (18), Culex (200), Culiciomyia (54), Eumelanomyia (77), Kitzmilleria (1), Lasiosiphon (1), Lophoceraomyia (112), Maillotia (9), Melanoconion (160), Micraedes (8), Microculex (33), Neoculex (26), Nicaromyia (1), Oculeomyia (19), Phenacomyia (3), Phytotelmatomyia (4), Sirivanakarnius (1) and Tinolestes (3). The larger subgenera are arranged in informal classifications that variously include Sections, Series, Groups, Subgroups and Complexes (see Culex classification). Genus abbreviation – Cx.

Tanaka (2014, 2018), in a catalogue of the mosquitoes of Japan, listed Mochthogenes and Protomelanoconion (synonyms of subgenus Eumelanomyia) as subgenera of Culex without indication of formal change of status. He recognised Mochthogenes for Cx. hayashii and Cx. okinawae and Protomelanoconion for Cx. brevipalpis. However, simply listing long-accepted synonyms as valid taxa in a catalogue does not justify their formal recognition. Such taxonomic changes should be based explicitly on sound morphological evidence. This was done by Sirivanakarn (1971, 1972). Sirivanakarn (1971) synonymised Mochthogenes, which was recognised as a subgenus by Edwards (1932, 1941) and King & Hoogstraal (1947), with Eumelanomyia, and transferred the Protomelanoconion Group from subgenus Neoculex to Eumelanomyia. Sirivanakarn (1972) then revised Eumelanomyia based on comparative morphological study of adult, larval and pupal stages, and established an internal classification that included Cx. hayashii as a member of the Tenuipalpis Subgroup and Cx. okinawae as a member of the Okinawae Subgroup of a larger Mochthogenes Group; and included Cx. brevipalpis as a member of the Protomelanoconion Group. In the absence of more recent comparative study and justification, Mochthogenes and Protomelanoconion must remain synonyms of Eumelanomyia, with Cx hayashii, Cx. okinawae and Cx. brevipalpis classified with morphologically similar species in subgroups of the Mochthogenes Group.

Characteristics: 

Culex adults are usually drab, unicolorous mosquitoes, but some species of the subgenus Culex have markings on the legs and pale spots on the wings similar to Anopheles. Culex are characterised by the presence of distinct pulvilli and the absence of prespiracular setae and postspiracular setae (the latter are present in Australian Cx. postspiraculosus). These characters, however, will not distinguish Culex from Deinocerites, Galindomyia and Lutzia. Culex differs from Deinocerites and Galindomyia in having the apical flagellomere of the antenna much shorter than the first flagellomere, and differs from Lutzia in having few (usually one) lower mesepimeral setae. Culex larvae are distinguished from other genera by the following characters: seta 2-C usually absent; seta 3-C located on dorsal side of head, sometimes absent; palatal brushes normal, not developed for grasping prey; mandible normal, without lateral lobe at base; maxillary brush present, well developed; seta 12-I and comb always present; siphon with three or more pairs of prominent setae (seta 1-S); pecten normally present; saddle usually complete, sometimes incomplete and greatly reduced but never divided into dorsal and ventral sclerites or longer than the siphon; ventral brush (seta 4-X) usually with three or more pairs of setae. See Culicini.

Phylogenetic relationships: 

Belkin (1962) indicated that the affinities of the subgenera of Culex were obscure, but surmised that Lutzia is an ancient derivative that appears to have a strong affinity with subgenus Culex. It is generally assumed that the Melanoconion Group of subgenera, i.e. Aedinus, Anoedioporpa, Belkinomyia, Carrollia, Melanoconion, Micraedes, Microculex and Tinolestes, includes the most derived mosquitoes of the genus (Belkin, 1968; Berlin, 1969; Adames & Galindo, 1973; Sirivanakarn, 1983). Sirivanakarn (1983) noted that Melanoconion shares several anatomical features with the “more primitive” and widespread subgenus Neoculex, suggesting that an offshoot of Neoculex may have given rise to the Melanoconion Group. Valencia (1973) suggested that Carrollia and the closely related Deinocerites and Galindomyia share a similar evolutionary history as derivatives from a primitive stock of subgenus Melanoconion. Miller et al. (1996) used sequence divergence in the ITS1 and ITS2 regions of rDNA to infer relationships between 14 species representing four subgenera of Culex. Neighbour-joining analyses produced a tree (rooted on Melanoconion) that supported the notion that Melanoconion bears a number of resemblances with Neoculex, and Lutzia shares an ancestry with subgenus Culex

Navarro & Liria (2000) conducted a parsimony analysis of 30 characters of larval mouthparts (mandibles and maxillae) to infer the phylogenetic relationships of Deinocerites and seven subgenera of Culex. The phylogeny indicated that Lutzia and Culex formed distinct monophyletic clades, with Lutzia being the more primitive of the two. Although only New World species were included in the analysis, members of the Melanoconion Group formed a distinct monophyletic clade in a sister-group relationship with subgenus Culex. It is interesting to note that this clade included Deinocerites in an unresolved polytomy with Anoedioporpa, Melanoconion and Microculex in a derived position relative to Carrollia.

Vesgueiro et al. (2011) used ITS2 sequences and neighbor-joining to infer the relationships of 17 Neotropical species representing genus Lutzia (1 species) and subgenera Culex (9 species), Microculex (1 species), Melanoconion (5 species) and Phenacomyia (1 species). In a companion study, Demari-Silva et al. (2011) used a 478-bp fragment of the COI gene and Bayesian methodology to assess the relationships of the same 17 species (and a species of subgenus Carrollia). The species of Lutzia was placed among species of genus Culex in both studies. In the neighbor-joining tree of Vesgueiro et al., Lutzia and Phenacomyia were placed in a clade among species of subgenus Culex. In the Bayesian analysis of Demari-Silva et al., Lutzia was recovered as the sister of a clade comprised of subgenera Culex and Phenacomyia. Harbach et al. (2012) explored relationships among taxa of Culicini using 169 morphological characters from 86 exemplar species representing the four genera and 26 subgenera of Culicini, most species groups and subgroups of subgenus Culex and an outgroup of five species from five other tribes. As in previous phylogenetic studies based on morphology (Navarro et al., 2000; St John, 2007; Laurito & Almirón, 2013), Lutzia was recovered as a clade separate from Culex. However, genus Culex was not recovered as monophyletic because it included Deinocerites and Galindomyia as derived members of the New World subgenera. With the exception of subgenera Culex, Eumelanomyia and Neoculex, there was strong support for the monophyly of all subgenera. They noted that subgenus Culex would be monophyletic if it did not include the Afrotropical Cx. duttoni, the Neotropical Cx. apicinus and the Australasian Atriceps Group. Based on a series of comparative and data exclusion analyses of the data set of Harbach et al. (2012) and a critical examination of the results of other phylogenetic studies, Kitching & Harbach (2015) concluded that no morphological or molecular data set analysed in any previously published study has adequate signal to place Lutzia unequivocally with regard to other taxa in Culicini.

Harbach et al. (2016) recently critically analysed a morphological data set comprised of 286 characters of the larval, pupal and adult stages of 150 species of subgenus Culex and an outgroup of 17 species representing genus Lutzia, 11 other subgenera of Culex and tribes Aedini, Culisetini and Sabethini. Unlike the results of previous analyses of morphological data that placed Lutzia outside genus Culex (Harbach et al., 2012; Navarro & Liria, 2000; St John, 2007; Laurito & Almirón, 2013), the more stringent assessment of clade support applied in their study indicated, in agreement with Kitching et al. (2015), that the placement of Lutzia relative to Culex based on morphology is highly equivocal.

Bionomics and disease relations: 

Culex larvae occur primarily in semi-permanent or permanent bodies of ground water, but a large number of species live exclusively in leaf axils, tree-holes, rock-holes and crab-holes. Some utilise artificial containers as well as the normal ground-water habitats. A few species, including the filarial vector Cx. quinquefasciatus, are found in organically polluted waters. Culex females mainly bite at night. Many species attack humans and other mammals. Some species are known to feed on birds and some are known to feed on amphibians and reptiles.

Several species of subgenera Culex and Melanoconion are of medical importance. Melanoconion mainly occurs in the Neotropical Region, with some species reaching northward into the USA. Several species of the subgenus are important vectors of encephalitis and other arboviruses. Subgenus Culex has species in all zoogeographic regions, and contains most of the medically important and pest species of the genus. Culex fuscocephala, Cx. tritaeniorhynchus, Cx. gelidus and Cx. vishnui transmit Japanese encephalitis virus in the Oriental Region and Cx. tarsalis, Cx. nigripalpus, Cx. restuans and Cx. pipiens are recognised vectors of encephalitis viruses in North America. Murray Valley encephalitis and Ross River viruses in Australia are spread by Cx. annulirostris. Three closely related species, Cx. univittatus, Cx. neavei and Cx. perexiguus, transmit West Nile fever virus in Africa. Rift Valley fever virus is transmitted by Cx. pipiens in Egypt and Cx. theileri in southern Africa. A few species of the subgenus, especially Cx. quinquefasciatus, are important vectors of Wuchereria bancrofti in the tropics. Culex pipiens and Cx. antennatus are important vectors of filarial worms in Egypt. Some species of the genus may be involved in the transmission of Brugia malayi.

Distribution: 

Species of Culex occur in all zoogeographical regions. They range from the tropics to cool temperate regions, but do not extend to the extreme northern latitudes where only Aedes and Ochlerotatus occur.

Principal references: 

Barraud, 1934 (southern Asia); Edwards, 1941 (adults, Afrotropical Region); Hopkins, 1952 (larvae, Afrotropical Region); Lane, 1953 (Neotropical Region); Mattingly & Knight, 1956 (Arabia); Belkin, 1962 (taxonomy, South Pacific); DuBose & Curtin, 1965 (keys, Mediterranean area); Forattini, 1965a (Neotropical Region); Cova-Garcia et al., 1966 (Venezuela); Delfinado, 1966 (Philippines); Bram, 1967 (Thailand); Bram, 1967 (subgenus Culex, New World); Belkin, 1968 (New Zealand); Sirivanakarn, 1968 (subgenus Lophoceraomyia); Belkin et al., 1970 (Jamaica); Sirivanakarn, 1971, 1972, 1976, 1977 (various subgenera, Oriental Region); Valencia, 1973 (subgenus Carrollia); Gutsevich et al., 1974 (former USSR); Tanaka et al., 1979 (Japan); Wood et al., 1979 (Canada); Berlin & Belkin, 1980 (subgenera, Neotropical Region); Ribeiro & da Cunha Ramos 1980 (Angola); Darsie & Ward, 1981, 2005 (keys, North America); Lu & Li, 1982 (China); Clark-Gil & Darsie, 1983 (keys, Guatemala); Sirivanakarn, 1983 (subgenus Melanoconion); Darsie, 1985 (keys, Argentina); Lu & Su, 1987 (China); Lee et al., 1988, 1989a, 1989b (Australasian Region); Harbach, 1988 (subgenus Culex, southwestern Asia and Egypt); Darsie & Pradhan, 1990 (Nepal); Harbach & Peyton, 1992 (subgenus Phenacomyia); Pecor et al., 1992 (subgenus Melanoconion); Rattanarithikul & Panthusiri, 1994 (keys, medically important species, Thailand); Reuben et al., 1994 (keys, Japanese encephalitis vectors, Southeast Asia); Sallum & Forattini, 1996 (Spissipes Section, subgenus Melanoconion); Lu Baolin et al., 1997 (China); González Broche & Rodríguez R., 2001 (subgenus Nicaromyia); Tanaka, 2004 (subgenera, Oculeomyia and Sirivanakarnius); Rattanarithikul et al., 2005a, 2005b (keys, Thailand); Rossi & Harbach, 2008 (subgenus Phytotelmatomyia); Vesgueiro et al., 2011 (phylogeny); Demari-Silva et al., 2011 (phylogeny); Harbach et al., 2012 (phylogeny).

Species - Subgenus uncertain: 
Nomina dubia

aikenii Aiken & Rowland, 1906
americanus Neveu-Lemaire, 1902
barkerii (Theobald, 1907)
bernardi (Borel, 1926)
chrysothorax Peryassú, 1908
chrysothorax Newstead & Thomas, 1910
decorator Dyar & Knab, 1906
epirus Aiken, 1909
fasciolatus Lutz, 1904 (in Bourroul, 1904)
gravitator Dyar & Knab, 1906
humilis Theobald, 1901
indecorabilis Theobald, 1903
lugens Lutz, 1905
maculatus (von Humboldt, 1819)
microtaeniata Theobald, 1911
mindanaoensis Baisas, 1935
molestus Kollar, 1832 (in Pohl & Kollar, 1832)
nigrescens Theobald, 1907
nigricorpus Theobald, 1901
novaeguineae Evenhuis, 1989 (in Evenhuis & Gon, 1989)
oblita Lynch Arribálzaga, 1891
pallipes Robineau-Desvoidy, 1827
suborientalis Baisas, 1938
ventralis Walker, 1865
virgultus Theobald, 1901
vulgaris Linnaeus, 1792

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith