A tremendous amount of research has been done on Culex mosquitoes, but much of the taxonomic work has been directed primarily toward discriminating species and not on organising them into natural groups. The result is that the classification of Culex is based on the intuitive interpretation of morphological similarity and few attempts have been made to resolve phylogenetic relationships using modern techniques.
The genus has a cosmopolitan distribution and includes 768 species divided among 26 subgenera. The current system of subgeneric classification is based primarily on external adult characters, especially features of the male genitalia. The species of the larger subgenera are arranged in informal classifications that variously include Sections, Series, Groups, Subgroups and Complexes. The infrasubgeneric categories are often based on superficial similarities that may not reflect natural relationships. In general, the larger the group, the less likely it is to be a monophyletic assemblage of species.
The complete classification of genus Culex is provided in the pdf below. Consult the individual subgenera in the drop-down list for information about their internal classification.