To better understand the distribution of Culex pipiens and Cx.
quinquefasciatus in Argentina, samples were collected from six
localities situated in a North-South line from Castelli (Chaco
Province) to Puerto Madryn (Chubut Province). Identification
was based on the morphology of male genitalia. Only Cx.
quinquefasciatus was found in Castelli and Esperanza, while in
Rosario, 95.3% belonged to this species and 4.7% represented
hybrid forms. Southern samples included only Cx. pipiens. With
the purpose of verifying if Cx. pipiens and Cx.
quinquefasciatus hybridize, different crosses between the two
species were performed. All crosses produced viable egg rafts.
Hatching ranged from 70 to 100%, except in one cross, female
Cx. pipiens x male Cx. quinquefasciatus, where a high
incompatibility was observed (11.1% hatch). The F1 hybrids
obtained from all crosses were fertile. The finding of hybrid
forms in nature can be interpreted as evidence for subspecific
status of Cx. pipiens and Cx. quinquefasciatus in Argentina.