Recent entomological studies carried out in Sakai City, Osaka, Japan showed a high density of Culex pipiens complex. We performed PCR-based molecular identification of Cx. pipiens complex to show local distribution of the members of Cx. pipiens complex and variation of the species composition in Sakai City. CDC miniature suction traps without a lamp enhanced with 1 kg of dry ice were used to collect adult mosquitoes at 12 collection sites from April 2009 to March 2010. Among 1,591 Cx. pipiens complex collected in this study, 1,044 (65.6%) were identified as Cx. p. pallens, 474 (29.8%) were Cx. p. form molestus, 62 were hybrids between Cx. p. pallens and Cx. p. form molestus, and 3 were identified as Cx. quinquefasciatus. Culex p. pallens were not collected in winter from December 2009 to March 2010. Culex p. form molestus were not collected in January to March 2010. Hybrids between Cx. p. pallens and Cx. p. form molestus were not collected in December 2009 and January 2010. Culex quinquefasciatus was collected at 3 different collection sites in summer from July to September 2009. The Cx. pipiens complex composition was significantly different among 3 different categories of collection site.
