Breeding populations of Ochlerotatus japonicus japonicus, 1st detected in 1998, are now found in several states in the United States. To be able to identify this mosquito with the keys to the mosquitoes of North America north of Mexico, changes are proposed, especially dealing with the new genus Ochlerotatus. Also, a checklist of the genera Ochlerotatus and Aedes in the Nearctic Region is given.