A key is presented for the recognition of adu Its of the twenty one species of Culícoídes occurrying in the area of the Yacyretá dam lake, located in the Paraná river, between Angentina and Paraguay. The following ten species are recorded for the first time for the studied area: C. aureus, C. charrua, C. cuiabai, C. gabaldoni, C. guttatus, C. horticola, C. ignacioi, C. limai, C. lutzi, and C. pusillus.