| Nototrachys annulicornis Ashmead, 1890 |
| Nuneches Förster, 1869 |
| Nythobia Förster, 1869 |
| Occia Tosquinet, 1903 |
| Occia elegans (Cresson, 1874) |
| Ochlerus Gistel, 1848 |
| Ocymorus Förster, 1869 |
| Odontagrypon Cameron, 1906 |
| Odontojoppa Cameron, 1903 |
| Odontopimpla Cameron, 1886 |
| Odontopimpla armatipes Cameron, 1911 |
| Odontopimpla fasciata (Brullé, 1846) |
| Odontopimpla laevigata (Smith, 1879) |
| Odontopimpla pulcherrima (Cresson, 1874) |
| Oedematopsis Morley, 1908 |
| Oedemopsis Tschek, 1868 |
| Oedemopsis davisi Carlson, 1979 |
| Oedemopsis nasuta (Cresson, 1868) |
| Oedicephalopsis Heinrich, 1930 |
| Oedicephalus Cresson, 1868 |