| Oestrophasia Brauer & Bergenstamm, 1889 |
| Oestrophasia calva Coquillett, 1902 |
| Oestrophasia signiferum (Wulp, 1890) |
| Okeopsis Townsend, 1927 |
| Ophirion Townsend, 1911 |
| Ophirion atlixcoensis (Reinhard, 1975) |
| Ophirionini Townsend, 1913 |
| Opsomeigenia Townsend, 1919 |
| Opsomeigenia epilachnae (Aldrich, 1923) |
| Ormia Robineau-Desvoidy, 1830 |
| Ormia bilimekii (Brauer & Bergenstamm, 1889) |
| Ormia ochracea (Bigot, 1889) |
| Ormia rufa (Wulp, 1890) |
| Ormiini Townsend, 1915 |
| Oswaldia Robineau-Desvoidy, 1863 |
| Oswaldia immissa (Reinhard, 1959) |
| Oxapampoepalpus Townsend, 1931 |
| Oxydexia Bigot, 1885 |
| Oxynops Townsend, 1912 |
| Oxynops anthracinus (Bigot, 1889) |