A new neotropical species of Aganaspis (Hymenoptera: Figitidae, Eucoilinae) is described and compared to other Aganaspis species occurring in the Neotropical Region. This thelytokous species was reared from pupae of 2 species of fruit flies in the genus Rhagoletis (Diptera: Tephritidae), both in the suavis species group, and collected from 2 species of native walnuts in Mexico. Evidence of host specialization through diapause timing and notes on basic biology are provided.