The genus Agrostocynips Diaz is redescribed, as well as two species endemic to the Nearctic: Agrostocynips diastrophi (Ashmead) and A. robusta (Ashmead). Previous to this study, only Neotropical species of Agrostocynips were well diagnosed both taxonomically and biologically. Agrostocynips belongs to the Zaeucoila group of genera, which are Neotropical eucoilines that principally parasitize Agromyzidae (Diptera); among these genera, species of Agrostocynips are some of the few representatives that are found in the Nearctic. Detailed host records and biological notes are provided for the Nearctic species.
