The dryinid wasp Gonatopus bonaerensis Virla is a planthopper parasitoid in Argentina. In Las Talitas (Tucumán) was found attacking Delphacodes sitarea Remes Lenicov et Tesón and D. latus Remes Lenicov et Tesón between last winter and the beginning of autumn. The aim of this contribution is to study the life cycle and behavior of this parasitoid. G. bonaerensis was successfully bred on Delphacodes kuscheli Fennah, Toya propinqua (Fieber), Peregrinus maidis (Ashmead) and Dicranotropis sp., but was not able to parasitize Dalbulus maidis De Long & Wolcottt (Cicadellidae). Delphacodes kuscheli, T. propinqua and P. maidis are well-known cereal’s disease vectors. Gonatopus bonaerensis is a solitary and anautogenous species, with telythokic parthenogenesis. Oviposition and development of the first four larval stages take place on the abdomen of its hosts, protruding in well-formed "larval sacs"; the mature larva abandon the host to find a place where pupate. The life cycle, at 23.5 °C, lasts around 23 days. Some biologic characteristics encourage studies to verify the potential of this parasitoid as a candidate for the biological control of planthopper vectors.