Abstract Teratocytes may control the physiology of the host and/or have trophic or secretory functions that may nutritionally affect the development of their associated parasitoid. The importance of these cells for the development of parasitoids in artificial diets has been investigated and in some cases they have been shown to improve the growth and development of such species. However, little attention has been directed to the functions that teratocytes from egg parasitoids may have on the interactions with the host. We developed an improved artificial medium to culture teratocytes of Trissolcus basalis (Woll.) as a tool to understand their role during parasitoid development. Teratocytes cultured in an insect cell medium supplemented with host-derived components achieved the same size as those reported developing in the natural host. We also found that these cells do not require components derived from the reproductive apparatus of parent females or from the developing larva of the parasitoid for their normal development. However, they require low- ( 100-kDa) molecular-weight host-derived components to fully grow. Both molecules are proteinaceous, and the high-molecular-weight components were identified as vitellin. The low-molecular-weight components were identified as peptides, and they are in the process of being isolated and identified. We also discuss the possible interactions between the teratocytes and the host and their combined role in the development of the parasitoid.