Biological control of stalkboring Lepidoptera often has been successful when the braconid parasitoids in the genera Cotesia and Apanteles were the natural enemies of choice. Constraints in using these gregarious, koinobiont, endoparasitoids have included host suitability, especially as influenced by the host's immune response. The suitability of a novel host, the New World stalkborer Diatraea considerata (Lepidoptera: Pyralidae), for parasitization by three Old World braconids, Cotesia chilonis, C. flavipes and C. sesamiae (Hymenoptera: Braconidae), was compared to the suitability of another New World novel host, Diatraea saccharalis. D. considerata was less suitable for all three parasitoids than was D. saccharalis. The frequent occurrence of parasitized D. considerata larvae that did not yield parasitoids, or pupate within an appropriate time interval, suggested encapsulation of the parasitoid progeny, which was visible through the host cuticle. Given the suitability results, these three parasitoids would not be appropriate candidates for use against D. considerata. The results also have important implications for the narrow host range expressed by these parasitoids. none