Technical Abstract: Research considered the potential for optimizing the production of Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae) from Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) in 270-ml rearing trays. Trays containing 200 ml of artificial diet provided a very suitable environment for gregarious feeding and development of S. exigua immatures when 60 to 100 eggs were implanted into each tray. Production of C. marginiventris progeny via insertion of five parental pupae (in cocoons) into a tray provisioned with artificial diet and 80 S. exigua eggs was possible. But, waiting until S. exigua were late first to second instars and then inserting a single adult female in the tray resulted in greater production, including more female progeny. Female age affected production; 1 - 2d old or 8 - 9d old females generated more progeny, including more females, than 15 - 16d old females. Rates of parasitism and superparasitism of hosts did not differ between 6h versus 18h of exposure at a density of one parasitoid female per tray. However, both rates were significantly greater at a density of three rather than one female per tray in 18 h of exposure. The 270-ml rearing tray can be used for partial automated rearing of C. marginiventris. Of the different approaches tested, insertion of a single, mated, 1 - 2d old female into each rearing tray containing S. exigua late first to second instars might be the best approach to optimizing the production of progeny in this system.