none This study describes the effects of host species and size on larval competition, survival and development in the gregarious parasitoid, Bracon hebetor Say (Hymenoptera: Braconidae). Wasp eggs were placed at a range of densities on three sizes of two host species--Anagasta kuhniella (Zeller) and Plodia interpunctella (Huebner) (Lepidoptera: Pyralidae)--and the number, sex, size, and date of emergence of emerging adults were recorded. Survival was lower on small hosts of both species, independent of density. In addition Plodia hosts from some cultures were unsuitable (produced no parasitoids), independent of size and density. Development time was unaffected by egg density or host size, and only very slightly by host species.