The southern corn stalk borer [Diatraea crambidoides (Grote)] has become a serious pest to eastern gamagrass [Tripsacum dactyloides (L.) L.]. Managing this insect will be important to the future of this forage crop in the United States. An experiment was conducted to understand the life cycle of the southern corn stalk borer infesting eastern gamagrass. For a two year period, four plant crowns which contained numerous shoots were dug randomly each week from a field plot located in Woodward, OK. All shoots from each crown were dissected and the number of larvae and pupae present was recorded for each shoot type, i.e., reproductive or vegetative shoot. The life stages of the southern corn stalk borer in eastern gamagrass can be described by three distinct populations in northwestern Oklahoma: a) over-wintering, b) first generation, and c) second generation. Over-wintering larvae feed within a cavity near the base of the shoot or within the proaxis. Pupation occurred within the feeding cavity. Larvae occurred in reproductive shoots 2.5 times more often than in the vegetative shoots, which suggested an oviposition preference by adult females for reproductive shoots. The life cycle of the southern corn stalk borer in eastern gamagrass was completed in about 911 cumulated growing degree days. Understanding the life cycle of this insect devastating to eastern gamagrass forage and seed production will help formulate methods of control.