The maize billbug [Sphenophoris maidis (Chittenden)] feeds on eastern gamagrass [Tripsacum dactyloides (L.) L.] causing economic damage. The incidence of maize billbug was studied in a six-year-old eastern gamagrass field plot, and cumulative growing degree-days (cGDD) were calculated for the morphological stages of the pest for two years. The adult population was more abundant and distributed throughout the year compared to larvae and pupae. On the basis of growing degree-days, the 99% quantile for larvae, pupae, and adult maize billbug population was estimated between 1396-1908 cGDD. Very few pupae were recovered from field sampling, which may be due to its short pupation period and weekly sampling interval. Findings of this study will be helpful to formulate sustainable maize billbug management strategies.