The seasonal occurrences of Macrocentrus cingulum Brischke and its host, Ostrinia nubilalis Hübner, were studied. Overwintering fifth-instar O. nubilalis were collected from the field in 1997, 1998, 2001, and 2002 and reared under controlled laboratory conditions to determine pupation and adult eclosion periods for M. cingulum and O. nubilalis. In addition, pheromone and yellow sticky traps were established in the field in 2001 and 2002 to monitor adult activity of O. nubilalis and M. cingulum. Mathematical equations were constructed based on the laboratory and field data. The equations confirmed the temporal co-occurrence of M. cingulum and O. nubilalis adults. However, third- and fourth-instar O. nubilalis, the preferred host stages of M. cingulum, occur later in the growing season. The timing of M. cingulum adult life expectancy and the occurrences of its preferred host stages in the field were predicted using the equations, published degree-day requirements for O. nubilalis and information from the literature on adult M. cingulum longevity. When the predicted period of M. cingulum adult activity was compared with the predicted timing of third- and fourth-instar O. nubilalis, M. cingulum adult presence was synchronized with preferred host stages.