The seasonal abundance and phenology of the borersDiatraea lineolata(Walker),D. saccharalis(F.), andEoreuma loftini(Dyar) were investigated on corn in northern Tamaulipas, Mexico, from 1985 to 1988.D. lineolatawas the dominant species throughout the study. The presence ofE. loftiniwas practically limited to the fall seasons, andD. saccharaliswasmostcommon during the fall of 1985. Positive interspecific associations between borer species were detected, particularly during the fall, when densities were highest. Two borer generations were detected within each corn growing season (spring or fall) for all borer species; the first generation was initially detected at middle to late whorl stage, whereas the second generation normally occurred after tasseling. All species overwintered as mature larvae in dry cornstalks, withD. lineolataalso expressing summer diapause. Plant maturation was the major factor responsible for diapause induction ofD. lineolataregardless of time of year. A minimal accumulation of heat units and contact moisture was required forD. linealatalarvae to terminate diapause. The relationship of these studies to those reported for the same species in the tropics or other species elsewhere is discussed.