Eighteen trapping sites were established in the Mexican state of Tamaulipas and adjacent areas of Nuevo Leon and San Luis Potosi, and the U.S. Lower Rio Grande Valley, to determine the spatial and temporal patterns of beet armyworm response to pheromone traps. Peak beet armyworm captures occurred in the fall and winter (primarily in October and November) at all sites. At most locations, trap captures in the spring and summer were low relative to the peak capture periods. The period of low capture may have resulted from a lack of available host plants caused by low rainfall during this period. Although beet armyworm moths were captured at all locations, there was considerable variation in the magnitude of capture and no major population source areas were indicated. The differences in capture profiles and magnitudes, suggest that environmental conditions and host plant availability may be more important than migration in governing the presence and magnitude of local populations within this region.