Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) enters reproductive diapause under short-day length (< 13.5 h) conditions. As an apparent increase of field populations of R. pedestris has been observed during the fall when aggregation pheromone traps are placed in soybean fields, we tested the hypothesis that R. pedestris becomes more responsive to the aggregation pheromone during fall as it enters its reproductive diapause. The response of R. pedestris females—either ones collected seasonally from fields or reared in the laboratory under short-day length (10:14 [L:D] h) conditions—to the aggregation pheromone was examined using a Y-tube olfactometer. Riptortus pedestris collected in fall showed a higher response to the aggregation pheromone (74–80%) than those collected in July (40%). Females in which diapause was induced in the laboratory also showed a higher response to the pheromone than those not in diapause. In a wind tunnel assay, female bugs in laboratory-induced diapause also responded positively to the aggregation pheromone. In addition, we assessed the reproduction of females to verify their diapausing status. Diapausing females never mated with either short- or long-day-reared males, nor did they reproduce, but non-diapausing females mated with short-day-reared males at a rate of 13%. Females collected from fields during fall never mated. In a soybean field evaluation, the number of adult female R. pedestris was higher in the presence of an aggregation pheromone trap than in the absence of one. This is the first confirmation of higher response to the aggregation pheromone of both field-collected and laboratory-reared R. pedestris in reproductive diapause.