The diel periodicity of pheromone-mediated aggregations and mating and feeding cycles of Euschistus conspersus Uhler (Heteroptera: Pentatomidae) was investigated in a series of laboratory and field experiments. The aggregation response of adult E. conspersus to lures loaded with the male-produced aggregation pheromone component methyl E2,Z4-decadienoate placed on common mullein, Verbascum thapsus L., peaked in the early hours of the scotophase, at ≈2100 hours. Peak mating occurred at 2300 hours, with 78.5% of the insects in aggregations mating at this time. Aggregations dispersed and declined to 30% of their maximum level by dawn on pheromone-baited plants. Equal numbers of males and females were found within aggregations. Aggregations continued to form nightly and disperse by morning throughout a 72-h observation period on pheromone-baited and unbaited mullein plants. A laboratory analysis of feeding periodicity indicated that although feeding occurred throughout the 24-h observation period, the percentage of feeding insects was significantly higher during the scotophase. There were no differences between feeding rates of males and females. The implications of these findings for monitoring and management of E. conspersus are discussed.