Egg incubation and nymphal development of the consperse stink bug Euschistus conspersus Uhler were studied in laboratory growth chambers under constant and fluctuating temperatures. Eggs did not hatch at 10, 12, and 37°C, and separately placed first-instar nymphs did not survive to become adults. Egg incubation and total nymphal development times were significantly shorter at 32°C than compared with the lower temperatures. Egg incubation and total nymphal development at the fluctuating temperature fell between the two optimal constant temperatures of 27 and 32°C. Linear regression of developmental times and constant temperatures for egg incubation, first–third instar nymphal development and fourth–fifth instar nymphal development provided an estimated lower developmental threshold of 12°C for E. conspersus. This threshold was used to develop a phenology model. Field validation of the model was based on canopy shake samples and pheromone trap captures obtained from processing tomato, Lycopersicon esculentum Miller, fields. Results supported the laboratory phenology model. Field observations supported the trap’s potential as a degree-day biofix in processing tomatoes.