Phenological asynchrony results from climate-induced warming that leads to changes in the timing of species' seasonal events. As soil temperature acts as the threshold for emergence of seasonal insects, it is possible that anomalous soil warming can lead to asynchrony through changes in emergence timing. In order to determine which threshold, photoperiod or thermal, becomes the limiting factor on the timing of emergence under anomalous soil warming, we used a validated ABM that simulated Lyric Cicada emergence and its trophic relationships in a New Jersey prairie ecosystem with soil temperature calculated using sinusoidal astronomical forcing. For six different thresholds (14–26°C, 10 runs per threshold) adult emergence took place simultaneously on Day 13 due to a fixed photoperiod threshold (dayOfYear > 90) while the soil temperature was meeting all thresholds earlier. Nymphs were trapped in a state where they were ready thermally but constrained by photoperiod and, therefore, there was a sharp one-day pulse of emergence consisting of 41 individuals (26°C) in contrast to only 4 (16°C). In the case of the high-threshold control (28°C), the need for a thermal gate to be an independent factor was reaffirmed by the delay in emergence in the absence of its presence until Day 26 and the production of a bigger pulse of 54 ± 5.8. The results above indicate that when the soil temperature activates the thermal threshold prior to the photoperiodic one, then the thermal stimulus loses its impact on emergence time and chronology takes control.