Figure 1

Illustration of the individual-based model (IBM).

(a) Image of the accumulated temperature. The area in green above T_thre represents growth based on accumulated temperature. When the sum of accumulated temperature (T_accume) reaches the threshold amount for maturation (T_mature), the non-periodical cicadas emerge. (b) Simulation flow. The variable T_thre is defined as the temperature threshold of individual cicada i, such that if T_t ≤ T_thre,i (for some t), then T_mature,i is fixed, resulting in a longer time of emergence. An individual cicada nymph i(t) emerges at time t if T_{accume,i(t−1)} ≥ T_mature. If T_{accume,i(t−1)} < T_mature, a nymph cannot emerge the next year. Illustration by Yoshihiko Ishimori.