We analyzed long-term surveillance records (from 22 to 37 years) of the Japanese smaller tea tortrix, Adoxphyes honmai at 16 research stations across mainland Japan. We found that the populations in all the stations showed remarkable signature of the generation cycles. We employed wavelet analyses to test whether the generation cycles are coming from 'seasonal disturbance' or 'temperature destabilization'. The seasonal disturbance, specifically the winter hardiness, burdens the population to be locked onto a certain developmental stage through diapause or differences in stage-specific mortality. On the other hands, theoretical models predict that warm temperatures cause population dynamics to become unstable giving rise to single generation cycles, i.e., temperature destabilization.
We found that both the annual and the sub-annual (generational) cycles are prominent in all the 16 population. The amplitude of the sub-annual cycle in each year at each location is extracted from the wavelet analysis and is plotted against the temperature. The amplitude increases as temperature rises in all the 16 populations. We believe that this is the evidence of temperature destabilization because the wavelet amplitudes should increase with temperature while it should decrease in the case of transient developmental synchrony after winter. Our tentative laboratory experiments also showed the generation cycle even in a constant temperature. We will discuss the mechanisms and the maintenance of the generation separation in the tortrix.