Developmental synchrony, and recurrent insect outbreaks caused by temperature-driven changes in system stability

Background/Question/Methods

Insect species often undergo regular outbreaks in population density.  Identifying the causal mechanism for such outbreaks in a particular species has proven difficult. The tea tortrix Adoxophyes honmai exhibits exceptionally regular outbreak cycles on Japanese tea plantations caused by lock-step developmental synchrony of each generation. We apply time series analysis and parameterize a temperature-dependent stage-structured model for the system to understand the outbreak cycles.

Results/Conclusions

Wavelet analysis of a 51 year long time series confirms that there is a threshold in outbreak amplitude each spring when temperature exceeds 15°C, and a secession of outbreaks each fall as temperature decreases. This is in close agreement with our independently parameterized mathematical model that predicts the system crosses a Hopf bifurcation from stability to sustained cycles as temperature increases. Our study is a unique illustration of how temperature may drive a plant-herbivore system to instability.