Life history and habitat explain variation among insect pest populations subject to global change

Population dynamic responses to global change have varied widely among taxa. Most studies of population dynamics of insect pests focus on one or a few species, leaving open the question of whether changes in outbreak patterns are species-specific or reveal predictable responses to global change, and what factors explain differences among populations. We analyzed 64 multi-decadal time series of agricultural and forest pest insect populations in the United States. We first characterized populations according to long-term trends, strength of population regulation, and cycle presence and length. We then asked whether these attributes could be predicted by geography, taxonomy, and life-history traits. Roughly half of time series exhibited a long-term trend, and agricultural pests were more likely to be declining, while forest pests were more likely to be increasing. Approximately one quarter of records exhibited periodic oscillations, and we used their statistical properties to infer whether the oscillations were environmentally forced or arose from density dependence. Insects hatching in early spring may be more strongly influenced by environmental forcing, for example, early springs or late spring frosts, than species hatching later. Our findings suggest roles of climate change, forest compositional change, and agricultural practices in driving long-term change in pest populations.