Climatic unpredictability and parasitism ofcaterpillars: Implications of global warming

Abstract

Insect outbreaks are expected to increase in frequency and inten-sity with projected changes in global climate through direct effectsof climate change on insect populations and through disruption ofcommunity interactions. Although there is much concern aboutmean changes in global climate, the impact of climatic variabilityitself on species interactions has been little explored. Here, wecompare caterpillar–parasitoid interactions across a broad gradientof climatic variability and find that the combined data in 15geographically dispersed databases show a decrease in levels ofparasitism as climatic variability increases. The dominant contri-bution to this pattern by relatively specialized parasitoid waspssuggests that climatic variability impairs the ability of parasitoidsto track host populations. Given the important role of parasitoidsin regulating insect herbivore populations in natural and managedsystems, we predict an increase in the frequency and intensity ofherbivore outbreaks through a disruption of enemy– herbivoredynamics as climates become more variable.