Potential effects of climate change on insect herbivores in European forests—General aspects and the pine processionary moth as specific example

The nature of “climate change” will differ with geographical regions and its final impact on ecosystems vary with the extent of temperature increase, changes in irradiance and levels of UVB, amount and patterns of precipitation and humidity, and alterations in the incidence and nature of abiotic disturbances. Despite many uncertainties, there is consensus in the fact that global warming already has and will have impact on the temporal and spatial dynamics of insect herbivores. Ectothermic organisms are affected by the changes in environmental conditions directly in dispersal, reproduction, development and mortality, and indirectly through altered plant nutritional quality, resistance and via community interactions. Ambiguous consequences are to be expected depending on the individual host plant and herbivore species, probably involving altered incidence and intensity of pest outbreaks and changes in distributional ranges. Regions that represent northern or upper limits of occurrence, such as the Alps or the boreal zone, are likely to be affected most by an increase in stability and population density of certain pest species, such as defoliating insects or bark beetles. At the same time, temperature increase and drought will render areas of distribution in southern and continental parts of Europe less suitable for heat susceptible species, which will probably not only result in northwards shifts, but range contractions. The review is based on chapters of the “Study on impacts of climate change on European forests and options for adaptation” led by the European Forest Institute (Efi) and on results of the EU project “PROMOTH - Global change and pine processionary moth: a new challenge for integrated pest management”. Thaumetopoea pityocampa serves as illustrative example for insect herbivores whose latitudinal and altitudinal distribution is mainly controlled by temperature and already modified by global warming.