Predicting insect distributions under climate change from physiological responses: spruce budworm as an example

Much evidence is accumulating that insect distributions are changing. The changing earth's climate is providing mobile species with an evolving hospitability template, and increasing global commerce expands opportunities for mobile species to colonize new habitats. Predicting the distribution of insects in the face of accelerating global commerce and climate change is quite a challenge. Many fruitful approaches are available and are being improved. Some are correlative; some are based on process-level knowledge. We have focused on an eco-physiological approach based on the known responses of species to specific weather factors at the physiological level. Of particular importance are developmental responses, of course, as they determine climates under which an insect can achieve a stable, adaptive seasonality. With this underlying minimal requirement, models can also take into account other weather influences such as cold tolerance and the deleterious effects of too much heat. In this paper, we illustrated the use of this approach to predict the change of distribution and potential impacts of the spruce budworm Choristoneura fumiferana (Clem.), a major native insect pest of conifer forests in North America. Like previous work on the invasive gypsy moth (Lymantria dispar L.) and the native mountain pine beetle (Dendroctonus ponderosae Hopkins), the present work points to the following conclusions concerning the effects of global warming on species distributions: (1) they will shift towards the poles (and to higher elevations); (2) temperate regions will bear the brunt of these shifts; and (3) distribution shifts may be good or bad, depending on the species and the regions concerned.