Climatic change and insect outbreaks

Insects represent the dominant natural disturbance factor in Canada's forests. Host trees are often killed over extensive areas. This paper examines how climate change may influence insect outbreak regimes in Canada's forests, primarily focusing on temperature, as the potential rate of increase of many insects is dependent on temperature. The extent and frequency of temperature extremes can have major impacts on insect populations. Temperature increases will accelerate development, activity and movement as well as influence reduced mortality from climatic factors. In addition, higher temperatures are likely to facilitate extended periods of activity at both ends of the season. It was concluded that a number of complex factors will likely determine the direct effect of increasing temperatures on insects. Changes in the abiotic environment, changes in species interactions, and changes in the regimes of natural selection will influence future insect activity. For example, increases in carbon:nitrogen ratios are expected to cause insects to eat more in order to maintain dietary nitrogen. The effects of climate change is expected to differ quantitatively among species in the complex food chains where most insect species are embedded. It is also assumed that if geographic distribution of insects shifts in response to climate change, their impact should basically remain static. Most published scenarios suggest that outbreaks of insects in Canada will last longer and occur more frequently where the climate will become warmer. However, climate warming may also allow certain insects to extend their ranges into regions of vulnerable host species. It was suggested that further research is necessary, as no data has been collected on how insects might respond to predicted, concurrent changes in atmospheric chemistry and climate. 19 refs