Spruce Budworm

Weather is a critical factor in determining spruce budworm distribution. Sudden upsurges in budworm numbers generally follow drought and the visible effects of these outbreaks begin after hot, dry summers. Drought stresses the trees, reducing their resistance, and elevated summer temperatures increase budworm reproduction. For example, female budworms lay 50% more eggs at 25˚C than at 15˚C. Also, higher temperatures and drought can shift the timing of budworm reproduction such that their natural predators are no longer effective in limiting budworm numbers. Conversely, cold weather can stop a budworm outbreak. Budworms starve if a late spring frost kills the new shoot growth of the trees on which the larvae feed.

Thus it is to be expected that climate warming would result in the northward movement of the spruce budworm and this has already occurred. Before 1990, spruce budworm had not appeared able to reproduce in the boreal forest of central Alaska. Then, in 1990, after a series of warm summers, a sudden and major upsurge in spruce budworm numbers occurred and visible damage to the forest canopy spread over several tens of thousands of hectares of white spruce forest. Populations of spruce budworm have since persisted in this area near the Arctic Circle. The entire range of white spruce forests in North America is considered vulnerable to outbreaks of spruce budworm under projected climate change. In the Northwest Territories of Canada, for example, the northern limit of current spruce budworm outbreaks is approximately 400 kilometers south of the northern limit of its host, the white spruce. Therefore, there is potential for a northward expansion of spruce budworm to take over this remaining 400 kilometer-wide band of currently unaffected white spruce forest.

Source & © ACIA Impacts of a Warming Arctic: Arctic Climate Impact Assessment  (2004),
 Key Finding #3, p.55

Related publication:
Arctic Climate Change homeArctic Climate Change
Other Figures & Tables on this publication:

The Earth’s Greenhouse Effect

Observed Arctic Temperature, 1900 to Present

Observed sea ice September 1979 and September 2003

Surface Reflectivity

Projected Vegetation, 2090-2100

Arctic Marine Food Web

Map subregions sub-I

Map subregions sub-II

Map subregions sub-III

Map subregions sub-IV

Arctic Thermohaline Circulation

Carbon cycle in the Arctic

Projected Arctic Surface Air Temperatures

Freshwater food web

Projected opening of northern navigation routes

Factors influencing UV at the surface

1000 years of changes in carbon emissions

People of the Arctic

Projected Surface Air Temperature change 1990-2090

Melt of the Greenland Ice Sheet

An ice primer

Spruce Bark Beetle

Spruce Budworm

Peary Caribou

The Porcupine Caribou Herd

The Gwich’in and the Porcupine Caribou Herd

A permafrost primer

Seals Become Elusive for Inuit in Nunavut

Observed Climate Change Impacts in Sachs Harbour, Canada

Indigenous knowledge and observations of current trends

Case study of interacting changes: Saami reindeer herders

Indigenous knowledge and observations of current trends

Indigenous knowledge and observations of current trends

Indigenous knowledge and observations of current trends