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Spruce budworm

The eastern spruce budworm (Choristoneura fumiferana) is a moth native to North America. It is found in every province and territory and lives throughout the Canadian boreal forest.

Eastern spruce budworm adult moth and caterpillar.

The eastern spruce budworm (top: adult moth; bottom: caterpillar).

Larger image

Eastern spruce budworm feeds mainly on balsam fir and white spruce, and to a lesser extent on red spruce and black spruce. Trees usually die after four or five consecutive years of severe loss of all or most leaves.

Quick facts

  • Outbreak cycles of eastern spruce budworm occur every 30 to 40 years.
  • During an outbreak, tens of millions of hectares of trees can be severely defoliated. An outbreak may last several years.
  • The most recent outbreak started in Quebec on the north shore of the St. Lawrence River in 2006, with about 3,000 hectares being defoliated.
  • By 2017, over 7 million hectares of forest in Quebec has suffered moderate to severe defoliation.
  • In western Canada, outbreaks of eastern spruce budworm occur intermittently at the edge of its range in northern boreal forests from Manitoba through the Yukon.


The eastern spruce budworm has a significant impact on Canada’s forests.

Aerial view of a forest disturbed by the presence of eastern spruce budworm. Photo: Johanne Delisle

Aerial view of defoliation caused by the eastern spruce budworm.

  • The most visual evidence of an infestation is rust coloured new-shoots at the tips of branches caused by caterpiller feeding. Other evidence includes the presence of larvae, silken larval feeding tunnels, excrement and strands of silk.
  • Defoliation begins at the top of the tree and quickly progresses downward as needles are partially or completely consumed.
  • Severely affected tree stands turn a rust colour as a result of dried-out needles being held together by strands of silk spun by the larvae.
  • High levels of defoliation weakens a tree, which makes it more susceptible to attacks from diseases and other insects.
  • Affected tree stands are very evident from small fixed-winged aircraft, which is the main method used to map infested areas.
  • Cumulative defoliation can cause significant mortality and growth loss in mature spruce-fir forests; resulting in significant losses of important timber and non-timber resources.

CFS scientific research

Research conducted by scientists at the Canadian Forest Service (CFS) has led to many insights into the spruce budworm’s population ecology and management.

  • Adult moths mate and lay eggs in clusters of 10-150 on the needles of host trees in July and August.
  • Newly hatched larvae spin cocoons in protected areas on the host tree where they spend the winter.
  • In the spring, larvae emerge and start feeding on new foliage using the needles as a frame to build a silken feeding tunnel to protect themselves from predators.
  • Defoliation becomes visually noticeable in late June when larvae have completed most of their feeding.
  • Budworm moths emerge from pupae in early to mid July and lay eggs on the foliage to complete their life cycle.

Working collaboratively to develop solutions

Through the Canadian Forest Service, Natural Resources Canada works in collaboration with provincial governments and other agencies, such as Quebec’s Société de protection des forêts contre les insectes et maladies and New Brunswick’s Forest Protection Limited, to develop management tools and tactics to predict and mitigate damage caused by spruce budworm outbreaks.

Want more information on the eastern spruce budworm?

Contact Rob Johns or Marc Rhainds of the Atlantic Forestry Centre or Deepa Pureswaran, Yan Boulanger, Michel Cusson, Veronique Martel or Jacques Régnière of the Laurentian Forestry Centre.

CFS Resources on the spruce budworm
Other resources on the spruce budworm
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