Spruce budworm

Spruce budworm -
  • Latin name: Choristoneura fumiferana (Clemens)
  • French name: Tordeuse des bourgeons de l'épinette
  • Order: Lepidoptera
  • Family: Tortricidae
Description

Distribution

Canada

Micro-habitat(s)

Needle, Male flower, Cone, Bud

Damage, symptoms and biology

Spruce budworm damage appears in May. Evidence of a spruce budworm infestation includes the destruction of buds, abnormal spreading of new twigs, defoliation of current-year shoots and, if an affected branch is disturbed, the presence of large numbers of larvae suspended from strands of silk.

Defoliation begins at the top of the tree and quickly progresses to the periphery of the crown from the top downwards. Current-year needles are partially or completely consumed and, if large numbers of larvae are present, previous-year needles may also be affected. Spruce budworm larvae also feed on staminate (male) flowers and cones. During epidemics, the larvae may destroy all of the cones.

Severely affected stands turn a rust colour due to the presence of dried out needles held by strands of silk spun by the larvae. In the fall, most dead needles are dispersed by the wind and defoliated stands take on a greyish appearance.

A single year of defoliation generally has little impact on the tree. However, it does cause weakening of the tree, making it more susceptible to attacks by other insects. Defoliation over a few consecutive years causes tree growth loss. However, if defoliation of current- and previous-year shoots continues uninterrupted over several years, some trees will die, while others will continue to gradually decline for several years, even after the end of the infestation. This is the case with fir, the species most vulnerable to spruce budworm attacks, which dies after four consecutive years of severe defoliation.

In July and August, the female deposits her eggs in clusters of 10 to 30 under the needles of shoots, preferring those exposed to sunlight. The newly hatched larvae move towards the interior of the crown in search of a suitable overwintering site and construct a silken shelter, called a hibernaculum.

Life cycle (East of the Rockies)

Life cycle (East of the Rockies)
Stage/Month J F M A M J J A S O N D
Egg
 
Larva
 
 
Pupa
 
Adult
 

Other information

A native species, the spruce budworm is considered the most serious pest of fir and spruce forests in North America. Its range coincides with that of fir, white spruce, and more and more with the range of the black spruce.

Radial growth analyses of trees have shown that cyclical invasions likely occurred between the 18th and 20th centuries. Spruce budworm populations are believed to have fluctuated during this period at intervals of 30 to 40 years. Since the beginning of the 20th century, three invasions have occurred in eastern North America.

The spruce budworm is generally found in large fir stands. Much research has been conducted on this insect by the Canadian Forest Service and it is being monitored by the provincial forest departments. Most control methods mentioned in the recent literature involve the use of biological insecticides, primarily Bacillus thuringiensis var. kurstaki (B.t.k.).

Through a combination of annual surveys, prediction models, targeted control strategies and proper forestry practices, it is now possible to reduce economic losses caused by spruce budworm outbreaks.

On isolated or ornamental trees, vigorously shaking the tree or spraying with a powerful water jet will cause the larvae to drop to the ground. On small trees, the larvae can be removed by hand.

Canadian Forest Service Publications

Spruce budworm

Diet and feeding behaviour

  • Heteroconophagous : Feeds occasionally on seeds and cones, but usually lives and feeds on stems and needles.
    • Borer: Bores into and feeds on the woody and non-woody portions of plants.
  • Phyllophagous : Feeds on the leaves of plants.
    • Webworm: Spins a silk shelter in which to hide or feed.
  • Pollinivorous : Feeds on pollen.
    • Webworm: Spins a silk shelter in which to hide or feed.
General information

Specimens are available for purchase from the CFS Insect Production Services.

Information on host(s)

Main host(s)

Balsam fir, black spruce, eastern hemlock, jack pine, Norway spruce, red spruce, tamarack, white spruce

Photos
  • Spruce budworm Larva feeding pollen
  • Spruce budworm Larva
  • Spruce budworm Mature larva on fir twig (length: 25 mm)
  • Spruce budworm Mass of healthy eggs on a fir needle
  • Spruce budworm Light-coloured female moth at rest (wingspan: 22 mm)
  • Spruce budworm Pupa in natural position (length: 20 mm)
  • Spruce budworm
  • Spruce budworm
  • Spruce budworm Parasitoid female feeding on spruce budworm pupa
  • Spruce budworm Pinned adults, male and female
  • Spruce budworm Larva on the male flower
  • Spruce budworm Larva
  • Spruce budworm Severely defoliated 50-year-old balsam fir stand in July
  • Spruce budworm Close-up of a defoliated fir twig
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