Spring cankerworm

Spring cankerworm - Larva
  • Latin name: Paleacrita vernata (Peck)
  • French name: Arpenteuse du printemps
  • Order: Lepidoptera
  • Family: Geometridae
Description

Distribution

Western Canada

This is a native North American species, widely distributed throughout the southern half of the three Prairie Provinces.

Micro-habitat(s)

Trunk, Soil, Leaf

Damage, symptoms and biology

The spring cankerworm is a defoliator of many deciduous trees and shrubs in various types of rural and urban tree stands and plantings.

Damage usually begins in late May when young larvae chew small holes in the developing leaves. As feeding continues, these holes gradually enlarge until only the larger leaf veins and midribs remain. When cankerworm populations are large, starving larvae in search of food may drop on silken threads and become a nuisance around homes or in well-used areas. During outbreaks lasting from 1 to 4 years, trees may be completely defoliated; however, most trees usually refoliate in July, 3–5 weeks after the first attack.

Three or more consecutive years of severe defoliation may cause many of the upper branches to die and affect tree appearance. Severe defoliation may also contribute to tree mortality.

The spring cankerworm has a 1-year life cycle. The larvae are slender and move with a looping motion. The mature larvae overwinter in the soil and pupate in the very early spring. Adult wingless females and winged males soon emerge to mate, and the females climb host trees and shrubs, where they lay eggs in clusters on the stems and lower branches. Mature spring cankerworm larvae are about 20–30 mm long, and they vary in colour from yellowish green to almost black, with a mottled appearance.

Other information

A number of natural agents may control cankerworm populations. Parasitic insects attack the egg, larval, and pupal stages of cankerworm life cycles, while other predators (insects, spiders, birds, and small rodents) may attack all the stages. Cold winter temperatures, late spring frosts, starvation, or disease may also cause the collapse of larval populations.

Canadian Forest Service Publications

Spring cankerworm

Diet and feeding behaviour

  • Phyllophagous : Feeds on the leaves of plants.
    • Free-living defoliator: Feeds on and moves about freely on foliage.
Information on host(s)

The preferred hosts of the spring cankerworm is Siberian elm but it also attacks ash, basswood, bur oak, Siberian elm, aspen, white birch, and various fruit trees. The spring cankerworm attacks many of the same trees as the fall cankerworm, but prefers Siberian elm.

Main host(s)

American mountain-ash, ashes, basswood, black ash, blue ash, bur oak, common prickly-ash, European ash, European mountain-ash, fruit trees, green ash, mountain-ash, northern red ash, Oregon ash, pumpkin ash, siberian elm, Sitka mountain-ash, trembling aspen, white ash, white birch

Photos
  • Spring cankerworm Larva
  • Spring cankerworm Row of eggs at the bottom of a bark crevice
  • Spring cankerworm Larva
  • Spring cankerworm Larva
  • Spring cankerworm Dorsal view of dark larva
  • Spring cankerworm Dorsal view of light-colored larva, showing the three X-shaped marks on middle segments
  • Spring cankerworm
  • Spring cankerworm Adult male at rest (wingspan: 21-30 mm)
  • Spring cankerworm Male
  • Spring cankerworm Larva
  • Spring cankerworm Larva
  • Spring cankerworm Pupa
  • Spring cankerworm Female
  • Spring cankerworm Adult female laying eggs in bark crevice (length: 10 mm)
  • Spring cankerworm Female
  • Spring cankerworm Side view of larva (length: 18-30 mm)
  • Spring cankerworm Pinned adult male
  • Spring cankerworm
  • Spring cankerworm
  • Spring cankerworm Close-up view of affected elm
  • Spring cankerworm Larva on leaf
  • Spring cankerworm Larva on leaf
  • Spring cankerworm Larva on leaf
  • Spring cankerworm Larva of Paleacrita vernata bearing hymenopterous parasite eggs
  • Spring cankerworm Residue of Paleacrita vernata larva parasited by an hymenoptera
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