Spring cankerworm

French common name: Arpenteuse du printemps
Scientific name: Paleacrita vernata (Peck)
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Lepidoptera
Family: Geometridae

Distribution

Western Canada

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

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.