Large aspen tortrix (Choristoneura conflictana)
Last Review/Updated: March 25, 2004
The large aspen tortrix (Choristoneura conflictana) is a serious aspen defoliator in Canada. Large aspen tortrix outbreaks may last 3-4 years.
Primary Hosts and Distribution
- all willow, aspen and poplar species; occasionally late instar larvae may feed on white spruce when population levels are very high.
Larger populations tend to occur in the parkland and boreal mixed wood areas. For historical maps, click here.
Life Cycle
The large aspen tortrix has a one-year life cycle.
Larvae
In the spring, yellowish-green larvae (caterpillars) emerge at the time when the buds begin to swell. Mature larvae are 1.5-2.0 cm long and dark green with two rows of small black dots along the back with black heads. They feed on the leaves until about the middle of June, stop feeding and growing, then search for places to pupate.
Pupae
They normally pupate within webbed leaves. The dark black empty pupal cases can be seen sticking out of rolled leaves. Under severe outbreak conditions, they may pupate anywhere including on the siding of houses and on outdoor household articles.
Adults and Eggs
Brownish-grey moths (with a 2.5-3.5 cm wingspan) emerge in late June through July, and mate. Females lay light green eggs (clusters of 50-450 eggs) on the upper part of leaves; they hatch about 10 days after. The young larvae feed until mid-August and then prepare for winter by making silken shelter (hibernaculum) under bark scales and crevices.
Detection and Damage
Look for the following signs and symptoms:
- Defoliation of aspen, willow and poplar species in April-June;
- Yellowish-green to dark green larvae feeding within tied or rolled leaves;
- Black pupal cases protruding from rolled leaves;
- Light green egg clusters on the top surface of leaves in July;
- Silken webbing on leaves.
Large aspen tortrix infestations cause growth reduction. Several consecutive years of severe defoliation may cause tree mortality, especially if other stress factors such as drought are present.
Management
As aspen becomes a valuable commercial timber species in Alberta, management of this pest may become more important. Management of the large aspen tortix may include:
- Aerial surveys, flown late spring to early summer. Aspen defoliation is sketch-mapped. For more information, click here;
- Control actions are not taken because infestations usually collapse after 3- 4 years due to the action of natural enemies.
