Large Aspen Tortrix, Choristoneura conflictana

Fig. 322   Adult large aspen tortrix.	Fig. 323   Large aspen tortrix larva.	Fig. 324   Egg mass on hybrid poplar leaf.
Fig. 325   Empty pupal cases protruding from webbed leaves.	Fig. 326,   Aspen leaves webbed together by large aspen tortrix.	Fig. 327   Defoliation by large aspen tortrix. Note webbing on understory vegetation.

Distribution:  Throughout the range of aspen, most common in Prince George, Prince Rupert, Nelson Forest Regions, and southwestern Yukon Territory. 

TREE SPECIES ATTACKED: Trembling aspen and balsam poplar are susceptible.

WHAT TO LOOK FOR: Dark, smooth caterpillars feeding within rolled or webbed leaves; egg masses on foliage.

INSECT DESCRIPTION & DAMAGE SYMPTOMS: Young larvae are 0.3 to 0.4 cm long. They have black heads, and yellowish or pale green bodies that become progressively darker with each molt. Mature larvae are 1.5 to 2.1 cm long, and are dark green, almost black in colour. Adult moths are brownish grey, and the forewings are light grey with three patches of darker grey. They have a wingspan of 2.5 to 3.5 cm. Overwintered larvae emerge and begin mining the buds in early spring, but the damage caused at this time is usually inconspicuous. However, during severe infestations, there might be a delay in the opening of buds, or buds may be completely destroyed, so no foliage is produced. Older larvae feed within rolled leaves, or pull two or more leaves together with silken threads and feed within the folded leaves. Affected foliage has a clumped, irregular appearance. Pupation occurs in mid-June, and the adult moths emerge about 10 days later. The empty pupal cases can often be seen protruding from the clumps of folded leaves. Light green eggs are laid in clusters on the upper surface of the leaves, and appear as overlapping scales. They hatch in about 2 weeks. The young larvae web leaves together and feed on the leaf tissue. In mid-August, they will cease feeding and construct silken hibernation shelters underneath bark scales, dead bark, or moss on tree stems and branches.

DAMAGE: Infestations usually last 2 to 3 years, recurring about every 10 years. Severe defoliation can result in reduced radial growth, but only rarely results in tree mortality. Outbreaks of the large aspen tortrix tend to precede those of the forest tent caterpillar.

SIMILAR DAMAGE: Damage caused by the large aspen tortrix can be confused with that caused by the bruce spanworm. However, if the damage was caused by the large aspen tortrix, pupal cases or egg masses will be found on the foliage, and hibernation shelters will be present on nearby stems and branches.

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Contact Tim Ebata if you have comments on the presentation of this information.

BC Ministry of Forests
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2

Section phone: (250) 387-8739
Section fax: (250) 387-2136

Last updated April 23, 2002