Forest Insect Defoliators
Large Aspen Tortrix
Choristoneura conflictana (Walker)

Host:  Aspen

Figure 50. Figure 50. Adult large aspen tortix.

Symptoms/Signs:  Presence of flat egg masses on the upper surface of foliage, partially eaten rolled-up leaves in which small, green to black larvae are feeding or pupating, incomplete defoliation before the buds have expanded in the spring.

Biology:  Pale green egg masses are laid in large, flat masses on the upper surfaces of the foliage in June and July. Second-instar larvae overwinter in silken hibernacula in bark crevices and other out-of-the-way places. The small larvae begin to migrate up the stems of aspen on warm days in early spring. The larvae mine the buds, sometimes causing complete defoliation before the buds open. Later stage larvae roll the leaves into shelters within which they feed and eventually pupate. The moths have a wingspread of 25 to 30 mm. The forewing is grayish with basal, middle, and outer brownish patches. There is one generation annually.

Effects:  During outbreaks, this insect can completely defoliate aspen stands. Outbreaks characteristically last 2 to 3 years and can result in growth loss and some twig and branch dieback.

Similar Insects:  Larvae and pupae are similar to those of the western spruce budworm. However, the larvae of the large aspen tortrix are green to grayish-black with a black head capsule while the western spruce budworm larvae are white to grayish-tan with a tan head capsule and feed on Douglas-fir, true firs, and spruce.

References:  4, 24

Figure 51. Figure 51. Closeup of damage caused by large aspen tortix and larva.
Figure 52. Figure 52. Large aspen tortrix defoliation of aspen in Colorado.