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
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.