Juniper Webworm
Egg-The whitish, pinkish, or dark reddish-orange egg is 0.5 mm by 0.3 mm. It is subcylindrical with rounded ends. The surface has many longitudinal, waxy lines.
Larva-The larva is a small, whitish to light-brown worm (0.5 to 15 mm) with reddish-brown stripes (Color Plate 3Y).
Pupa-The light or dark reddish-brown pupa is almost as long as the adult (5.5 mm).
Host Plants -Irish juniper is the preferred host, although Chinese juniper, red cedar, and Juniperus communis varieties aurea, horizontalis, depressa, hibernica, suecia, and squamata meyeri are also infested. Juniperus procumbens and J. squamata are infested only occasionally.
Damage The leaf-mining by newly hatched larvae is inconsequential. The feeding of larger worms in the fall and following spring may seriously damage ornamental junipers. Large masses of dead needles appear, and the shrubs look unthrifty. Small shrubs may be completely webbed (Color Plate 3Y).
Life History -Juniper webworms overwinter as partially to nearly grown worms inside webbed masses of foliage. Adult emergence occurs from May to July, peaking in June. Males live about 12 days; females, about 14. After mating, females lay from 50 to 200 eggs singly at the base of new needles in the axil. About 10 days later, tiny larvae hatch, puncture the leaf surface, and feed as leafminers, causing the leaves to turn brown. The mined leaf is used as a protective retreat from which the tiny worm emerges to feed on fresh foliage. A tiny, white web is soon formed around the infested leaf. As the worm grows, the web expands to encompass dead leaves. Silken tubes are then constructed in which the worms retreat when not feeding. The worms mature throughout the summer, fall, and winter. By the following spring, they feed gregariously and form a community web. Considerable amounts of foliage may be spun together, and small trees may be completely webbed. The worms pupate inside whitish silken cases, and new adults appear in about 14 days to continue the infestation. There is one generation per year. Braconid and ichneumonid wasps parasitize the larval and pupal stages of juniper webworms.
Where practical, the webbed masses should be pruned and burned. For specific chemical controls, see the current state extension service recommendations.