However, it was not initially recognized as a serious threat to coniferous forests in the western U.S. Aerial spraying apparently terminated some smaller epidemics in the southern and central Rockies; others subsided naturally.

The insect then appeared to be dormant in U.S. forests until 1922, when two outbreaks were reported near Priest Lake in northern Idaho.

Since then, significant outbreaks in the Rockies and in the Pacific Northwest have caused top-killing with serious economic losses in tree growth.

An epidemic which began in 1949 in the northern Rocky Mountains has persisted for over 30 years despite insecticidal treatment of more than 6,000,000 acres (24,000 km2) between 1952 and 1966.

The gray- or orange-brown forewings are banded or streaked, and each usually has a conspicuous white dot on the wing margin.

Mature larvae are 1 to 11/4 inches (25 to 32 mm) long, with tan or light chestnut-brown heads and collars and olive- or reddish-brown bodies with large ivory-colored areas.

Throughout most of its range, the western spruce budworm completes one cycle of development from egg to adult within 12 months.

Larvae do not feed, but seek sheltered places under bark scales or in and among lichens on the tree bole or limbs.

If adopted, the replacement name for the then later described North American species has been formally proposed as Choristoneura freemani Razowski, 2008.[4].

However, the need for a replacement name for the American species was then questioned, with proposals of alternative ways to revise the taxonomy.