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How to identify it
- Look for needles tied together with silk into feeding shelters on new shoots, with one to five caterpillars per shoot. As the damaged needles dry in midsummer the tree crown turns red.[1][2]
- The grown caterpillar is up to 18 mm long, reddish brown to pale rust, with two pairs of pale spots on the back of each abdominal segment. Its head and thoracic shield carry brown patterns on a reddish-tan to yellowish background, distinctly lighter than those of the spruce- and fir-feeding budworms.[1]
- The moth's forewings are 9 to 10 mm long and about two and a half times longer than wide, reddish brown to brick red with whitish bands. Color varies a lot, which led to several local forms being named as species.[1][2]
- Eggs are pale green and laid in overlapping clusters on needles. They are the largest eggs in the spruce budworm group.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Jack pine budworm | Jack pine budworm (Choristoneura pinus) is the eastern pine budworm. Where it reaches lodgepole pine in the United States, old records probably refer to the western pine budworm instead.[2] |
| Western spruce budworm | Western spruce budworm (Choristoneura occidentalis) feeds on Douglas-fir, true firs and spruce rather than pines, and its caterpillars have darker heads and thoracic shields.[1] |
Where it lives
A northern form occurs from western Saskatchewan through the northern and central Rocky Mountains to central Oregon, mainly on lodgepole pine at higher elevations. A more common southern form ranges from south coastal British Columbia through the Cascades and Great Basin to the Rockies and south to New Mexico, with scattered populations in California.[1]
Biology and life cycle
The northern form feeds mostly on lodgepole pine and, at the eastern edge, some jack pine. The southern form takes sugar, ponderosa, lodgepole, limber, Washoe and Jeffrey pines. Current-year buds and needles are eaten, and especially immature seed and pollen cones.[1][2]
There is one generation a year, with the possibility of a two-year cycle in northern and high-elevation sites. Moths fly in July and August and lay eggs on needles in clusters averaging about 22 eggs. The eggs hatch in 9 to 13 days.[1][2]
The newly hatched caterpillars do not feed. They spin silk hibernacula in bark crevices on the trunk and branches, molt, and overwinter as second-stage larvae.[1][2]
In spring the caterpillars emerge before the buds open and feed on pollen cones, then build silk shelters around the expanding shoots and feed for four to six weeks. They pupate in the feeding shelter among the webbed needles; the pupal stage lasts about two weeks.[1][2]
Natural Resources Canada notes that this life cycle is described largely from the better-known budworm species, because the western pine budworm itself has been little studied.[1]
Damage and signs
- Early feeding on buds and pollen cones is visible only on close inspection. Later the webbing and chewed needles show throughout the crown, and by midsummer the crown of a heavily fed tree turns red, a change that can come quickly in dry interior forests.[1]
- Extensive outbreaks are uncommon, so uncommon that general surveys have trouble finding many specimens. Local populations can reach very high densities on a few trees, but these episodes are short-lived and the trees recover. If defoliation continues for several years the crown thins and branches may die.[1]
- One form top-killed lodgepole pine extensively in Idaho in 1965 and 1966 and in Montana in 1967 and 1968, and the insect is at times destructive to the new buds and pollen bodies of sugar pine. It could in principle damage seed orchards by eating immature cones, but that has not been reported.[2][1]
Health risk
The sources treat it only as a defoliator of pines and report no risk to people.[1][2]
Control
Prevention
Because prolonged outbreaks have not occurred, there has been little need for a management strategy. On a landscape pine, the damage is a short-lived flush of webbed, reddened shoots from which the tree recovers.[1]
Biological control
Pheromone traps and the egg-mass and larval sampling methods developed for other budworms could be applied to this species if monitoring were needed.[1]
Pesticides
Natural Resources Canada says registered pheromone and pesticide products change from year to year and should be looked up in the current registry, applied only when population size justifies it and against the approved life stage, and that consulting a local tree care professional is recommended.[1]
Common questions
- Why did the tips of my ponderosa or lodgepole pine web up and turn red this summer?
- Caterpillars of the western pine budworm tie new needles together with silk and feed inside the shelter. When the damaged needles dry in midsummer the crown looks red. The trees normally recover.[1]
- Is the western pine budworm the same as the spruce budworm?
- No. It is a close relative in the same group, but it is the only pine-feeding budworm west of the Rockies, and it has never produced the large, recurring outbreaks the spruce budworms are known for.[1]
- Do I need to treat it?
- Usually not. Local outbreaks are short-lived and trees recover. If a valuable tree is hit year after year, ask a tree care professional about currently registered products.[1]
Sources
- Natural Resources Canada, Canadian Forest Service, “Western pine budworm (V. G. Nealis, 2025), Trees, insects, mites, and diseases of Canada's forests.” tidcf.nrcan.gc.ca/en/insects/factsheet/12019 (accessed 2026-11-10)
- USDA Forest Service, “Western Forest Insects, Miscellaneous Publication 1339 (R. L. Furniss and V. M. Carolin, November 1977; scanned copy).” archive.org/details/CAT78702369 (accessed 2026-11-10)
- iNaturalist, “Choristoneura lambertiana taxon page (order and family).” www.inaturalist.org/taxa/216807 (accessed 2026-11-10)