Western spruce budworm
Alberta, British Columbia
Damage, symptoms and biology
The western spruce budworm is a damaging defoliator in British Columbia. Budworm feeding damage includes killing of mined buds by early-instar larvae and stripping of the current year's foliage primarily in the upper crown by mid- to late-instar larvae. Budworms often consume only parts of needles and chew them off at their bases. By mid-summer heavily infested trees appear scorched and have heavily defoliated upper crowns and branch tips. Severe defoliation over several consecutive years results in reduced increment, top dieback, bole deformity and in some cases tree mortality.
Mature larvae are 25 mm long. The head is unmarked and brown to black in colour. On the final instar, the body is pale to dark brown, sometimes with a distinct greenish tinge, and the dorsum of each abdominal segment is marked with two pairs of ivory white spots. The moths measure approximately 12 mm in length and have a wingspan of 22-28 mm. The forewings are grey or orange-brown marked with lighter-coloured striations. The border of the wings is marked with clearly visible white patches.
This insect produces only one generation per year. It overwinters as a second-instar larva protected in a hibernaculum (silken shelter) on a branch or on the trunk. The larvae become active in April and initially mine needles and buds. As the buds swell in May, the larvae feed on the expanding needles. Eventually, they form a loose webbing in the new foliage around the feeding site. Mature larvae pupate within this webbing from mid-July to late July and adults emerge 12 to 18 days later. After mating, the female lays up to 150 eggs in shingle-like masses on the underside of needles. The eggs hatch within 12 days. The newly emerged larva does not feed but crawls to a sheltered location and forms a small hibernaculum in which to overwinter.
Life cycle (West of the Rockies)
In Canada, the first western spruce budworm epidemic was reported in 1919 on Vancouver Island. Since then, several periodic infestations have been reported mostly in the southern interior of the province of British Columbia and occasionally in southwestern Alberta. Extensive outbreaks resulting in defoliation over 100,000 ha occurred in the late 1950s and again in the 1970s. More extensive outbreaks damaging more than 800 000 ha occurred in the 1980s and 2000s, all in the interior forests of the region.
Canadian Forest Service Publications
Diet and feeding behaviour
: Feeds on the leaves of plants.
- Free-living defoliator: Feeds on and moves about freely on foliage.