The spruce budworm is the most destructive insect of coniferous stands in North America. In Quebec, spruce budworm mainly consumes the annual foliage of balsam fir, white spruce and, to a lesser extent, red spruce and black spruce.
The insect plays an important ecological role, including the rejuvenation of some old-growth forests and the creation of many habitats for many species. Caterpillars feed on balsam fir and spruce needles of any age, whether they are in deciduous, mixed or coniferous forests. The fir tree is less resistant than spruce to TBE attacks. It’s said that he is more vulnerable. This vulnerability increases with the age and density of the stands.
When the epidemic continues for several years, the foliage of the tree sometimes becomes insufficient to ensure the survival of the tree and tree mortality begins and progresses according to their vulnerability. During the first year of significant defoliation, the trees take, at the end of June, a reddish hue, due to the presence of dead needles at the ends of the branches. Over the years, defoliated trees become grayish in color, reflecting the gradual disappearance of foliage.
At least four close years of severe defoliation of the shoots are needed before the first trees die. Epidemics of spruce budworm are cyclical. They come back every 30 to 35 years. Each epidemic can last from 15 to 20 years in the same sector.