 During a 1957 budworm outbreak in Quebec, balsam fir mortality was greater than 75% in stands in which no mortality was reported among the smaller component of white spruce.However, while balsam fir is the preferred host, severe outbreaks have occurred among white spruce stands in the Prairie Provinces and Northwest Territories containing little or no balsam fir.The white spruce is less susceptible to budworm attack but can experience extreme defoliation during severe outbreaks.