 According to one common theory (the double equilibrium hypothesis), popularized in the 1970s, periodic outbreaks of the spruce budworm are a part of the natural cycle of events associated with the maturing of balsam fir.A key point is that outbreak frequency cannot be predicted.The catastrophe theory of budworm outbreaks holds that particularly major infestations occur every 40–60 years, as the result of a cusp-catastrophe event, whereby populations jump suddenly from endemic to epidemic levels.