In eastern Canada, B.t.k. has been sprayed on outbreaks of eastern hemlock looper to control outbreaks. In British Columbia two formulations of B.t.k. were tested in 1993 and shown to effectively control the western hemlock looper. However, incorporation of the western hemlock looper into the registration of these two B.t.k. formulations is still pending. Therefore, at this time there are no biological insecticides regisitered for use against the western hemlock looper. The eastern spruce budworm is the most destructive defoliator of spruce-balsam forests in North America.
Outbreaks usually cover extensive areas and last several years.
Short-term population fluctuations often occur during outbreaks. Such fluctuations influence the rate of tree mortality thereby affecting control programs and potential salvage operations. Unfortunately, these fluctuations usually can not be reliably predicted. Fire suppression and the retention of overmature spruce stands render forests more susceptible to attack. Spectacular increases in outbreaks have also coincided with unusually heavy production of staminate flowers on spruces and balsam.