• Morris, R.F.
  
• Miller, C.A.
  
• Greenbank, D.O.
  
• Mott, D.G.
  

The spruce budworm is the most destructive defoliator in eastern Canada and intensive studies on its population dynamics have been in progress for ten years on the Green River Watershed in northern New Brunswick. Life tables are developed for successive generations of the budworm in different types of forest stands and this paper presents the conclusions reached through the analysis of a large series of life tables. T he important sources of mortality are related to stand factors, population density, and or climate. Because of the high dispersal losses suffered by early-instar larvae and by moths, stand factors are the essential predisposing cause of outbreaks and outbreaks do not develop where the forest is sufficiently discontinuous or variable. Parasites respond to host density, in a delayed manner, and are capable of exerting control in stands where the increase in population in not too rapid or sustained; but in stands that are favourable to rapid population development, parasites suffer some limitation that is not yet understood and appear incapable of overtaking the host. Also, the transport of gravid moths stood and appear incapable of overtaking the host. Also, the transport of gravid moths by turbulent winds is related to topography and can destroy the synchronization in space between the budworm and its enemies. When stand factors are favorable, climatic cycles determined the general incidence of budworm outbreaks in time and place.