Population trends of a specialist herbivore, the spruce bud moth, in youngwhite spruce stands

We investigated the factors responsible fur changes in abundance of the spr uce bud moth, Zeiraphera canadensis Mut. and Free. (Lepidoptera: Tortricida e) in one unmanaged and several managed (i.e., planted) young white spruce, Picea glauca (Moench.) Voss (Pinaceae), stands in northern New Brunswick, Canada. Spruce bud moth densities declined when one stand closed (branches from neighbouring trees overlapped) acid had already declined in another si milarly aged closed stand, but remained high on 8- to 22-year-old open-grow n white spruce. Both the intrageneration survival rate and the egg-to-moth ratios increased when population densities increased, and generally decreas ed, although the egg-to-moth ratio fluctuated, during the population declin e in a managed stand. Increases in intrageneration survival rates of spruce bud moth on 5- to 10-year-old trees were due to increased larval or pupal survival. Crown closure explained 76 and 81% of the variability in larval a nd intrageneration survival, respectively, in four managed stands. The stro ng inverse relationship between larval survival and degree of crown closure resulted in statistically significant but spurious relationships between l arval survival and larval density and between larval survival and tree age. A reduction in larval survival occurring as degree of crown closure increa sed was the most important factor influencing decreases in intrageneration survival at the beginning of population decline. Increases in the egg-to-mo th ratio during the population increase, and decrease during population dec line, suggested that dispersal behaviour and (or) realized fecundity of fem ales also contributed to annual changes in population.