Differential defoliation and mortality of white spruce and balsam fir by eastern spruce budworm

•Eastern spruce budworm defoliation causes tree mortality in forests.•In white spruce-balsam fir forests, balsam fir are typically preferred host trees.•Spruce budworm feed on reproductive buds and foliage.•Following a budworm outbreak, we found vastly higher mortality in white spruce.•Using model selection, only tree species came out as a primary explanatory factor.•Differential timing in mast-seeding events may contribute to differential mortality.