Counts of SBW larvae collected in the fall as L2 or in the following spring as L4, from 75-cm branches or 45-cm branch tips (respectively) of balsam fir in the Ottawa River valley from 1998-2001, North Shore 2008-2010, and New Brunswick 2017-2022. Defoliation measured at the end of the feeding period after the L4 sample. Data linked to scientific paper: Régnière, J., Johns, R., Edwards, S., Owens, E., Dupont, A., 2023. Overwintering spruce budworm population density as predictor of following-year larval density and defoliation on balsam fir. For. Ecol. Manag. (submitted).