Abstract

Eastern spruce budworm (Choristoneura fumiferana) outbreaks have long shaped boreal forests by affecting tree health and stand composition. Prior work shows that warming can shift spring timing for both insects and trees, and that even small changes in synchrony between larval feeding and newly flushed foliage can affect larval development and survival. Host trees also differ in how their buds and tissues respond to temperature, so outbreaks depend on which tree species are pre-sent and when newly flushed foliage is available.
Within this context, we examined how temperature and host plant together influence budworm per-formance across the intake-to-growth pathway. Larvae were reared on balsam fir (Abies balsamea), white spruce (Picea glauca), and black spruce (Picea mariana) under ambient and warm condi-tions to see how warming might change feeding behavior and growth achieved on the three differ-ent hosts.
Warming did not affect performance in the same way for all hosts. It changes which processes lim-ited larvae and shifted the rank order of hosts. On white spruce (Picea glauca), growth increased despite lower feeding because digestibility and conversion of ingested material improved. On black spruce (Picea mariana), growth increased mainly because larvae ate more. On balsam fir (Abies balsamea), conversion and growth decreased even though feeding increased. Overall, warming enlarged host differences. The results show that at ambient temperature, balsam fir has the highest growth which exceeded both spruces species. Under warming, the pattern shifts: both spruce spe-cies show increased growth, whereas balsam fir declines because its conversion efficiency is re-duced.