How do spruce beetles and spruce budworms damage taiga trees?

In the taiga, spruce budworms and spruce beetles cause significant damage to trees, often during population outbreaks triggered by environmental stress or unusual weather.1

• Spruce Budworms: These are the larvae of a leaf-rolling moth (Choristoneura fumiferana). They damage evergreens by feeding on needles and pollen. During severe outbreaks, they can completely defoliate spruce and related trees, leading to widespread injury or death.21
• Spruce Beetles: These insects are wood-boring beetles that infest conifers. They damage trees by burrowing into the wood, often inoculating the tree with fungi as they move through the bark and wood tissues.13

These outbreaks can become self-sustaining, affecting large areas of the forest until the population is limited by the depletion of host trees or the production of defensive chemicals by the plants.1