What is the primary feeding source of bark beetles?

Bark beetles primarily feed on the living layer of wood located just beneath the bark of trees, known as the cambium layer. This layer is essential for transporting nutrients and supporting the growth of the tree. When bark beetles infest a tree, they bore into this layer, which can ultimately lead to the tree's decline or death if the infestation is severe.

The other options do not accurately represent the feeding habits of bark beetles. While they may interact with dead wood or dry bark in their lifecycle or during certain stages, their main source of nutrition comes from the cambium layer of living trees. This highlights their role in the ecosystem as both pests and agents of decay, as they can contribute to the natural cycle of forest health when they infest trees that are already stressed or dying. However, when healthy trees are targeted, the impact can be detrimental to the tree population and surrounding ecosystem.