Insect pests of forest trees

Plants and insects have coevolved for millennia, providing a rich history of evolutionary reactions and relationships. Insects use plants for every stage of their life, and some plants depend on insects for survival. Forests cover nearly a third of the world, and there is a wide range of diversity in forest-herbivore interactions. Different insect species have evolved to utilize every part of a tree, from the fine roots to the leaves, for things such as food, shelter, and reproduction. Insects employ several different feeding strategies to target specific tree tissues; likewise, trees have evolved several defense mechanisms to protect themselves from herbivory. Most insect herbivory will not kill the host tree; however, there are exceptions. Some native species are very aggressive herbivores, capable of killing large expanses of forest. Invasive species, nonnative to their new environment, are much more likely to cause tree mortality and widespread damage to forests. This chapter will discuss the diverse and complex interactions between insects and trees, as well as several case studies with native and nonnative insect pests and potential impacts of future climate change on tree-herbivore relations.