What's New Forestry Important Insect and Disease Pests of Pennsylvania Forests Hundreds of insects have adapted to living and feeding on forest trees, and in most cases, without harm to the host. These species of insects have specialized their behaviors to reduce competition among themselves.
Most insects have a short life cycle and produce many offspring.
Almost all of the offspring die before reaching adulthood. When more than the usual number of offspring survive to the adult stage, the numbers increase and develop into insect outbreaks. There are about a dozen species of insects which sometimes reach outbreak numbers and cause a lot of damage to forest trees. These can also be a nuisance for people who live, work or recreate in the forest.