The following is information on damage from Leopard moth caterpillars, a pest you may see in Delaware.
At 2-3” long, the leopard moth (Zeuzera pyrina) is a large moth, introduced from Europe/N. Africa and found May-September in Delaware. Adults have black and white spots on their wings. Early symptoms of damage from Leopard mothe caterpillars are girdled or broken twigs and branches with wilted/yellow foliage. Monitor trees for branch and limb dieback, which may be mistaken for squirrel activity. Scout dead limbs for exit holes (possibly with silk coverings and resin flow) at the end of broken stems. Fine white frass pellets and possibly pupal skins may be left in bark crevices and inside these galleries.
Larvae damage over 125 tree species incl. oaks, maples, lilacs and apples. They have an unusual life cycle (2 years or longer). Several yellow eggs are laid in small clusters usually in bark crevices. After 10 days, newly hatched larvae crawl some distance before burrowing into a young branch and tunneling into the heartwood to begin feeding. When a branch is too small, the caterpillar exits the branch, migrates along the outside, and tunnels into a larger branch to complete its next caterpillar stage. At the end of the first year, caterpillars are 1” long, yellow with dark spots. At maturity (2”), tree branches up to 3.5 inches and tree trunks may have been fed upon. Pupation occurs in its final gallery.
Leopard moth seems to strike only individual trees and does not spread rapidly. Female moths are not strong fliers. Spread may be through infested nursery stock. Control by pruning out affected limbs/branches. Woodpeckers, other birds and squirrels are important biological controls. As with all borers, growing a healthy tree is the best defense against injury. Chemical control is not practical because of the lengthy flight time. Note that this species shouldn't be confused with the Great/Giant Leopard Moth (Hypercompe scribonia) a native woolly bear caterpillar.
Leopard moth. Photo by James Solomon, USDA Forest Service, Bugwood.org
Leopard moth caterpillar tunnelling in wood. Photo by James Solomon, USDA Forest Service, Bugwood.org
Information from Casey Sclar, IPM Coordinator, Longwood Gardens and Emma Seniuk, Professional Gardener Student, Longwood Gardens