Several factors can cause a plant to lose its leaves and become defoliated. Defoliation is a natural and regular occurrence in the case of deciduous trees and shrubs that drop their leaves each year with the approach of winter. This process is aided by an abscission layer that develops at the base of the leaf petiole, weakens the attachment to the plant, and eventually causes the leaf to drop. Severe drought may also cause leaves to wilt, dry and drop from a plant. The result of severe dehydration is usually lethal for herbaceous plants, although some woody species may survive an episode of drying. Heavy infestation by leaf-eating insects can lead to partial, or complete defoliation. The gypsy moth (Porthetria dispar) is an important defoliator that attacks many trees, defoliating, and weakening, or killing them. Parasitic wasps that feed on the larvae can help to control gypsy moth...