What Will the Gypsy Moth Do to My Trees?

Gypsy moth caterpillars have the potential to eat large numbers of leaves and therefore a logical question to ask is "what effect will it have on the tree?" Gypsy moth caterpillars begin feeding on leaves immediately after leaves appear in the the mid-to-late spring. Feeding by the caterpillars interrupts the natural growth of trees and nutrient cycling.

Many trees respond to extreme defoliation by producing new leaves (refoliation) during the same growing season. These new leaves are smaller in size and number and are lighter in color than the original leaves that were consumed earlier. The reduction of energy reserves during refoliation can result in the death of buds, twigs, branches, and entire trees. Most trees, even those that are healthy, may die if they undergo the defoliation/refoliation process for 2 or 3 consecutive years.

The stressed and weakened condition of defoliated trees often makes them more susceptible to attack by diseases, especially the shoestring fungus and another insect, a beetle called the two-lined chestnut borer . These organisms are often involved in the death of trees during gypsy moth outbreaks. The shoestring fungus lives in the soil and attacks the roots of stressed trees (those that have been defoliated) and then rapidly prevents these infested trees from obtaining nutrients. Larvae (immature stage) of the chestnut borer feed through the bark to the inner parts of the tree. As they feed, they make extensive tunnels and weaken the tree.

Does the gypsy moth kill trees? Tree death is usually caused by the cumulative effect of several different stresses. Defoliation and subsequent refoliation, together with infestation by other organisms is too much for many trees to withstand. Another signficant stress is drought. Trees that grow in dry areas and are defoliated by the gypsy moth or other insects are more likely to die after one defoliation episode than those trees that are well watered and fertilized.