However, defoliation does decrease the energy reserves of the tree, reducing its ability to resist disease and insect pests to which it is normally resistant. Furthermore, defoliated trees are also much more susceptible to the damaging effects of drought. During the summer, trees should receive a combined total of one inch of water per week from rain and irrigation. Trees previously weakened by transplanting, drought, or other insects may be killed by gypsy moth defoliation. Evergreen trees, on the other hand, are frequently killed by one severe defoliation.
Gypsy moths can also have detrimental effects on the ecology of forests.
Severe defoliation disrupts the natural cycle of nutrients. It also increases the temperature and amount of sunlight that reaches the forest floor, which can be damaging for shade-adapted wild flowers and other plants. Widespread defoliation can also have negative impacts on wildlife. Defoliation of oak trees decreases acorn production, which is an important food supply for many animals. Many leaf-feeding insects can also starve when gypsy moth strips the forest canopy.