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. Successful management requires an integrated approach based on a number of techniques. The BT sprays used for gypsy moth affect only caterpillars, and are completely harmless to all other animals, including bees and other insects, birds, pets, and humans. In regions where gypsy moth has been established for a number of years, natural controls help keep populations in check during most years.