The Impact of the Gypsy Moth to Sugar Maples

Junk Food for Caterpillars

• Maple and oak tree leaves contain the same kind of protein, but oak leaves have as much as 30 to 40 percent more essential amino acids, the building blocks of protein, than maple leaves. As the name "sugar maple" implies, subsisting solely on maple leaves is the caterpillar equivalent of trying to feed a growing child a strict junk food diet. Researchers believe this is why gypsy moth caterpillars rarely do as well eating maple leaves as their oak-consuming counterparts. With less nutrition come slow-growing caterpillars, smaller pupae and fewer adolescents reaching adulthood.

Too Many Toxins

• Other than their amino acid content, oak and maple leaves have about the same texture and toughness, as well as similar nitrogen and polyphenol levels. Polyphenols are naturally occurring alcohols in plants that can have positive or negative effects on the consumer. In the case of the gypsy moth larva, these trees' polyphenols have negative effects. However, as spring heats into summer, the polyphenol levels in red oak leaves declines, but they increase in sugar maple leaves. This serves as another reason why sugar maple is an inhospitable host to the gypsy moth offspring.

Why Gypsy Moths Are Pests

• The gypsy moth was brought to the United States in 1868 and has made itself a nuisance throughout North America ever since. The female gypsy moth is unusual among winged insects because she cannot fly. The female lives out her entire life on the same tree and will repopulate it with new moths, which attributes to infestation. When an adult female gypsy moth hatches from her pupa, she emits a pheromone to attract males. After mating, the female deposits a clump of eggs on the tree trunk or a branch. The adult portion of her life lasts only about one week, and she dies before her eggs hatch. When the eggs hatch and caterpillars emerge, the cycle of infestation begins again for the tree. After molting, feeding and growing throughout the summer the caterpillars pupate. Pupae that survive the winter then emerge in spring as adult moths. Adult moths do not feed.

Impact on Sugar Maple and Other Trees

• The level of damage gypsy moths inflict on trees is classified as light, moderate or severe. Destruction of zero to 30 percent of a tree's leaves is classified as light defoliation, 30 to 50 percent is moderate, and greater than 50 percent is considered severe. In most cases, the caterpillars only do light damage to sugar maple trees and the trees can easily survive with no long-term effects. Moderate to severe defoliation is more likely with other kinds of trees. Severe defoliation can cause the death of a tree, and repeated years of moderate defoliation can do permanent damage, stunting the tree's growth and limiting its ability to obtain nutrients.