Gypsy Moths and Trees

It's hard to believe that a small moth can be so deadly to something as hardy and large as a tree and yet the gypsy moth is one of North America's most devastating forest pests.
What does the gypsy moth primarily feed on? Typically its most common hosts are oaks and aspen but they have been known to feed on the foliage of hundreds of species of plants in North America with the highest concentrations of host trees are in the southern Appalachians, the Ozarks, and in the northern Lake States.
This moth becomes powerful due to its numbers. It lays its eggs in masses, typically on branches and trunks of tree. The egg clusters are buff in color when first laid but may bleach out over the winter months when exposed to direct sunlight and weathering. Egg clusters contain from a couple of hundred to about 1200 eggs, although some batches may be as small as 50 eggs. Gypsy moths are dispersed in two ways; the first is through wind carrying newly hatched larvae hanging from host trees on silken threads. Larvae can travel for up to one mile with eggs carried even longer distances. Artificial dispersal occurs when people accidentally transport gypsy moth eggs thousands of miles from infested areas on cars and recreational vehicles, firewood, household goods, and other personal possessions. Females are flightless in most varieties, so these are the only means of spreading.
Tree damage is caused when the insect larvae, or caterpillars, emerge from their eggs to the leaves of trees and begin to eat them. The feeding occurs mostly at night. The gypsy moth caterpillar has a special preference for the leaves of deciduous hardwood trees such as maple, elm, and particularly oak.  They can also feed on apple, alder, birch, poplar and willow trees.  As the moth grows it will also attack evergreens like pines and spruces.  Gypsy moths appear to dislike ashes, sycamores, butternuts, black walnuts, dogwoods and balsams.  However, during heavy infestations, competition for food will drive the caterpillar to attack almost any tree or shrub.
Depending on the degree of infestation, tree damage ranges from light to almost complete defoliation.  Most deciduous trees can survive a moderate degree of defoliation.  Many can even survive one complete defoliation by the gypsy moth caterpillar.  However, continuing attacks can fatally weaken a tree or leave it vulnerable to other insects or disease. The condition of the tree at the time it is defoliated, the number of consecutive defoliations, available soil moisture, and the species of host will determine if the tree continues to live or dies. If less than 50 percent of their crown is defoliated, most hardwoods will experience only a slight reduction (or loss) in radial growth. If more than 50 percent of their crown is defoliated, most hardwoods will refoliate or produce a second flush of foliage by midsummer. Healthy trees can usually withstand one or two consecutive defoliations of greater than 50 percent. Trees that have been weakened by previous defoliation or been subjected to other stresses such as droughts are frequently killed after a single defoliation of more than 50 percent.
A number of tactics have the potential to minimize damage from gypsy moth infestations and to contain or maintain gypsy moth populations at levels considered tolerable. These tactics include monitoring gypsy moth populations, maintaining the health and vigor of trees, discouraging gypsy moth survival, and treating with insecticides to kill larvae and protect tree foliage. The tactic or combination of tactics used will depend on the condition of the site and of the tree or stand and the level of the gypsy moth population.
Yes, believe it or not this small insect can cause this much damage. If you think your trees have been infested by gypsy moths, call your local agricultural cooperative agency or arborist to find out what you can do to stop the damage.

Andrew Johnson is the owner of Central Texas Tree Care, a leading tree service provider in Central Texas (Travis County and surrounding areas) offering services such as pruning and removals, cabling and bracing as well as arborist reports, diagnostics, pest management, fertilization and Austin tree service trusts. For more information please visit http://www.centraltexastreecare.com.