Gypsy Moth History
The Gypsy Moth (Lymantria dispar) is a pest of forests in North America. It is able to cause massive tree defoliation in a very rapid amount of time and many devastating outbreaks have occurred since it’s original, accidental, introduction to North America from Europe in the late 19th century.
Occurrences of Gypsy Moth have spread widely across North America and have been found in the following areas: Northeastern United States – Vermont, Massachusetts, New Hampshire, Rhode Island, Connecticut, New York, Pennsylvania, New Jersey, Delaware, Maryland, Wisconsin, Michigan, Illinois, Indiana, Ohio, West Virginia, North Carolina, Virginia, Maine, California, Utah, Oregon, Washington, Canadian Provinces of Ontario, Quebec, and British Columbia.
Gypsy Moth Hosts
It can affect a wide variety of tree hosts. In its larval stage, preferred hosts are alders, birches, aspen, hawthorn, mountain ash, oaks, willows, poplar, beech and more. Red cedar, chestnut, hemlock, plums, pines and spruces are preferred by older larvae, but are not as susceptible against younger larvae. Junipers, sycamores, ash, dogwood, yew, lilac, arborvitae, arrowwood and tulip trees tend to be less susceptible, overall, to gypsy moths.
Conifers tend to be more at risk because if they are defoliated by larvae, they do not push another flush of growth. Deciduous trees are able to produce new leaves even after a severe defoliation, but conifers, pines, and spruces are not able to produce new needles, so a severe defoliation event can cause tree death.
Economic Impact
Gypsy moth damage can be a very serious ecological concern in some areas. When severe infestation and defoliation occurs, it can result in ecological shifts for the entire area. Defoliation of trees by gypsy moths can also make trees more susceptible to other insect or disease infections. Dead trees may also be a safety hazard in parks or other wooded areas where people enjoy outdoor activities.
Gypsy Moth Identification
Eggs
Gypsy moth egg masses are light brown/ tan and the eggs inside are black. A single mass may contain between 400 and 600 eggs.
Larvae
Gypsy moth larvae are hairy. Older, mature, larvae are between 50 and 65 mm long. They can be distinguished by the yellow and black head, on the thorax and abdomen there are five pairs of blue spots and six pairs of red spots.
Pupae
Gypsy Moth pupae are dark brown with a reddish tint. They are hung by small silk strands.
Adults
Male adult Gypsy Moths are dark and fly frequently during the day. Female moths do not fly and are identified by white coloring with black marks. Their wingspan can be as large as 5 cm.
Gypsy Moth Life Cycle
Gypsy Moths go through a complete metamorphosis in their lives, from egg to larvae/ caterpillar to pupa to adult Moth. Eggs typically hatch in Spring (late april to mid-may), the exact timing is dependent on weather and location. Larvae emerge and are active during May and June. Weather based models are one way to help predict egg hatch and provide context for when to begin scouting for larvae. The Pest Prophet app provides an easy way to implement weather based models, including for Gypsy Moths, for a given location.
Larvae are voracious feeders that feed on a wide variety of trees including beech, birch, elm, maple and, though not preferred, pine, spruce or hemlock. They typically do not geet on ash or tulip poplar. As the caterpillars feed and grow, they go through several growth stages and molt 3 or 4 times, shedding their skin each time to accommodate new growth. These periods are called instars. The first instar larvae are very small, but by the fourth or fifth instar stage, the caterpillars are quite large. These large instars feed heavily and do the most damage to trees.
After the larvae stage, the caterpillars pupate before emerging as adults. Adult gypsy moths do not feed at all, and only live for about 2 weeks. In this time period, their only goal is to reproduce successfully. Adult females cannot fly, even though they do have wings. Male gypsy moths can fly long distances to pursue females. Their large antennae are used to sense pheromones from females. Males may mate multiple times in a season.
After successful mating, Gypsy Moths females lay from 600 to 1,00 eggs in one egg mass. The eggs appear as small, tear-dropped shaped masses. These eggs may be placed in a variety of places. Both adult and females moths die after mating season, and eggs are the means of overwintering.
Gypsy Moth Damage
Gyspy Moths damage trees and forest by feeding on leaves, defoliating them. 0-30% loss of foliage is defined as light defoliation. Defoliation of this level is usually not easily detectable, and the trees can recover. 31-50% is defoliation is defined as moderate defoliation and may cause problems for some trees, and while most trees will not die, Gypsy Moth management should be considered.
Heavy defoliation is above 50% of foliage lost. This level of defoliation can cause tree mortality in just one year to hemocl, pine or spruce. Deciduous trees will die after 2 or 3 consecutive years of heavy defoliation. At the heavy defoliation level, most trees will start to produce new leaf buds to establish new foliage in late Summer, but this comes with an energy cost to the trees and can cause plant stress.
Two years of light defoliation are usually the first signs of a more serious outbreak. Two years of moderate defoliation usually follow if no management steps are taken. Two years of heavy defoliation follow, and this can cause tree mortality.
In addition to damage to trees, Gyspsy Moths, can also be an irritant to people. Some people are allergic to the caterpillars, and the caterpillars’ hairs can cause rashes. Children are typically more affected, and symptoms are usually seen in May with smaller larvae.
Gypsy Moth Management
Cultural Control Methods
In some cases, when gypsy moth populations are very small, finding and destroying egg masses might be enough to suppress gypsy moth populations, before the larvae emerge. Egg masses might be found on trees or buildings. They can be killed with soapy water, or through burning them. Gloves should be used when handling egg masses, because some people might have an allergic reaction to the hairs that cover them.
Burlap can also be used to wrap around tree trunks. This can provide a place for older larvae, which allows for easy monitoring, and in cases of low population, the larvae can be killed directly. Barrier bands around trees, such as double-sided sticky tape, or grease can keep larvae from climbing up trees and reaching the leaves.
Stressed trees are also more susceptible to Gypsy moth defoliation. Watering trees, during drought, applying fertilizer if there a nutrient deficiency, or applying mulch to increase soil moisture are all methods to reduce stress on trees, which will help reduce Gypsy moth defoliation. Also, control other tree pests can be important.
Male moths are attracted to pheromones, and these can be used to bait adult moths into traps. This can be helpful for scouting, or quantifying gypsy moth populations, but large scale trapping has not been effective as a control method.
Chemical Control of Gypsy Moth
In cases of larger Gypsy moth populations, insecticide treatments may be required. There are several different active ingredients, including Bt (Bacillus thuringiensis) and other chemicals that have control against Gypsy Moths. Applications should be made after most of the eggs have hatched to kill smaller larvae before they cause serious damage.
The Pest Prophet app can be used to help time this initial application, based on that year’s weather data to maximize effectiveness. In some cases, repeat applications should be made with a rotation of chemicals. Always carefully read and follow the label when considering any pesticide use, and be aware of the possible negative effects to beneficial insects, or other animals.
Biological Control
Some areas of the United States have had some success with introducing native predators to an area with Gypsy Moth problems. For example there are fly and wasp parasitoids that have been released and established in Pennsylvania. Parasitoid predators can help keep lower populations under control, but generally will not be very helpful against large outbreaks.
Other predators such as birds, rodents or beetles can help keep gypsy moth populations under control. If the population of these predators are affected, gypsy moth populations may increase as a result.
There is also a naturally occuring virus that can kill gypsy moths. This virus is usually always present, but only really affects gypsy moths after heavy defoliation, when populations are very high, and moth larvae are in close contact with each other. The fungal insect pathogen, Entomophaga maimaiga can also infect Gypsy moth larvae, but like the virus, usually only occurs when gypsy moth populations have reach very high levels.
English 
Spanish