The gypsy moth passes through 4 stages: egg, larva (caterpillar), pupa, and adult (moth stage). Only the larval stage damages trees and shrubs.

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1 Gypsy Moth Revision Date: 3/1/2004 Dewey M Caron, Extension Entomologist Derby Walker, Extension Agent ENT-18 The gypsy moth (Lymantria dispar L) is the most serious insect pest of hardwood trees in Delaware In the 80 s & 90 s, the gypsy moth defoliated more than a million acres each year in the eastern US Infestations alternate between years of little defoliation followed by periods of 2 to 4 years of heavier defoliation when gypsy moth populations are heavier Of late infestations have been considerably reduced Gypsy moth caterpillars eat a wide variety of plant materials They have been recorded to feed on over 500 tree, shrub, and vine species Oak trees are the preferred food Infestation and heaviest defoliation in Delaware have been along our western boundary with Maryland where oaks predominate in our woodlots Populations are highest in Kent County and western Sussex County The gypsy moth is not a native insect It was brought to the US before laws governing importation of organisms were in force It was considered a potential caterpillar for production of silk An amateur French naturalist accidentally released gypsy moths from his home in Medford, Mass, in 1869 The first outbreak of the moth as a forest pest was 1889 It remained a local pest in Massachusetts and New England until more recently Today it continues to spread westward in the US It is a major eastern forest pest Life Cycle The gypsy moth passes through 4 stages: egg, larva (caterpillar), pupa, and adult (moth stage) Only the larval stage damages trees and shrubs The female adult gypsy moth lays her eggs in buff-colored egg masses during the summer They remain on host trees over fall and winter months Hatching of eggs coincides with budding of trees in early spring, usually by mid-may The small, first instar larvae are easily dispersed by "ballooning" The wind carries the tiny caterpillar sometimes great distances as it hangs by a silken thread Shortly after emerging from the egg in early May, the caterpillar is mostly black and 1/8 to 3/16 inch long Its long hairs are somewhat bristly, not soft and silky like the hairs of the tent caterpillar These hairs grow out of knob-like tubercles along the back The tubercles It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, color, sex, disability, age, or national origin

2 just behind the head are larger than the others, which helps distinguish the gypsy moth from other caterpillars After a few days, each larva (caterpillar) sheds or molts its skin After the first molt, the caterpillar increases in length to about 3/8 inch and has a tan stripe down the back When it molts the second time, it is larger, about 5/8 inch long, and has several bright-orange marks down its back By the time it is fully grown, to about one inch long, it will have five pairs of blue spots down its back, followed by six pairs of red spots The first 3 larval instars stay in the branches of the crown of host trees Larger fourth instar caterpillars move down the tree to rest during daylight hours, returning up the tree trunk to feed at night Larvae reach full size by mid- June to early July The pupa stage is spent in locations where the larvae hide, such as in bark crevices or on the ground Males emerge before females Males fly in a characteristic zigzag pattern Females do not fly; they attract the males to their location by emitting a pheromone After mating, females lay eggs in July or August to complete the life cycle Is that a Gypsy moth? It is important to distinguish gypsy moth caterpillars from other caterpillars that defoliate trees Tent caterpillars are usually full-grown caterpillars of 2 to 2-1/2 inches long when gypsy moths are still in their third stage of growth (about 5/8 inch long) The fall webworm will be smaller than most gypsy moth caterpillars The cankerworm is hairless and pale to dark green and should readily be identifiable from gypsy moths To be certain you have gypsy moths check reference materials or with local authorities It is difficult to distinguish adult gypsy moths from other moths Traps with synthetic pheromone are commonly used to capture males to help detect early infestations In the established range of the gypsy moth (New England west to Michigan, Ohio, West Virginia, and southward to Virginia), state agencies conduct egg mass surveys in the fall months Action thresholds vary from 250 to 1000 egg masses/acre Effect of defoliation on trees The initial defoliation of Delaware forest/shade trees by gypsy moth was in 1981 when an estimated 250 acres were defoliated Heavy defoliation (over 14,000 acres) occurred in 1984 Since then, defoliation has varied from under 1000 acres to over 5000 acres annually Compared to neighboring states, Delaware has not yet experienced heavy deforestation of our approximately 225,000 acres of forested land Defoliation effects depend on the amount of defoliation, the condition of the trees during and following the damage, the host itself and soil moisture availability With less than 50% defoliation, trees may show slightly slower growth but not otherwise be harmed With more than 50% leaf loss, the host tree usually produces a second flush of midsummer leaves with

3 reduced annual growth Healthy trees can withstand one or two consecutive defoliations of 50% or greater Some trees in some stands such as conifers will die with a single defoliation, but most broadleaf tree species can survive a single defoliation Defoliation weakens trees and leads to other stresses Refoliation uses tree energy reserves Heavier infestations and subsequent defoliation may result in large numbers of trees dying In heavy caterpillar infestations, even evergreens like pines and hemlocks may be defoliated These are normally not preferred hosts A single defoliation will kill 50% of pines and 90% of hemlocks Effects of defoliation can be reduced by providing heavily defoliated trees with ample water during the summer following defoliation Feeding, either before or after defoliation, should help to save trees Mulching is also desirable Some biologists believe gypsy moth outbreaks are temporary phenomena that will decline to tolerable levels if people do not interfere with natural events by spraying toxic chemicals While this may be true, there are few data to support such a belief Gypsy moth control It is impossible to eliminate gypsy moth populations but something can be done to keep populations within manageable limits Tactics include monitoring gypsy moth populations, maintaining the health and vigor of trees, enhancement and encouragement of natural enemies, and using insecticides to treat potential outbreak populations Natural enemies Natural enemies play an important role in gypsy moth control during normal years of light infestations Scientists are actively looking for parasites and predators of the gypsy moth, principally in Europe and Asia Over 10 foreign biological control agents (parasites, predators and disease organisms specific to gypsy moths) have been introduced for control purposes Natural enemies include wasps, flies, ground beetles, and ants Spiders eat many small caterpillars Birds such as chickadees, bluejays, nuthatches, towhees, and robins are control agents as are several woodland mammals like whitefooted mice, shrews, chipmunks, and squirrels Gypsy moths have several diseases, caused by bacteria, fungi, or a virus The NPV virus disease is the most destructive to this pest When conditions are right, it will nearly eliminate gypsy moths in an area for a few years The disease occurs, and works best in control after a long period of rain or during very humid weather when the caterpillars are feeding Homeowner control Homeowners can use measures that would be too costly for large forested areas These will provide some measure of control in normal years, but none of these measures will be effective during a gypsy moth outbreak year Control options for the homeowner include the following:

4 Remove objects around homes that shelter caterpillars or provide egg-laying spots for females Diversify composition of trees and plants on your property to include species not preferred by gypsy moths such as tulip poplar, honey locust, ash, hickory, dogwood, mountain ash, or conifers Destroy gypsy moth egg masses in fall and winter Place burlap on valuable trees like oaks and destroy larvae that rest beneath the flaps during active season (banding) Use sticky barriers to help keep larvae from climbing up trees to feed on their foliage It is important not to apply sticky materials directly to tree bark Keep ornamental trees healthy, well-watered, and fertilized Avoid mechanical injury to roots or trunks or conditions that lead to root compaction Chemical control Only one emergency measure is available in a gypsy moth-outbreak situation spraying with an insecticide To be effective, insecticidal sprays must be applied before caterpillars reach the fourth instar Insecticide sprays must be applied early enough to affect the young caterpillars, and they must cover nearly all the foliage to be effective They could be applied with ground equipment such as hydraulic sprayers, mist blowers, or small, hand-operated sprayers Aerial application by helicopter or small plane on small lots or in forested areas is practical only if the whole area is treated Streams, ponds, reservoirs, and similar bodies of water must not be contaminated with chemical insecticides It is recommended that Bacillus thuringiensis be used in such places This biological insecticide should also be used in areas where there is concern about the effects of spraying on song birds, wildlife in general, and where people may protest the use of chemical insecticides It is more expensive than chemical insecticides and may not be quite as effective, but because it has less adverse environmental impact, it may be worth the extra cost If Bacillus thuringiensis is used, do not expect to see the caterpillars dropping dead right away Timing of insecticide sprays will vary according to temperature and other weather conditions In Delaware, most gypsy moths will be in the second and third stage of growth about mid-may, and that's the best time to spray For precise timing, check caterpillars for development Most should be between 1/5 and 1/2 inch long for best results Acephate, carbaryl, cyfluthrin, esfenvalerate, difluibenzuron, and permethrin are other insecticide products that can be used Pesticides mentioned in this publication are generally listed as the active ingredient or common chemical name The active ingredient is the chemical in the formulation that is active against the pest Read the pesticide label to determine if the correct active ingredient is present Regardless of the product you choose, be sure the plant and/or the pest you want to control is on the label Disclaimer: Mention or exclusion of any product is not intended to discriminate for or against any products No endorsement is intended for the products mentioned, nor is criticism meant for products not mentioned Please read labels before purchasing and then read them before using to ensure that target sites are listed

5 Additional information The state of Delaware has a flyer entitled "The Gypsy Moth in Delaware" It includes some color photos of life stages and life history It also discusses control of gypsy moth The Delaware State Department of Agriculture publishes a newsletter on gypsy moths that provides details on plans for the large-scale, state-supported spray program The extent of this program varies each year, depending upon egg survey results and funds available for support of the program Contact the Delaware Department of Agriculture ( ) to be put on their mailing list