The European strain of gypsy moth (Lymantria dispar), one of the most destructive defoliating insect pest to attack the trees and forests of the northeastern United States, is well established in Ohio.  The European strain of gypsy moth was brought into the United States in 1869 for breeding experiments with silk worms.  It escaped from a research laboratory in Medford, Massachusetts, and has gradually spread throughout the Northeast.  It has spread slowly, largely due to the short life span of the adult moths, the inability of the adult female to fly, and the low density of preferred host tree species in the some geographic areas (such as northeast Ohio).  To date, the Asian strain of gypsy moth, discovered for the first time in the United States in 1991 in Oregon and Washington and again in 1993 in North Carolina, has not been observed in Ohio.

            The European strain of gypsy moth is a serious rural and urban pest, and a social and political problem, as well as an ecological menace.

            In rural areas, gypsy moth defoliation has resulted in reduced forest health and growth, the death of individual trees and the death of entire forest stands (Figure 1).  Literally millions of acres of forested land in the northeastern U.S. have been defoliated by gypsy moth. These impacts result in substantial economic loss, not only from timber products, but from the many outdoor recreation activities that rely on the appearance and health of forests.  In addition, major long-term changes often occur in the forest, which affect their future value and appearance.

            In the urban environment gypsy moth impacts can be devastating.  Reduced urban tree health, increased tree mortality, and the abundance of larvae and larval feces all reduce the attractiveness of a community for both residents and travelers (Figures 2A and 2B).  This translates directly to major economic losses as property values fall and excursionists, tourists, and conventioneers choose not to visit the community.  At the same time, community budgets are additionally strained with attempts to control gypsy moths, remove dead and dying trees and maintain a sanitary environment.  Also, the larvae have stinging hairs that can cause mild to severe reactions in some people.  Peoples’ reactions to these various impacts may result in psychological problems and general public unrest.  Situations where neighbors threaten each other or violently disagree over control methods are not uncommon.

Life Cycle of Gypsy Moth (European Strain)

           

The European strain of gypsy moth produces one generation each year consisting of four stages:  egg, larva (caterpillar), pupa (cocoon) and adult.  During July and August, tan to buff-colored egg masses, approximately 1 ½ inches long and ¾ inch wide, containing as many as 1,000 eggs, are deposited by female moths on tree trunks, branches, logs, rocks, buildings, etc. (Figure 3). Eggs over winter and hatch in late April or early May.

            Newly hatched larvae are about ½ inch long, hairy and mostly dark brown to black.  Shortly after they hatch, young larvae climb into the tops of trees in response to light.  Many of these small caterpillars will suspend themselves on silken threads and be picked up by wind currents and carried into trees from a few feet to several miles away.  This “ballooning” is an important method of dispersal for gypsy moths because adult female moths do not fly.

            Larvae of the European strain of gypsy moth pass through five or six growth stages, called instars.  Most defoliation is caused by the last two instars.  At this time, the caterpillars are 11/2 inches or longer in length, predominately black, and have two rows of spots down their backs, the first five pairs blue in color and the remainder red (Figure 4).  Late in June or early in July caterpillars seek out protected spots and transform into immobile pupae, which resemble hairless, dark brown teardrops, approximately ½ - 1 inch long (Figure 5). Pupation requires about two weeks.  Adult moths emerge in July or August.  Male moths emerge first and fly in a characteristic zigzag manner during daylight.  Females emerge and crawl only a short distance.

            Male moths have brown bodies, brown wings with black markings, and a wingspread of approximately 11/2 inch.  Female moths are off-white with yellow to buff colored markings on their abdomens, black markings on wings, and a wingspread of approximately 2 inches (Figure 6).  The female emits a pheromone (sex attractant) that guides the male to her.  Mating occurs and the female lays eggs shortly thereafter.  The male dies after mating; the female after laying eggs.  Adult moths do not feed.

The Spread of Gypsy Moth in Ohio

           

The European strain of gypsy moth is now generally found northeast of a line extending from Toledo to Marietta, with spot infestations scattered throughout the other parts of the state.  Populations within this area vary considerably from one wooded area to the next, depending upon the mixture of tree species.  Woodlots containing a relatively high proportion of oak are the most likely to contain the greatest number of gypsy moths.  Gypsy moth populations within the area are capable of causing complete defoliation to the woods they inhabit.

            Aerial surveys conducted during June and July each year reveal that in 1996 and again in 1999 forest defoliation levels reached about 50,000 acres in Ohio   This represents a substantial increase over the previous high of 34,000 acres in 1995. This increase is due, in part to the increased availability of more preferred host material as gypsy moth entered the un-glaciated portions of Ohio, which are predominantly oak-hickory forests containing high proportions of gypsy moth preferred host tree species. Gypsy moth populations also change in response to weather patterns, increasing dramatically during hot, dry conditions.  About 23,300 acres were also defoliated in twenty counties by gypsy moth in 2000. 

The natural spread of gypsy moth is continuing to occur out of the northeastern corner of Ohio in a south – southwesterly direction.  Storm systems crossing the state during May are thought to be responsible for transporting young larvae into new counties, especially those nearest to the leading edge of infestation.  This, together with the people assisted movement of egg masses on a variety of articles, such as automobiles, campers, outdoor furniture and firewood, has caused the gypsy moth to be found, at some level, in nearly all counties of Ohio. 

Minimizing the Impact of Gypsy Moth

           

The statewide effort to minimize gypsy moth impacts in Ohio is a four-pronged approach involving eradication of isolated populations, suppression of gypsy moth in areas of high impact, regulation of the movement of articles that might transport gypsy moth, and education.  The Ohio Department of Agriculture is the state agency charged with lead responsibility for dealing with gypsy moth.  In many activities, however, it is joined by a variety of agencies and organizations including the United States Department of Agriculture Animal and Plant Health Inspection Service (APHIS), the Untied States Department of Agriculture Forest Service, Ohio State University Extension, and the Ohio Department of Natural Resources.

 

Eradication   High moth catches in a county remote from the leading edge of infestation may indicated the presence of a new gypsy moth population, particularly if those catches are concentrated within a small geographical portion of the county.  When a new isolated population is found to exist under such circumstances, an eradication plan to eliminate that population is devised.  Eradication plans usually include one or more applications of an insecticide over the entire infested site.   These treatments are conducted during the period of larval feeding in May and Bacillus thuringiensis (commonly called BT) is the most commonly used insecticide (see discussion following under suppression).  The expectation is that by eliminating these outlying populations, the spread of gypsy moth to the west and south of the generally infested areas will be more gradual event than if the outlying populations are allowed to expand and coalesce.

 

Slow The Spread  A new national program called Slow-The-Spread is replacing the old eradication programs in states along the leading edge of the gypsy moth infestation. Ohio is currently one of these states. An extensive network of traps is used to determine male moth densities present in local areas.  This information can then be used to identify the isolated infestations out in front of the advancing edge of the gypsy moth infested area. These isolated populations are controlled by the use of biologicals, such as Bt or by the use of pheromone flakes for mating disruption.  Pheromone is a sex attractant released by the female moth to attract the male moth for mating purposes. When this material is applied in large quantities it can confuse the male and disrupt the mating process, thus lowering or eliminating the population.

 

Regulation   A state gypsy moth quarantine was established in 1987.  This quarantine complements the eradication program by attempting to minimize the movement of egg masses into non-infested areas of Ohio.  Specifically, the quarantine identifies infested areas of Ohio, identifies those articles that commonly harbor gypsy moth (eggs), and sets forth conditions for moving those articles from infested areas to non-infested areas within the state.  A long-standing federal quarantine regulates the interstate movement of regulated articles in a similar manner.

 

 

Suppression  Within the generally infested counties of northeastern Ohio, a state-sponsored suppression program has evolved that is intended to mitigate or suppress the impact of the gypsy moth within that area of the state.  Typically, suppression projects include a single aerial application of insecticide to selected wooded sites where the potential for impact is considered high.  Factors used to select such sites include: a) high gypsy moth population; b) high percentages of susceptible tree species; and c) land use of area including economic, social and cultural impact.

             Approximately 7,220 acres of wooded and wooded residential areas in three northeastern counties were treated during the 1995 gypsy moth suppression program.  Suppression treatment acreage has risen to a high of almost 60,000 acres in 2000. Treatments are expected on around 30,000 acres in 2001. Unlike eradication projects, suppression treatments are conducted only with each landowner’s consent and after the treatment proposals have been discussed and endorsed by county officials.  In several counties local advisory committees have been formed to provide the county commissioners with guidance and recommendations on the proposed treatment sites and choice of insecticides.

            At the present time, two insecticides are being used for most suppression treatments:  Bacillus thuringiensis (commonly called BT) and Dimilin.  A third insecticide, Gypchek, is a virus-based material available for suppression treatments in very sensitive areas.  Gypchek is very target-specific with respect to the insects it affects, but is only available in very limited quantities.

            Bacillus thuringiensis, the most frequently used insecticide, is a biological insecticide (a bacterium) that produces a toxin lethal to gypsy moth and other moths and butterflies.  To be effective, BT must be ingested by caterpillars as they feed on foliage.  Dimilin is a growth regulator that prevents the synthesis of chitin, an essential ingredient in an insect's skeleton.  Like BT, Dimilin must be ingested by the caterpillars as they feed on foliage.  After ingesting Dimilin, gypsy moth larvae cannot successfully grow to a larger size and soon die.  Neither insecticide is considered to have any significant contact toxicity.

            BT is generally perceived as an environmentally “safer” insecticide because it is toxic to fewer non-target insects than Dimilin.  On the other hand, Dimilin has proved to be a more effective at reducing gypsy moth populations.  Both insecticides provide foliage protection, and each may have a role in suppression programs.

            In the late 1980s a fungus, Entomophaga maimaiga, was identified as an effective gypsy moth pathogen, capable of decimating older (late instar) larvae populations over a wide range of densities.  This fungus appears to be one of the most promising “natural” controls to emerge in some time.  The Ohio Department of Natural Resources has been working in cooperation with Dr. Barry Hunter, of the California University of Pennsylvania, to release this fungus on State Forests and other public lands and study its effect on Ohio gypsy moth populations.  Interestingly, during the course of this project, some existing fungus populations have been identified in Ohio.  Favorable weather conditions in 1996-1998 contributed to the natural spread of the fungus to many gypsy moth infested areas.

 

Education   Current demand for education/information about gypsy moth in Ohio is low.  Over the past nine years numerous meetings, news releases and publications have been presented, primarily at the instigation of concerned agencies or organizations.  Experience in the eastern U.S. suggests that few citizens will become interested or concerned with gypsy moth until it is well established, highly visible, and directly affects them.  This often translates to when gypsy moth substantially impacts a major urban county, such as Cuyahoga or Lucas.

            As citizens become actively concerned, a wide variety of kinds of information will be increasingly demanded, including general information on the problem, survey information on population levels, impact assessment, control/management strategy development, pesticide safety and use, potential health hazards and solutions, and training sessions for effective community strategy development.  A listing of groups or individuals requiring information to effectively address gypsy moth problems would be extensive, but certainly includes municipal, township, county, and state leaders and administrators; state legislators; media; public agencies; individuals and agencies with control/management responsibility; rural landowners; urban home-owners; individuals and agencies with educational responsibility; tree management professionals such as grounds superintendents, golf course managers and park managers; and general public.  Again, experiences in the eastern United States suggest that when citizens become concerned the demand for all forms of education will be overwhelming.

 

Authors

 

Daniel R. Balser

Forest Health Administrator

Ohio Department of Natural Resources

Division of Forestry

Columbus, Ohio

 

Randall Heiligmann

Associate Professor & State Forestry

Extension Specialist

The Ohio State University

Columbus, Ohio

 

 

Dr. Bill Pound

Gypsy Moth Program Manager

Plant Pest Control Section

Ohio Department of Agriculture

Reynoldsburg, Ohio