Asian Gypsy Moth

The Asian gypsy moth (AGM) (Lymantria dispar),

named for its home continent, is a voracious pest of

trees that poses a major threat to forest habitats in

North America.

Background 

AGM was first identified in North America late in

1991 near the Port of Vancouver in British Columbia,

Canada. Moths were discovered in Washington,

Oregon, and British Columbia shortly after that.

Ships infested with egg masses from ports in

eastern Russia probably introduced the pest to North

America while visiting ports on the West Coast.

Scientists believe that while the ships were docked,

larvae hatched from the eggs and were blown

ashore. APHIS and State officials eradicated that

infestation in the Pacific Northwest through trapping

and spraying activities.

Another AGM infestation, this one in Sunny Point,

NC, was caused by moths emerging from a ship 

carrying infested cargo containers from Germany.

AGM was not known to occur in Europe until 

tracebacks of this introduction led the U.S.

Department of Agriculture (USDA) there. The North

Carolina infestation was declared eradicated in

November 1997. Also in 1997, AGM was again

detected in the Seattle–Tacoma, WA, area. The joint

Federal and State eradication program ended in

1999. Finally, in 2000, AGM was discovered in

Portland, OR.

Impact

If established in the United States, each AGM

female could lay egg masses that in turn could yield

hundreds of voracious caterpillars with appetites for

more than 500 species of trees and shrubs. AGM

defoliation would severely weaken trees and shrubs,

killing them or making them susceptible to diseases

and other pests. Caterpillar silk strands, droppings,

destroyed leaves, and dead moths would be a 

nuisance in homes, yards, and parks.

A pest–risk assessment prepared by the USDA’s

Animal and Plant Health Inspection Service (APHIS)

and the USDA’s Forest Service concluded that

because of similarities between Asian and North

American ecosystems, the AGM has great potential

for colonization in North American forests.

Comparing Gypsy Moth Pests

The AGM is similar to the European gypsy moth

that is found in the northeastern United States and

southeastern Canada. Like the European gypsy

moth, AGM prefers forest habitats and can cause

serious defoliation and deterioration of trees and

shrubs. The European gypsy moth has more than

250 known host plants but prefers oak. The AGM

has a much broader host range, including larch, oak,

poplar, alder, willow, and some evergreens.

AGM females are active fliers, unlike the 

flightless female European gypsy moths. The ability

of AGM females to fly long distances (up to 20 miles)

makes it probable that the AGM could quickly infest

and spread throughout the United States. In contrast, the European gypsy moth has taken more than

130 years (since 1869) to spread throughout the

Northeast.

In the East, European gypsy moths defoliate an

average of about 4 million acres each year, causing

millions of dollars’ worth of damage. If AGM were to

become established in the United States, the damage

could be even more extensive and costly.

Life Stages

The AGM matures through four life stages: egg,

larva (caterpillar), pupae (cocoon), and moth.

AGM egg masses may be found on trees, stones,

walls, logs, lawn furniture, and other outdoor objects.

Each egg mass can contain more than 1,000 eggs.

The mass is covered with buff or yellowish fuzz from

the abdomen of the female. While the velvety egg

masses average about 1–1/2 inches long and about

3/4 of an inch wide, they are often as small as a

dime.

AGM eggs begin hatching into caterpillars in the

spring. All of the damage caused by the AGM is

done during the caterpillar stage, as the insects feed

on leaves during this active period of growth. AGM

caterpillars stop feeding when they enter the pupal or

cocoon stage. This stage begins in June or July,

depending on weather and temperature. Adult moths

emerge from the dark brown pupal cases in 10 to 14

days. Adult males have grayish-brown wings and a

wingspan of 1–1/2 inches. Adult female moths are

white and larger, with wingspans up to 3–1/2 inches

or more.

AGM’s do not feed in the moth stage (which lasts

1 to 3 weeks) but only mate and lay eggs. Eggs are

laid between July and September, depending on

weather and location. The eggs remain dormant 

during the winter and develop and hatch the following

spring.

Factsheet

Plant Protection and Quarantine April 2003

APHIS
Spread of Infestations

AGM infestations spread in several ways. Adult

female moths may fly to previously uninfested areas

to lay eggs, thus spreading the infestation. Or, newly

hatched AGM caterpillars may climb to tree crowns,

where the wind picks up their silken thread and 

carries them to other areas.

In addition, people can inadvertently transport egg

masses. AGM egg masses are tolerant of extremes

in temperature and moisture and travel well on logs,

lawn furniture, nursery stock, pallets, shipping 

containers, and on the hulls and riggings of ships.

Eradication Tools 

The most common eradication method used

against AGM is the naturally occurring Bacillus

thuringiensis (Bt) bacteria. Bt produces a 

caterpillar–specific toxin. When sprayed on tree

leaves, Bt will disrupt the digestive system of 

caterpillars that ingest the leaves, suppressing their

appetites. The caterpillars' movement then slows, and

death results, generally in 7 to 10 days.

Public Participation

People can take several actions to assist in the

detection and management of this pest:

• Report any findings of egg masses on trees, lawn

furniture, fences, walls, or elsewhere on private 

property to Federal or State agriculture officials;

• Cooperate with any restrictions that might be 

imposed locally because of an AGM detection;

• Allow authorized agriculture workers access to 

property to inspect insect–monitoring traps.

Additional Information

For more information about the AGM, or to learn

more about Federal regulations on moving outdoor

household articles, contact one of the following:

• Your State’s regulatory officials, usually listed 

under department of agriculture, plant protection 

or regulatory division, in the State government 

section of your telephone directory.

• A U.S. Federal regulatory official, listed in the 

Federal Government section of your telephone 

directory under USDA, APHIS, Plant Protection 

and Quarantine. (If you have access to the World 

Wide Web, point your browser to 

http://www.aphis.usda.gov/ppq and use the 

“Comments” link to send us an e-mail request for 

more information.)

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United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture