APHIS Factsheet

Plant Protection and Quarantine April 2015

Asian Gypsy Moth

The Asian gypsy moth (AGM, including Lymantria 

dispar asiatica, Lymantria dispar japonica, Lymantria 

albescens, Lymantria umbrosa, and Lymantria postalba) is an exotic pest not known to occur in the 

United States. Although in many ways similar to the 

European gypsy moth, AGM larvae feed on a much 

broader range of plant species, covering over 100 

botanical families. This broad range of possible host 

plants, combined with the female’s ability to fly long 

distances, could allow AGM to spread rapidly. Large 

infestations of AGM can completely defoliate trees, 

leaving them weak and more susceptible to disease 

or attack by other insects. If defoliation is repeated 

for 2 or more years, it can lead to the death of large 

sections of forests, orchards, and landscaping. Any 

introduction and establishment of AGM in the United 

States would pose a major threat to the environment 

and the urban, suburban, and rural landscapes. 

Since 2009, the U.S. Department of Agriculture 

(USDA), in partnership with the Canadian Food 

Inspection Agency, has worked with foreign trading 

partners to monitor populations of AGM and inspect 

ships before they leave to certify that they are free 

of AGM life stages. Ships are also inspected for AGM 

when they arrive at U.S. ports. Although these preventive measures are effective, occasional introductions of AGM have occurred. When AGM is detected, 

USDA works with other Federal and State agencies 

to evaluate the infestation and take appropriate 

actions to keep it from spreading. 

Background

AGM was first identified in North America in late 

1991 near the Port of Vancouver in British Columbia, 

Canada. Moths were discovered shortly thereafter in 

Washington, Oregon, and British Columbia. Ships 

infested with AGM 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. 

USDA and State officials eradicated these infestations in the Pacific Northwest through trapping and 

treatment activities.

In 1993, another infestation, this time in Sunny 

Point, NC, occurred after moths emerged from a ship 

carrying infested cargo containers from Germany 

and then flew into the surrounding area. AGM was 

not known to occur in Europe until tracebacks of this 

introduction provided evidence of other populations 

there. Between 1991 and 2012, AGM was detected 

and eradicated on at least 20 occasions in locations 

across the United States. 

The most recent AGM detections occurred in 2013 

and 2014 when male moths were caught in survey 

traps, one moth each year in Pittsburg County, OK 

and one moth in 2014 in the port community of North 

Charleston, SC. Survey work in 2015 will help determine whether infestations are present and what 

followup actions may be needed to address them.

Several USDA pest risk assessments over the 

years have concluded that, because of similarities 

between Asian and North American ecosystems, left 

unaddressed, the AGM has great potential for colonization in North American forests.

Potential Damage

If established in the United States, AGM could 

cause serious, widespread damage to our country’s 

landscape and natural resources. Each AGM female 

can lay hundreds of eggs in fuzzy egg masses that, 

in turn, yield hundreds of voracious caterpillars who 

feed on more than 600 species of trees and shrubs. 

AGM caterpillars can defoliate plants at an alarming 

rate. This defoliation can severely weaken trees and 

shrubs, killing them or making them more susceptible 

to diseases and other pests and destroying habitats 

for mammals and birds. Caterpillar silk strands, droppings, destroyed leaves, and dead moths would also 

be a nuisance in homes, yards, and parks.

Comparing Gypsy Moth Pests

The AGM is similar to the European gypsy moth 

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.

In the eastern United States, European gypsy 

moths defoliate an average of 700,000 acres each 

year, causing millions of dollars in damage. If AGM 

were to become established in our country, the damage could be even more extensive and costly.

Unlike the flightless female European gypsy moths, 

AGM females are active fliers. Their ability to fly long 

distances makes it probable that AGM could quickly 
spread throughout the United States. In contrast, the 

European gypsy moth has taken more than 140 years 

(since 1869) to spread throughout the United States 

from the Northeast to the Southeast and the Midwest.

Life Stages

The AGM matures through four life stages: egg, 

larva (caterpillar), pupa (cocoon), and moth. AGM egg 

masses may be found on tree trunks, limbs, or leaves, 

as well as on stones, walls, logs, lawn furniture, and 

other outdoor objects. Each egg mass can contain 

hundreds to 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 

1 1⁄2 inches long and three-fourths 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 happens 

during the caterpillar stage, as the insects feed on 

leaves during this active period of growth. Once AGM 

caterpillars stop feeding, they enter the pupal stage. 

This stage typically begins in June or July. Because 

egg hatch and pupation depend on weather and 

temperature, they may occur earlier or later in different areas. Adult moths emerge from their dark-brown 

pupal cases in 10 to 14 days. Adult males have grayishbrown wings and a wingspan of 1 1⁄2 inches. Adult 

female moths are white and larger, with wingspans 

of 3 1⁄2 inches or more.

AGM do not feed in the moth stage (which lasts 

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

laid between June and September, depending on 

weather and location. The eggs remain dormant during 

the winter and develop and hatch the following spring.

How AGM Can Spread

AGM infestations spread in several ways. Adult 

female moths may fly to previously uninfested areas 

to lay eggs. Or, newly hatched AGM caterpillars may 

climb to tree crowns, where the wind picks up their 

silken threads and carries them to other areas.

In addition, people can inadvertently transport egg 

masses or pupae. AGM egg masses tolerate extremes 

in temperature and moisture and travel well on logs, 

lawn furniture, nursery stock, pallets, shipping containers, and the hulls and rigging of ships.

Protecting the Country From AGM

The first line of defense against AGM is USDA’s 

work to prevent this pest from reaching the United 

States. In partnership with Canada, the USDA works 

with China, Japan, South Korea, and Russia to make 

sure AGM population levels are monitored at and near 

ports. Ships and cargo headed for the United States 

are inspected for AGM and certified as pest-free 

before departing. On arrival, ships and cargo undergo 

another inspection to ensure that AGM is not present. 

These protective measures are highly effective but, on 

rare occasions, AGM introductions do occur. A robust 

survey program at and near ports of entry helps detect 

any possible introductions at an early stage—when 

eradication efforts are most effective and least costly.

Several treatment options are available to eradicate 

AGM. The most common method used against AGM is 

the naturally occurring bacteria, Bacillus thuringiensis 

(Bt), which produces a caterpillar-specific toxin. When 

sprayed on tree leaves, Bt disrupts 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. Dimlin, an 

insecticide that inhibits AGM growth and development, 

is also frequently used. Another AGM eradication tactic 

is mating disruption—using the pheromone emitted by 

female AGM to attract mates. This mating pheromone 

is released at high levels in and around infested areas, 

overwhelming the pheromone signal emitted by the 

female AGM and, as a result, making it difficult for the 

male moths to locate the females and mate. 

What You Can Do

You can support efforts to detect and manage AGM by:

•	 Reporting any findings of egg masses on trees, 

lawn furniture, fences, walls, or elsewhere to 

Federal or State agriculture officials.

•	 Cooperating with any restrictions in your local 

area that might be imposed because of an 

AGM detection.

•	 Allowing authorized agricultural workers access 

to your property to place and inspect insectmonitoring traps.

Learn More

For more information on AGM and associated Federal 

restrictions, contact your:

•	 Local Extension office (www.nifa.usda.gov/

Extension), 

•	 State Plant Regulatory Official (www.national 

plantboard.org/member), or

•	 Nearest USDA Animal and Plant Health 

Inspection Service office (www.aphis.usda.gov/

planthealth/sphd). 

USDA is an equal opportunity provider and employer.

APHIS 81-35-027

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