Gypsy moth : a major pest of trees

Historic, Archive Document

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gypsy
moth

A MAJOR PEST
OF TREES

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U.S. DEPARTMENT OF AGRICULTURE • PA-1006

ST-5322-15

The gypsy moth is an insect that is one of the
most important forest pests. They are harmless in
the moth stage, but as caterpillars feed on the
leaves of forest, shade, ornamental and fruit trees
and shrubs. A single defoliation can kill some
softwood trees; two or more defoliations can kill
many types of hardwoods.

Gypsy moths have been in this country since
1869, when specimens imported from Europe
escaped during experiments being performed by a
Massachusetts naturalist. Extensive Federal-State
control and quarantine operations confined de-
structive gypsy moth populations to New England,
New York and Pennsylvania for many years.

In recent years, gypsy moth populations have
built up to high levels, with spread occurring
throughout much of the Northeast and into parts
of the South. Approximately 25 percent of the
nearly 2 million acres of trees damaged in 1971
suffered from 70 to 100 percent defoliation. Trees
on over 40 percent of the acreage were lightly
defoliated, with from 5 to 60 percent loss of leaves.
The 2 million figure is twice the acreage defoliated
in 1970, more than six times the 1969 damage,
and twelve times more defoliation than recorded
in 1968.

DAMAGE

A single two-inch caterpillar eats one square
foot of leaf surface every 24 hours. Large in-
festations contain millions of caterpillars and de-
grade aesthetic and recreational values of forests,
parks and wooded homesites.

Tree losses can be severe following an outbreak.
For example, in 1968, gypsy moth infestations
were observed for the first time in the Newark,
N.J., watershed. Over the next two summers, a
total of 17,855 acres sustained repeated defolia-
tions at levels ranging between 75-100 percent
on nearly all susceptible tree species. In 1971,
New Jersey foresters reported more than
1,000,000 oaks, 39,000 eastern hemlock and
8,000 white pine killed as a direct result of gypsy
moth feeding.

The number of trees killed by gypsy moth de-
foliations is actually a small percentage of those
stripped of their foliage each year. Even a single
defoliation may seriously weaken a tree, how-
ever, making it susceptible to secondary attack
by other insects or plant diseases. A 1971 survey
in the Morristown National Historical Park, for
instance, showed that many oaks weakened the

previous spring by gypsy moth defoliations died
during the winter from "secondary" causes.

The question arises: "If gypsy moths are so
destructive, why do we still have forests in New
England after nearly 100 years of infestation?"
The answer is that sizable tree losses did occur
during the moth's first 50 years in New England.
The forest makeup of New England is not the
same now as it was 100 years ago. Tree stands
susceptible to gypsy moth damage have, in large
part, been killed off and replaced with species
more resistant to, or not favored by, the insect
pests. Southern areas now being invaded are
those with a high percentage (up to 90 percent)
of susceptible trees used for wood products. The
extensive oak forests of the Appalachian and
Ozark Mountain ranges, and Southern oak-pine
forests, are considered especially vulnerable to
gypsy moth defoliation.

HOSTS

Preferred hosts of the gypsy moth are oak,
apple, alder, aspen, bass-wood, gray and river
birch, hawthorn, and willow. The insects also
attack beech, other birches, cedar, cherry, elm,
black gum, hemlock, hickory, hornbeam, larch,
maple, pine, sassafras and spruce. Species not
favored by the gypsy moth include ash, balsam
fir, butternut, black walnut, catalpa, red cedar,
dogwood, holly, locust, sycamore and yellow-
poplar.

NATURAL CONTROLS

Gypsy moth populations and damage are regu-
lated to some degree in countries where the pest
originated by the activities of parasites, preda-
tors, and insect diseases. Pesticides are also
needed. Periodic outbreaks still occur despite a
full complement of "natural enemies."

Native enemies of the gypsy moth also exist in
the United States — but not in large enough num-
bers and kinds to effectively check the gypsy moth
in this country. Natural controls on U.S. gypsy
moth populations include insectivorous birds such
as cuckoos, black birds, grackles; and mammals

BN - 38774

such as shrews and white-footed mice. Native
Calosoma beetles are voracious killers of the cater-
pillars. Wilt disease, caused by a polyhedral virus,
attacks gypsy moth larvae, often wiping out large
concentrations of caterpillars. In addition, low
winter temperatures can cause considerable egg
mortality in unprotected situations.

ST-5321-9

IMPORTED ENEMIES

USDA began importing and attempting to
colonize foreign enemies of the gypsy moth as
early as 1905. More than 40 species have been
introduced. Eleven parasites (seven attack larvae,
two feed on eggs, and two destroy pupae) and
two predators have become established in the
Northeast. USDA and cooperating States have
set up rearing laboratories and, in 1970 alone,
released approximately 51,825,000 parasites.

Control of the gypsy moth by its natural ene-
mies has been less effective than hoped for be-
cause ( 1 ) several of the most important parasites
from Europe could not be established in the
United States, (2) pesticides used to suppress
intolerable gypsy moth populations can reduce
temporarily some insect parasite and predator
levels, and (3) alternate host insects are not al-
ways available in outbreak areas for the second
or succeeding generations of many imported para-
sites. This lack of alternate hosts also places
severe limitations on USDA's ability to establish
parasite colonies in uninfested areas as a deterrent
to pest spread.

USDA RESPONSIBILITIES

USDA has been working with gypsy moth in-
fested States since 1906 in an effort to control
and prevent the spread of this pest. Department
responsibilities in cooperative Federal-State pro-
grams are divided among four USDA agencies.

IMPORTED ENEMIES

USDA began importing and attempting to
colonize foreign enemies of the gypsy moth as
early as 1905. More than 40 species have been
introduced. Eleven parasites (seven attack larvae,
two feed on eggs, and two destroy pupae) and
two predators have become established in the
Northeast. USDA and cooperating States have
set up rearing laboratories and, in 1970 alone,
released approximately 51,825,000 parasites.

Control of the gypsy moth by its natural ene-
mies has been less effective than hoped for be-
cause ( 1 ) several of the most important parasites
from Europe could not be established in the
United States, (2) pesticides used to suppress
intolerable gypsy moth populations can reduce
temporarily some insect parasite and predator
levels, and (3) alternate host insects are not al-
ways available in outbreak areas for the second
or succeeding generations of many imported para-
sites. This lack of alternate hosts also places
severe limitations on USDA's ability to establish
parasite colonies in uninfested areas as a deterrent
to pest spread.

USDA RESPONSIBILITIES

USDA has been working with gypsy moth in-
fested States since 1906 in an effort to control
and prevent the spread of this pest. Department
responsibilities in cooperative Federal-State pro-
□s are divided among four USDA agencies.

The Animal and Plant Health Inspection Service

enforces provisions of the Federal gypsy moth
quarantine and carries out detection surveys to
pinpoint pest spread or population buildups.
APHIS initiates control operations in recreation
areas and trailer courts in conjunction with State
agencies when such action is essential to prevent
long-range pest spread; conducts methods devel-
opment investigations to find better ways of using
pest control techniques and weapons; and releases
parasites and predators.

The Forest Service conducts control projects
on Federal lands and cooperates with State agen-
cies in infested areas to protect endangered forest
resources. FS also conducts research on biological
and chemical agents to develop new control tools
and technology, integrating them into the gypsy
moth pest management system.

The Agricultural Research Service initiates re-
search and development to provide safer and more
effective tools such as sex attractants with which
to control the gypsy moth, and introduce poten-
tially effective parasites and predators.

The Extension Service coordinates USDA's
education and information activities designed to
keep the public informed about all phases of co-
operative gypsy moth programs.

IN-8259

DESCRIPTION AND HABITS

The gypsy moth develops in four stages — egg,
larva (caterpillar), pupa (cocoon), and moth. It
has one generation a year and overwinters in egg
masses attached to trees, stones, walls, logs, and
other objects. Each gypsy moth egg mass contains
up to 1,000 eggs and is covered with buff or
yellowish hairs from the abdomen of the female.
The velvety egg masses average about \Vi inches
long and about 3A inch wide.

Eggs begin hatching in late April or early May.
The brownish, hairy caterpillar is easy to identify
in later stages by the pairs of red and blue dots
on its back. Mature caterpillars are from Wi to
2Vi inches long.

Natural spread occurs during the pest's larval

592 EGGS

BN-15039 LARVAE

stage. Caterpillars drop from tree tops on silken
threads. During high winds these threads act as
sails and the lightweight larvae may be blown
over many miles.

Caterpillars enter the pupal "cocoon" stage
late in June or early in July, emerging from their
pupal cases in 10 to 14 days as moths. Males
have dark brown forewings and a IVi inch
wingspread. Female moths are white, with a wing-
spread of about 2 inches.

The pests do not feed in the moth stage and
female moths do not fly. Depending upon weather
and location, egg laying in the Northeast occurs
between July and September.

YOU CAN HELP

One of the main avenues of artificial gypsy
moth spread today is through the movement of
mobile homes and recreational vehicles. In 1970,
for instance, trailer owners who stopped at an
infested campground in Connecticut unwittingly
carried gypsy moth egg masses (each containing
from 100 to 1,000 individual eggs) as far away
as California, Florida, Minnesota, Texas, Virginia
and Wisconsin.

Campers and mobile home owners can help
stop the spread of gypsy moths by carefully in-
specting their recreational vehicles, mobile homes
and camping equipment before traveling from
infested to uninfested areas. The undersides of
trailers, hitches, vehicles, joints of truck cab and

camper, steps, awnings, camper-trailer extensions,
gas bottle rims, any loose metal underneath trailers
and any other equipment should be thoroughly
inspected. Also, all wheels should be checked on
both sides. Any egg masses, caterpillars, pupae, or
moths found should be removed and destroyed.

ADVICE TO HOMEOWNERS

Individual homeowners can do little to protect
their trees in heavily infested areas. Small trees
and shrubs can be treated, but equipment needed
for spraying trees of 25 ft. or more is not readily
available to individuals.

Nonchemical methods of killing gypsy moths
are available. Homeowners can hand kill cater-
pillars, trap the j)ests by encircling tree trunks
with a wide band of sticky substance called
Tanglefoot; tie burlap or cloth strips around trees
to trap the caterpillars so they can be destroyed;
hand remove pupal cocoons; or smash egg masses.
But, none of these methods is very effective be-
cause the caterpillars can spread from neighboring
infested properties.

The only way to successfully reduce gypsy moth
populations in heavily infested areas is through
communitywide action. Communities interested in
initiating gypsy moth control projects can obtain
technical advice from State agriculture or environ-
mental agencies, Federal plant protection and
forestry officials, or local county agricultural
agents.

PROGRAM ACTIVITIES

Federal-State cooperative gypsy moth programs
consist primarily of four related functions — regu-
latory, survey, control, and research and develop-
ment.

Regulatory: Federal and related State quaran-
tines are imposed to prevent artificial spread of
gypsy moths by regulating the inter and intra-
state movement of materials that might carry
hitchhiking moths, larvae, pupae or egg masses
from infested to noninfested areas. Such materials
include timber and timber products, woody plants,
and stone and quarry products.

Survey: Gypsy moth surveys help Federal and
State officials plan and conduct regulatory and
control work and aid USDA scientists seeking
new and better methods of combating the de-
structive moths. Basically, three types of surveys
are conducted: (1) In the winter, ground crews
compile egg mass counts used for predicting
caterpillar populations and in planning control
and regulatory activities. (2) The trapping of male
moths is conducted during late summer in parks
and campgrounds within infested areas (to dis-
cover where the danger of spread via trailers or
mobile homes is high) and traplines are maintained
outside infested portions of the northeast (to
spot natural or artificial spread). (3) Finally, aerial
surveys are conducted throughout the summer and
fall to determine the extent and intensity of
gypsy moth defoliations.

Control: Federal and State pest control officials
give prime consideration to the safety and health
of people, crops, livestock and wildlife when
planning and conducting control programs. They
avoid spraying lakes, rivers and reservoirs and
similar areas of environmental or health concern.

The insecticide currently used against the gypsy
moth is carbaryl. It is nonpersistent, breaking
down quickly and leaving no harmful residue.
Carbaryl is low in toxicity to birds, fish, wildlife
and humans; but precautions must be taken to
safeguard bees. In 1971, some 350,000 acres were
treated with carbaryl to protect trees and stop
artificial spread by hitchhiking gypsy moths.

Pilot projects are underway integrating bio-
logical methods into Federal-State cooperative
gypsy moth control programs. For example,

USDA scientists are attempting to counter natural
gypsy moth spread by intensifying trapping and
by releasing parasites wherever moths are caught
for the first time.

Research and Development: USDA has under-
way an intensified research and development pro-
gram to provide weapons to bring the destructive
gypsy moth under control. The program concen-
trates on developing means of managing gypsy
moth populations. Selective biological controls
having minimal adverse effects on nontarget or-
ganisms and the environment in general are being
sought. Limited use of chemicals will also be
part of the overall gypsy moth management sys-
tem of the future — which will capitalize on the
best features of each control method, while mini-
mizing possible environmental hazards.

Techniques and weapons expected to be op-
erational in the next five years include: an im-
proved scientific procedure for predicting and
evaluating gypsy moth population trends, environ-
mental impact and the consequences of applying
different pest control methods; a bacterial insec-
ticide, Bacillus thuringiensis; production and use
of a virus that is a critical factor in halting natural
outbreaks; and the use of disparlure to confuse
male moths and prevent mating.

ANIMAL AND PLANT HEALTH
INSPECTION SERVICE
FOREST SERVICE • EXTENSION SERVICE

Issued May 1972

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