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J2/^^\ United States

^ili^^j] Department of

Agriculture

Combined Forest Pest

Research and

Development Program

Agriculture Handbook

No. 543

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Douglas-Fir

Tussock Moth

Handbook

You Could

Spot the Next

Tussock Moth

Outbreak!

Here's How

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You Could Spot the

Next Tussock Moth

Outbreak! Here's How

by Jerald E. Dewey*

In 1974 the U.S. Department of

Agriculture initiated the Combined

Forest Pest Research and Development Program, an interagency

effort that concentrated on the

Douglas-fir tussock moth in the

West, on the southern pine beetle

in the South, and on the gypsy moth

in the Northeast. The work reported

in this publication was funded in

whole or in part by the Program.

This manual is one in a series on

the Douglas-fir tussock moth.

Trees attacked by the Douglas-fir

tussock moth quickly lose their

beauty. Treetops first become ragged

and cüscolored, and some trees turn a

bright rust color as needles are

destroyed. Then small patches of injured trees may begin to show up in

forested areas. In the later stages of a

full-blown outbreak, hillsides are

often covered with a sickly, brown

mantle of dead trees. This happened

in eastern Oregon and Washington,

and northern Idaho in a major outbreak that occurred between 1972

and 1974. Over a million acres of

Douglas-fir and true fir trees were

damaged. Forest managers struggled

with the problems of timber salvage

and what the tussock moth damage

would mean to wildlife habitat, loss

of esthetic values in recreation and

scenic areas, and increased hazard of

forest fires.

^Forest Service, Northern Region,

State and Private Forestry, Missoula, Mont.
Caterpillars

(Late May through July)

Can anything be done to prevent

damage like this in the future? The

answer is yes—and you are one of

the keys! Long before an outbreak

reaches epidemic proportions, there

are numerous warning signs that

could alert foresters to the problem—

in time to do something to stop the

outbreak. Sophisticated, scientific

detection methods are being

developed to help warn of the next

tussock moth outbreak. But there are

many telltale signs of an outbreak

that people like you—woods workers

and others who frequent forests—can

spot before serious damage occurs.

By keeping your eyes open and alerting forest managers, you can help

save many board feet of timber, as

well as esthetic values of the forest.

If you spot any of the following

signs of increasing tussock moth

populations, report them to the appropriate forest manager's office

listed on pages 10-11.

Symptoms of tussock moth populations on the rise may include:

Large numbers of caterpillars

crawling or feeding on needles

Cocoons and egg masses

Silken "tents" in treetops

Needles stripped from trees in

urban or rural areas

Ragged-looking treetops

Small clusters of defoliated trees.

Figure 1.—Newly hatched caterpillar.

Figure 2.—Mature caterpillar.

Even when tussock moth populations

are low, woods workers such as

timber inventory crews, trail crews,

and loggers may find Douglas-fir

tussock moth caterpillars on trees or

even on clothing.

Hundreds of species of hairy caterpillars inhabit western forests, but the

tussock moth caterpillar is quite easy

to distinguish from most others.

Newly hatched caterpillars (fig. 1) are

gray or brovm and about 1/8-inch

long. As they feed and grow, they

develop a set of four distinctive tufts

of hair—usually a bright reddish

brown—on their backs (fig. 2). Just

behind the tufts is a bright yellow or

red spot. Each caterpillar also has

two black tufts on its head that very

much resemble horns and a similar

tuft on the other end of the body.

Body color ranges from light cream

to dark brown.
SUken "Tents" in Treetops

(May and June)

Newly hatched tussock moth caterpillars often move into treetops, spin

silken strands, and float on the wind

to other feeding locations. When

many caterpillars spin strands in the

top of the same tree, conspicuous

white silken tents are created. This

may be the first sign of an outbreak.

If you see such tents, check the

foliage for caterpillars.

There are a number of other caterpillars that make tents, but most

occur on hardwood trees rather than

conifers.

Figure 3.—Silken tent of the

Douglas-fir tussock moth.

Figure 4.—A tent caterpillar colony.
Cocoons and Egg Masses

(Late July and August)

At the end of the caterpillar stage,

the insects form cocoons and become

inactive. In about 10 to 14 days adult

moths emerge. The wingless females

remain on the cocoon, mate, and lay

their eggs. Cocoons are usuEilly

securely attached to branches—near

the treetop during low-level populations. Some cocoons contain mottled

gray egg masses up to an inch long.

Cocoons and egg masses are quite

obvious to anyone cutting host trees.

Figure 5.-

Figure 6.-

cocoon.

-Egg mass.

-Female tussock moth on
Defoliation of Trees in

Urban or Rural Areas

Outbreaks of the Douglas-fir tussock

moth in forests are often preceded a

year or more by defoliation of ornamental or shade trees (spruce and fir)

in urban or rural areas. For example,

individual trees on farmsteads near

Moscow, Idaho, were defoliated a

year or two before widespread

damage to forests occurred in the

1940's, 1960's and 1970's.

Figures 7 and 8.—Defoliation of

ornamental and shade trees in urban

and rural areas.
Ragged-Looking Treetops

Defoliation of treetops, especially in

taller trees, is indication of a developing tussock moth outbreak. This is

caused by large numbers of caterpillars feeding in the upper tree

crowns. Damage is most apparent

near the end of the feeding period—

usually late July. This type of injury

can be confused with damage caused

by other defoliators such as the

western spruce budworm, western

hemlock looper, and false hemlock

looper, which cause feeding injury

throughout the tree with heaviest

damage to tops. Tussock moth

damage, in contrast, has a more

distinct separation of the damaged

and undamaged portions of Douglasfir or true fir trees. Look for

evidence such as caterpillars,

cocoons, adults, eggs, or shed

skins to aid in identification

of the insect that is causing the

problem.

Figure 9.—Treetop defoliated by the

Douglas-fir tussoclc moth.

Figure 10.—Treetop defoliated by

another defoliator.
Small Clusters of Defoliated Trees

Small clusters of severely defoliated

trees often show up in the early

stages of an outbreak. Complete

defoliation of the trees within the

cluster is common even though adjacent forest areas show no signs of

feeding injury. This type of damage

is characteristic of the Douglas-fir

tussock moth.

When Douglas-fir trees are first

defoliated, they turn a bright reddish

brown. Later, as the injured needles

die, the tree fades to grayish purple. Vi mÈL^Mil,, ^1

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12

Figure 11.—A small, severely

defoliated tree cluster.

Figure 12.—Individual trees in

severely defoliated area.
How to Report a

Suspected Outbreak

Both State and Federal governments

have forest management organizations trained to identify, evaluate,

and suppress forest insect problems.

At the State level, this responsibility

resides with State forestry departments. The Forest Service has

responsibility at the Federal level.

Suspected outbreaks should be

reported to these agencies. Insect

samples should be sent to these agencies, if possible, with the following

information:

Name and address of persons

reporting the damage

Exact location of observed damage

or infestation

Date of observation

Tree species involved

Size of damaged area

Landowner's name

Any other pertinent information.
Federal and State Organizations Responsible

for Evaluating Forest Insect Problems

State Federal Agencies State Agencies

Arizona Forest Insect and Disease Management

U.S. Forest Service

Federal Building

517 Gold Avenue, S.W.

Albuquerque, N. Mex. 87102

California Forest Insect and Disease Management

U.S. Forest Service

630 Sansome Street

San Francisco, Calif. 94111

Arizona State Land Department

1624 West Adams

Phoenix, Ariz. 85007

State Department of Forestry

1416 Ninth Street

Sacramento, Calif. 95814

Colorado Forest Insect and Disease Management

U.S. Forest Service

11177 West 8th Avenue

P.O. Box 25127

Lakewood, Colo. 80225

Idaho, northern Forest Insect and Disease Management

U.S. Forest Service

Federal Building

Missoula, Mont. 59801

Idaho, southern Insect and Disease Control Group

U.S. Forest Service

1075 Park Boulevard

Boise, Idaho 83706

Montana Forest Insect and Disease Management

U.S. Forest Service

Federal Building

Missoula, Mont. 59801

Colorado State Forest Service

Colorado State University

Fort Collins, Colo. 80523

Bureau of Private Forestry

Division of Forest Resources

Idaho Department of Lands

RO. Box 670

Coeur d'Alene, Idaho 83814

Same as above

Division of Forestry

2705 Spurgin Road

Missoula, Mont. 59801

10
State Federal Agencies State Agencies

New Mexico Forest Insect and Disease Management

U.S. Forest Service

Federal Building

517 Gold Avenue, S.W.

Albuquerque, N. Mex. 87102

Oregon Forest Insect and Disease Management

U.S. Forest Service

319 S.W. Pine Street

P.O. Box 3623

Portland, Oreg. 97208

Utah Forest Insect and Disease Management

U.S. Forest Service

Federal Building

324 25th Street

Ogden, Utah 84401

Department of State Forestry

P.O. Box 2167

Santa Fe, N. Mex. 87501

Department of Forestry

2600 State Street

Salem, Oreg. 97310

Utah Forestry and Fire Control

1596 W. North Temple

Salt Lake City, Utah 84116

Washington Forest Insect and Disease Management

U.S. Forest Service

319 S.W. Pine Street

P.O. Box 3623

Portland, Oreg. 97208

Wyoming, western Forest Insect and Disease Management

U.S. Forest Service

Federal Building

324 25th Street

Ogden, Utah 84401

Department of Natural Resources

Olympia, Wash. 98504

Wyoming State Forestry Division

1100 W. 22nd Street

Cheyenne, Wyo. 82001

Wyoming, eastern Forest Insect and Disease Management

U.S. Forest Service

11177 West 8th Avenue

P.O. Box 25127

Lakewood, Colo. 80225

Same as above

11
Issued September 1978

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lir U.S. GOVERNMENT PRINTING OFFICE : 1978 0-274-644

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402

Stock Number 001-000-03865-6