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UNITED STATES 5. LN i
DEPARTMENT OF AGRICULTURE:
Miscellaneous Publication No. 273

INSECT ENEMIES
OF WESTERN FORESTS

Compiled by
F. P. KEEN

Entomologist
Division of Forest Insect Investigations
Bureau of Entomology and Plant Quarantine

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UNITED STATES

DEPARTMENT OF AGRICULTURE
Miscellaneous Publication No. 273

Washington, D.C. February 1938

INSECT ENEMIES OF WESTERN
FORESTS |

Compiled by F. P. KEEN, entomologist, Division of Forest Insect Investigations,
Bureau of Entomology and Plant Quarantine

CONTENTS
Page Page
TGANTRO COLOR OOS OE eS i ee eee 2 Key to diagnosis of insect injury to young
Kinds of forest insects and the losses they (treeSea=eee = eee ee ieee ee pied Shae aT 28
CLUS Famer fan te ergs 8 Loe, ee ee eis 2 Insects affecting twigs, terminal shoots,
Winrectloscesmaser wes se A ke 5 GVO! WO so see cone ee sos pease ae 29
hm Ginec tl OSSCSa mee wk Nee eee Rel ee 8 Sep su ee Ine Fa eae sented caare i a
Relation of insects toforest management. 9) eedarson the inner bark of young tees.
Determining causes of forest-tree damage__-__- 1 Insects injurious to mature forest trees________ 57
Insects affecting seed production________-____- 15 Key to recognition of insect injury to ma-
Key to diagnosis of insect injury to cones CHTECELOGS Bee et nak ene! S 58
ROO! SEQ 2 5s = 5 es ee 15 Leaf feeders and defoliators.______________ 58
Woneweellessae ase kee es A a SE ae 16 Miners in the inner bark and phloem____-_ 95
Cone mmOth Sees een See Le To ee 16 | Insects injurious to wood and forest products__ 141
WONne Mace OLSmas were Se er ge et 20 Key to diagnosis of insect injury to wood
@oneiborerss sss ee AAPL ee Spee 21 and wood products______________-_______ 142
Saag CTC Sw ey ne ee en aa 21 Insects working in unseasoned logs or lum-
Nut and’acorm weevils:.-.-- 2. ee 22 ber_------- SS al ea ee eee ees, eR)
NGS RN ne 2 ge 93 yasects working in seasoned or decaying ae
. . . . . WwW SOS SSE SS SOS as soe esc essence See SoS3e5 ve
Boat dae ee S ae = = a hd gues es 23 Insects injurious to forest range plants_______- 164
Key to diagnosis of insect injury to seed- Natural control factors _________- p7n77-------- 166
lingo eee wee EL ie Se 24 Climatic and environmental influences_-_ _ 166
WihikGerUnsee meee Ae) o kee) oy. ls 24 Naturalionemicsssen=seas sees seer eee 169
LOO CRW CC lS ee en a ad Bh 9¢ | Control of injurious forest insects_____-__-_-_-- 171
NGC WOLIIGe nee ne eh et 26 Silvicultural control___._=..-___._=__-_--- 172
@utworms..2... 2022: Be I antes ee, Oar 2%6 Biological control____- DE ce ae Det hoe Ms he Se 173
OOD AR DCOtleS te Um an ee 27 Direct artificial or remedial control_____-_- 174
EV OO LATO lal Gl See weep a eS gel Meiteratunrelcltedis ses ao) eae es Se 197
Insects injurious to young trees (saplings and limndextof hosts treesemes sas eae on eee ieee 202

OC 22 sane s ase 2. apf ap ee eeed De eR 3 ||. Craovrall waolsse oe ese 205

1 For many years entomologists of the Bureau of Entomology and Plant Quarantine
engaged in the study of forest-insect problems have considered compiling the great mass
of records in their files so that it would be in more usable form. There has been a
growing need for 2 manual or handbook for use by forest rangers and others entrusted
with the administration of forest lands and the prevention of insect losses. Recently
the tremendous impetus given to forest conservation by the establishment of the Civilian
Conservation Corps camps has made insect control an actuality in many forests where
previously it had been impractical. This called for the instruction and education of
these men and of their leaders and has crystallized efforts toward bringing together the
material in this handbook. In compiling this manual all sources of information have
been drawn upon to make the presentation as comprehensive and up to date as possible.
Published bulletins, records in the files, unpublished work of field men, and previously
mimeographed manuals or instructions issued by the leaders of the forest-insect field
laboratories of the Bureau of Entomology and Plant Quarantine in the Western States
have been used as needed. It is obviously impossible to give full credit to all the workers
who have contributed to the making of this publication. F. P. Keen has taken the
initiative in its compilation, with the assistance of J. M. Miller, J. C. Evenden, and
J. E. Patterson, and, in fact, the entire technical personnel of the Bureau’s western
forest-insect laboratories have contributed parts in their respective specialties. This
manual is restricted to the insects of the western forests, although the general discus-
Sion and control methods are in a large measure applicable to any part of the United
States. It is planned to follow this with another manual covering the eastern forests.—
F. C. CRAIGHEAD, in charge, Division of Forest Insect Investigations.

136650°—38——1 1

2 MISC. PUBLICATION 273, U. 8. DEPT. OF AGRICULTURE

INTRODUCTION

Protecting forests from destruction is the first ‘basic requirement
in the practice of forestry. Important destructive agencies include
not only fire but also insect pests, fungous diseases, animals, drought,
flood, and wind. While damage from insects to timber is less spec-
tacular than that caused by either fire or wind, timber losses from
any of these three agencies may be of catastrophic magnitude. More-
over, Insects are constantly at work in the forest and are the cause
of a steady drain on timber supplies. To allow fire or insects to run
unchecked in our forests is to invite disaster and seriously to threaten
the present and future timber supply.

Protection from fire has been given intensive study, and notable
progress has been made in fire control. Less attention has been given
to the control of timber- destroying insects, partly because practical

control methods have not always been available and partly because
the expense of applying them has not been warranted in view of cur-
rent timber values. Moreover, practicing foresters in the West have
been handicapped by lack of a convenient reference manual, and as
a result have considered insect control a specialized subject with
which only the entomologists were prepared to deal. With the new
emphasis on forest conservation, there is, however, an increasing
demand by foresters for information on insects, as this information
is intimately related to many phases of forest protection and man-
agement (fig. 1).

Forest insects other than tree-killing species also present many
special problems. They may be encountered in every operation, from
the collection of seed through the planting, growing, and harvesting
of forest trees, in the handling and protection of utilized wood prod-
ucts, and even in the management of grazing lands. In all of these
cases some special knowledge of the insects concerned and of their
habits is required in order that suitable methods of prevention or
control may be effectively applied.

This field handbook has been prepared to meet this need. The dis-
cussions are limited to the insects and the problems which they raise
in the management and protection of the forests of the Western
States, although the general principles of control are applicable to
other forest regions as well. It 1s hoped that the information assem-
bled will aid timber owners and foresters in recognizing the work of
important western forest insects, in applying suitable control meas-
ures, or in adjusting forest practices so as to reduce losses from this
source to the lowest possible point.

KINDS OF FOREST INSECTS AND THE LOSSES THEY
CAUSE

All forests are swarming with insect life. This insect population
serves many functions and is as much an essential part of the com-
plex association of living, growing, and dying organisms which we
call the forest as are the trees themselves.

Of the thousands of insect species found within our forests, many
are harmless or even beneficial, A great many feed on dead trees and

INSECT ENEMIES OF WESTERN FORESTS

1.—Insect control is one of a forest ranger’s many routine
infested tree,

tasks.

Marking an

4 MISC. PUBLICATION 278, U. S. DEPT. OF AGRICULTURE

on fallen limbs and other debris upon the forest floor, and thus hasten
the disintegration of dead material and make room ‘for new growth,
Many others prey upon destructive insects and hold them in check.

A certain proportion of the insect species, however, are distinctly
harmful in that they attack healthy or partially weakened trees and
impair their vitality or even cause their death. Of this group, bark
beetles destroy more standing timber in our western forests than all
other insects combined. Defoliators—insects which feed directly on
the foliage of forest trees—are the next greatest destroyers of stand-
ing timber. Other insects, such as weevils, tip moths, pitch moths,
and cone beetles, attack various portions of the green trees, often
with serious results, In spite of the large number of insect species
which prey upon the forests, comparatively few cause damage of eco-
nomic importance.

The injurious species of insects may be roughly classed as primary
or secondary, depending on the health of the trees which they nor-
mally attack. Thus certain species, such as the leaf-chewing insects,
show a decided preference for perfectly healthy trees and are consid-
ered primary in their attack. Others, such as most bark and wood-
boring insects, can inhabit only those trees previously weakened by
some other agency.

From the standpoint of control it is important to know whetner
an insect species is primary or secondary in its attack, as it is wasted
effort to proceed against an insect, even 1f found apparently destruc-
tive, if its presence is conditioned by previous injury or death of the
tree from other causes. It is the primary injury that must be discov-
ered and dealt with. There are, however, a number of species that
are primary under certain conditions and secondary under others.

Every species of western forest tree has its insect enemies. West-
erm yew is probably as nearly free from insect attack as any other
forest tree in the West; an occasional scale or caterpillar may be
found on its foliage, and beetles on rare occasions enter its heartwood
through wounds, especially if the wood is beginning to decay, but no
serious enemy is known. The cedars, cypresses, redwood, and juni-
pers have very few injurious insect enemies and none that threaten
the life of mature trees. Larch also is comparatively free from insect
pests. The broad-leaved trees are the favored hosts of many leaf-
feeding species, but since these trees can readily replace their de-
pleted foliage such feeding rarely results in any fatal injury. Some
species, howe ever, are much more subject to insect attack than others.
Certain oaks are reported to be hosts for more than 1,000 species of
insects. Pines, spruces, firs, and hemlocks suffer much, in the order
named.

Injurious forest insects are constantly at work, taking toll at every
stage in the development of the stand, and even after the lumber has
been manufactured into its final form. Some insects feed on the
roots, others on the leaves, the terminal shoots, the branches, or the
phloem and bark of the main trunk, Still others feed on the sap-
wood, and even the heartwood. The fruits and the seeds also are
subject to attack by many insect species.

In certain types of old-growth timber stands, particularly those
that are overmature, steady loss through insect activity is normal.

INSECT ENEMIES OF WESTERN FORESTS 5

(This loss is for the most part counterbalanced by new growth.)
On the other hand, epidemic insect outbreaks occurring from time to
time definitely de-
plete the forest capi-
tal over large areas
to such an extent
that long periods are
required for replace-
ment (fig. 2). An-
nual loss by forest
insects in the West-
ern States, imcelud-
ing depredations on
standing timber and
damage to logs,sawed
lumber, and finished
wood products in use,
is variously estimated
at from $20,000,000
to $100,000,000.

A considerable por-
tion of this loss is as
unavoidable as losses
from lghtning or
windstorms. On the
other hand, much of
it can be prevented
through silvicultural
practices, proper for-
est management, and
direct control meas-

Ficurp 2.—Not fire but bark beetles destroyed this basin
ures. of lodgepole pine in Yosemite National Park.

DIRECT LOSSES

In the mature timber stands of the West the largest single item of
insect loss results from activities of bark beetles. Surveys indicate
that these pests destroy annually 1 billion to 5 billion board feet of
mature timber in our westerir forests.

A survey made in California in 1931 indicated that losses of mer-
chantable timber due to bark beetles in that year totaled about 1,250,-
000,000 board feet, which represents a loss of nearly $3,000,000 in
stumpage values, aside from the regional asset represented by the
manufacturing value of the lumber.

In southern and central Oregon, during the 10 years ended with
1934, the western pine beetle caused a net depletion of the ponderosa
pine stands (fig. 3) amounting to 2,240,000,000 board feet. A typical
section in the Klamath Indian Reservation, carrying a stand of
11,074,000 board feet in%1921, lost 3,875,000 board feet through bark-
beetle attack’ during the 11- ~year per iod 1921-31. Growth during the
same period, which, owing to drought and to defoliation by the

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6 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

Ficure 3.—Destruction of commercial ponderosa pine stands by bark beetles is a serious i
problem in many Western States.

INSECT ENEMIES OF WESTERN FORESTS Tf

pandora moth, was only 48 percent of the normal, amounted to 294,-
000 board feet, leaving a net loss for the 11 years of 32.3 percent of
the stand.

The lodgepole pine forests of Idaho, Montana, and Wyoming, par-
ticularly those in and around Yellowstone National Park, have suf-
fered tremendous losses in recent years. It has been conservatively
estimated that during the 10 years that ended with 1932 these losses
amounted to 7,250,000,000 board feet, more than 36,000,000 trees hav-
ing been killed in one national forest alone. Many mature lodgepole
pine forests in regions 1, 4, and 6 have been completely destroyed
during the last 20 years, or are in process of destruction, by the
mountain pine beetle.

During the 10-year period 1923-32 the mountain pine beetle is also
estimated to have destroyed 110,000,000 board feet of valuable stands
of western white pine in northern Idaho.

It must be clearly understood that these loss estimates cover the
normal as well as the unusual drain on the forest. In the surveys in
the ponderosa pine type of California and Oregon, for example, all
trees killed by bark beetles were tabulated. Normally, on the best
sites but few trees (30 to 40 M board feet per section) are thus killed
each year, but on poorer sites losses of 50 to 100 M board feet per
section may not be unusual. In lodgepole pine stands normal losses
by bark beetles are practically negligible, so any marked losses indi-
cate abnormal conditions.

Defoliating insects at times destroy considerable stands of mature
timber. These outbreaks, however, usually occur at rather long in-
tervals and are nearly always of short duration. In western forests
some of the worst defoliators are the pine butterfly, the Douglas fir
tussock moth, the spruce budworm, and the hemlock looper. In
1893-95 the pine butterfly practically wiped out the mature ponderosa
pine stand on 140,000 acres of the Yakima Indian Reservation in
Washington. Since then less severe outbreaks of this insect have oc-
curred from time to time. In the 3 years 1930-32 the Douglas fir
tussock moth destroyed a high percentage of the Douglas fir stands
on 300,000 acres of the Colville National Forest in northeastern
Washington. Along the coast of Oregon and Washington the hem-
lock looper appears at intervals of about 10 years and completely
destroys the western hemlock and associated trees over large areas.
In Pacific County, Wash., between 1930 and 1932 this insect killed
approximately 200,000,000 board feet of western hemlock and other
species on an area of approximately 32,000 acres. An outbreak
in 1919-21 covered 500,000 acres in Tillamook and Clatsop Counties,
Oreg. Defoliators in general cause either little loss cr widespread
destruction. |

Forest plantations are particularly subject to the destructive ac-
tivities of insects, chiefly because a plantation is usually made up of
a large planting of a single species. Then, again, many plantations
are established on soils that are not especially suitable for the tree
species used; in such cases soil-infesting insects, such as white grubs,
wireworms, root maggots, and cutworms, play an important part by
feeding on the roots. Young trees and second-growth stands are
often seriously damaged also by insects that feed on the terminals.

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8 MISC. PUBLICATION 273, U. 8. DEPT. OF AGRICULTURE

Bud and twig moths, tip weevils, and twig beetles not only damage
and deform the terminal shoots but at times become so numerous as
to kill out seedlings, saplings, and poles over large areas. Pine
plantations in the Nebraska sand hills have been badly set back by tip
moths. Many areas of second-growth pine near logging operations
have been swept by aggressive infestations of engraver beetles.

The destruction of trees especially valuable from a recreational or
aesthetic standpoint has recently come into prominence because of
rapid progress in the development of forest recreation. The impor-
tance of forest cover on national parks, game preserves, and other
recreational areas cannot be estimated in board-feet values. Insect
depredations which mar the beauty or destroy the protective value
of the forest cover on park and other recreational areas justify higher
expenditures for suppression than might be reasonable on a strictly
commercial stand.

Injuries to the wood of living trees are manifested in lumber as
defects greatly reducing its value. Furthermore, all kinds of forest
products, from the time the tree is felled and for many years after
the wood is put into use, are subject to destruction by insects. Green
sawlogs and storm-felled timber, green sawed lumber and seasoned
lumber, rustic construction, poles, posts, cross ties, and all manner
of finished products, from flooring to furniture, are attacked. Losses
in finished products are particularly heavy, since they include cost
of manufacture or replacement, or both. Losses of this class, it 1s
estimated, amount to from 0.5 to 5 percent of the total value of vari-
ous classes of finished products.

INDIRECT LOSSES

Besides direct damage through destruction of trees and forest
products, forest-tree insects cause important indirect losses in the
way of reduction in forest growth and alteration of the stand from
valuable to inferior species.

In some forest types insects often are one of the chief limiting
factors in successful management. They frequently upset well-or-
ganized plans aimed at the continuous production of forest crops.
In the western white pine and lodgepole pine forests of the northern
Rocky Mountain region bark beetles so affect the proportion of
species as to convert many stands to entirely different composition.
In Modoe County, Calif., a bark-beetle epidemic in a mixed second-
growth stand of ponderosa pine and white fir killed out all the pine
and converted the stand into pure fir.

Much less frequently the effect of insect activity on stand compo-
sition is beneficial. In the Yosemite and Crater Lake National Parks,
for instance, lodgepole pine stands completely destroyed by bark
beetles have been succeeded by stands of the hemlock-fir type, which,
for park purposes at least, is far superior to the lodgepole pine type.

Certain defoliators, even though they do not kill the timber, may
cause a cessation or reduction of growth which may increase the ro-
tation period of the stand by from 5 to 10 or more years, or they
may so weaken the trees as to make them easy prey for tree-killing
bark beetles. Such defoliation may be local and confined to a single
tree species. or may spread over an enormous area and involve sev-

INSECT ENEMIES OF WESTERN FORESTS 9

eral species. For instance, an outbreak of the pandora moth in the
ponderosa pine stands of southern Oregon, between 1918 and 1925,
covered approximately 400,000 acres. Growth measurements on plots
on this area showed that over a period of 11 years the normal forest
increment was reduced by an average of 32 percent, or approximately
100,000,000 board feet. The weakening of these trees was followed
by heavy bark-beetle killing, as much as 30 percent of some stands
having been killed by the beetles.

The spruce budworm, which is so destructive in the Northeast and
in Canada, is present also in the Douglas fir and balsam fir forests
of the northern Rocky Mountains and the Pacific Northwest. Out-
breaks of this insect, besides resulting in destruction of extensive
stands of Douglas fir in the Rocky Mountain region, have left many
trees in a weakened condition that renders them susceptible to bark-
beetle attack. Many other defoliators, by partially reducing the leaf
surface of trees, adversely affect their growth; and in most cases the
forester has little opportunity to prevent this damage.

Another indirect result of bark-beetle and defoliator damage is
increase in forest-fire hazard. The old snags of insect-killed trees
scattered throughout mature forests, averaging on some ponderosa
pine areas as many as 10 per acre, stand for many years and greatly
increase the cost, difficulty, and danger in fire control. The felling
of snags is now required in many sales of national-forest timber,
and many private operators have adopted this precautionary meas-
ure. The cost of controlling forest fires that have spread from burn-
ing snags within fire ines would alone justify large expenditures for
insect control.

After the defoliation of large forest areas, the debris beneath the
stripped trees dries out quickly and becomes highly inflammable. A
flash of lightning, or a carelessly handled match or cigarette sets off
the mass, causing a widespread conflagration almost impossible to
control. Heavy defoliations in Douglas fir and hemlock stands and
epidemics of the mountain pine beetle in lodgepole pine have put
the forest in such a condition that, more often than not, forest fires
have followed. The increased fire hazard is an added reason why
forest-insect outbreaks should be controlled wherever possible.

RELATION OF INSECTS TO FOREST MANAGEMENT

Since the practice of forestry is concerned with the growth, pro-
tection, and perpetuation of timber resources, it must take into con-
sideration any agency having so important a bearing on the growth
and development of forests as insects. As has already been pointed
out, insects cause enormous losses in mature stands of timber which
are being held in reserve for future needs; they affect the rate of
erowth of developing stands and lower the yields; frequently they
so change the composition of a forest that a complete reshaping of
the plan of management is necessary; they take a varying toll from
crude and finished forest products; and they create serious fire haz-
ards. For these reasons insect problems enter into nearly every phase
of forest management and protection.

Under virgin-forest conditions no checks were placed on the activi-
ties of destructive agencies other than those imposed by Nature her-

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10 MISC. PUBLICATION 278, U. S. DEPT. OF AGRICULTURE

self, Fires as well as insects and disease outbreaks developed, spread
destruction, and ran their course. The whole process was very waste-
ful but seldom resulted in the permanent destruction of the forests
over any large areas. Natural checks were imposed and the processes
of regeneration were brought into play.

With the development of the country and a corresponding increase
in values came the necessity for better protection and management.
The first step in stopping Nature’s wasteful processes was the con-
trol of forest fires. Later, with more intensive forest management
and the development of control methods, attention was turned to the
prevention of losses from forest insects and disease. As time goes
on and forest values increase, more and more attention will be given
to preventing or controlling forest-insect damage, and a greater re-
finement in methods will become economically justifiable.

In a managed forest the first objective of forest-insect control is
to so regulate conditions as to maintain a natural balance between
the insect population that is destructive and the beneficial predacious
forms, as well as between the insects and their food supply, so as to
prevent the development of destructive insect outbreaks. This ob-
jective will be attained more fully in the future through silvicultural
practices applied to growing stands whereby unfavorable conditions
for the development of insects are maintained and a greater resist-
ance of the stand to insect attacks is developed. This may involve
such measures as prompt disposal of slash and correction of other
insect-breeding conditions, the regulation of stand density and com-
position, the regulation of environmental factors through drainage
or other methods, and the selection of insect-resistant varieties and
species of trees.

When preventive methods fail to avert insect outbreaks, direct con-
trol measures must be considered. The total elimination of a forest
insect is quite impractical, but fortunately this need not be attempted.
Instead, the objective of direct control is the restoration of the natural
balance in which the destructive insects are not greatly out of propor-
tion to their natural enemies. In such proportions the destructive
species are relatively harmless, and the damage they do is insig-
nificant.

In view of present forest values it is hardly practical to attempt
to control all insect outbreaks. Much of the insect damage to forest
trees of low value will have to be allowed to run its course, for if a
policy of combating all threatening insect outbreaks were adopted
the cost would be enormous and in many cases would exceed the
damage probable if Nature were allowed to control the epidemic in
her own way. The older forests, as they stand today, are ripe and
an easy prey to bark-beetle attack, and if we are not prepared to
utilize such timber and are willing to wait for Nature to replace any
losses by the slow process of growing a new crop of trees, no further
consideration need be given to control. On the other hand, in the
many cases in which timber is in demand and satisfactory control
measures are available, failure to take the necessary protective meas-
ures should be viewed in the same light as failure to control forest
fires,

INSECT ENEMIES OF WESTERN FORESTS 11

DETERMINING CAUSES OF FOREST-TREE DAMAGE

Many agencies may cause injury or death to forest trees, so before
observed damage is charged to insects, other possible causes should
be investigated. Often several agencies, such as fire, insects, fungi,
and physiological injuries, are so closely associated or interrelated
that it is difficult to determine the primary cause of the damage.

Injury by fire is usually easy to identify. Destruction of the
ground cover, scorching of the bark, and reddening of the needles
constitute ample evidence of fire damage. Usually bark beetles,
either primary or secondary species, attack fire-weakened trees and
complete their destruction. In some areas fire scars serve as 1mpor-
tant entrance points for fungi. Witches’ brooms and damage by
mistletoe are frequently conspicuous in either killing small trees or
so distorting them that they can never grow into timber trees. In-
juries by fungi, bacteria, and higher parasitic plants are not so
easily determined by the layman, and can rarely be identified without
the assistance of a trained forest pathologist. The discussion of
diseases, decay, and wood rots caused by these various organisms 1s
not within the field covered by this publication.

Mechanical and physiological injuries are frequently the primary

cause of sickliness, weakness, or death of forest trees. The insects
that invade the wood after such injuries have occurred are usually
only secondary enemies, and cannot be charged with primary respon-
sibility under such circumstances.
In some years a combination of weather conditions causes what
is known as “winter injury”, “red belt”, or “parch blight”; that is,
all trees of certain species on exposed hillsides within definite alti-
tudinal limits turn a bright wine-red color. The injury is thought
to be due to excessive transpiration during warm periods in winter
when the ground, roots, and tree trunks are frozen and water cannot
rise to supply the deficiency in the leaves. Twigs are sometimes
killed, but the trees usually recover unless subsequently attacked by
bark beetles or fungi.

Sometimes the tender bark on the south and southwest sides of
trees and the tops of branches is killed by the sun’s heat. This is
referred to as “bark scorch” or “sun scald.” The bark breaks away
from the wood and sloughs off. Such damage is rare under forest
conditions but occurs more frequently in young trees grown in open
plantations.

Excessive quantities of dust in the air, as along dirt roads, causes
a clogging of the stomata or breathing pores of leaves and results in
partial suffocation of trees. In the Western States such injury is
frequently followed by an attack of scale insects, which add to the
injury and in some cases have caused the death of many young trees.

Smelter smoke, and chemicals or oils deposited on the ground in
some instances cause injury to trees which leads to attack by many
species of insects.

Mechanical injury to trees may result from a number of causes,
such as logging operations, lightning, road building, and packing of
soil or exposure of roots (as in camp grounds), or from the work of
animals such as bear, beaver, and porcupines and that of sap-sucking

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12 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

birds. Such injury is usually inconsequential in its effect upon a
forest as a whole, and trees show remarkable powers of recovery from
limited mechanical injury unless insects or fungi enter to complicate
the situation.

In most cases of damage by insects the source of injury is readily
apparent from the very start. but even in such cases it 1s well to make
certain whether other conditions are partly responsible before taking
steps to control the insect pests. If insects are not the primary cause
of injury, little benefit can be expected from the effort to control
them.

A forest. officer should become familiar with the appearance and
characteristics of those insects capable of killing or injuring trees and
destroying wood products on the area under his care. The insects
he really needs to know are comparatively few, but ability to recog-
nize the injurious forms comes only after considerable study, not only
of the insect stages but of their typical work, whether it be markings
on the bark and wood, tunneling of needles, or deforming of termi-
nals. In the following discussions special emphasis is placed upon
the habits and typical work of the most injurious forms; for it is
through these that the forester first becomes acquainted with the de-
structive species, and only after considerable experience does he learn
to recognize insect adults and larvae dissociated from their work and
from typical host trees.

Adult insects can be distinguished from other small invertebrate
animals by the fact that they have jointed bodies of three parts (head,
thorax, and abdomen), breathe through tracheae, and have one pair
of antennae and three pairs of legs.

The larval form is the one most frequently encountered by the for-
ester; but unfortunately it is difficult to distinguish insects when in
this form by any simple characters. Usually, however, for the for-
ester’s purpose it is sufficient to be able to recognize the larvae as
those of insects of a certain group. ‘The forester easily acquires the
ability to recognize some of the more common forms through becom-
ing familar with their work.

The insects most important from a forestry standpoint are in-
cluded in seven main groups or orders under the large class Hexa-
poda or Insecta. These common groups (fig. 4) include the beetles
(Coleoptera), butterflies and moths (Lepidoptera), wasps (Hymenop-
tera), flies (Diptera), scales and aphids (Homoptera), bugs (Hemip-
tera), and termites (Isoptera). There are a number of other orders
of insects, but these are less frequently encountered. Some small ani-
mals closely related to insects, and frequently confused with them,
are of importance in forestry. The mites, belonging to the class
Arachnida, are sometimes injurious to trees. The spiders, belonging
to the same class, are predacious and usually beneficial. The mil-
lipedes and centipedes, belonging to the classes Chilopoda and Dipiop-
oda, are occasionally of importance in the forest.

Most insects pass through either three or four stages of develop-
ment. The beetles, wasps, flies, butterflies, and moths pass through
four such stages, and so are said to undergo “complete metamorphosis.”
The adult female lays eggs, from which the second stage, the larvae,
develop. The larvae usually are soft bodied and wormlike. The
larvae of beetles are called grubs; those of moths and butterflies are

INSECT ENEMIES OF WESTERN FOREST

S 13

FIcuRE 4.—Examples of six groups or orders to which most forest insects belong. Flat-
headed beetle (Coleoptera): A. adults; B, larvae. A moth (Lepidoptera) ; ©, adult;
D, caterpillar. Wood wasp (Hymenoptera): H, adult female; Ff, adult male; G, grub.
Flies (Diptera): H and K, maggots; J and L, puparia; J, adult fly. Secale insects
(Homoptera) (drawings by Edmonston): M, adult male; N and O, scales on pine
foliage. P, termites (Isoptera). All ratural size; except H. J, J, K, L, X2; M, Q,
greatly enlarged.

14 MISC. PUBLICATION 2738, U. 8S. DEPT. OF AGRICULTURE

called caterpillars; those of flies with two clear wings are called mag-
gots; and those of wasphke flies with four clear wings are called
grubs, slugs, or false caterpillars. The larvae feed and grow, the final
size which they attain being influenced to some extent by the abun-
dance of food and moisture. As they increase in size they molt or
shed their skins several times. The larvae transform to the pupal or
resting stage, and the pupae in turn change to the fourth stage, the
adult insects. Growth takes place only in the larval stage. Although
some adult insects do some feeding, none of them increase in size.
Their chief function in life is to mate and produce eggs, and thus
initiate another life cycle.

Scale insects, aphids, bugs, and termites undergo what is called an
“incomplete metamorphosis”; that is, they have only three forms—the
egg, the nymph, and the adult. Growth takes place during the
nymphal stage, in which the insect has very much the form and ap-
pearance of the adult but lacks fully developed wings.

Certain insects, such as the termites, aphids, and ants, have several
specialized adult forms, Thus, in addition to the usual stages, there
may be workers, soldiers, and secondary sexual forms. Certain scale
insects and aphids give birth to living young without producing eggs.
Others are able to reproduce by means of eggs laid by virgin females,
which develop without being fertilized. In some cases, as among the
gall midges, larvae are able to give birth to similar larvae without
passing through other stages. These are all exceptions to the general
rule.

Insect damage to trees may be caused in any one of several ways.
Adults of some species cause injuries by feeding on the leaves, twigs,
or tender cambium, or by slitting bark or leaves in order to deposit
egos. Adult bark beetles do considerable damage in constructing egg
tunnels under the bark. Most commonly, however, the damage is done
by the larvae or nymphs in their feeding on various parts of the tree.
No damage is ever done by the insects while in the egg or pupal stages.

The principal methods of feeding by which insects injure trees are
chewing, sucking, and gall forming. The great majority of forest
insects belong to the chewing group, and in the larval or the adult
stage, or both, these chew and ingest plant material. This group in-
cludes the leaf eaters, the cambium miners, and the wood borers.
Aphids, scale insects, and bugs feed by sucking plant juices by means
of slender mouth parts which they insert into the tender portions of
the tree. A group of specialized insects irritate portions of the tree
and thus cause it to form a swelling or gall which encloses them. The
method of feeding has an important bearing on the methods of
control.

The important forest insects might be classified, for the purpose of
discussion, according to their natural relationships, according to the
species of trees attacked, according to the parts of the tree affected,
or according to the stage of the life of a forest tree upon which they
inflict their greatest injury. For the purposes of this publication, it
seemed that the last-mentioned arrangement would be the most helpful
for the forest field man. In this publication, therefore, the western
forest trees will be followed through their life cycle, from seed to
final finished product, and at each step the insects that are of greatest
importance in injuring them will be discussed.

INSECT ENEMIES OF WESTERN FORESTS 15

INSECTS AFFECTING SEED PRODUCTION

The natural reproduction of forests, the artificial reforestation of
denuded areas, and the future supply of timber depend to a consider-
able extent upon the production of a prolific supply of sound, unin-
jured seed. In most instances insect damage to tree seeds is not
sufficiently severe to be of any great importance; in some seasons,
however, insects destroy practically all the seed of certain tree species
in certain localities.

Destruction of seeds may be caused by insects that attack the buds,
flowers, or immature cones, as. well as by those that attack the seeds
themselves. Damage at these early stages causes wilting, bighting,
or premature dropping of the parts affected. The fruit or cones de-
veloping after insect attack may be deformed or “wormy”, riddled by
the borings of various grubs, caterpillars, or maggots. In many cases
the cones show no damage, but the seeds are infested with the small
white larvae of seed chalcids. Even the old, hard, dry cones of cer-
tain pines are often mined by wood borers. The insects that affect
seed production in these various ways belong to a number of dif-
ferent orders and families, of which some work only on cones or seeds
while others work also in the bark or cambium of succulent growing
shoots, stems, and twigs, or even in dry wood.

Knowledge of the presence of seed-infesting insects will often pre-
vent the disappointment and loss attendant on the collecting, han-
dling, and sowing of insect-damaged seeds (58) .?

KEY TO DIAGNOSIS OF INSECT INJURY TO CONES AND SEEDS

A. Injuries to cones and coniferous seeds.
1. Cones wither and die before they are half grown.
a. Interior mined by small, white, curled larvae or
by small dark-brown beetles; pine cones only,
cone beetles, page 16.
b. Cones deformed and interior mined by active cater-
pillars; exterior with exudation of pitch or
WEDVEGO, DOLINGS£ = 22 ai a yy Se cone moths, page 16.
2. Cones reach full growth but are riddled with insect borings.
a. Borings made by active caterpillars which leave
pitchy masses of boring and excrement within the
cone and similar exudations at the point of en-
trance, or larval mines in axis and mature seeds,
without resinous exudations___-___ cone moths, page 16.
b. Soft cones riddled by small white maggots which
leave fine excrement in tunnels, but free from
TMASSESEOLy UGC eee ee ee cone maggots, page 20.
c. Hard, dry cones of pine mined by slender, white,
round-headed or flat-headed larvae,
cone borers, page 21.
B. Injuries to coniferous seeds, with or without injury to cone.
1. Seeds show no external injury, -but interior is hollowed out
by small, white, curled, legless grubs_____ seed chalcids, page 21.
2. Seeds swollen and galled, containing small pink maggots,
seed midges, page 20.

fave .- .— a 2earm*..- ae Fe

Sy

C. Injuries to nuts or seeds of broad-leaved trees.
1. Acorn showing no injury externally but mined by small,

Wane Cun ledseruly. rte ee ee acorn weevils, page 22.
2. Interior of acorn mined by active caterpiller which discharges
webbed frass through exit hole______-______ acorn moth, page 23.

“Italic numbers in parentheses refer to Literature Cited, p. 197.

WA RN ee SE) -

16 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

CONE BEETLES

Pine cones which dry and wither before they are half grown
(fig. 5), and either drop to the ground or are retained as blighted
immature specimens, usually have been killed by the cone beetles,
Conophthorus spp. (49).

The adults are small, dark, shining cylindrical beetles, from one-
sixteenth to five thirty-seconds of an inch in length. They bore into
the base or supporting stem of the immature pine cones in the spring
soon after the beginning of the second year’s growth. A small
tunnel is projected through the axis of the cone, and in this the
female beetle deposits her eggs. From these hatch small, white,
curled, legless grubs which feed upon the scales, seeds, and tissues of
the withering cone. Development to the adult stage is completed
during the summer within the dead cone, where the beetles usually
remain over the winter. The damage to the cone crops of ponderosa
pine, western white pine, and sugar pine is often very severe. In
some years from 25 to 75 percent of the cones of sugar pine have
been killed over large areas. In other pines the damage is less
conspicuous. No method of control seems feasible under forest
conditions,

A number of species found in western pines have been described
by Hopkins and named for their principal host trees. The following
list gives the species of Conophthorus that may be found in western
forests:

Species of Conophthorus Hosts and distribution

GC. ponderosae Hopk2=- 22s Ponderosa pine, lodgepole pine, and Jeffrey
pine. Pacific States.

CU -Scopuloniim Hop =. oe Ponderosa pine. Rocky Mountain region.

C. lambertianae Hopk-— = Sugar pine and western white pine.

C. monticolae Hopk] = = Western white pine and ponderosa pine.

C27@01atie- Hop kee a ee ee Monterey pine.

C3 CONtOTICE THO Kee eee Lodgepole pine.

Cmonopiyliag Hopke= = ss Singleleaf pinion pine.

OS COATS ENO ee eee eee Pinon pine. Colorado, Arizona, and New
Mexico.

CAGpCCheCCe CHO pk eas ene ee Apache pine. Arizona.

CG. fleniis sno pk eee Limber pine.

CONE MOTHS

The caterpillars of certain species of moths feed on the bracts,
scales, and seeds of tender growing cones. Such feeding dwarfs or
deforms the cones and sometimes causes their death, but more fre-
quently destroys a large percentage of the seeds without killing the
cones. The work of certain species is characterized by larval tunnels
within the cones and an opening at the surface through which resin
mixed with larval castings exudes. Other caterpillars attack the
cones and mine through the axis and into the seeds without causing
resinous masses or deformity of the cones.

The adults are mostly small inconspicuous moths which are seldom
noticed. They usually fly early in the spring and deposit their eggs
on the scales of young cones. The eggs hatch in a few days, and the
young larvae bore into the cones, where they feed until fall. When
the caterpillars reach full orowthe they form silken cocoons on the
surface of the cones, among - the cone scales, or in the pith, in which

INSECT ENEMIES OF WESTERN FORESTS li

they overwinter. Most moths have one generation annually, and the
adults emerge the following spring, but a few may retard their
emergence and appear the second or third season. Thus in the event

vr

(RE i Sa

in 5 ae ae ie o> eee er

=
ed

at

FIGURE 5.—Cone beetle damage: A, Sugar pine cone and cone beetle, the latter xX 7
(drawings by Edmonston). 8B, Pitch tubes on the stem, indicating cone beetle attack.
C, Knobcone pine cones riddled by cone beetles: a, Cone showing pitch tube at point
of attack near stem and exit hole near center; c, cone showing larval excavations and
adult beetle.

that one or two cone crops fail, the species is still able to survive.
No methods have been devised for the control of these insects, nor
would control be economically justifiable under present forest con-
ditions.
136650°—38

2

TS? MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

PINE CONE MOTHS

Pine cones are attacked early in the spring of their second year of
growth by several species of cone moths. The caterpillars of one
group are dirty white in color and about one-half inch in length when
full grown. They burrow through the central axis of the cones and
enter the seeds through the point of attachment. They are especially
destructive to the seeds of ponderosa pine (fig. 6) and Jeffrey pine.
Pupation takes place in the pith. The moths are small, one-half inch
in length, and gray to black in color. The species included in this
group are the following:

Species Hosts and distribution
Laspeyresia piperana Kearf_____~ Ponderosa pine and Jeffrey Pine. Cali-
fornia, Oregon, Washington, Idaho, and
Montana.
Laspeyresia miscitata Hein__----— Ponderosa pine and Jeffrey pine. Cali-
fornia, Oregon, and Nevada.
Hedulta injectiva, Hein? = == Jeffrey pine and ponderosa pine. Cali-

fornia, Oregon, and Nevada.

Those which are
most frequently in-
volved in this type
of injury belong to
the genus Laspey-
TSU.

Other cone moths
which attack pine
cones bore tunnels
through scales and
seeds. The seeds and
a large portion of
the interior of the
cone are destroyed.
Sometimes the at-
tack distorts and de-
forms the cone or
kills it before it
reaches maturity.
Most of the species
of this group also
feed on the succulent
new growth of pines.
FIGURE 6.—d@, Adult of the pine cone moth (Laspeyresia Their work 1s char-

piperana) * 2; b, caterpillars feeding through ponderosa acterized by a resin-

nes cone. and pupa in the pith. (Drawing by Edmon- ous exudation of

pitch and larvel cast-

ings mixed with webbing. The following species belong in this
group:

Species Hosts
Dioryctria zanthaenobares Dyar__ Ponderosa pine, knobcone pine, and other
pines.
Dioryctria abietella D. and S_____ Pines, Douglas fir, balsam fir, and spruce.
Eucosma bobana Kearf___________ Ponderosa pine, Jeffrey pine, and knobcone
pine.

Eucosma rescissoriana Hein-____- Lodgepole pine.

INSECT ENEMIES OF WESTERN FORESTS 19

FIR CONE MOTHS

Cones of white fir, red fir, and other balsam firs, and of Douglas
fir, are most seriously injured by the attack of small moths of the
genus Barbara (formerly Hvetria). The yellowish-white caterpillars
mine through scales and seeds, making a tortuous resinous tunnel and
an opening at the surface through which resin and larval castings
exude. The pupae overwinter near the axis of the cone in a papery,
resin-coated cocoon among the resin-matted scales. The adults, which
are gray moths about one- half inch in length and with speckled fore-
wings, emerge the following spring and day their eggs on the young
budding tender cones. The several species and varieties listed below
cause this type of damage:

Species Hosts and distribution

Barbara colfaxiana Kearf________ Douglas fir. California, Oregon, Washing-
ton, and British Columbia.
Barbara colfaxiana var. tawxifoli-

C2 REEA) BSL BSTC) SSS. ph lS ei Douglas fir. Montana.
Barbara colfaxiana var. coloraden- .
ARTS BI SH gaa a a a a Douglas fir and white fir. Colorado.
Barbara colfaxiana var. siskiyou-
CALONNG AN, feoieee ae Aes aos de White fir and red fir. California and
Oregon.
Barbara ulteriorana Hein ___—____ Douglas fir. Oregon.

Similar damage to fir cones is frequently caused by the caterpillars
of the cone pyralid, and the fir cone geometrid.
The cone pyralid, Dzo-

ryctria abietelia D, and 8S.
(fig. 7), in the full grown Zoe
larval stage is a large, ac- 2 LE WA ANN
tive, irridescent, greenish- 2722 SIE S
red caterpillarthree-fourths Ws Su i a y
: F aie GZ Sl Ag KMS
of an inch in length, which SSN N/a aN
bores through scales and f, Ui LOS iy
seeds of Douglas fir, bal- la ZN q
sam fir, pine, and spruce ne ZN
cones, leaving a round clean- Ses
cut hole. In contrast to
the work of Barbara its ie
webbed castings on the sur- ye
face of an infested cone are Ce
free from pitch. The adults
are gray moths mottled
with black and have a wing
expanse of about 1 inch.
The fir cone geometrid
Eucymatoge spermaphaga eee
Dyar in the adult stage is a "™00ER,7-—A fx cone moth (Dioryotri abstetie),
gray moth with black and fir cones. (Drawings by Edmonston.)
red-brown markings and a
wing expanse of about 1 inch. The caterpillars, which are somewhat
similar to the above, are of the measuring worm type. They bore
through seeds and cone scales of Douglas fir, the balsam firs, mountain
hemlock and probably other conifers.

WS

Lore

Sy

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a0 SES
I

a, eee

Taal

- ae sf : "4 le SF dl

i 9

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OS fee rg gy oy

20 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

Another group of small moths, belonging to the genus Laspeyresia,
are destructive to fir, spruce, and other cones. The larvae are less
than one-half inch in length when full grown, pink or white in color,
with a few bristles. The moths are small and dull colored. They
are of the following species: )

Species Hosts
Laspeyresia bracteatana Fern___.. White fir, red fir, and other firs.
Laspeyresia youngana Kearf______. Spruce.
Laspeyresia cupressana Kearf___.. Monterey cypress.

Cones of incense cedar in Oregon are sometimes injured by the
slugs of a sawfly (Augomonoctenus libocedri Rohw.) which does
work similar to that of cone-feeding caterpillars. The adults are
one-fourth to three-eighths of an inch long, shining blue-black, with
the first five segments of the abdomen brick red.

FIGURE 8.—Cone maggots (Lonchaea viridana) are commonly destructive to seeds of
white fir. De

CONE MAGGOTS

The insects encountered in seed collecting probably more often
than any other group are small, white or pink, legless maggots which
emerge from the cones in vast numbers as these are spread out to
dry. These are the larvae (fig. 8) of tiny gnats, midges, or flies.
A few cause considerable injury to cones and seeds, whereas others
do no appreciable damage.

Cone and seed midges (Cecidomyiidae) are found in cones as small
pink maggots, the larvae of small gall gnats or midges. The adults
are small and very similar in appearance to mosquitoes. They lay
their eggs on the young, green cones, and the maggots work within
and cause little masses of resin to form among the cone scales or
cause hard resinous galls to form on the scales or in the seeds. The
damage from these insects is usually insignificant. Of the many
western species, only one, Janetiella siskiyou Felt, from the seeds of
Port Orford cedar, has been named.

INSECT ENEMIES OF WESTERN FORESTS PHN

The white fir cone maggot (Lonchaea viridana Meig.) 1s the com-
mon white maggot found so abundantly in white fir and other bal-
sam fir cones (fig. 8). These maggots mine through scales and
seeds, often causing great damage. The larvae leave the cones as
soon as they fall and form small ] puparia in the ground. Here they
overwinter, and in the spring some of them emerge as small, black,
shining flies. The great majority of the brood go through a 2- -year
life cycle, emerging ‘the second spring after pupation.

CONE BORERS

The hard, dry cones of certain pines are frequently attacked by
the larvae of flatheaded and roundheaded borers which riddle the
interior and destroy the seeds.

The roundheaded cone borer (Paratimia conicola Fisher) has the
habit of boring tunnels through the hard pitch and scales of knob-
cone pine cones. It works also in the dry limbs of the species. ‘The
adults are a rusty reddish brown, and one-half inch in length.

The flatheaded cone borer (Chrysophana placida Lec.) has been.
found boring through the hard, dry cones of knobcone and_ponde-
rosa pine. It also bores in the dead limbs, branches, trunks, and
stumps of practically all western pines and firs. In the adult stage
it is a small green or greenish-red beetle, about one-half inch in
aes

SEED CHALCIDS

Seeds of many conifers are attacked by small wasps of the genus
Megastigmus (71), which drill through the young green cones with
their long evipositors and lay their eggs within the immature seeds
(fig. 9). The small, white, legless larvae feed on and destroy the
tissue within the seeds. The normal outer shell is formed later and
shows no evidence on the surface that the seed is infested. The
feeding habits of these insects are similar to those of the gall makers.
In the following spring the larvae reach maturity and emerge as
small yellow or nearly black wasps. Each adult leaves a smooth
round emergence hole in the seed coat. Some hold over and emerge
the second or even the third year. The damage by these seed-in-
festing insects is an important factor in seed collecting, and often
a high percentage of cleaned commercial seed will be found to have
been ruined by these insects.

There appears to be no practical means of preventing this damage;
but to avoid the introduction of this insect into other countr les, in-
fested seeds should be fumigated in a tight container with carbon
disulphide. As this fumigant has a deleterious effect upon the ger-
mination of the seed if used in excessive dosages, not more than 1
ounce of fumigant should be used to 100 pounds of seed, and the
fumigant should be completely removed by thoroughly aerating the
seeds after they have been in the container for 48 hours. Carbon
disulphide vapor mixed with air is explosive, and fire should be
guarded against. Calcium cyanide may prove to be a more satis-
factory fumigant, but which form of it should be used and how it
affects the germination of seeds has not yet been fully determined.
Since the gas evolved from calcium cyanide is a deadly poison this
material should be used with caution, preferably by persons who
have had experience with it.

==

43
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a De SY LE OF
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Si ALIS :
ys Fie {hy i

RR er

292 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

The different species of this genus and the hosts from the seed of
which they have been reared are as follows:

Species Hosts

Megastigmus albifrons Walk____~_ Ponderosa pine.

Megastigmus lasiocarpae Crosby_— Alpine fir.

Megastigmus picea Rohw_____-__ Blue spruce, Engelmann spruce, and Sitka
spruce.

Megastigmus pinus Parfitt_______. sileer fir, lowland white fir, white fir,
Shasta fir, and bristlecone fir.

Megastignus tsugae Crosby_____ Mountain hemlock.

Megastigmus spermotrophus

Wiaciths (60!) Ss he ee eer Silver fir, bristlecone fir, grand fir, red fir,

white fir, Douglas fir, and other conifers.

NUT AND ACORN
WEEVILS

Nuts and acorns of
various western hard-
woods are frequently
infested by the
curled white grubs
of the nut and acorn
weevils, belonging to
the genus Balaninus.
The adults are me-
dium-sized, yellow,
brown, or nearly
black weevils with
robust bodies, long
legs, and prominent,
slender, curved or
nearly straight beaks.
The adults appear in
the summer. With
their beaks they
enaw holes in the
shells of new acorns
or nuts and in these
they place their eggs.
The larvae feed on
the meat and destroy
the seed. The win-
ter is passed in the
larval stage, either
within the acorn or
in the ground. Pu-
pation occurs the
FicurE 9.—A and B, Adults of the ponderosa pine seed chal- pext spring, and the

cid (Megastigmus albifrons) laying eggs through small 5
green cones into seeds (drawings by Edmonston). En- adults emerge in the

larged. OC, Larvae, pupae, and adults of same species of
Megastigmus, X 3. Female above, male below. summer, Several

INSECT ENEMIES OF WESTERN FORESTS 23

species of Lalaninus are found in the Western States. These are
listed below :

Species Hosts and distribution

Balaninus uniformis Lee ~~ Oak acorns. New Mexico, Arizona, Utah,
California, Oregon, and Washington.

Balannws caryae Horm 2. 2. Hickory, pecans. Eastern States and west-
ward into Colorado.

ESQLONWUILILS “RECLUS. SAY. = Chestnuts, acorns. Eastern States and
westward into Arizona.

PLOVUILUS MUASICUS: SAY] 252 Ee Oak acorns. Eastern States and westward
into New Mexico and Arizona.

Balaninus q-griseae Chittn__ —__-_ Griseous oak acorns. Arizona.

ACORN MOTH

Small white or pinkish caterpillars, about three-fourths of an
inch in length when full grown, the immature stage of the acorn
moth (Melissopus latiferranus Wls.), may at times be found boring
through acorns and throwing out larval castings, which are held
together by a web, at the entrance hole. They also infest the seeds
of Catalina cherry in southern California and may likewise be found
in the large green cynipid galls formed on various oaks. There is
only one brood a year, and the larvae hibernate in cocoons within
the ground.

INSECTS INJURIOUS TO SEEDLINGS IN NURSERY OR
FOREST

In nurseries and plantations, and even in natural forests, young
seedlings are the easy prey of a great variety of insect enemies. In
seedbeds the nurseryman must guard against insects as well as
against damping off, rodents, heat injury, and unfavorable soil con-
ditions. In transplant beds insect damage may be more severe than
in the seedbeds. In some cases white grubs alone have destroyed 90
percent of seedlings planted in badly infested soils. In western
nurseries the strawberry root weevils have occasionally taken a heavy
toll in the transplant beds. Cutworms, grasshoppers, leafhoppers,
and other insect pests become abundant at intervals. After planting
in the forest, nursery stock is subject to damage by a great many
insect enemies before it becomes well established and able to resist
attack. So far, western forest nurseries have been more fortunate
than those in the East in escaping troublesome insect pests.

It is at these early stages in the tree’s life cycle that root-feeding
insects do their greatest damage. After the trees have become fully
established in the field and have developed a large root system there
is less danger that soil-infesting insects will injure them seriously.
Most of the soil-inhabiting insects that feed on the roots of seedlings
show little preference for any particular tree species. Root bark
beetles and root aphids are among the few that confine their feeding
to the roots of certain host plants. White grubs, wireworms, root
weevils, cutworms, and root maggots feed not only on the roots of
forest seedlings but on the roots of many other plants. The stems
of young seedlings may be attacked above ground by cutworms,
grasshoppers, leafhoppers, and various bark-chewing beetles; and
the leaves may be fed upon by caterpillars and sawflies and by vari-

:

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am Terme uae or

DY eae) wee SS | Gees Se Se © oa SS eee oe

—t————¥

94 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

ous scales, aphids, and bugs. Most of these insects, since they are
enemies of larger trees as well, will be treated in later discussions.

While the control of insect pests in forest nurseries is sometimes a
difficult matter, the nurseryman, at least, has measures at his dis-
posal which would be impractical to use under forest conditions.
Some root-feeding insects can be controlled by applying a fumigant
to the soil, or by using poisoned baits, but much can be done to avoid
injury through regulating cultural methods. Transplant beds which
have become | heavily infested should be plowed and allowed to re-
main fallow for a year. If they are cultivated often enough to
prevent the growth of any weeds, most of the insects will have been
starved out In a year’s time, and the beds can be used again for a
short period without serious injury to the transplants. Leaf- feeding
insects usually are easily controlled by the use of sprays.

To protect seedlings from root-feeding insects after they are set

out is not so simple, and, so far as is known, no attempt has been
made to control soil-inhabiting insects in plantations or forests in
the Western States.

KEY TO DIAGNOSIS OF INSECT INJURY TO SEEDLINGS

A. Roots of seedlings chewed, injured. or dying.
1. Rootlets completely bitten off or the bark badly chewed* by
soil-inhabiting insects, appearing as
a. Curled, white grubs with three pairs of prominent
legs and with brown heads *______ white grubs, page 24.
b. Small, curled. white grubs with small brown heads
but without Jé@2s (2 ae root weevils, page 26.
c. Long, slender, hard-shelied, yellow or brown “worms”
with feebly developed legs ~_______ wireworms, page 26.
d. Nearly hairless, soft. sluggish, dark-colored caterpil-
lars working below surface of ground *

cutworms, page 26.

bo

Tunnels or borings under bark of larger roots
root bark beetles, page 27.
3. Large, dark, soft-bodied aphids sucking sap from roots
root aphids, page 28.
B. Stems of young seedlings badly chewed or injured.°
1. Stem bitten off, or bark badly chewed—
a. Nearly hairless, sluggish caterpillars working at

TB ne ee ee Se ee cutworms, page 26.
6.-Grasshoppers. 2 te ee Ss grasshoppers, page 164.
2. Borings under bark of larger seedlings________ bark beetles, page 96.
i: Leaves of seedlings either chewed. skeletonized, mined, discolored. or
attacked by leaf-sucking inseets= 2225 ee defoliators, page 58.

WHITE GRUBS

White grubs (29) are probably more common in forest nurseries
than any other soil-inhabiting insects. These are the larvae of
June beetles (Scarabaeidae), which are widely distributed and feed
on the roots of a great variety of plants. The adults are voracious
feeders and in the Lake States and elsewhere are often very injurious
to the leaves of plants.

* Damage meeting this description is done also by root-feeding mammals such as
gophers, moles, ete. é =

*+These characters are not specific and sometimes noninjurious larvae of similar
appearance may be confused with these forms.

> Similar damage is often done by small animals, such as mice, squirrels, and porcu-
pines.

a

a

=.

INSECT ENEMIES OF WESTERN FORESTS 25

The large, shining, brown “June bugs” (fig. 10) often lay their
eges in grassy places or where the ground vegetation 1s heavy. In
the North, where the life cycle is 3 or more years in length, the small
white grubs feed during the first summer on organic material and
on small rootlets near the surface of the soil. As cold weather ap-
proaches they burrow more deeply into the soil and hibernate. ‘The
second season the grubs are larger and do their greatest damage to
the roots of seedlings and small trees. They again hibernate over the
second winter and again feed during the following spring. ‘The full-
grown grubs are white, thick-bodied, with dark-brown heads and
three pairs of well-developed legs. They always le in a tightly
curled position and are familiar ob-
jects to everyone who has dug for fish
bait. In midsummer of usually the
third season they reach full growth,
transform to the pupal stage within a
cell in the ground, and emerge the fol-
lowing spring as full-grown beetles.
In the Southern States the cycle may
be completed in 2 years, or possibly
less, while in the North and in Canada
it may take 3, 4, or even 5 years.

The prevention of white grub dam-
age can be accomplished to a great
extent through modification of cul-
tural operations. New ground that is
to be used for nursery purposes should
be put under cultivation for 2 or 3
years to allow for the emergence of
beetles already in the ground and to
avoid new egg laying.

If transplant beds are cultivated
frequently in the seasons when they
are lying fallow, and these periods of

Figure 10.—Adult beetle, eggs, and

resting are interspersed between the larva or white grub of Polyphylla
period of use, the damage by white ee ae

grubs will usually be comparatively

light. Infestation in seedbeds is likely to give the most trouble, since
the dense growth produces a favorable condition for egg laying, and
the beds cannot be cultivated until the seedlings are taken up. Beds
can be protected by covering them with a 14-inch mesh wire screen
during the egg-laying period. If the beds become infested, the young
seedlings should be dug the second spring to avoid heavy damage.
Clean cultivation, screening of seedbeds, and rotation of transplant
beds are first steps in holding white grub damage to a minimum, but
even these are not always successful.

Seedbeds which must be repeatedly used may become heavily in-
fested. Recent experiments have indicated that the grubs can be
killed by the use of 50-percent miscible carbon disulphide. A satis-
factory dosage consists of 1 quart of the miscible carbon disulphide to
50 gallons of water and an application of 3 pints of the emulsion to
each square foot of soil surface. Care should be taken not to allow
any of the solution to come in contact with the leaves of the young

GSE 4 FL

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26 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

seedlings, and in hot weather a weaker emulsion should be used to
prevent injury to the roots. While this treatment has given satis-
factory results in the experiments so far conducted, it should not be
adopted on a large scale until it has been demonstrated that it is
applicable on the particular type of soil at the nursery, and puddling
of the soil should be carefully avoided.

Treating some soils, especially light sandy loams, with arsenical
compounds has been shown to be destructive to seedlings, and in many
cases it has left the ground in a toxic condition for 3 or 4 years.

ROOT WEEVILS

In forest nurseries of the Pacific Northwest the strawberry root
weevil has proved to be one of the most serious insect pests. Three
species are involved in this damage—Brachyrhinus ovatus L., B.
rugosostriatus Goeze, and B. sulcatus F.

The adults are small, brown, hard-shelled, wingless beetles about
one-fourth inch in length, with head extended into a snout. When
the adult weevils emerge in the early summer they migrate on foot,
crawling everywhere, in search of suitable places for egg laying.
Eggs are laid only at the root crown of plants, and the small, white,
curled grubs develop in the soil, where they feed on the roots of
various plants. ‘The life cycle is completed in 1 year, and the full-
grown larvae pupate in the soil and emerge as new adults the follow-
ing summer.

Seedbeds can be protected from infestation by encircling them dur-
ing the migration and egg-laying period with barriers, such as boards
or metal strips placed on edge in the ground and painted with sticky
substances, such as coal tar or sticky tree-banding material. Poi-
soned baits have also proved effective in destroying the weevils in
larger fields. An effective poisoned bait consists of 5 pounds of pow-
dered calcium arsenate and 95 pounds of ground dried-apple waste,
applied at the rate of from 50 to 70 pounds per acre.

The most satisfactory method of control is through clean cultiva-
tion and rotation of seed and transplant beds, allowing infested plots
to remain fallow and be cleanly cultivated in alternate years.

WIREWORMS

Under certain conditions wireworms (Elateridae) (53) may prove
to be troublesome nursery pests. They are most frequently found in
heavy, moist soil, where they feed on undecayed plant material and
small roots. These long, slim, cylindrical, hard-shelled “worms” with
feebly developed legs are the larvae of click beetles, which are most
easily recognized by the layman by their ability to flip into the air for
several inches when turned on their backs.

No satisfactory method of controlling wireworms has been de-
veloped, and soils which are abundantly infested with them should be
avoided for nursery purposes.

CUTWORMS

From time to time cutworms make their appearance in forest
nurseries and do considerable damage to the young trees by feeding
on the roots or clipping off seedlings at the ground line.

INSECT ENEMIES OF WESTERN FORESTS Di

The adults of cutworms are the dull-colored, yellow, tan, or brown
moths which collect around lghts at night and are commonly re-
ferred to as “millers.” They fly at night, usually early in the spring,
and lay their eggs on the ground where there is ample vegetation for
larval food. ‘The larvae or cutworms work underground, feeding on
the roots of various plants, or during the night they often feed above-
ground on the foliage or clip off the stems at the ground line. They
are dull-colored, with very few or sometimes no hairs on the body, and
some have a greasy, slimy appearance that is in keeping with their
ground habitat. They reach full growth late in the summer or in the
fall and overwinter in the soil as full-grown larvae or as pupae in
earthen cells. Emergence takes place the following spring, or in
some cases there may be several broods a year.

Clean culture in the nursery to avoid the establishment of weeds or
ground cover that would be suitable for egg-laying, and cultivation
in the fall and winter to destroy the hibernating larvae, will do much
to prevent cutworm damage. Where such methods fail, poisoned
baits made of bran and white arsenic are effective. A good formula
for this purpose is as follows:

Vne mt rane w ee eo oper anew ae LIne eS . 25 pounds.
NVinitesAEseniGroraparis, Sreen= 222s eee dl fg pS) GAIN MGIC) Se age ey 1 pound.
RiacksuraMemolassess across Ne ee ae II HS aD C7 LC RD a

NY BCS a iT pao a 1 to 2 gallons.

Where seedbeds can be flooded for a time without damage to the
young trees, cutworms can be drowned. Such treatment is often both
simple and effective.

ROOT BARK BEETLES

Although bark beetles (Scolytidae) are primarily enemies of large
forest trees, a few species are of importance in killing large seedlings
through attack on the roots. Species of the genera Hylastes and
Hylurgops have been found doing this type of damage. Normally
these are secondary bark beetles which breed in slash and under the
bark of trees killed by fire or insects, but they appear to be primary
in attacking the roots of suppressed or weakened seedlings. The
attacking beetles make entrance burrows at the ground line and con-
struct winding galleries which extend downward into the larger
roots and are partly filled with frass. The larvae work through the
cambium, away from the egg tunnels, and feed together without scor-
ing the wood. Seedlings an inch or more in diameter are killed by
the attacks. The species which have been found doing this type of
damage are noted below:

Species Hosts
Wylastes nigrinus Mann =) <= 2.___. Douglas fir, western white pine, western
hemlock, and probably other conifers.
TIUIASTCS MGCer AueC ss ete Engelmann spruce, ponderosa pine, and
lodgepole pine.
Hylurgops lecontei Sw____---- --- Lodgepole pine, ponderosa pine.
Hylurgops porosus Lee____------ . Lodgepole pine, western white pine, and

probably other pines.
Pseudohylesinus granulatus Lec_. Balsam firs.

The general habits of bark beetles are more fully discussed in a
later section (page 96).

, Ra 7 st SS YE OSes SO OC BRS OMS CORE BREE.

I8 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

ROOT APHIDS

Some aphids are root-feeders. One species, Cinara (Lachnus)
curvipes Patch, was recently found feeding on the roots of small
white firs in Oregon. The large carpenter ants (Camponotus her-
culeanus var. modoc Wheeler) were carefully tending them. The
ants had gnawed the outer bark and cambium of the fir roots, and
colonies of aphids were feeding on the fresh wounds. They were
observed working the full length of their beaks into the cambium
and feeding on the juices. This same aphid has been found working
on the bark of twigs of balsam firs and Cedrus atlantica.

INSECTS INJURIOUS TO YOUNG TREES (SAPLINGS
AND POLES)

Trees in plantations and forests are subject to attack by a great
many insect pests while they are growing from saplings to maturity.
After having been at first beset by the root-feeding insects, they
are later attacked by another group of injurious insects—those which
feed on the rapidly growing terminal shoots, laterals, tips, or buds.
This type of damage seldom results in the death of the young trees,
but it often seriously deforms or stunts them. As buds and termi-
nals are killed the tree throws out new buds and shoots, which results
in much branching. ‘The tree becomes bushy in form, with the main
trunk crooked and gnarled, and is often permanently ruined for
commercial use. At this stage of the tree’s life, leaf-eating and
bark-feeding insects also begin to be of importance.

The control of insects affecting young trees rarely calls for the
application of direct control measures. A certain amount of insect
damage is normal in natural forests and is only a part of the natural
thinning process. When an epidemic develops as the result of some
disturbance of the natural balance, as through the creation of an
abundance of slash, windfall, or fire-injured trees, some direct con-
trol action may be necessary to protect the younger trees. Usually
the indicated remedy is avoidance of the conditions that induce epi-
demics or the prompt disposal of breeding material. In plantations,
or in the case of trees of special value, some attention to insects may
frequently be justified.

The control of terminal-feeding insects presents an extremely diffi-
cult problem. In general little can be done except through spraying,
dusting, or hand-picking of damaged shoots and encouraging of
parasites. The cambium-feeding insects can usually be controlled
by felling and burning the infested material, and leaf-feeding forms
can be controlled by spraying or dusting. Special methods adapted to
the control of each group will be mentioned under later discussions.

KEY TO DIAGNOSIS OF INSECT INJURY TO YOUNG TREES

A. Terminal shoots, laterals, or tips deformed or killed. Trees weakened
or stunted but seldom killed (except a few of the smaller seed-
lings).

1. New or old twigs, branches, or succulent shoots killed. Insect
tunnels or borings found under the bark.

a. Point of attack showing a small pitch tube with exu-

dation of fine boring dust. Under the bark or in

pith are found small egg tunnels of uniform

eee

INSECT ENEMIES OF WESTERN FORESTS 29

width, free from packed boring dust, made by
small brown beetles; and larval tunnels packed
with fine borings made by small, white, curled,
leclessularvaes eee eee a twig beetles, page 30.
b. Point of attack not conspicuous and not showing a
small pitch exudation. Tunnels under bark, nearly
round, free from pitchy exudations, filled with
coarse or powdery boring dust. Made by small,
white, curled, legless grubs__----- twig weevils, page 33.
ec. Point of attack not conspicuous. Tunnels under bark
broadly oval or nearly flat and filled with boring
dust. Made by slender white grubs with broad
NEED CS at Rea OT RE es twig borers, page 25.
d. Bark and wood of twigs conspicuously gnawed and
girdled, causing death and breakage
twig girdlers, page 35.
e. Point of attack showing resinous exudation, with lar-
val castings webbed together, or pitch nodule.
Resinous tunnels under bark or in the shoots
made by active caterpillars
twig moths or tip moths, page 37.
2, Leaves and buds at tips of branches webbed together and
killed. Very little damage to other parts of the shoots
bud moths, page 44.
3. Tips of branches appearing unhealthy, sickly, badly swollen
and deformed, or killed. No borings under the bark.
a. Sueculent tips covered with small, soft-bodied insects,
or stems covered with powdery, cottony incrusta-
tions or shell-like seales; trees dripping a sticky
exudation ; often covered with a black smut
sap-sucking insects, page 44.
b. Terminal shoots or leaves enlarged, galled, or swollen
gall makers, page 52.
ce. Twigs with dying and dead needle tufts, bark filled
with resinous pockets containing small red maggots
pitch midges, page 54.
B. Entire tree, or a large part, sickly, dying, or dead; foliage fading, turn-
ing yellow or red.
1. Tunnels or borings found under the bark of the main trunk or

ANGE OTA CHIC Sosa eas ae cambium feeders, page 56.
2. Insects found feeding on the roots___-________ root feeders, page 24.
3. Foliage fed upon, partially or wholly stripped from the trees,

or appearing sparse and sickly_____________ defoliators, page 56.

INSECTS AFFECTING TWIGS, TERMINAL SHOOTS, AND BUDS

Injury to leaf buds, succulent terminal shoots, and growing tips
may be caused by insects of a number of different groups, such as
twig-boring caterpillars, twig weevils, twig beetles, roundheaded or
flatheaded borers, or even pitch midges, aphids, and ‘scale insects (fig.
11). Such insects show a decided preference for these tender, grow-
ing parts of the trees. The damage they do to the new growth of
older trees is of much less importance than that done to young trees
in the formative stage. In the normal forest the damage of this
character to native trees is rarely extensive enough to be of serious
consequence, but on cut-over lands and in plantations it is frequently
disastrous.

The seriousness of this type of damage is shown in the sand-hill
plantations of the Nebraska National Forest. Two species of pine
tip moths (Rhyacionia spp.), which were of little importance in their
native habitat, found their way into these new isolated plantations.
In the new environment, freed from their native parasites and find-

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320 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

ing the newly planted trees nonresistant to their attacks, they pro-
ceeded to cause serious damage.

The control of insects that feed on twigs and terminal shoots pre-
sents many difficult problems, and under forest conditions little of a
practical nature can be done to control them, after they have become
established. Under management, however, much damage from this
source can be avoided by growing trees in dense stands or by keeping
the trees in as vigorous growing condition as possible.

Under special conditions, where the value of the young trees justi-
fies the expense, control can be accomplished by hand picking the

FIGURE 11.—Group of young, thrifty ponderosa pines killed by scale insects. (Group

killings of this type are most frequently caused by engraver beetles. )

infested shoots and either burning them or placing them in cages
designed to retain the destructive species, but ailow the escape of its
parasites. Recently one or two projects of this character have been
carried out with very satisfactory results. In the case of the isolated
Nebraska sand-hill plantations much good was accomplished by in-
troducing the native parasites of the tip moths.

TWIG BEETLES

The bark and pith of the smaller twigs, and branches of various
coniferous and broad-leaved forest trees, are frequently mined by
the smaller species of bark beetles of the family Scolytidae. These
small twig beetles are often very abundant in the branches and twigs
of dead, dying, or recently felled trees and in the twigs of healthy
trees in the vicinity of slashings. Usually they confine their attacks
to the twigs of trees of various ages and are commonly referred to as
“twig beetles.”

The attack of the twig beetles on living trees (fig. 12) is indicated
by a small pitch tube or the exudation of fine boring dust at the point

|
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j
1
4

INSECT ENEMIES OF WESTERN FORESTS 31

of attack on the twig. Under this will be found small tunnels of
uniform width, free from packed boring dust, which are made by
small brown to black beetles. From egg niches along the sides of
the egg tunnels, larval mines extend under the bark. ‘These are made
by small, white, curled, legless larvae that leave fine, packed boring dust
behind them. In many cases several egg tunnels start from a circular
entrance chamber under the bark and run lengthwise of the stem.

This type of work may
be done by members of sev-
eral genera of bark beetles
represented by hundreds of
species, so only a few of the
more common species can
be mentioned here. More-
over, there is no well-defined
dividing line between the
species that work in twigs
and those that work in the
larger limbs, branches, and
trunks. Some species may
be found breeding in all of
these places; so, in addition
to the species listed in this
section, those described un-
der the heading of “Bark
beetles” on page 96 should
also be considered.

The control of twig
beetles has never been at-
tempted in western forests,
as their damage is seldom
serious enough to warrant
control measures. If they
are especially bad in planta-
tions or on shade trees, prun-
ning the infested branches
and buring the twigs may Ficurr 12.—The Douglas fir twig beetle (Pityophtho-

rus pseudotsugae Sw.) and character of its work in
be of some benefit. mountain hemlock. Natural size.

PINE Twic BEETLES

There are a large number of twig beetles that work under the bark
and in the pith of pine twigs and sometimes in larger branches and
even in the trunks. These species develop readily in slashings and
broken twigs, and frequently cause the death of twigs and limbs on
living trees. The twig beetles most frequently found attacking pines
belong to the genera Pityophthorus, Pityogenes, Pityoborus, Pityo-
philus, Myeloborus, Carphoborus, Orthotomicus, and Ips (p. 110).

The typical work of the Pityophthorus (5) consists of a central
nuptial chamber under the bark, from which radiate several egg gal-
leries each occupied by a female beetle (fig. 18). Eggs are placed
in large niches along the sides of these egg galleries, and the larvae,
on hatching, work through the cambium of the twig and, on reaching

iW
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32 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

full growth, pupate at the end of the larval mines. There are usually
two or more generations of the beetles each year, the number varying
with the locality. As over 100 species have been described from
western pines, no attempt will be made here to list or segregate them.

The species of IMyeloborus (5) con-
struct their egg tunnels principally in
the pith of pine twigs. The larvae bore
into the wood, without making definite
larval mines, and so destroy the interior
of the twig as to cause its death. In gen-
eral their work is beneficial in that the
death and dropping of lateral branches
leaves the trunk of the tree freer from
knots. In some cases, however, they are
injurious to small trees.

Fir Twice BEETLES

Twigs of Douglas fir and the balsam
firs are frequently attacked by several
species and genera of twig bark beetles.
These usually are secondary enemies, at-
tacking dying or felled trees, but occa-
sionally they have been found attacking
small standing trees in crowded stands.
The most common species found in twigs
belong to the genera Pityophthorus,
Pityokteines, Carphoborus, Cryphalus,
Crypturgus, Pseudohylesinus, and Sco-
lytus.

Species of Pityophthorus and Pityok-
teines make a central nuptial chamber
from which several egg galleries radiate.
One of the most common species is

Pityophthorus pseudotsugae Sw. (fig.
Ficurp 13.—Typical galleries ofa 12). Another common species found at-

Plus Mann) “Natural size, «tacking balsam firs is Pityokteines ele-

gans Sw. The adults of both species
are about one-eighth of an inch long, and the females have long,
yellow hairs on the front of the head.

Twig beetles attacking spruce and hemlocks usually belong to the
genera Scolytus, Pityophthorus, Pseudohylesinus, Pityokteines, or
Ips.

CeparR Twia BEETLES

Small twig beetles belonging to the genus Phloeosinus are com-
monly found working in the twigs and limbs of cedarlike trees, but
they rarely are numerous enough to cause any appreciable damage.
In the limbs and twigs of incense cedar are found P. hoppingi Sw.,
P. antennatus Sw., P. fulgens Sw., and P. vandykei Sw. P. nitidus
Sw. works in Alaska cedar. P. swainei Bruck works in the twigs
af Sargent cypress in California.

|

INSECT ENEMIES OF WESTERN FORESTS 33

In addition to breeding under the bark of twigs and branches,
adults of the larger species of PAloeosinus have the feeding habit of
nipping off the leaflets and of feeding by boring into the small twigs
of various cedars and cypresses. ‘This injury is frequently very
severe 1n the case of ornamentals and shade trees.

Broad-leaved trees are attacked by various genera of bark beetles,
including many species of Micracinae. Oak twig beetles belong
to the genus Pseudopityophthorus (p. 182).

TWIG WEEVILS

Twig weevils, belonging to the family Curculionidae, are often the
cause of serious damage to the terminals of young coniferous trees.
The adult female weevil uses her long, curved beak to excavate a
small pocket in the bark of the terminal shoot in which to place
her eggs. The young larvae, on hatching, burrow beneath the bark
and excavate winding tunnnels between the bark and wood. On
reaching full growth each constructs an oval cell, partly in the wood
and partly in the bark, in which to pupate. Weevil work is dis-
tinguished from that of the twig moths in that there is lttle exu-
dation of resin or pitch, and such as does occur is not mixed with
webbing or larval castings to indicate the presence of the insects
under the bark. The first conspicuous evidence of injury is the
dying of the terminal shoot.

The two most important genera concerned are Pissodes and Mag-
dalis. In the Kast the white pine weevil (Pissodes strobi Peck) is
a well known example of the importance of these insects. In the
Western States there are several species which do similar damage;
though not of economic importance as yet, they are almost sure to
be so when second-growth stands and plantations are more widel
established. :

Proper silvicultural methods offer the best solution of the weevil
problem. Where young trees are grown in dense stands, or under
the shade of other trees, weevil injury may be negligible. If in
handling young stands subject to weevil injury the shade of older
trees can be provided until the young trees reach 25 feet in height,
or if the young trees can be grown in dense stands until they have
passed the susceptible period, the damage should be lessened. In
plantations, where individual care can be given, control can be ob-
tained by cutting off the infested stems in May and September and
storing these in wire cages of a mesh small enough to hold the beetles
but large enough to allow the parasites to escape. If this is done
for several seasons almost complete control of the weevils should
be obtained.

The Sitka spruce weevil (Pissodes sitchensis Hopk.) is the insect
most injurious to Sitka spruce reproduction in the Northwest. The
small weevils attack and kill or seriously injure the terminal shoots
of many young trees, causing a crook in the trunk or a forked and
worthless tree. Trees from 2 to 8 inches in diameter and 5 to 25
feet in height are the most susceptible to attack. The species is
distributed throughout the range of Sitka spruce.

The adults are light to dark brown, oval-shaped beetles, about
three-sixteenths of an inch in length, with a prominent curved beak.

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34 MISC. PUBLICATION 2738, U. 8S. DEPT. OF AGRICULTURE

Late in the spring and in the early part of the summer the adults
feed on the tender bark of the previous year’s terminals and with
their beaks make little cavities in which eggs are laid. The young
larvae, which are white, legless, curled grubs, work down the stem,
boring through the bark and into the wood. Upon reaching maturity

FicurRE 14.—The lodgepole terminal weevil (Pissodes terminalis): A, Grubs in
Me ce shoots; 6b, weeviled tip showing emergence hole; C, adults, natural
they form in the wood or pith an oval cell lined with shredded wood
fiber in which to pupate. There appears to be only one generation
a year, but some of the insects transform in the fall of the year and
others change and emerge the following spring. The winter is passed
in all stages except the egg. Upon emergence the new adults do
some feeding on the fresh bark of the terminal shoots and make
numerous small feeding punctures, which later heal over with a bit
of resin. No effort has yet been made to control this species.

Similar in habits and appearance to the above is the Engelmann
spruce weevil (Pissodes engelmanni Hopk.). It works in the termi-
nals of Engelmann spruce throughout this tree’s range, in the Rocky
Mountain region and the Pacific Northwest.

The lodgepole terminal weevil (Pissodes terminalis Hopp.) (71b)
mines through the pith of lodgepole pine terminals (fig. 14) and kills
them down to the first whorl of branches. It is particularly de-
structive in open-grown stands of young lodgepole pine in California.

INSECT ENEMIHS OF WESTERN FORESTS 25

Other species of Pissodes which work in the terminals of young
trees include the following:

Species Hosts and distribution
Pissodes yosemite Hopk—-_~-—_-_- Ponderosa pine, western white pine, and
sugar pine. California, Oregon, and Wash-
ington.
Pissodes schwarei Hopk——-—-__-_- Ponderosa pine. Rocky Mountain region.

Certain species of the genus Magdalis are also twig borers during
the larval period (fig. 15). The adults feed on the foliage and make
punctures in the twigs of conifers and broadleaved trees, in which
egos are deposited. The grubs burrow beneath the bark and cause
the death of small branches
and terminal twigs. The
larvae are white, legless,
ahd curled and are practi-
cally indistinguishable from
those of Pissodes, but the
work is usually distinct in
that the larval borings are
fine-grained and powdery
instead of shredded, and the
pupal cells are oval and
smooth, without the lining
of shredded wood fiber. The
adults are bright blue,
green, or black, with promi-
nent curved beaks. West-
ern species include the fol-

FIGURE 15,—Pine twig weevils (Magdalis lecontei),

natural size. lowing:
Species Hosts and distribution
Magdalis lecontei Horn (fig. 15)_ Pines. Pacific States.
Magdalis cuneiformis Horn--_~-~- Ponderosa pine. Western States.
Magdalis hispoides Lec_____--__. Lodgepole and other pines. Maine to British
Columbia, New Mexico, and California.
Magdalis gentilis Lee___________- Jeffrey pine. California.
Magdalis proxima Fall__________- Monterey and probably other pines. Cali-
fornia and Oregon.
Magdalis alutacea Lec__---__---- Spruce. Colorado and other Western States.
MAGCUAMS OAciiis WWees.= ths Fruit trees and broadleaved trees. Califor-
nia, Nevada, and New Mexico.
Magdalis aenescens Lec_____----- Alder and apple. Alaska to California and

eastward to Montana.
TWIG BORERS AND GIRDLERS

A few bark and wood boring insects (407) belonging to the families
Buprestidae and Cerambycidae are of some importance as twig
borers, or girdlers, in various forest, park, and shade trees.

Beetles of the family Buprestidae lay their eggs on the bark of
twigs, and the larvae, which are referred to as “flatheaded borers”
on account of their horseshoe-nail appearance, work under the bark
and into the wood, forming nearly flat tunnels filled with boring
dust. The larvae are slender and white, without legs, and the
enlarged forward segment of the body has horny plates on both the

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36 MISC. PUBLICATION 2738, U. S. DEPT. OF AGRICULTURE

top and lower side. Species which attack the twigs of coniferous
trees usually belong to the genera Anthaxia, Chrysophana, Chryso-
bothris, or Melanophila. ‘There are many small species of flatheaded
borers which mine under the bark and kill the twigs of broad-
leaved trees. Some of the most striking work of this character is
done by species of Agri/us, which make spiral girdles in the twigs

FIGURE 16.—Spiral twig girdling is characteristic of Agrilus.

of oak, birch, willow, and other broadleaved trees (fig. 16). Some
of the western flatheaded twig borers and girdlers include the
following:

Species Hosts and distribution
Anthagvia aeneogaster Cast______ Pines, firs, cypress, redwood, oak, willows,
and other forest and shade trees. West-
ern States.
Chrysophana placida Lec__----_- Pines, firs, cedars, and hemlock. All West-

ern States.
Chrysobothris mali Horn (15)-— Alder, ash, aspen, beech, maple, poplar,
willow, and many other’ hardwoods.
Throughout the Western States.
Chrysobothris femorata F. (15)__ Alder, ash, aspen, oak, poplar, willow, maple,
beech, and many other hardwoods.
Throughout the United States.

Agrilus angélicus Morne 222 Oak. California.

AGTIVULS: DOVITUS “Say. 2 ee ee Alder, willow, and other broadleaved trees
and shrubs.

AQrilus -anDiUs: GOry == 2s a: Birch, willow, and aspen. Eastern States
and west into Colorado and Idaho.

Agrilus bilineatus Web 22 222 Oak and chestnut. Eastern States and west

into Colorado.

The adult long-horned beetles of some species of the family
Cerambycidae girdle the limbs and twigs of various hardwoods and
thus prepare them for the feeding of the larvae. These roundheaded

INSECT ENEMIES OF WESTERN FORESTS 37

borers are very similar to flatheaded borers, except that the body is
usually thicker and has a horny plate only on the upper surface of
the first enlarged segment. The larvae feed under the bark and
through the deadwood of the killed twigs, forming broadly oval
tunnels which are filled with boring dust. The beetles that are most
frequently involved in this type of damage are the following:

Species Hosts and distribution
Oncideres trinodatus Casey______- Mesquite, huisache, huajilla, and Parkin-
sonia. Texas, New Mexico, and Arizona.
Oncideres quercus Skinner_______. Oak. Arizona.
Oncideres pustulatus Lee________- Mesquite. Texas, New Mexico, Arizona,

and California.
Other species of roundheaded borers which may be found in twigs
and branches of western forest trees include the following:

Species ' Hosts and distribution
Opsimus quadrilineatus Mann____. Spruce, fir, hemlock, and Douglas fir. West-
ern States.
Oeme sCOStata “Wee so Ponderosa and pinion pine. Colorado and
Arizona,
Oeme stranguiata Horns 2 L. Cypress and juniper. Arizona.
Callidium hirtellum ec. _______. Ponderosa pine. California and Oregon,
Callidium hardyi Van D____---__~—- Douglas fir, fir. Pacific coast.
Callidium californicum Casey——_—- Juniper and cedar. Oregon, California, and
Nevada.
Callidium pseudotsugae Fisher___. Douglas fir. California and Oregon.
Neoclytus muricatulus Kirby-—___- Spruce, larch, Douglas fir, and pines. West-
; ern States.
Pogonocherus oregonus Lec______- Fir. Western States.
Pogonocherus crinitus Lec______ _- Oak. California to British Columbia.
Oberea ferruginea Casey_________ Willow. Colorado.

TWIG MOTHS AND TIP MOTHS

The caterpillars of a large group of moths bore into and feed on
the fresh, tender bark, and cambium layers of growing terminal and
lateral shoots. Their feeding causes the deformation or death of
these parts and results in a many-branched, poorly shaped tree, and
in some instances results in the tree’s death. Such damage is par-
ticularly serious in young plantations or to cut-over lands where a
second crop of straight, vigorous trees which will produce sound
lumber in the shortest possible length of time is desired. Older trees
also are attacked by these moths, but the damage is much less con-
spicuous and of little significance.

Damage of this type is caused principally by the caterpillars of
moths belonging to the genera Deoryctria and Pinipestis of the
family Pyralidae and the genera Rhyacionia, Petrova, Eucosma,
and Laspeyresia of the family EKucosmidae.

The control of cambium-feeding twig and tip moths is a very dif-
ficult undertaking, and as yet no completely satisfactory methods
have been evolved. Spraying with a light miscible oil in May, at the
time the eggs are hatching, has given fair results, but the time of
application is such an important consideration that the method
should be used only with the advice of an expert. The use of other
sprays is still in the experimental stage. Hand picking of the in-
fested tips offers some hope of control on small valuable plantations
that are isolated from sources of reinfestation.

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38 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

PircH MotTHs

While in the caterpillar stage the pitch moths, belonging to the
genus Dioryctria, bore into the cambium of trunk, branches, and
twigs or into the fresh green cones of pines, Douglas fir, balsam fir,
and spruce. ‘The entrance to the tunnel is usually indicated by
webbed. larval castings. If the tree offers resistance to attack a co-
pious flow of pitch forms a resinous mass at the entrance. The
damage results in serious injury or death of the parts affected or
even death of the entire tree.

The ponderosa pitch moth (Dioryctria ponderosae Dyar) causes
considerable injury in the plantations of the Nebraska National For-
est, where it attacks ponderosa, Scotch, Austrian, jack, and Norway
or red pines. Most of the tr ees attacked are under 8 inches in diam-
eter, and the bole and tops are frequently girdled by the larval tun-
nels. This damage is particularly serious in the case of the two
European species, “Scotch and Austrian pines. This insect is prob-
ably distributed through most of the Western States, having been
recorded from Nebraska. Montana, and northern California.

The adults are blackish- -gray moths with a wing expanse of
nearly 114 inches. There are two narrow W-shaped bands extending
across each forewing; the hind wings are dusky white. The moths
appear from late in July to early in September and deposit eggs
singly on the under side of bark scales, on trunk, or branches. The
small larvae hatch in from 1 to 4 w eeks, depending upon the tem-
perature, and spin small hibernacula under bark scales, in which
they overwinter. The first evidence of attack appears the following
spring in the form of a small quantity of larval castings on the
bark surface, followed by an exudation of pitch from the entrance
hole. The larvae feed in the cambium region and construct irregu-
larly shaped galleries beneath the bark. Some of these are rounded
cavities with short side galleries, while others extend for several
inches around the tree. The mature larvae are about 1 inch in length,
usually hght brown, though occasionally with a greenish tinge, and
the bodies are marked with about six rows of small, dark-brown dots
or tubercles. These larvae spin white papery cocoons in the burrows,
or sometimes in the dried pitch mass near the surface, in which
pupation takes place in July. The new adults leave the pupal skins
in the cocoons and force their way through exit holes previously pre-
pared by the larvae but concealed by flakes of bark or small’ webs.
Control has been attempted by spraying the infested part of the stems
with orthodichlorobenzene, diluted 1 to 5 with water, to which a
small quantity of soap and linseed oil was added. The results were
only partially satisfactory. Winter cutting and removal of the
most heavily infested trees in the plantations resulted in a consider-
able reduction in the infestation. Control measures, however, are
still in the experimental stage.

Dioryctria xanthaenobares Dyar is a golden-brown moth about
three-fourths of an inch in length, which in the caterpillar stage at-
tacks the twigs and cones of ponderosa and knobcone pines and pos-
sibly other pines. The caterpillar is pinkish and about 1 inch in
length when full grown. It is known in California, Oregon, and
Washington.

INSECT ENEMIES OF WESTERN FORESTS 39

Dioryctria abietella D. and S. is a gray moth about three-fourths
of an inch in length. The reddish caterpillars feed in the twigs and
cones of knobcone, lodgepole, western white, sugar, and ponderosa
pines, and many of the balsam firs. There appear to be two annual
generations.

The Zimmerman pine moth (Pinipestis zimmermani Grote), a me-
dium-sized moth, light to reddish gray, closely related to the above,
is reported by Brunner (9) as being destructive to all coniferous trees,
especially ponderosa pine, throughout the Pacific Northwest. He
credits the “spike top” of mature trees and the spike top, stunting,
and destruction of smaller trees, to the work of this insect. However,
its importance has probably been greatly overemphasized, as its dam-
age is usually negligible in most localities.

PINE-Tie Morus

The pine-tip moths belonging to the genus Rhyacionia may cause
considerable damage to new leaders and shoots of young pine in lo-
calities where heavy infestation occurs, especially in plantations or
on cut-over lands where trees are openly spaced and growing on
sunny exposures. Trees from seedling size up to a height of about.
25 feet are the most susceptible to injury. The small moths are yel-
low, gray, or reddish brown. They lay their eggs on the pine needles,
and the young caterpillars start feeding at the tips of shoots, bur-
rowing into the buds and down into the new growth. Their work is
characterized by a resinous exudation at the point of attack, but they
do not form a pitch nodule on the stem. Though trees are seldom
killed, they are often deformed or forked, and height growth is re-
tarded. Several species have been described from the Western States,
where they normally work on the tips of young forest trees. Two
species are particularly destructive in the pine plantations of the
Nebraska National Forest.

Rhyacionia frustrana Busck (28, 38, 83) causes a limited amount
of damage to seedlings and saplings in its native range in the Black
Hills, the Lake States, and northwestern Nebraska but has done se-
rious damage where introduced in the isolated pine plantations of
the Nebraska National Forest. In the ponderosa pine plantations
of this forest about 90 percent of the leaders have been injured an-
nually for many years by this tip moth. The adult moths are small,
with a wing spread of about one-half inch. The front wings are
mottled with yellowish gray and reddish brown. The larvae are
yellowish and when full grown are nearly a half inch long. A single
generation occurs in the Black Hills, the moths flying late in May
and early in June to lay their eggs on the pine needles, and the larvae
feeding during June and July. In Nebraska two generations de-
velop annually, the moths flying in April and May and again late in
June and early in July. The winter is passed in the pupal stage in
cocoons spun by the larvae in the litter or soil.

Rhyacionia neomexicana Dyar has caused considerable injury to
ponderosa pine seedlings and saplings at various places in the South-
west and is becoming a serious pest at present in the Nebraska Na-
tional Forest plantations. It is known to occur in New Mexico,
Arizona, southern and eastern Colorado, the Black Hills, and Ne-

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braska. The moths measure about 1 inch in wing spread. The base
of the front wings is dark gray and the outer third reddish orange.
The larvae, when full grown, are nearly three-fourths of an inch long
and reddish. ‘There is but one generation annually. The moths fly
in April and May in most localities, but in the latter part of May
and early in June in the Black Hills. The full-grown larvae leave
the tips during July and spin cocoons, usually in the bark crevices on
the base of the tree below the litter. Here they transform to pupae
and pass the remainder of the season and the winter. Infested tips
can be identified, after the larvae leave, by the dead, partially de-
veloped needles toward the apex of the shoot, and by the fact that this
part of the shoot, and usually the buds, have been riddled by the
larval burrows and crumble readily when dry.

Rhyacionia pasadenana Kearf. is a silver-gray moth with reddish
markings and a wing spread of five-eighths of an inch. In the
caterpillar stage it bores through the buds and twigs of Monterey
pine, ponderosa pine, and probably other pines in California, causing
a pitchy exudation and the deformation or death of the terminal
growth. It has recently been found attacking ponderosa pine seed-
lings and saplings up to 6 feet in height, where these are growing in
open stands unshaded by mature trees, on cut-over lands in eastern
California.

Rhyacionia montana Busck does similar injury to the buds and
twigs of lodgepole pine in Idaho and Montana.

PitcH NopuLe Morus

The pitch nodule moths belonging to the genus Petrova (Fvetria),
while in the caterpillar stage, bore into both the new and old growth
of pine stems, twigs, and branches. Their work is characterized by a
nodule or round dirty lump of pitch and frass which is formed at the
point of attack. They do not attack the buds but usually work at
nodes or whorls of branches, and finally pupate within the pitch
nodule. ‘Trees are seldom, if ever, girdled by the larval channels but
often are so badly weakened that the tops are broken by wind or
snow. The moths are speckled with brown, yellow, or gray mark-
ings and have a wing expanse of about three-fourths of an inch.
The following species are found in the Western States:

Species of. Petrova Hosts and distribution

P. metallica Busck (fig. 17)--_._ Lodgepole and ponderosa pine. California
to Montana.

P.SQ0UTMONGANS Cari 2 Nee ee Digger pine. California.

P. monophylliana Kearf_________. Singleleaf pinon pine. California.

Bo tucitlentang. eins]. ==) —— si Ponderosa pine. Colorado.

Po burkeane Keats ess a ae Sitka and Engelmann spruce. Washington
and Montana.

iPS DiC Colang. Dyars ss 2 ae White fir and alpine fir. Washington.

P. albicapitana Busck=_2__-— == Lodgepole and ponderosa pine. Idaho and
Montana.

PINE PitcH Motruys

The caterpillars of the pine pitch moths, belonging to the genus
Eucosma (39), bore through the pith of terminal shoots and leaders
and cones of various coniferous trees. Owing to the drooping of the

INSECT ENEMIES OF WESTERN FORESTS 4]

dead lateral shoots the damage is often referred to as tip droop.
The terminal leaders of young, thrifty trees are seldom killed, but
the growth may be shortened. Lucosma sonomana Kearf. in the
larval stage bores through the pith of the terminal twigs of pon-
derosa pine and Engelmann spruce. “. bobana Kearf. is an och-
reous-colored moth with white spots on the forewings and a wing
expanse of about Linch. The larvae have been found boring through
the pith, cones, and seeds of ponderosa, Jeffrey, and knobcone pines
in California and Oregon. /. rescissoriana Hein. is a dark brick-
red moth with faint sprinklings of black scales. It has about seven-
eighths of an inch wing expanse. The larvae feed through the pith
and cones of lodgepole pine in California and Oregon.

SS

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FiGurE 17.—A pitch nodule moth (Petrova metallica): A, Pitch nodule opened to show
larval mine; B, larva, X 3; C, pitch nodule with chrysalid protruding; D, adult moth,
Xx 1.8; H, nodule opened to show larva of moth surrounded by three parasite pupae
and at right adult chalcid fly, parasite of the larvae of P. metallica, X 4. (Drawings
by Edmonston.)

BarRK MorTHs

Some of the species of the genus Laspeyresia are cambium miners,
working in the bark of various coniferous trees. Laspeyresia
inopiosa Hein. works in the bark of lodgepole pine in Idaho. ZL.
laricana Busck feeds in the cambium of larch and Douglas fir. Z.
leucobasis Busck works in the bark of larch and Engelmann spruce.

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L: populana Busck breeds in the bark of Populus trichocarpa in
Montana and Colorado.

The cypress twig moth Laspeyresia cupressana Kearf. (fig. 18) is a
small coppery-brown moth with a wing expanse of about five-eighths
of an inch. The caterpillars, which are reddish green, bore into
fresh green cones and into the bark of trunks and limbs of Mon-
terey cypress in California. Usually the attack is made at the forks
of branches or at points of injury. It causes an exudation of resin,
and a deformation or the death of the affected part. In this work
it probably plays a part secondary to that of a tree-killing bark
disease, Coryneum.

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cypress: A, Adult, x 2.25; B,-eggs, x 2; °C; larva, < -3:;"D; pupa; <-3.15.- (Draw:
ings by Edmonston. )

CeDAR Tip MotTHs

The cedar tip moths, a group of small moths belonging to the genus
Argyresthia, while in the caterpillar stage mine in the twigs and
leaflets of the various cedar and cypresslike trees, causing the foliage
to turn brown. The damage is not serious except to the appearance
of shade and ornamental trees. Most of the feeding is done early in
the spring. When the caterpillars reach full growth they emerge
from the twigs and spin white, feathery cocoons on the surface of
the leaflets; and in about 2 weeks the small moths emerge, fly, and
lay their eggs in the crevices between the leaf scales. An oil and
nicotine spray applied early in the spring is recommended for the

INSECT ENEMIES OF WESTERN FORESTS 43

prevention of damage to ornamentals. Several western species of
these moths have been described.

The cypress tip moth (Argyresthia cupressella Wlsm.) attacks
Monterey and other species of cypress in central California. Two
related species, A. ¢r7faciae Braun and A. franciscella Busck, are

3H) S ‘ CERN
(Abeta 2 Wess Fa
EAL

.

FiGuRE 19.—The cypress webber (/pinotia subviridis): A, Adult moth, X 3.25; B, eggs,
greatly enlarged; C, larvae, X 10; D, pupa, X 10; H, cocoons on twig, natural size,
and abdominal tip of pupa. (Drawings by Edmonston.)

often associated with the cedar tip moths and cause similar damage.
The incense cedar tip moths (Argyresthia libocedrella Busck and
A. arceuthobiella Busck) attack the twigs and leaflets of incense
cedar in Oregon.

The cypress webber (Z'pinotia subviridis Hein.) (fig. 19) in the
caterpillar stage burrows through cypress leaflets, leaving a webby
trail, and then ties bits of gnawed twigs and leaves together to form

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44 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

a small nest. Its work causes the foliage of cypress to turn brown
early in the spring. It is distributed through central and southern
California and often is found working with the cypress tip moth.

BUD MOTHS

Frequently the tips of branches on young and older trees appear
to be killed, but on close examination it is found that the twigs are
not injured and the damage is confined to the buds, developing
needles, or terminal leaves. These are webbed together to form a
case, within which a smooth, hairless, very active caterpillar is
found. Work of this character is done by a group of bud moths,
mostly belonging to the family Tortricidae, which are true leaf eaters
and therefore belong to the group of defoliators (p. 78). Usually
their damage is confined to the leaves at the tips of branches, but
during epidemics the older needles on the branches.are also fed upon,
and large forest areas may be completely defoliated and the trees
killed. This group of bud moths, while it includes hundreds of
species of only minor importance, also includes such conspicuous
forest-tree defoliators as the spruce budworm, hemlock budworm, and
lodge-pole pine needle tier.

SAP-SUCKING INSECTS

A large group of insects, such as bugs, aphids, and scales, belonging
to the orders Hemiptera and Homoptera, and the mites and red
spiders of the class Arachnida, which are closely related to insects,
are equipped with slender beaks which they insert into the tender
leaves or shoots of plants and feed by sucking the juices from these
succulent parts. ‘These various insects and mites are more important
in the orchard and garden, or to shade trees, than they are in the
forest. A few species, however, do noteworthy damage to small
forest trees, and a few are important enemies of larger trees. Since,
on the whole, they are more apt to be found seriously affecting young
trees than older trees, they are considered at this time. :

On shade and ornamental trees they can be controlled through
the use of such contact sprays as lime-sulphur, miscible oiis, or nico-
tine sulphate mixed with soap solution. Under forest conditions,
however, the use of such sprays seldom is practical, and so far no
control work of this kind has been undertaken in western forests.

KEY TO DIAGNOSIS OF SAP-SUCKING INSECT INJURY

A. Trees appearing sickly, leaves or stems not chewed but yellowing or
covered with small incrustations, scales, powdery or cottony tufts,
or small, soft-bodied insects. Trees frequently dripping with sticky
exudation or covered with black smut.
1. Trees dripping with sticky exudation, black smut usually
abundant. Colonies of small, soft-bodied bugs, usually
with two cornicles or protuberances on rear of abdomen,
appearing on leaves or tender stems____--__--~ aphids, page 45.
2. Leaves yellowing in spots, or bent. Small tufts of cottony
wax appearing on under sides of leaves
adelgids and scales, pages 47, 49.
38. Small, circular, oval, or elongated shells or scales on leaves
or twigs. Black smut not usually abundant_____ seales, page 49.
4, Leaves yellowing, covered with fine, nearly invisible webs or
SUVery COMtING io So eee spider mites, page 51.

|
|
|

INSECT ENEMIES OF WESTERN FORESTS 45

B. Trees appearing in fairly good health but leaves or stems badly
stunted, galled, or swollen; sometimes with queer protuber-
CFI CES ae a a al . ae gall makers, page 52.
1. Cone-shaped galls on terminal twigs of spruce
spruce gall bark lice, page 47.
2. Swollen twigs of white pine, covered with white incrusta-

HONSSe Eo ae ee BESS Sane Pres er woolly pine louse, page 48.
3. Galls at base of pine needles causing premature shed-
(ONG Sega Sass tee ee ee ace econ Pe a ee pine needle mite, page 52.

APHIDS OR PLANT LICE

Aphids are small, delicate, soft-bodied insects with pear-shaped or
globular bodies and long legs. They range from almost colorless
translucent to greenish or almost black. As a rule they are without
protective covering and often occur in dense colonies on leaves or
tender terminals of trees, where they feed by sucking the juices.

The aphids exude quantities of honeydew, which drips over the
leaves and onto the ground beneath. This is a favorite food of
ants, who cultivate and tend the aphids for it, and for this reason
the aphids are often referred to as “ant cows.” ‘The honeydew also
becomes a fertile medium for the growth of a black smut that covers
the leaves, causing the trees to appear as if they had been sprayed
with crude oil. Shade and ornamental trees are rendered particularly
unsightly, besides being weakened by the aphid feeding; and forest
trees are sometimes so weakened that after a season or two they
die from the injury.

Aphids are remarkable because of their peculiar manner of de-
velopment and the difference in the mode of reproduction of sepa-
rate generations of the same species. They reproduce both sexually
and also without mating, and both winged and wingless forms
occur. The number of generations of aphids may vary from one or
two to several in a single season, with more or less overlapping.

On shade and ornamental trees the aphids can be controlled by
spraying the insects, when they are first observed, with a mixture
of 4 or 5 pounds of fish-oil soap in 20 gallons of water, or with one-
half pint of nicotine sulphate in 50 gallons of water in which 2
pounds of soap has been dissolved. Crude-oil emulsion and com-
mercial lime-sulphur solutions are used as dormant sprays to kill
the eggs. They are applied in the spring, about the time the buds
begin to swell. |

The spruce aphid (Aphis abietina Walk.) is by far the most
destructive member of this group of sap-sucking insects that attack
forest trees in the West. In recent years it has killed millions of
feet of Sitka spruce along the tidelands of the Oregon and Wash-
ington coast (fig. 20) and the Columbia River, as well as having
caused considerable damage to this conifer on the better inland sites.
The wingless aphids occur early in the summer on the needles and
tender growth of Sitka spruce. These insects are dull green and
range in size from very minute young insects to full-grown winged
aphids about three-sixteenths of an inch in length. Apparently this
insect has an alternate host, disappearing from the Sitka spruce in
midsummer, only to reappear again the next spring. No practical
remedy has been suggested under forest conditions, but on shade
and ornamental trees the pest can be controlled by spraying with

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A6 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

such contact insecticides as nicotine solutions, miscible oil, or lime-
sulphur.

The Monterey pine aphid (£'ssigella californica Essig) is a small,
hight-green, pear-shaped insect about one-eighth of an inch in length
and with very long hind legs. It is reported as feeding on the
needles of Monterey pine, ponderosa pine, and Douglas fir in Cali-
fornia and Oregon.
Schizolachnus pini-
radiatae Davidson
is a dark-green
aphid, much small-
er than the last
named and covered
with a cottony wax.
This species attacks
the needles of Mon-
terey and other
pines in central
California. S. to-
mentosus DeG. is a
yellow to brownish-
black species which
lives on the needles
of ponderosa pine
in Colorado. There
are a large number
of species that in-
fest the leaves of
various broad-
leaved forest trees,
but these are of lit-
tle importance from
the forestry stand-
point.

4
pant eat:

ponte

besiege ont ny ae

sit

.
.

BARK APHIDS

F 20.—Sitl long the Wash kill ee ee
IGURE 20.—Sitka spruce along the Washington coast kille ae FS
by the green spruce aphid (Aphis abietina). : legged, br Own OF

dark-colored plant
hee with naked bodies or lightly covered with a powdery wax belong
to the genus Cinara (Dilachnus). They are frequently found feed-
ing on the terminal twigs of coniferous trees, where they insert their
beaks through the tender bark. The copious flow of honeydew
causes a dense smutting of the trees, sometimes making them appear
as if they had been sprayed with creosote. At times their work
causes considerable injury.

The following species are recorded from the Western States:

Species of Cinara Hosts and distribution
C. ponderosa) WMS. 20 eee Ponderosa pine and Jeffrey pine. California,
Nevada, and Colorado.
C2SQ0INAG USES Wes = ee eee Digger pine. California.
C2 drizonica, WNW ison- 222 =e Pine. Arizona.
Ci earliseWwalson]-= 222-42 ee Pifion pine. Colorado.

INSECT ENEMIES OF WESTERN FORESTS AT
Species of Cinara Hosts and distribution
GCARSChivarei wWillsSOne=} sa att Ponderosa and other pines. Arizona and
Colorado.
C. pseudotsugae Wilson__________ Douglas fir. Oregon.
ORLOV OG SWee sae Douglas fir. California.
(Oi ATA OC a ULI as TR Blue spruce. Colorado.
Ccaudell4 Wilson___-__-.-_____-— Spruce. British Columbia.
Ceanmenrenae- Galli tate 2 2s eee Engelmann and other spruce. Colorado.
WreniGed Panzer 22. 22) =. ts Spruce. California.
Candie Wilson 22 22 Spruce. Washington.
CR ERT UST OWesee a a ns White fir. Northern California.
C. pacifica Wilson Pa) hc eek _.._ Lowland white fir. Northern California.
0. occidentalis Davidson_.________ White fir. Oregon and California.
CeO Grell WVASON = 3 ee Juniper. Colorado and Idaho,
Garujapelunus DelG@= 2-22 8 es Aborvitae, cypress, and cedars. California.

SPRUCE GALL BARK LICE

Cone-shaped galls which form on the twigs of spruce trees are
caused by several species of gall and bark lice belonging to the genera
Adelges and Pineus (1) (formerly called Chermes). These galls fre-
quently kill the terminals but rarely endanger the life of the trees and
are of little importance under forest conditions. On seedlings and
saplings in nursery or plantation, and on ornamental trees in gardens
and parks, the formation of these galls is of more consequence, since
they kill the tips of branches and tend to stunt and deform the trees.

Most of these insects have an alternate host tree upon which they
appear in a different form. On pines and Douglas fir these alternate
forms appear as a dirty white wax on the bark or as small tufts of
cottony wax on the needles. Often these bark lice exude a honey-
dew upon which a black smut grows, and accumulations of this make
trees very unsightly.

In nursery and plantation the gall lice can be controlled by cutting
and burning the green galls before the insects have emerged in the
spring, or by spraying the trees early in the spring, when the young
begin to colonize or. the new growth. For this purpose use a miscible-
oil spray composed of 5 gallons of miscible oil, 1 quart of 40-percent
nicotine sulphate, and 200 gallons of water.

Cooley’s gall louse (Adelges cooleyt Gill.) 1s the species most fre-
quently responsible for the formation of cone-shaped galls on ter-
minal twigs of blue spruce, Engelmann spruce (fig. 21), and Sitka
spruce in the West. Two or more other species do similar damage.
The galls are from 1 to 2 inches in length, ight green to dark purple,
and are formed by the growing together of the basal portion of the
needles so as to form chambers between the base of the needles and
the stem. These chambers, which are not communicating, usually
contain from 3 to 30 small wingless insects covered with a white
waxy coating. These galls turn brown, dry, and hard on the trees
after the insects have escaped, and they may persist for many years.

The alternate host is Douglas fir, on which these gall lice appear
as small cottony tufts on the underside of the needles. Their feeding
punctures cause the needles to turn yellow in spots. Sometimes the
damage is so severe as to cause a browning and premature shedding
of the foliage.

The seasonal history is very complicated. The form found on the
Douglas fir needles during the winter represents hibernating females

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AS MISC. PUBLICATION 213, U. S. DEPT. OF AGRICULTURE

or stem mothers. These lay eggs early in the spring, and the young,
which settle on the tender fir foliage and feed, later mature into
winged and wingless females. The wingless forms deposit eggs which
hatch later into ‘females that will hibernate, while the winged females
migrate to the spruce and lay eggs at the base of the needles. The
young hatching from these cause the formation of the cone-shaped
galls. About the middle of J uly the forms in the galls become ma-
ture, full- grown, winged migrants which return to the Douglas fir
to lay eggs that also
produce hibernating
females. Altogether
there are five stages
or forms in which
these Adelges appear
during different pe-
riods of their devel-
opment.

The species is dis-
tributed from Brit-
ish Columbia to Cali-
fornia and eastward
into Idaho, Montana,
Wyoming, ‘and Colo-
rado.

Adelges oregonen-
sis Annand appears
as a small woolly
louse on the twigs
and base of needles
of larch in Oregon,
Washington, and
Montana, but does
little damage.

Adelges piceae
Ratz. attacks the ter-
minal twigs of low-
FIGURE 21. = Gals formed Ene Im oe by Cool and plese ir and

21.—Galls formed on Engelmann spruce by Cooley" noble fir and causes a
swelling to form
around the bud, leaving it in a depression and making the twigs
appear to end 1 in asolid knob. This causes the trees to become Vale
gnarled.

Adelges tsugae Annand may be found on the needles and bark of
western hemlock in California, Oregon, and British Columbia and
appears as white cottony tufts.

The woolly pine louse (Pineus pinifoliae Fitch) (Chermes pini-
corticis Fitch (Chermes montanus Gill.) is found in the Northwest
from British Columbia to California and in {[daho, Montana, and
Colorado, where it attacks blue spruce, Engelmann spruce, Sitka
spruce, and western white pine. On spruce it forms loose terminal
cone-shaped galls somewhat similar to those of Adelges cooleyi, ex-
cept that the poorly formed chambers are intercommunicating and

INSECT ENEMIES OF WESTERN FORESTS 49

contain only one or two young in each chamber, and when the in-
sects emerge the galls flare open, and the scales drop from the twigs.

The alternate form attacks western white pine and is easily recog-
nized by the waxy secretion that appears as a whitish-gray mold on
the bark and needles. The attacked foliage is apt to be sparse and
stunted; the needles fall prematurely, and the fascicles or bundle
sheaths are left protruding from the limbs as short spurs. The dam-
age is most frequently found on young white pines. In the last few
years it has become a rather important enemy of white pine seedlings
in eastern Washington, Idaho, and western Montana. The adults
appear as little hemispherical, brown scales one-sixteenth of an inch
in diameter, with a fringe of white hairs. The head and thorax are
completely covered by this shield. The life history has not been
thoroughly worked out, but 1s supposed to be as follows: Eggs are
laid for the new generation early in the summer. These soon hatch
and the young bark lice start sucking the juice from the white pine
twigs. Part of these insects develop wings and fly to the spruce,
where they construct the terminal cone-shaped galls. The others
grow and reach the adult stage by the following spring.

Pineus boycet Annand makes similar galls on Engelmann spruce in
Oregon and Montana. The needles with enlarged bases are pressed
closely against the twigs and form intercommunicating chambers in
which about 15 nymphs are found. The alternate host is not known.

Pineus bornert Annand feeds on the needles and twigs of Monterey
pine in California.

Pineus coloradensis Gill. causes dense mats of dirty wax, covered
with mold, to form on the twigs of various pines, including ponderosa
pine, lodgepole pine, pion, white pine, sugar pine, and single leaf
pinon. It is found in Washington, Oregon, California, and Colorado.

Pineus similis Gill. is found forming cone-shaped galls on blue
spruce and Engelmann spruce in Colorado, Oregon, and British
Columbia. The galls are shorter and thicker than those of Adelges
cooleyi, and the chambers are intercommunicating. An alternate host
is not known.

SCALE INSECTS

(Coccidae)

Scale insects form one of the most abundant and variable groups
of sap-sucking plant enemies. The young are mobile, small, and
inconspicuous, but unlike most other insects, after they have become
attached to a plant they lose all power of locomotion. They develop
a hard epidermis, a thick waxy covering, or a round or oblong shell,
and remain fixed in one position until they die. It is the female that
causes all of the injury to plants. The adult males often have wings,
eyes, antennae, and legs, but no mouth parts and so cannot take food.
They live only for a short time and are rarely seen. A large number
of species of scale insects infest nearly all forms of plant life, but
only a few of those that feed on forest trees are of major importance.

Scale infestations on conifers, particularly those of the pine leaf
and California pine scales, are often associated with conditions where
dust and smoke occurs regularly in the atmosphere. Heavy scale
attacks on ponderosa pine trees bordering dusty roads have been
frequently observed as well as on trees exposed to air currents which

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50 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

carry the smoke from mills. The choking of stomata in the leaves
by foreign particles probably renders them susceptible to these insects.

Scale insects are controlled through the use of contact sprays (35),
such as miscible oils, distillate or petroleum emulsions, and in orchard
work by fumigation. None of these methods are practical under
forest conditions, but fortunately none of the scale insects attacking
forest trees have become serious enough to call for control.

The pine needle scale (Chionaspis pinifoliae Fitch) (fig. 22) is prob-
ably the scale most commonly found on the foliage of western conifers.
It occurs throughout
the Western States,
where it attacks all
species of pine and
sometimes Douglas
fir, spruce, and cedar.
Small trees, saplings,
and poles, especially
along dusty roads,
are often so heavily
infested that the foli-
age appears white.
In some cases trees
have been killed by
the attack. The ma-
ture scales are small,
nearly pure white,
elongated, and about
one-eighth inch in
length. Eggs are
laid in the fall and
overwinter under
the female scale.
These hatch late in
the spring, and the
new scales became
full grown by mid-
summer, An oil and
nicotine spray will
control this species
: : if apphed late in the
FIGURE 22.—The pine needle scale (Chionaspis pinifoliae). spring when the eggs

are hatching.

The California pine scale (Aspidiotus pini Comst.) 1s often asso-
ciated with the pine leaf scale in its attack on various pines, and it
is also found in abundance on Douglas fir and hemlock and may
attack other conifers. Many young pines in California have been
killed by this scale. It is distributed over most of North America.
The mature scales are almost circular, about one-sixteenth of an
inch in diameter, and yellowish brown to black. The young hatch
early in the spring and summer and settle upon the new needles of
the host. From one to three generations are produced during the
year, and the winter is passed in a half-grown condition.

INSECT ENEMIES OF WESTERN FORESTS 51

Other common scales infesting western coniferous trees include the
following:
Species Hosts
Matsucoccus fasciculensis Herbert__ Ponderosa and digger pines.
Toumeyella pinicola Ferris (fig. 23)_- Monterey pine and other pines in California.

Physokermes insignicola Craw __-_- Monterey pine.

Physokermes concolor Cole________ White fir.

Physokermes coloradensis Chiltaes: slue spruce in Colorado.

Aspidiotus ehrhorni Cole_2----____- Douglas fir and cypress in California.
Ehrhornia cupressi Ehrh. (41)--__ Monterey cypress.

Xylococcus macrocarpac Cole-—_—_—_. Monterey cypress.

AGHLOLa shastae Coles -—- Bigtree in California.

Some of the mealy-
bugs also attack for-
est trees. ‘These are
small, soft-bodied
bugs covered with a
white powdery wax.
They are represented
by Pseudococcus ry-
ani Coq. on cypress,
incense cedar, and
redwood, and P. se-
gquoiae Cole on red-
wood.

The foregoing is
only avery brief and
incomplete treatment
of the scales and re-
lated insects which
may be found attack-
ing forest trees, since
the species attacking
various broadleaved
trees (42) are too
numerous to mention
here.

SPIDER MITES

Another group of
small animals of sap-
sucking habits is TOR na
(Mie oteeseben ge ole 9 2 71G paiawonterey ‘pine twice” Natural sie) 0
mites. Strictly
speaking, these are not insects, since they have bodies divided into
two segments instead of three and have four pairs of legs instead of
three. However, since they are so closely related to insects, and their
work is so similar, they are considered in this discussion. The dam-
age resulting from their natural habit of sucking the juices from
leaves and tender stems of various plants, including many orna-
mental, shade, and forest trees, is considerable. The leaves turn
yellow and drop, and the trees attacked are often seriously weakened,
rendering them susceptible to attack by tree-killing insects. This

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52 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

type of damage, while important on shade trees, is seldom so on forest
trees under natural conditions.

The pine needle mite (L’riophyes pini Nalepa) is a very minute
yellow blister or gall mite which has been found causing considerable
injury to the needles of Monterey pine in Golden Gate Park, San
Francisco, and to Torrey pine and Jeffrey pine in other parts of
California. It feeds within the basal sheath of the needle cluster and
causes a premature shedding of the needles and a weakening of the
tree. A 10-percent miscible-oil spray has given fairly satisfactory
control, but the removal of badly infested pine may at times be
necessary.

Red spiders (Z'etranychus spp.) are frequently the worst enemies
of shade trees in the central valleys of California, especially during
long, dry, hot seasons, when they attack the leaves and cause them
to fade and die. One species in particular is found on incense cedar
and another on Monterey pine. Many species are found on the broad-
leaved trees. Both sulphur dusts and the combination oil and nico-
tine sprays have given good control on shade trees. More than one
application during a year is frequently needed.

Oligonychus americanus Riley has appeared as a rather common
pest of Douglas fir along the Madison River of Yellowstone National
Park. It webs the needles and turns them a dirty brown.

GALL MAKERS

A very large group of insects and mites have the unique ability to
irritate various plants so as to produce a gall, swelling, or peculiar
malformation. The common oak apple is a familiar example. Some
galls take the form of large, globular protuberances, others take
the appearance of buds or flowers, while some are simply an enlarge-
ment of the leaf or stem. These galls seldom are seriously harmful,
however, and control measures are called for only where ornamental
trees are made unsightly by such growths. On forest trees their
presence can usually be ignored.

Galls may be formed by several groups of insects. The cynipids,
sawflies, gall midges, and gall aphids include most of the gall-form-
ing insect species. Gall mites of the family Eriophyidae are also
responsible for a large number of peculiarly shaped galls on broad-
leaved and other trees. Other important plant galls are formed by
fungi and various parasitic plants.

On ornamental trees some of the gall-forming insects can be con-
trolled by spraying at the proper season of the year, but for forest
trees such treatment is impractical and seldom would: be justified
by the importance of gall damage.

There are innumerable types of galls on the various species of
western forest trees (32), particularly on the broadleaved trees, such
as poplar and willow. Space in this publication would not permit
even the listing of the various species. However, a few of the more
important gall insects on commercially important forest trees will be
mentioned,

INSECT ENEMIES OF WESTERN FORESTS 53

KEY TO THE RECOGNITION OF SOME IMPORTANT INSECT GALLS

A. Galls formed on coniferous trees.
1. Galls affecting pine needles.
a. Needles greatly enlarged or swollen at the base
gall midges, page 538.
b. Needles blistered within the sheaths, causing pre-
MAcuUreySHedCINne= =a se pine needle mite, page 52.
2. Twigs with dying and dead needle tufts; bark filled with res-
inous pockets containing small red maggots
pitch midges, page 54
3. Swollen twigs of western white pine covered with gray, cot-
OM Vs SCCTEGlONE He ey. Na ee woolly pine louse, page 48.
4. Cone-shaped galls on terminal twigs of spruce
spruce gall bark lice, page 47.
5. Prickly, burrlike or conical galls on juniper___ gall midges, page 53.
B. Galls formed on broadleaved trees.
1. Galls inhabited by small, white, legless, apparently headless
i 2s Vise Care eer hein an ee EL TAS Tap CS ile cynipid wasps, page 53.
2. Galls inhabited by small pink or red maggots__ gall midges, page 53.
3. Galls inhabited by small bugs with cottony wax secretions
gall aphids, page 47.
4. Galls inhabited by microscopic eight-legged mites
gall mites, page 52.

GALLFLIES OR CYNIPID WASPS

(Cynipidae)

One group of small, four-winged, usually somber-colored yellow to
brown or black, antlike wasps are responsible for the formation of a
great variety of galls on the different parts of various forest trees,
but particuarly on the oaks. These galls may be large, round, and
shiny, like the common oak apples, or very irregular in shape and
spiny, or may consist of just a tiny swelling on. leaf, twig, or root.
The larvae that inhabit these galls are white, legless, and without
a distinct head. There are over 200 species described from various
plants in the Western States. Only a few, however, do any appre-
ciable damage.
GALL MIDGES

The gall midges belonging to the family Cecidomylidae are re-
sponsible for the formation of a great variety of small galls on many
different forest trees and plants. The adults are tiny pink flies re-
sembling mosquitoes and are called midges. The larvae are small
pink or red maggots, without legs or definite head, but with a dark
“breastbone.” Almost any part of the tree may be affected, but most
galls are formed on the needles or leaves, in the cones or seeds, or in
the bark of twigs. A few species on forest trees are of some economic
importance.

The Monterey pine midge (Vhecodiplosis pini-radiatae S. and M.)
works at the base of the newly formed needles of Monterey pine in
central California and causes them to become swollen and shortened
(fig. 24). Sometimes heavily infested twigs are killed and the orna-

mental value of the trees seriously impaired. Other species that

produce swellings at the base of needles on pines include /anetiella
coloradensis Felt on pines in Colorado and Utah, and 7'hecodiplosis
cockerellt Felt on Pinus edulis in Colorado.

a eee

54 MISC. PUBLICATION 2738, U. S. DEPT. OF AGRICULTURE

Apical, budlike swellings are formed on ponderosa pines in Colo-
rado by Contarinia coloradensis Felt and Dicrodiplosis gillettei Felt.

Several of the juniper galls are caused by species of gall midges.
Walshomyia juniperina Felt causes a slightly enlarged fruit of
Juniperus californica, also a purplish, apical bud gall with three or
four diverging lobes. Oligotrophus betheli Felt forms reddish, api-
cal, conical galls on Juniperus utahensis. Allomyia juniperi Felt
produces a prickly, burrlike bud gall with numerous short, nearly
straight, leaves and none reflexed. Rhopalomyia sabinae Felt attacks
Juniper in Colorado
and Utah and pro-
duces thick-walled,
purplish, apical bud
galls which split
open in four sections
when the midges
emerge.

PINE PitcH MIDGES

Some of the pitch
or gall midges attack
the tender twigs or
terminals of young
trees and, by form-
ing pitch pockets un-
der the bark, either
cause their death or
the deformation of
the wood. Their
work can be recog-
nized by the small
pink or red larvae
found imbedded in
pitehy pockets or
galls under the bark.
The adults are frail,
two-winged flies or
midges resembling
mosquitoes. Many
FIGURE 24.—Monterey pine needles galled by the Monterey of the western forms

Pee ees. (Thecodiplosis pini-radiatae). Insert, adult have not been named

as yet.

The birdseye pine midge (Retinodiplosis sp. near inopis O. 8.) is a
common species in southern Oregon, where for many years it has
killed the lateral tips of many young ponderosa pines (fig. 25). In
some years this damage has been so severe as to deform and in some
cases actually kill the trees. The damage is first noticeable very
early in the summer, when the new lateral shoots fade, droop, and
gradually turn yellow and die. In some cases nearly every new shoot
is affected. On examination of the dying tips the bark will be found
to be pitted with small resinous pockets, in each of which are small

INSECT ENEMIES OF WESTERN FORESTS 55

bright-red maggots. If the pockets are not numerous enough to kill
the terminal the injury heals over, but for several years the annual
rings are distorted into a peculiar w "horl until the pocket is completely

FIGURE 25.—Work of the birdseye pine midge (Retinodiplosis sp.) : A, Twig tips killed by
midge attack; B, pitch gall in cambium; CO, birdseye effect in pine lumber.

covered. This produces a defect in the grain of ponderosa pine

lumber known as “birdseye pine” which actually enhances its value
for finishing purposes,

56 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

The Monterey pine resin midge (etinodiplosis resinicoloides
Wms.) is another small pitch midge which inhabits the resin exuda-
tions of Monterey pine but apparently is not injurious to the trees.

FEEDERS ON THE INNER BARK OF YOUNG TREES

The most frequent damage to young trees by insects that feed on
the inner bark is that suffered by intermediate or suppressed trees
growing under crowded conditions or those weakened by drought,
fire, or mechanical or other i injury. Vigorous, young, dominant trees
in the stand have a good chance to escape damage from these insects,
except under conditions where they become epidemic. Usually the
normal damage of this character in the virgin forests is of more
benefit than otherwise, since it represents a natural thinning process
and the release of the more dominant trees from competition. At
times, however, such damage may become serious when outbreaks of
bark beetles or other cambium- or root-feeding insects sweep through
the young stands and kill a high percentage of thrifty as well as
weakened individuals.

The insects which feed on the inner bark of trunk or roots of
young trees are usually those which also feed on thin bark of older
trees. These include certain groups of bark beetles, bark borers, and
bark weevils. Since most of these insects do their greatest damage
to older, mature trees they will be discussed later under another
heading ‘(p. 95)

Many species of bark beetles (Scolytidae) inflict their greatest
damage on small or thin-barked trees. Many of these are rarely, if
ever, primary and aggressive in their attacks upon large trees, but
may breed in windfalls, slash, or large trees that are dying or have
been attacked first by other bark beetles. Breeding in such trees or
felled material, they may emerge in large numbers and become very
destructive to the small trees in the stand.

In pines, the pine engraver beetles of the genus /ps are the ones
most frequently responsible for this type of damage. Less frequently
species of Pityogenes or Pityophthorus are involved.

In young stands of Douglas fir Pseudohylesinus nebulosus Lec.
and Scolytus unispinosus Lec. frequently kill groups of small trees,
particularly in the vicinity of slashings.

Small balsam firs are similarly affected by species of Scolytus,
Pseudohylesinus, and Pityokteines. Young spruce and hemlock also
may be killed by species of these and other genera.

Young redwoods, cedars, cypresses, junipers, and related cupressine
trees are frequently killed by species of Phloeosinus, which breed
in the trunks and limbs of dying or dead larger trees.

DEFOLIATORS OF YOUNG TREES

The insects that feed upon the leaves of young trees are in nearly
every instance the same species as those that feed on the leaves of
older trees. Defoliating insects usually show no particular choice as
to the age or size of tree that they attack, and young trees in the
forest may be fed upon by almost any leaf-feeding form. In some
cases the young trees in the stand are actually avoided by defoliating
insects. ‘This was particularly noticeable in the case of the hemlock

INSECT ENEMIES OF WESTERN FORESTS 57

looper outbreaks, where heavy defoliations ceased when stands of
young growth were reached.

Since the damage done by defoliators to mature forest trees is
usually of oreater importance than that done to young trees, this
group of insects will be discussed in the following section (p. 58).

INSECTS INJURIOUS TO MATURE FOREST TREES

The insects that prey upon young forest trees and that may, during

the formative years, cause serious Injury through stunting, deform.

ing, or halting growth are of little importance “after the trees have

FIGURE 26.—Ponderosa pines severely defoliated by the pine butterfly.

reached maturity. The mature trees may still be fed upon by root-
feeding or terminal-feeding insects, but such damage within reason-
able limits can be borne without fatal consequences, and the small
loss in. growth increment on mature trees is of minor importance.
In general, there are only two large groups of insects that may bring
about the death of mature trees, (1) those that feed on the leaves and
cause severe defoliation and ( 2) those that bore into the inner bark of
the main trunk and cut off the supply of moisture and food.

In many ways the defoliators are the most dangerous. They are
primary and aggressive in their activities and attack healthy, vigor-
ous trees as quickly as undernourished, weakened ones (fig. 26). The
injury they cause does not always result in the immediate death of
the tree but often so greatly weakens it that it becomes readily sus-
ceptible to bark-beetle attack. On the other hand the miners of the

58 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

inner bark usually direct their attack against trees previously
weakened through drought, defoliation, fire, or some other cause.
Most of the bark beetles are decidedly secondary and only attack
trees already in a weakened or dying condition. A few species, how-
ever, are ageressive and primary in their attacks.

It is true that the destruction of older, mature trees in the forest
through attack by insects is more or less of a natural process. It is
nature’s way of disposing of the old decadent trees to make room for
the younger, thriftier, growing individuals. Although a natural one,
this 1s a most wasteful process from the economic standpoint, since
the old trees carry a large volume of high-grade lumber. The pre-
vention of this type of damage, therefore, is an important phase of
forest protection.

When more of our forests come under intensive management, and
mature trees are utilized before they become decadent, much of the
present loss in virgin. forests will be avoided. Until such a time, the
only alternative is the application of the direct-control methods dis-
cussed at the end of this section.

KEY TO RECOGNITION OF INSECT INJURY TO MATURE TREES

A. Foliage fed upon; partially or wholly stripped from trees; or turning
yellow or red. Trees sickly or dying. No insects working on

main <trunk: ‘branches: OF TOOUS= ses ane es ae defoliators, page 58.
B. Terminal shoots, laterals, or tips deformed or killed. Remainder of
treecappearing healthy = 25a" 2s ae Oreo Dees ee ee twig feeders, page 29.

C. Entire tree, or a large part, sickly, dying, or dead; foliage fading,
turning yellow or red. Bark and phloem of main trunk or roots
mined-by:insects and *killeg==]28 2 we eae bark miners, page 95.

LEAF FEEDERS AND DEFOLIATORS

No part of a forest tree offers nourishment to such a host of insects
- as do the leaves. There are literally thousands of insect species that
feed on them in one way or another. Some mine within the needles,
some skeletonize the leaves, and others eat the entire leaf tissues or
suck the juices. Trees can withstand a great deal of such feeding
without being seriously affected, and some such insect work is going
on more or less constantly. If the feeding is heavy, the growth of the
tree is retarded. If a high percentage of the leaf surface is de-
stroyed, death of the tree may result. The damage done to the forest
by defoliators is difficult to estimate since a large part of it involves
only a loss of increment and not the death of trees. On the other
hand, when epidemics of defoliators occur, their ability to destroy
timber, especially coniferous timber, over large areas in a short time
places them at the top of the list of destructive forest insects.
Defoliation. affects very vital functions in a tree’s life processes.
Without leaves a tree is unable to regulate its moisture content, to
acquire its carbon supply from the air, or to throw off its waste gases.
When these important functions of transpiration, assimilation, and
respiration are greatly retarded the tree dies. Death does not take
place at once but only after a lapse of time in which certain peculiar
changes take place. Craighead (25) has shown that spruce bud-
worm defoliation of fir and spruce not only results in a general
reduction of growth but that this reduction is not evenly distributed
(82). Growth is greatly retarded at the top of these trees, as shown

INSECT ENEMIES OF WESTERN FORESTS 59

by the annual rings, while for the year of defoliation the ring at the
base of the tree is enlarged over that of the previous year. Unable
to throw off the excessive moisture brought up by the roots, the water
and sap accumulate under the bark and ferment. Often this sets up
an attractive influence that draws the bark beetles into the area, and
trees are then killed which otherwise might have recovered.

The extent to which a tree may be injured by defohation will de-
pend upon the tree species, whether evergreen or deciduous, the posi-
tion of the tree within the stand, its general health, the insect species
involved, and the time of year when the defoliation occurs. Since
evergreens cannot replace their leaves as readily as deciduous trees,
they are much more seriously injured by defoliation than those that
normally shed their leaves each year. One year of severe defoliation
may be enough to kill such trees as Douglas fir, hemlock, and pon-
derosa pine. Alders and oaks, on the other hand, can sometimes
withstand several seasons of defoliation without fatal injury. Domi-
nant trees are more resistant than their suppressed neighbors, and
vigorous trees have a better chance of resisting attacks than those
weakened from one cause or another. Defoliators usually show little
preference for weakened trees as do many of the bark beetles and are
more apt to feed indiscriminately on whatever folage of their
favorite hosts happens to be at hand,

Outbreaks of defoliators are characteristically sporadic. For
many years the forester may not observe a single specimen of some
important leaf-feeding insect, and then without warning a sudden
outbreak may occur and. the forest is sWarming with millions of
caterpillars or slugs that devour everything in their path. Such
outbreaks usually go through a 3- to 5-year cycle. First, there is a
preepidemic stage in which the insect becomes unusually numerous,

Then there is the epidemic stage, which usually lasts for 3 years,
the first year showing evident damage, the second year a peak of
damage, and the third year one of declining numbers but still with
evident injury. Third, there is the post-epidemic period in which
the insect returns to a normal or quiescent status. This decline in
the epidemic is brought about by natural control factors such as an
increase in parasitic enemies and disease or through some climatic
condition which is unfavorable to a continued activity of the de-
foliators.

The aim in‘control is not to eradicate the insects but to protect
the forest from heavy and concentrated feeding during the height of
occasional epidemics. Although more expensive methods can always
be used on individual trees of high value, such as ornamental, park,
and shade trees, spraying and airplane dusting are the only methods
now used to protect large timber stands during outbreaks of defoliat-
ing insects. These methods are discussed under the heading “Con-
trol of defoliating insects” (p. 175).

The leaf-eating insects include all of those leaf-feeding forms that
have biting mouth parts and actually bite into and swallow their leafy
food. ‘They may be divided into three groups: (1) the leaf chewers,
that feed externally upon and devour any part of the leaf, (2) the
leaf skeletonizers, that eat out the green chlorophyll and leave only
the network of veins and midribs, and (3) the leaf miners, that bur-
row through and feed between the surfaces of the leaves or needles.

—— =

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60 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

Some leaf-feeding insects are skeletonizers in their early stages and
then devour all of the leaf as they become more mature. Some
mine the interior of the leaf when very young and then, later on,
eat all of it.

Outbreaks of leaf chewers do not always result in the death of the
defolated trees. For instance, large forest areas in Washington,
Canada, and Alaska have been badly defoliated by the hemlock bud-
worm for 2 or more years in succession and yet most of the trees
have recovered. On the other hand, outbreaks of the hemlock looper,
the pine butterfly, and the Douglas fir tussock moth have resulted
in the death of billions of feet of standing timber, with a high per-
centage of the stand killed over hundreds of thousands of acres.

While the work of leaf feeders is easily detected, considerable
injury frequently occurs before their activities are noticed. Since
voung caterpillars are more easily killed by poison than older ones,
early detection and control are important.

As these leat chewers actually swallow and digest their leafy food,
the method of artificial control is to spray or dust the foliage with
a stomach poison, such as an insecticide containing arsenic. Where
small trees that can be reached with dusting or spraying machinery
are involved, the application of such a poison is a simple operation.
Treating large forest areas is quite a different matter, and this usually
can be done only by means of airplanes. Application of insecticides
by this method is discussed in the section on forest insect control.

Insects comprising the group of leaf eaters are mostly either cater-
pillars (Lepidoptera) or sawflies (Hymenoptera), but a few beetles
do similar work. No attempt will be made to list all the insects
which under certain conditions may prove destructive, and in the
following pages are mentioned only those that have proved particu-
larly injurious and with which the forester should, if possible, become
familar.

KEY TO DIAGNOSIS OF INJURY FROM IMPORTANT DEFOLIATING INSECTS

A. Foliage appearing thin or sparse. Leaves chewed, mined, skeletonized,
or stripped from the trees.
1. Leaves chewed, and defoliated part of tree covered with silken
web. Work of caterpillars with three pairs of true legs
and less than six pairs of prolegs.
a. Leaves and buds at tips of branches webbed together
and fed upon by nearly hairless caterpillars, that
wriggle violently backwards or fall to the ground
when disturbed_____~_ bud moths or budworms, page 78.
b. Large, dense, conspicuous, silken tents formed at end
of branches or in crotches; made by very hairy
caterpillars with blue, red, or yellow markings.
tent caterpillars, page 72.
c. Loosely woven tents formed at ends of branches of
broadleaved trees; made by yellowish-brown or
gray caterpillars clothed with long white hairs,
arising from black and orange tubercles.
fall webworm, page 68.
d. Defoliated portion or entire tree covered with a very
light fine cobweb of silken threads.
(1) Caterpillars nearly naked or with only fine
hairs.
aa. Dark-green caterpillars with fine,
closely set hairs and two lateral
white stripes on each side. Feed-
ing on pine_-_-- pine butterfly, page 62.

INSECT ENEMIES OF WESTERN FORESTS 61

bb. Caterpillars travelling with a loop-
ing motion; with three pairs of
true legs in front and two or
three pairs of prolegs in the rear.
loopers or measuring worms, page 74.
ce. Olive-green caterpillars with black
and yellow stripes on top and
sides, brown or red heads; feed-
ing on California oaks.
California oak worm, page 68.
(2) Caterpillars very hairy.
aa. Caterpillars brightly marked with
blue, red, or yellow spots and
long pencils or distinct tufts of
hairs like a toothbrush.
tussock moths, page 69.
bb. Caterpillars of dull colors, black,
and yellow, feeding in masses on
terminal branches.
tiger moths, page 66.
cc. Blackish eaterpillars with row of
nearly square, white blotches
along the back, irregular white
marks along the sides, and brown
spines and longer, paler hairs.
Feeding on poplar and willow. \
satin moth, page 72. be
2. Leaves chewed, but defoliated part of tree not covered with
silken webbing.

a. Work done by caterpillars with seattered’ spines or
hairs; three pairs of front legs, four pairs of
median prolegs, and one pair of anal larvapods.

(1) Yellowish-green or brown, leathery cater-
pillars with short dark hairs and seven
or eight stout branched spines on nearly
every segment; feeding on ponderosa pine.
pandora moth, page 64.
(2) Black caterpillars with fine, branched spines
on each segment, middle row of spines
bright yellow; feeding on _ species of
Ceanothus.
California tortoise shell butterfly, page 165.
(3) Large, stout caterpillars with sparse, stout
tubercles; feeding on broadleaved trees
DTN ES STAT LIS oat so a ee ya giant silk moths.
(4) Yellow and black caterpillars with branched
Spines; feeding on willow, popular, and
other broadleaved trees and_ shrubs
brown day moth.

b. Work done by naked slugs with three pairs of true
legs and six to eight pairs of prolegs; sometimes
covered with slime; one end of body frequently
held in midair when disturbed______~_ sawflies, page 87.

3. Leaves mined internally.
a. Working inside of coniferous needles
needle miners, page 85.
b. Working in broad leaves_____________ leaf miners, page 86.
4. Leaves skeletonized, with midribs and veins still evident.

a. Work on broadleaved trees done by active grubs

with three pairs of true legs, or by hard-shelled

ro see = =

beetles Shee Waa TU ed leaf beetles, page 92.

B. Trees sickly, leaves not chewed but yellowing or covered with a sticky
extldanronyorblacksmut. we as sap-sucking insects, page 44.
Greaves; stumped called. or swollen. 9.922) 3 gall makers, page 52.

_*Similar work is done on broadleaved trees by a great variety of caterpillars, saw-
Hie, ue and to be certain of the insect responsible, specimens must be captured and
identified.

62 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

MOST IMPORTANT PINE DEFOLIATORS

The pine butterfly (Veophasia menapia Feld.) (31) is potentially
one of the most dangerous enemies of ponderosa pine in the North-
western States. One of the earliest recorded outbreaks occurred near
Spokane, Wash., in 1882. Since that date several outbreaks have
developed in the ponderosa pine stands of Oregon, Washington,
Idaho, and British Columbia. One of the worst of these occurred
on the Yakima In-
dian Reservation in
Washington during
the period 1893-95.
Ponderosa pine over
approximately 150,-
000 acres was af-
fected and from 20 to
90 percent of the
stand killed over this
largearea. The total
loss amounted to
nearly a billion
board feet, and the
effects of this out-
break are still evi-
dent. A more recent
outbreak severely de-
foliated thousands of
acres of ponderosa
pine along the Little
Salmon and Payette
Rivers in Idaho in
1922 and 1923. Old,
mature ponderosa
pines are more sus-
ceptible to injury
than the younger,
thriftier trees. West-
ern white pine and
lodgepole pine, when
FicURE 27.—The pine butterfly (Neophasia menapia) : Eggs, 1 mixture with pon-

eS pupae, ae ae male above, female below. derosa pine, are also

attacked, and Doug-
las fir is reported to have been injured in outbreaks of the pine
butterfly along the coast of British Columbia.

The adult (fig. 27) is a white butterfly with black markings and
a wing expanse of about 184 inches, resembling in general the
common cabbage butterfly. The wings of the male are pure white
except for some black markings on the tips. The forewings of the
female have similar black markings, but have a distinct yellowish
cast; the hind wings have the same yellowish cast but have a much
heavier black marking than in the male. With many females, but
not all, there are bright orange spots along the apical margin of the
hind wings. These butterflies may be seen nearly every year flying
about in pine and fir forests and hovering about the tops of trees.

INSECT ENEMIES OF WESTERN FORESTS 63

Flight of the butterflies occurs in August, September, and October,
and emerald- green eggs are laid on the needles a few hours after
mating. These eggs are attached to needles near the tops of the
trees and are laid in rows at an angle of 45°, with from 5 to 20 eggs
in each row, and are firmly cemented together (fig. 28). The winter
is passed in the egg stage, and the eggs hatch the following June,
or about the time the new needles begin to appear on ponderosa pine.
The larvae, as they hatch from the eggs, are very small, pale-green
caterpillars, with shiny black heads. The young larvae feed in
clusters, encircling the needle with their heads pointed toward the
tip, forming a little ring of tiny black heads. Later on they feed

FIGURE 28.—Progressive stages of the pine butterfly. (Drawings by Edmonston.)

singly and reach maturity by the latter part of July. When mature
they are approximately 1 inch long, dark green, and covered with
fine, closely set hairs, and with two white lateral stripes down each
side. The anal shield is produced behind into two blunt, well-
separated projections. The head is pale green and covered with
short hairs. The full-grown larvae lower themselves to the ground
by silken threads and then ascend low- growing vegetation to trans-
form to pupae, forming chrysalids attached to shrubs, g grasses, limbs,
and tree trunks. From 15 to 20 days are spent in the pupal stage,
and then the insects emerge as mature butterflies. Normally there is
one generation a year.

Outbreaks of the pine butterfly seldom last for more than 3 or 4
years, for nature has provided a wasplike parasite (Zheronia ful-
vescens Cress.) which was apparently responsible for the reduction
of past outbreaks of this destructive pest. In the recent outbreak
in central Idaho, it was found that during the third year of the
epidemic over 90 percent of the caterpillars were parasitized by this

64 MISC, PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

beneficial insect, and during the following season it was practically
impossible to find a living caterpillar or butterfly within the de-
fohated areas. Before natural control becomes effective, however,
tremendous loss of timber may occur.

In the future, artificial control by airplane dusting may prove
useful in protecting the forests from heavy defoliation during the
peak of the outbreak and until the defoliator is brought under
control by natural means. Even if only 50 percent of the foliage
ot a tree could be saved by such a method it probably would be
sufficient to prevent its death.

The Pandora moth (Coloradia pandora Blake) (68) (fig. 29) is
an important defoliator of ponderosa pine in the forests of central
and southern Oregon and in California east of the Sierra Nevada.
This moth and closely related species and varieties have been re-
ported from practically all Western States, where they feed upon
various pines. The preferred hosts of the pandora moth are pon-
derosa and Jeffrey pines, though lodgepole pine may also be attacked
during epidemics when in mixture with one of the preferred species.
Though distributed over a wide area, it is only in pine forests grow-
ing on loose pumice soil, where thé caterpillars can easily bury
themselves for pupation, that serious damage has occurred.

The most recent destructive outbreak occurred on the Klamath
Indian Reservation of southern Oregon from 1918 to 1925. Thou-
sands of acres of ponderosa pine forest were heavily defoliated, with
an accompanying serious loss of timber. Heavily defoliated trees
were unable to recover and died after 2 or 3 years as a direct result
of the injury. Others were greatly reduced in growth and re-
covered only after a period of several years. The loss in growth
throughout the defolated area amounted to several million board
feet. Even more serious was the bark-beetle damage which fol-
lowed the defoliation and increased to alarming proportions in the
weakened trees.

While some infestation may be found every few years, the records
indicate that epidemics occur at fairly regular intervals of 20 to
380 years and continue in intensity for from 6 to 8 years. During
periods of abundance fairly heavy feeding may occur without serious
consequences. This is due to the fact that the terminal buds are
not eaten, and since the insect has a 2-year life cycle and the larvae
feed only in alternate years, the trees have an opportunity to re-
cover. For this reason the more vigorous trees survive the attacks,
and only during the major outbreaks are heavy losses likely to
be sustained,

The adults are large, heavy-bodied, grayish-brown moths with a
wing expanse of 3 or 4 inches, and a small dark spot near the center
of each wing. The base and interior margins of the hind wings are
clothed with pinkish hairs, which in the male shade to wine color.
The males have large, feathery antennae, while the females have
slender antennae and heavy bodies, During epidemics thousands
of these large moths will be seen fluttering over the tree trunks
and flying through the woods. The eggs, which are globular in
shape and about one-tenth of an inch in length, are laid in clusters
on the trunks or branches of trees or on litter on the ground. The

INSECT ENEMIES OF WESTERN FORESTS 65

FicgurRE 29.—The pandora moth (Coloradia pandora): A, Adult male, natural size; B,
young larvae on pine needles ; C, eggs, X 3; D, pupa; H, full-grown caterpillar, K 1.25.

newly hatched caterpillars are about one-fourth inch in length, with
shiny black heads and black or brownish bodies covered with short,
dark hairs. When mature, the caterpillars are from brown to yel-
lowish green and 214 to 3 inches in length, with each segment sup-
porting a few stout branched spines.

136650°—38——5

66 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

Two years are required for this insect to complete its life cycle.
Adults appear during the latter part of June and in July, and the
females deposit eggs that hatch in August. The young larvae crawl
up the trees and during the early molts feed in groups on the new
foliage. At the end of the season they are about 1 inch in length.
The first winter is spent by these immature larvae hibernating in
clusters at the base of the needles. Feeding is resumed in the follow-
ing spring, and the caterpillars reach full growth by the last of
June. When mature, they crawl down the trees and enter the soil
to a depth of 1 to 5 inches, where they form elliptical cells, some-
times sparsely lined with a silky material, in which they transform
to the pupal stage. The pupae are dark reddish brown and from
1 to 11% inches in length and about one-half inch in width. The
pupal stage lasts a full year, and the moths are not ready to emerge
until the following June and July.

An interesting side light on the economic importance of this in-
sect is that the larvae or pupae form a delectable food for certain
Indian tribes. The Mono Indians of California dig trenches around
the infested trees and build smudge fires which cause the cater-
pillars to drop to the ground in great numbers. They are caught
in the trenches, killed, dried, and subsequently cooked with vege-
tables to make a stew. The Klamath Indians in Oregon prefer
the pupae, which, when dug from the ground and roasted or boiled,
are considered a great delicacy.

Epidemics of the pandora moth are brought under control by a
number of natural enemies. Probably the most important is a wilt
disease that attacks them at about the time they reach full growth
and start to descend the trees. Once this disease becomes well estab-
lished it runs rampant through the hordes of caterpillars, and very
few of the insects escape. Ground squirrels and chipmunks dig up
and destroy large quantities of pupae. Birds feed only sparingly
on the caterpillars, which appear to be distasteful to most of them.
Four or more species of insect parasites attack the caterpillars and
dispose of a large number.

This defolator could be held in check by spraying or dusting
trees with arsenicals during the spring period of maximum feeding,
provided such insecticides could be applied at a reasonable cost.
Airplane dusting is about the only way in which such poisons could
be applied to large forested areas, and because of the cost it 1s ques-
tionable to what extent such a method could be used.

Another method of control which was tried by a private timber
company on a large tract of privately owned land in southern
Oregon is light burning. In the fall of 1922, fire was run through
this tract while the pandora caterpillars were feeding. The smoke
and heat caused them to drop to the ground, where they were de-
stroyed. On account of the damage and danger which may ensue
in the use of fire, this method is of questionable benefit. The remedy
may easily be “worse than the disease.”

TIGER MOTHS
(Arctiidae)

The tiger moths are so named on account of the contrasting colors
shown by many. Some of the species are without markings, but
the majority are unusually beautiful. The caterpillars are robust

INSECT ENEMIES OF WESTERN FORESTS 67

and very hairy, some of them being referred to as “woolly bears.”
Most of the family are important as leaf feeders.

The silver-spotted halisidota (Halisidota argentata Pack.) (fig.
30) is a strikingly colored yellowish-brown moth with a wing spread
of about 2 inches and a body covered with long yellow hairs. The
forewings are reddish brown with numerous uniform silvery-white
spots. The hind wings have a few brown marks near the outer

FIGURE 30.—The silver-spotted halisidota; A, Full-grown caterpillar; B, eggs on needles ;
C, adult male; D, adult female. All natural size.

margin. The large moths emerge, fly, and mate during July and
August. Pea-green eggs are deposited in clusters on the twigs and
needles of the host trees. As many as 325 eggs have been laid by
one moth. The caterpillars, which are densely clothed with long
brownish to black hairs, congregate and feed heavily on the needles
of young Douglas fir, balsam firs, pine, and spruce and are often

68 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

found in dense clusters on the twigs, where they hibernate during
the winter. In June the mature caterpillars spin cocoons, which are
composed of silk and larval body hairs, and attached to the needles
or twigs of the defoliated trees. In these cocoons they pupate. The
species is distributed from Colorado to California and Oregon.
Contro: measures under forest conditions are not likely to be
justifiable.

There are several closely related species of the genus which are
also forest-tree leaf feeders. Halisidota ingens Hy. Edws. feeds on
the needles of ponderosa and pinon pine in Colorado. Hf. maculata
Harr. and its various varieties are found in all of the Western
States, feeding on willow, oak, maple, alder, poplar, and a variety
of other trees and shrubs. /. sobrina Stretch feeds on Monterey pine
in California.

The fall webworm (/7yphantria cunea Drury) is a common defoli-
ator of broadleaved trees, such as madrona, alder, willow, cottonwood,
and various other shade trees, fruit trees, and ornamentals, but it is
of little importance from a forestry standpoint. The caterpillars,
when full grown, are pale yellow to brown but appear grayish be-

cause of the long whitish hairs that arise from black and orange
tubercles. They : spin very large webs, within which they feed upon
the fohage. These tents often enclose an entire branch and are very
conspicuous late in the summer. Feeding takes place from July 1
to September 15. Maturity is reached late in the fall, and the winter
is passed as pupae in dark-brown cocoons on the eround or attached
to the tree trunks. The following spring the adult moths appear.
These are nearly white, with a few black spots on the wings and
orange markings on body and legs. A spotless form is called Z.
textor Harris.

The California oak worm (Phryganidia californica Pack.) (18)
(fig. 31) periodically defoliates the various species of oaks in Cal
fornia and sometimes attacks other trees in the vicinity of heavily
infested oaks. It is particularly injurious to shade and ornamental
oaks in the San Francisco Bay district, and not only renders the
trees unsightly but may seriously weaken them or even cause their
death.

The moths have a body about one-half inch in length, and wings
of light brown with darker veins and a spread of about 114 inches.
The males are distinguished by having yellowish patches near the
center of the forehead and by their broader and more feathery an-
tennae. Full-grown caterpillars are about 1 inch in length, and of
a dark olive green with conspicuous black and yellow longitudinal
stripes on the ‘back and sides.

The females lay eggs in groups of 2 to 40 on the under sides of
oak leaves, on tree trunks, or other convenient places. The young
caterpillars skeletonize the leaves, and later, as they reach full
growth, consume all of the leaf. Two generations are produced each
year. The moths fly in June and again in November. The winter
is passed in the egg and early larval stages.

Natural enemies include the spined soldier bug, a tachinid fly, and
several species of wasplike parasites. A wilt disease takes a heav y toll
of the caterpillars during epidemics. As a result of these natural
control agencies, outbreaks occur only at irregular intervals.

é

INSECT ENEMIES OF WESTERN FORESTS 69

The control of this defoliator can be accomplished by spraying in
March and April with lead arsenate spray when the worms are very
small and again during the last of July and first part of August.

OSS
re Sh Wy

( \ AM
Wan arin’

f y i Fal |

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FicurE 31.—The California oak worm (Phryganidia californica) : A, Adult moth, natural
size; B, eggs, X 4; C, young larva, xX 3; D, full-grown larvae, X %; H, pupa, xX 2.
(Drawings by Edmonston. )

TUSSOCK MOTHS

(Hemerocampa spp.)

The tussock moths represent a very destructive group of leaf-
feeding insects that attack coniferous species as well as broadleaved
trees. The adults are dark-brown or dull colored, very fuzzy moths,
that are chiefly nocturnal in habit. The males fly, but the wings of
the females are but short. pads, of no use for flight. The abdomens of
the females are large and covered with a mat of dark-gray hair.
The full-grown caterpillars are strikingly marked and very hairy
with prominent pencils or small tufts of hairs on all the body seg-
ments, the whole giving much the appearance of a toothbrush. The
larval hairs are easily detached and in some species are somewhat
poisonous, causing a rash or eczema when they come in contact with
the skin. 3

The female lays small white eggs in a mass on top of her own
cocoon and covers them with a frothy, gelatinous secretion in which
are embedded hairs from her body. The eggs hatch into tiny, very
hairy caterpillars. Since the females are unable to fly, the principal
time of dispersion is probably during this young caterpillar stage,

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70 MISC. PUBLICATION 273, U. 8. DEPT. OF AGRICULTURE

for the light, hairy caterpillars can be easily picked up and carried
by air currents for: long distances. When disturbed or when in
search of food, the larger larvae lower themselves to the ground by
silken threads and travel rapidly, but dispersion at this stage could
only be for short distances at most. Pupation takes place within a
eray cocoon made of silk mixed with larval hairs. These may be
attached to the twigs, limbs,
or trunks of trees or on the
underbrush. These cocoons
are sometimes formed in
masses six or seven layers
deep, and in such cases the
moths from the lower ones
are unable to emerge.

The Douglas fir tussock
moth (/lemerocampa pseu-
dotsugata McD.) (2) (fig.
32) is a defoliator of major
importance in the Douglas
fir and balsam fir forests
of eastern Oregon, Wash-
ington, and British Colum-
bia, and in Nevada and
Idaho. It was first dis-
covered in British Colum-
bia in 1918, where it was
severely defoliating Doug-
las fir, and since then local
damage has been noted at
several points. The species
was not recorded from the
United States until 1927,
when an outbreak occurred
in Nevada. Then in 1929
several outbreaks were
found in different sections
Figure 32.—The Douglas fir tussock moth (Hemero- of Idaho ) northeastern

v=.

campa pseudotsugata): A, Female laying eggs Washinoton, and eastern
on cocoon; B. larva; C, male moth; D, female 5 4 3 Seo
moth. Natural size. Oregon. The epidemic in.
the Colville National For-
est, Wash., reached a peak in 1930, spread over many square miles, and
killed at least 300,000,000 board feet of Douglas fir and balsam fir,
The Douglas fir which was not killed outright by the defoliation
subsequently succumbed in many cases to the ‘attacks of the Douglas
fir beetle. These extensive killings have been followed by some
- disastrous fires.

The Douglas fir tussock moth shows a decided preference for
Douglas fir and species of balsam fir and can increase to epidemic
numbers only when feeding on these preferred host trees. It will,
however, feed on other species of conifers when mixed with firs,
and even on the underbrush. Defoliation first occurs at the tops of
trees, and as this foliage is destroyed the caterpillars work down on
the lower foliage.

INSECT ENEMIES OF WESTERN FORESTS TeAt

The caterpillars of this tussock moth are striking looking creatures,
decorated with brightly colored tufts of hairs. When full grown
they are from three-fourths to 1 inch in length, with gray or light-
brown bodies and black, shiny heads. There are two long brushes
or pencils of black hairs fully one-fourth inch in length, suggesting
horns, directly behind the head, and a similar but longer tuft at the
posterior end of the body. On the upper side of the first four and
the last abdominal segments are dense, light-brown or cream-colored
tufts of hairs about one-sixteenth of an inch in length, and numerous
red spots. Along the sides of the body are somewhat broken, nar-
row, orange stripes, while the lower side of the body is nearly naked,
with the prolegs only sparsely covered with hairs.

The adult moths are far more ordinary looking than their hand-
some larvae, being a dull brownish gray. The males are about
one-half inch long and have a wing expanse of nearly an inch. The
wingless females are about one-half the length of the males.

Normally there appears to be one generation a year. The small
caterpillars hatch from the eggs and commence feeding on the new
foliage early in spring, but it is not until about the Ist of August
that the defoliation is likely to become severe enough to be noticeable
at a distance. The larvae reach full growth early in August and then
pupate. The moths appear the latter part of August and mate soon
after emergence. The winter is passed in the egg stage.

One of the most important parasites is a tachinid fly, somewhat
larger and more hairy than the ordinary housefly. The larvae of this
fly live in the caterpillars and emerge after these have formed their
cocoons. A very small wasplike insect, 77ichogramma minutum
Riley, attacks the eggs and destroys a high percentage of them.
There are at least five other wasplike insects that are important
parasites of the larvae.

Determination of the feasibility of artificial control of this Ge-
foliator involves not only the consideration of effective methods but
the cost of applying them. The spreading of arsenical dust by air-
plane probably would offer the best chance of success of any method,
but at this time it cannot be recommended on account of risk and
cost. Such methods as collecting and destroying the egg masses
during the winter months, jarring the caterpillars from the trees,
banding the trees to prevent ascent of the caterpillars, and power
spraying, are applicable to the control of this insect only under park
or shade-tree conditions. |

Other closely related species of tussock moths which feed on forest
trees in the Western States include:

Species Host and distribution
Hemerocampa oslari Barnes__—-~- White fir. California and Colorado.
Hemerocampa vetusta Bdv_--_--~ Oak, poplar, willow, and various other
broadleaved trees. Pacific coast.
Hemerocampa gulosa Hy. Hdw__— Oak. California Sierras.

Hemerocampa leucostigma A.andS. Poplar and other broadleaved trees. In
the East, and west into Colorado and
British Columbia.

Nototophus antigua, Lies —--—---~ Alder, ash, aspen, larch, oak, pine, poplar,
willow, and other broadleaved trees and
shrubs. From California to British Co-
lumbia and east to Montana.

qe MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

THE SATIN MOTH

The satin moth (Stilpnotia salicis L.) (10) is a very injurious leaf-
eating enemy of poplars and willows. This moth, which is native
to Europe, was first reported in 1920, both in New England and
British Columbia. Since then the British Columbia introduction
has spread throughout western Washington and into Oregon. It is
a serious pest of planted shade and roadside trees, and may prove
destructive to native poplars and willows.

The adults are large white moths with a satiny luster, a wing
expanse of approximately 134 inches, black eyes and legs, and a tuft
of hairs at the tip of the abdomen. The full-grown caterpillars are
about 2 inches in length, black with white markings on the sides, a
row of nearly square white marks along the back, and with brown
spines and long hairs.

There is but one generation a year. During the flight of the
moths in July eggs are laid on trees or other objects in oval patches
covered with a white, satiny secretion which glistens in the sun. The
young larvae feed for a short time and then spin small cocoons or
hibernacula in bark crevices, where they pass the winter. Feeding
is resumed in the spring, and the larvae reach maturity in June.
Pupation occurs in loosely woven cocoons attached to leaves or other
objects.

It was introduced without its European parasites, but it is at-
tacked by several native enemies, including tachinid flies, parasitic
wasps, sarcophagid beetles, mites, and birds. Some of these have
proved very effective in holding it in check. From 1929 to 1934,
five species of parasites of European origin were colonized and lib-
erated in Washington. Four of these have become established and
at least one, Apanteles solitarius Ratz., has become abundant enough
to show apparent effect.

Direct control is obtained by spraying the trees in the spring with
a stomach poison such as lead arsenate. When egg masses are
exceptionally abundant they should be treated with creosote.

TENT CATERPILLARS

(Mfalacosoma spp.)

Tent caterpillars (78), which are responsible for the defoliation of
many different species of trees and shrubs, can be recognized by the
large compact webs at the terminals of branches, which are such a
common sight during April and May. ‘The various species are
indigenous to this continent, being widely distributed over the
United States. Outbreaks were recorded from Massachusetts as early
as 1646. Coniferous trees are sometimes attacked, but the preferred
hosts are deciduous trees and shrubs. While large forest areas are
sometimes defoliated, the resultant damage is usually of no great
importance, since deciduous trees can readily recover from the loss
of foliage.

The caterpillars that construct the tents are usually yellow to
brown, with rows of blue or orange spots and lines, and are lightly
covered with long hairs. A heavy, silk-lined cocoon is usually formed
in bark crevices or in leaves webbed together. The adults are tawny
yellow or brown moths or millers and are frequently seen flying about
lights at night.

eee

INSECT ENEMIES OF WESTERN FORESTS 73

There is usually but one generation, of these insects a year. Adult
moths appear in midsummer and deposit masses of eggs in bands
encircling small twigs. The eggs do not hatch until the leaves appear
the following spring. The young larvae feed on the new foliage, con-
struct the large tents on terminal branches, and reach maturity early
in the summer. They then form pupae, and the adult moths appear
soon after. ,

Aside from the several species of predacious beetles and bugs that
feed on the caterpillars, there are parasitic insects that lay their
eggs within those of the moth, and the resulting minute larvae
develop within the host eggs and destroy them. Further control is
accomplished by parasitic insects that breed within the caterpillars
and the pupae. Birds also play an active part in controlling the
tent caterpillar nuisance, many species feeding upon the caterpillars,
others feeding on the eggs, and still others, although to a lesser degree,
on the moths. Often the most complete control is accomplished by
a wilt disease that rapidly spreads among the colonies of caterpillars
and leaves but few survivors.

There are six common species of tent caterpillars in the West, and
they are most easily distinguished in the field by the markings on
the caterpillars.

The forest tent caterpillar (Afalacosoma disstria Hbn.) is dusky
brown with a row of diamond or keyhole-shaped white spots along
the back and sides and with fine brown hairs. It feeds in large
colonies, without forming tents, on alder, birch, poplars, willows,
and a large number of broadleaved trees. They are distributed
generally over the United States.

The eastern tent caterpillar (Malacosoma americana F.) has a
white line on the back, bordered with reddish brown, and on the
sides a row of blue spots and reddish-brown and yellow lines. It
feeds on various fruit, shade, and forest trees in the Eastern States
and is found in the Rocky Mountain region from New Mexico to
British Columbia.

The California tent caterpillar (Malacosoma californica Pack.) is
orange red to brown above and paler brown below, with a blue line
on each side. This species is found in California, where it feeds on
ash, madrona, oak, willow, and other forest, shade, and fruit trees.

The blue-sided tent caterpillar (M/alacosoma constricta Stretch) has
an orange-brown body, with distinctly blue sides and blue dots along
each side of the center. It feeds on oak and other trees in Arizona,
California, and Oregon.

The Great Basin tent caterpillar (Mfalacosoma fragilis Stretch)
(fig. 38) is distributed in the Great Basin region between the Rocky
Mountains and the Cascade-Sierra Nevada ranges, where it feeds on
bitterbrush, aspen, oak, poplar, willow, and other shrubs and trees.
The caterpillars of this species are distinguished by having a pale-
blue head and brown to black body, with a broad, pale-blue stripe
down the middle, fine orange lines on each side of the center, and
two blue spots on the sides of each segment. The hairs are whitish.

The western tent caterpillar (Afalacosoma pluvialis Dyar) (fig. 34)
is the common coastal species in the Pacific Northwest, that has as its
favorite food the alder, though feeding on other forest and fruit trees.

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74 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

the center and two orange spots on each segment. On the sides are
pale orange lines and spots.

7

FIGURE 33.—Great Basin tent caterpillar (l/alacosoma fragilis) : A, Adults, natural size;
B, larva, pupa, and cocoon, X 2.

LOOPERS, SPANWORMS, OR MEASURING WORMS

(Geometridae)

:
j
i

The leaf-feeding caterpillars of this family of moths infest a great
many species and varieties of trees and plants. Some species are _—
among the most destructive defoliators of forest trees. The cater- _

INSECT ENEMIES OF WESTERN FORESTS 75

pillars are smooth, nearly hairless, with three pairs of true legs in
front and two or three pair of prolegs on the rear of the abdomen,
These species can easily be recognized by the characteristic way in
which the caterpillars travel. T hey move along by grasping with the
hind pairs of prolegs while they extend the body forward, then
holding with the front legs while they hump their backs to bring
up their rear. This produces a looping motion, from which arises
the common names of loopers, spanworms, inchw orms, or measuring
worms. Adults are
medium-sized,
slight-bodied, and
light-colored moths
of which the hem-
lock or oak looper
isatypicalexample.

The hemlock loop-
er (Lllopia fiscel-
lara Guen.) (85)
(496) is a very de-
structive defoliator
in the spruce, hem-
lock, and balsam fir
forests of the North-
eastern States,
through Canada,
the Lake States, and
along the north-
western coast. At
intervals it appears
in great numbers,
strips the needles
from trees over
large areas and
causes their death.
These defoliated
trees become very
dry, and jungles of
fallen trees and
broken tops 2 Oi FicurE 34,—The western tent caterpillar (Malacosoma plu-

follow that are fre- vialis): A, Egg mass on alder branch: B, full-grown cater.
pillar; C, cocoon webbed in curled leaf; D, pupa; H#, adult

quently swept by moths. All natural size.
disastrous fires.

The species that destroys the spruce-hemlock forests along the
coast of Oregon, Washington, and British Columbia has been re-
ferred to as the variety luqubrosa Hulst (fig. 35). During the last
40 years it has figured in three major outbreaks. The earliest out-
break of record occurred about 1889 to 1891, when a vast amount
of timber in Tillamook and Clatsop Counties, Oreg., and Grays
Harbor County, Wash., was destroyed. The second outbreak oc-
curred again in Tillamook County in 1918-21, when several town-
ships were affected and 500,000,000 board feet of hemlock and Doug-
las fir were reported to have been killed. The latest outbreak
occurred in Pacific and Grays Harbor Counties, Wash., from 1929

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76 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

to 1932, when 50,000 acres were involved and about 200,000,000 feet
of hemlock timber destroyed.

Although western hemlock is the preferred host, the caterpillars
appear in countless thousands when an outbreak occurs and feed on
any foliage at hand. Douglas fir, Sitka spruce, and western red
cedar may be heavily attacked when in mixture with hemlock;
also huckleberry, salal, and broadleaved forest shrubs and trees
are frequently eaten.
In fact, when the cater-
pillars are exceptionally
numerous, nothing
green is left on the in-
fested areas.

The moths are light
buff, with a wing ex-
panse of about 1%
inches. The forewings
are marked with two
wavy lines and the hind
wings with one wavy
line. They fly, mate,
and lay eggs late in
September and during
October. The eggs are
about the size of a pin-
head, gray green or
brown, and are attached
to the moss on the tree
trunks, or to twigs or
branches. It is in this
stage that the winter is
passed, and the eggs
hatch the following
spring. The young lar-
vae, which are about
one-fourth inch in

! cribs length, crawl up the
FiGuRE 35—The hemlock looper (Hilopia Ascellaria var. tree trunks and start
moh Natural ste DERE Gy vag SEAS oe aaa cos feeding on the young
needles. The first feed-
ing takes place in May, June, and the early part of July and
is not particularly noticeable. However, from the middle of July
to October the feeding of the caterpillars causes a heavily infested
forest to turn yellowish red and then brown, as though scorched by
fire. Late in summer the caterpillars feed on the foliage, clip off
small twigs, crawl over the trunks, cling to shrubs, and drop by
silken webs from the trees to the ground. These silken webs may
become so abundant that the whole forest looks and feels like one
big cobweb. When full grown, the caterpillars are about 114 inches
long, green to brown, with diamond-shaped markings on the back.
They drop to the ground in August and September and secrete them-
selves in protected places, such as crevices of the bark or under
debris on the ground, and there transform to pupae.

INSECT ENEMIES OF WESTERN FORESTS Pf

The pupae are mottled, greenish brown, about one-half inch long,
and are unprotected by a cocoon. The moths appear within 10 to 14
days and during an epidemic are so abundant as to give the im-
pression of a snowstorm in the woods. Creeks, springs, and rivers
are covered with the dead bodies, and tree trunks are plastered with
them until heavy rains wash them into the ground or carry them
away. There is one generation annually.

Outbreaks usually last for about 3 years, after which they are
generally brought under control by the action of parasites, predators,
and disease. Heavy
rains during the
flight period reduce
egg laying, checking
an epidemic and
hastening its decline.

Although nature
will ultimately bring
outbreaks under con-
trol, a vast amount
of timber might be
saved if artificial
control measures
could be appled to

from heavy defolia-
tion. It has been
found. that trees can
recover from a_ 50-
percent defoliation,
and in some cases a
75- percent defolia-
tion is not fatal un-
less the trees are sub-
sequently attacked by
bark beetles. At

HIGURE 36.—Thbe oak looper (Hllopia Se a Cater presen t, airplane
pillars on defoliated branch; B, pupae; @, adult moths, : DG 3
female above, male below. Natural size. dusting (33, 54) of

fers the only prac-

tical means of controlling this defoliator on large forest areas, but
because of high risk and cost, it can be apphed only under par-
ticularly favorable circumstances. (See discussion on p. 178.)

The oak looper (Zllopia somniaria Hulst) (fig. 36) is so closely
related to the hemlock looper that some entomologists consider the
distinction questionable. At least this probably represents a variety
or race of loopers that shows a distinct preference for Oregon white
(Garry’s) oak, on which it feeds in Oregon and northward into
British Columbia. Other trees may be attacked but usually only
when intermingled with the preferred host tree. In some seasons the
oaks in Willamette Valley in Oregon are completely defoliated over
large areas by this species. No permanent damage is done, how-
ever, since the oaks are able to leaf out again the following year.

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Flee MISC. PUBLICATION 273, U. 8. DEPT. OF AGRICULTURE

The New Mexico fir looper (Galenara consimilis Hein.) (fig. 37)
has periodically destroyed timber over considerable areas in the
spruce-fir type at the higher elevations of the southern Rocky Moun-
tain region, particularly in New Mexico. Douglas fir seems to be
the preferred host, but balsam fir and spruce foliage is also eaten.

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B, female moth, X 1.3; C, pupa, X 1.6; D, egg, greatly enlarged. (Drawings by
Edmonston. )

BUD MOTHS, BUDWORMS, AND LEAF ROLLERS

One group of moths, belonging largely to the family Tortricidae,
lay their eggs on the needles of coniferous trees or the leaves of
various broadleaved trees, and the young caterpillars feed on the
opening buds and new leaves or needles, drawing these together with
a silken web. Later, as they become larger, they may leave their pro-
tective web and feed openly on the leaves or older needles and if
numerous will completely defoliate the tree. When growth is com-
pleted the larvae transform to the pupal stage, usually in small
webs spun about the dead foliage at the tips of the branches, and
from these the full-grown moths emerge.

Under normal conditions the damage consists only of a few dead
tips or partly eaten leaves. When buds are killed, subsequent
branching results at these points, but seldom is the life of the tree
threatened. When epidemic outbreaks occur, large forest areas may
be completely defoliated and killed.

INSECT ENEMIES OF WESTERN FORESTS 79

The spruce budworm (Harmologa fumiferana Clem.) (25, 82)
(fig. 88) is one of the most destructive members of this group. In
the Northeast, in Canada, the Lake States, and the northern Rocky
Mountain region it has caused widespread destruction of spruce,
balsam firs, and Douglas fir. There are many records of budworm
epidemics in the Northeast in which enormous numbers of spruces
and balsams have been destroyed. It was not until 1922, however,
when two outbreaks were recorded in widely separated sections of

FIGURE 38.—The spruce budworm (Harmologa fumiferana) : A, Eggs on under side of fir
needle; B, half-grown caterpillar; C, full-grown caterpillars; D, pupae; H, fir twig
with pupa attached; F, defoliated fir twig with empty pupal cases; G, adult moths.
All natural size. (Hvenden.)

Idaho, that it was recognized as an important enemy in western
forests. The following season it was found that a budworm epi-
demic had been present for several years in the southwestern corner
of Yellowstone National Park and the adjacent Targhee National
Forest, and in the next few seasons outbreaks were reported from
many Western States. In some areas these outbreaks reached alarm-
ing proportions and heavy timber losses followed. Though it is not
known whether this insect migrated or spread to the western part
of the United States from infested areas in the East, it is believed
that it is indigenous to the West and that during the last 30 or 40
years it has been at such a low endemic stage as to escape attention.

The adult spruce budworms are-small, mottled, brownish moths
with a wing expanse of approximately 1 inch, with no distinctive
markings, the general color tone being a dull gray. The oval, scale-
like eggs, which are light green and about one-sixteenth of an inch
in diameter, are laid on the under side of needles, in an overlapping
form like shingles, with about one-third of the egg exposed, The

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SO MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

mature larvae are approximately 1 inch in length, deep brown, with
yellowish, pale-green markings and numerous small, wartlike erowths
along the sides.

The moths can be seen hovering around infested trees late in
July or early in August. The females lay their eggs on the needles
of the upper branches of fir and spruce trees, where the tops are
in the sunlight. A female lays approximately 150 eggs in masses
of about 12, “and these hatch during the latter part of J uly. After
hatching, the young larvae wander about for a few days in search
of a suitable place to spin their cocoons and in these they hibernate.
It is not definitely known whether the young larvae feed before
hibernation, but if they do, it is very sparingly. The following
spring they emerge from their winter nests simultaneously with
the opening of the new buds, which they immediately attack, enter-
ing them either directly through the base or between the opening
scales, and hollowing them out. As the new tender needle growth
develops this is fed upon. Later on the larvae bind together the
needles at the tips of the branches loosely with silk, bite them off
at the base, and form a shelter of dead needles, bud scales, and
frass. When disturbed, the larvae hide in these ‘retreats, or "drop
from the limbs and hang by silken threads, which are used to return
to the nests if no further disturbance occurs. After 3 or 4 weeks of
feeding, about the last of July, the larvae reach maturity and con-
struct loose cocoons of silk and dead needles, in which they pupate.
The moths emerge in from 10 to 12 days. Thus there is one gen-
eration annually.

When attacks are heavy entire trees are stripped of foliage and
killed and large areas of forest take on a brownish, scorched appear-
ance (fig. 39). When defoliation is not so complete the trees show
a blighted or scorched appearance at the tips of limbs where the
new foliage has been destroyed. Even moderate feeding tends to
reduce growth, weaken the trees, and render them susceptible to
later destruction by secondary insect enemies.

In the western part of the United States the balsam firs and
Douglas fir appear to be preferred hosts of the spruce budworm,
and the greatest damage has occurred in pure stands of these two
species. ‘The budworm has also been found attacking Engelmann
spruce, western larch, western hemlock, western white pine, pon-
derosa pine, and lodgepole pine. Budworm attacks on pines are
usually limited to individual trees occurring in association with
the preferred hosts, though serious outbreaks in pure lodgepole. pine
have occurred in and adjacent to the southwestern corner of Yel-
lowstone National Park. In all cases the new foliage is destroyed
first, old needles being attacked only when the preferred supply is
exhausted. Larvae will often migrate from one tree to another in
search of new fohage rather than feed on old needles.

As in the case of most defohators, the spruce budworm is preyed
upon by numerous insect parasites and predators and by disease,
and these in normal years tend to keep the pest under control. The
natural enemies and a shortage of food usually are responsible for
eventually subduing an outbreak.

The control of spruce budworm epidemics by artificial methods
is not ordinarily practical because of the difficulties and expense

INSECT ENEMIES OF WESTERN FORESTS 81

involved. As the caterpillars feed within the buds, or within clusters
of needles, they are difficult to reach with stomach poisons. Out-
breaks usually cover thousands of acres of rough, mountainous
country, and it is rarely possible to apply poisons with any type
of ground machine. Airplane dusting has been used in eastern
Canada with fair success. Along roadways and in parks the bud-
worm can be controlled by the application of arsenical sprays with
the aid of power pumps just after the buds open in the spring.
Such control work has recently been done in the Shoshone National
Forest, Wyo., with fair results.

Figure 39.—A forest after defoliation by the spruce budworm.

The black-headed budworm (Peronea variana Fern.) is an im-
portant defoliator in balsam fir, hemlock, and spruce forests in the
northern part of the United States, Canada (3), and Alaska. In the
Northeast and in eastern Canada it has appeared in destructive
numbers only where mature balsam fir forms a high percentage of
the stand.

In the Pacific Northwest hemlock appears to be the preferred host,
although Douglas fir, balsam fir, spruce, and larch are also attacked,
Tn this region one or two outbreaks have been recorded in which
thousands of acres of western hemlock have been severely defoliated.
Fortunately, however, this has resulted in killing very little mer-
chantable timber. Frequently the black-headed budworm occurs 1
outbreaks with the hemlock looper and assists in the destruction
wrought by this insect.

136650°—38——6

—

82 MISC. PUBLICATION 273, U. 8. DEPT. OF AGRICULTURE

The small moths, that are gray or dappled with brown, black,
orange, and white, and have a wing expanse of three-fourths of an
inch, appear during August and September, mate, and lay their eggs
on the under side of the needles. The eggs remain unhatched during
the winter, but in the spring the small, pale caterpillars appear and
start feeding on the new foliage of opening buds. They work in
much the same way as the spruce budworm, boring into and feeding
on the opening buds and webbing the new needles together to form
a protective case within which they feed. As they develop they
become bright green, and the head turns black. If disturbed they
actively wiggle backwards and drop to the ground by silken threads.
They reach full growth by the last of July, at which time they are
a trifle more than a half-inch in length and may have brown heads.

Usually they confine their work to the new growth, but if they are
numerous the larger caterpillars will leave the nests and feed upon
the older needles, bringing about complete defoliation. Pupation
takes place within a web made among the dead needles and frass on
the twigs. Prior to emergence, the pupa, which is dark reddish
brown with a greenish tint, works partly out of the web so as to
allow the moth freedom to emerge. There is but one generation a
year.

A small amount of feeding by the black-headed budworm takes
place every year, but it is scarcely noticeable. When an attack is
heavy toward the end of July, the forest takes on a reddish-brown
appearance. This is due to the dying of the new foliage that is
partly eaten but remains attached to the twigs by the webs of the
caterpillars. Their presence can be confirmed by finding the small,
wiggly, green caterpillars, or the brown pupae, among the webs at
the tips of the branches. For some reason heavy defoliation by
this insect does not prove so disastrous to the trees as similar work
by other species, such as the hemlock looper. Even repeated heavy
defoliations of western hemlock for 2 or more years have not caused
any serious loss of timber.

The larvae of the black-headed budworm are parasitized by
numerous insects and are affected by a wilt disease. These agencies
become dominant and bring outbreaks under control within 2 or 3
years.

' The sugar pine tortrix (Tortrix lambertianae Busck) (fig. 40) is
at times very destructive to the new buds and pollen bodies of sugar
pine, killing as much as 90 percent of the new growth on the trees.
The caterpillars feed in colonies within a web on the terminal shoots
and transform to adults in July. The adults are speckled tan to
golden moths with a wing expanse of about seven-eighths of an inch.

The lodgepole pine needle tier or pine tube moth, Lula (Argy-
rotaenia) pinatubana Kearf., (16) (fig. 41) is found in the Rocky
Mountain region, where it works on ledgepole pine. Usually it is
not particularly destructive, but from 1921 to 1925, working in con-
junction with the lodgepole sawfly (Neodiprion burkei Midd),
it destroyed trees over a large area of immature lodgepole pine near
West Yellowstone, in Montana. Since the cessation of the sawfly
epidemie the needle tier is still present in many areas, but has ceased
to be destructive.

INSECT ENEMIES OF WESTERN FORESTS 83

The adult needle tier is a small brownish-gray moth with darker

patches and bands on the forewings and a wing expanse of about -

one-half inch. Eggs are laid during the latter” part of June and
early in July in groups of 2 to 30, with an average of about 10 per
cluster, on the concave side of lodgepole pine needles. These eggs
hatch in 7 to 10 days, and the young larvae crawl over the foliage
until needles satisfactory for their attack are found—usually those
of the current year’s growth. Each larva then enters a needle by

FicureE 40.—The sugai pine tortrix (Tortrix lambertianae) and its damage to sugar
pine terminals.

biting a circular hole near the tip and spends from 2 to 3 weeks in
feeding on the interior tissues. The inside of the mined_ needle
is lined with a papery, white, closely woven web to form a tube. At
an early period in the growth of the larva or when it becomes too
large for the mined needle, several other needles are drawn to it and
bound together so as to form a new and larger tube (fig. 41, B).
This tube is also lined with a papery white web and has an opening
at each end, that allows the insect to leave quickly when disturbed.
Often a caterpillar will abandon one tube and form a new one. Feed-
ing takes place within the tube, and as the caterpillar becomes larger
the tube is extended farther down the needles, often to the base.

84 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

During the latter part of August the mature caterpillar, which is
dark green and about one-half inch in length, drops to the ground on
a silken thread and, after crawling into the mat of old needles,
spins a loosely woven cocoon in which the winter is passed in the
pupal stage. The
adult emerges the
folowing May or
June, completing one
single annual gener-
ation. The work of
the lodgepole pine
needle tier is recog-
nized by the silk-
lined tubes, that may
consist of as many
as 16 needles webbed
together, and which,
as a result of the
feeding, turn brown
and clie.

A. related species,
Argyrotaeniacitrana
Fern., feeds on the
needles of Monterey
pine in California.

The spruce bud-
moth (Zeiraphera
ratzeburgiana Ratz.)
is an introduced pest
that has become
established in the
Pacific Northwest.
The small, lght-
brown moths, with
darker diagonal
markings, and a
wing expanse of
about one-half inch,
lay their eggs on
spruce needles. Each
young caterpillar
crawls into an open-
ing bud and feeds on
FicurE 41.—The lodgepole pine needle tier (Hulia pinatu- the Gen der new

eee eae B, a silk-lined needle tube; necdle S, webbing

them together to
form a shelter within which it feeds. Growth is completed late in the
summer, and the chrysalid is formed in the shelter at the tip of the
infested twig. The adults emerge late in the summer. There
appears to be one generation a year. The damage has been fre-
quently noted on young Sitka spruce trees along the coast of Oregon
and Washington. In many cases all of the new tips are killed and
the tree made to branch excessively. |

INSECT ENEMIES OF WESTERN FORESTS 85

There are a large number of other budmoths and leaf rollers that
infest the buds and young, tender leaves of various broadleaved
trees and shrubs. This damage is often of a serious nature in
orchards but seldom is of any importance in the forest. No attempt
can be made to discuss these interesting but relatively unimportant
species.

NEEDLE MINERS

Some leaf-eating insects have
the habit of feeding internally
on coniferous needles and thus
protecting themselves within a
thin, leafy covering. ‘These are
called needle miners. <A great
many of them cause only an in-
significant amount of damage,
but a few, such as the lodge-
pole needle miner, may defoli-
ate extensive areas and con-
tribute to the destruction of
the timber cover on entire wa-
tersheds, as has happened in
parts of the Yosemite National
Park. The needle miners be-
long mostly to one small genus
of moths.

Outbreaks of needle miners
are eventually brought under
control by the action of native
parasites and the influence of
climatic conditions. ,Direct con-
trol through the use of the ordi-
nary sprays or dusts offers
httle hope of being effective
since the insects work within
their protective covering and
would not be reached by these
poisons. Recent experiments
indicate that light, penetrating
oul sprays to which nicotine has
becteaddedmoticrepromiseof ©" “—Gymcric hives) © oon”
being effective.

The lodgepole needle miner (Recurvaria millert Busck) (66)
(fig. 42) is the best representative of this group in the West. As its
name implies, it mines the needles of lodgepole pine and is found
through the lodgepole pine forests of the Sierra Nevada in California.
It has defoliated extensive areas of lodgepole pine in the Yosemite
National Park and so weakened the trees that they readily succumbed
to the attacks of the mountain pine beetle. The adults are very small
white or grayish moths only about one-half inch long. The cater-
pillars are very small greenish worms with black heads. In the
Yosemite National Park this species has a 2-year life cycle, the moths
flying in alternate years,

86 MISC. PUBLICATION 278, U. S. DEPT. OF AGRICULTURE

Other very similar species of Recurvaria attack lodgepole pine in
Oregon and Montana. These differ from the foregoing in having
one generation annually. Extensive areas in the Deschutes National
Forest have recently been seriously defoliated.

Another species, Recurvaria moreonella Hein., attacks ponderosa
pine needles in southern Oregon on the Klamath Indian Reservation
and occasionally causes heavy loss of foliage.

The spruce needle miner (Yaniva albolineana Kearf.) bores into
and mines the needles of Engelmann spruce near the base, webbing
them together to form a mat of dead needles held to the twigs by
.the webs. Sometimes three or four larvae mine a single needle.
They do considerable damage at times in Colorado.

LEAF MINERS

The leaves of many broadleaved trees are attacked by the larvae of
many leaf-eating insects that bore within and feed internally on the
leaf tissue. The damage they do is usually insignificant, since these
trees are able to replace
their foliage each year.
Insects with the leaf-
mining habit belong in
the main to the order
of the moths and butter-
flies (Lepidoptera), but
a few beetles (Coleop-
tera), flies (Diptera),
and wasps (Hymenop-
tera) also have this habit.

The leaf blotch miners
hollow out irregular-
shaped mines or blotches
between the upper and
lower surfaces of leaves.
There are many species
that work on the leaves
of various western
broadleaved trees.

The madrona shield
bearer (Coptodisca arbu-
tiella Busck) mines the
leaves of madrona and
: arate cuts out elliptical holes
pee 43-——W Sao anion peter miner (Phylloc- when constructing the

pupal cases. Commonly
associated with it in leaves of madrofia is another leaf-mining
species, Marmara arbutiella Busck.

The poplar leaf blotch miner (Phyllonorycter tremuloidella
Braun) attacks the leaves of aspen and poplars and constructs ir-
regularly shaped mines between the upper and lower leaf surfaces.
It has been reported from California, Idaho, and British Columbia
and no doubt has a more extended range. When mature, the larvae
change to small black pupae within the mines and then emerge as

INSECT ENEMIES OF WESTERN FORESTS Si

small, drab-colored moths. During heavy infestations practically all
of the leaves on the lower portions of the trees are attacked, but
infestation seldom extends above 50 feet. The damage results in a
premature shedding of the foliage. Other species of Phyllonorycter
include P. salicifoliella Chamb., which works in the under side of the
leaves of willow, poplar, and cottonwood; P. apicinigrella Braun,
which works in the under side of willow leaves; P. felinella Hein.,
which works in the under side of sycamore leaves in California; P.
incanella Wlism., which works in both sides of alder leaves; and P.
arbutusella Braun, which works in the leaves of madronia.

Cameraria agrifoliella Braun works in the upper surface of leaves
of coast live oak. C. alnicolella Wlsm. works in the upper surface of
alder leaves. C. wmbellulariae W\sm. makes blister blotches on leaves
of California laurel.

The aspen leaf miner Phyllocnistis populiella Chamb. (fig. 43)
leaves a labyrinthian trail of frass as characteristic of its work in the
under side of aspen and poplar leaves.

Common leaf miners in live oak include Bucculatrix albertiella
Busck and Abebaea subsylvella W\sm.

SAW FLIES

Sawflies form another important group of leaf-eating insects that
in Many cases cause extensive defoliation and destruction of timber.
In the Northern States and in Canada, such species as the larch saw-
fly, the European spruce sawfly, and the jack pine sawfly have been
responsible for the death of as much as 85 percent of the stand over
thousands of acres. In the West the native sawflies occasionally de-
velop widespread outbreaks and may cause heavy defoliation over
hmited areas, but the total timber destruction so far has not been

reat.

5 The sawflies (fig. 44) belong to the order of wasps (Hymenoptera)
but in appearance are usually more like flies than wasps. They have
thick, cylindrical bodies with four membranous wings, the hind pair
somewhat smaller than the forewings. The head, thorax, and base
of the abdomen are nearly equal in width. They range in size and
color from small grayish insects not over one-fourth inch in length
to large, showy species (Cimbew) over 1 inch long. They are called
sawflies because of a sawlike attachment which the female carries
at the tip of the abdomen and uses to slit open leaves or stems for
the reception of her eggs. Usually only one egg is deposited in each
slit, but as many as 14 or more punctures may be made in a single
pine needle.

The larvae resemble hairless caterpillars except that most of them
have from six to eight pairs of abdominal legs, or larvapods, on the
abdominal segments, in addition to the usual three pairs of true legs
on the thoracic segments. Because of their resemblance to cater-
pillars the larvae are sometimes called “false caterpillars”; and since
many are wormlike and often slimy, they are called “slugs” or
“worms.” Most of them are typical external leaf chewers, but a few .
are leaf miners and even gall makers.

One of the most characteristic features distinguishing sawflies are
the cylindrical, papery, capsulelike cocoons which the larvae fre-

S8 MISC. PUBLICATION 2738, U. S. DEPT. OF AGRICULTURE

<a a
of a pine sawfly, natural size; C, grubs and pupa, X 3.5; D, cocoons, X 1.5
of the lodgepole sawfly (Neodiprion burkei), xX 4.

_Ficure 44.—Pine sawflies: A, Eggs on pine needles, B, larvae, adults, and cocoons

Ey adult

INSECT ENEMIES OF WESTERN FORESTS 89

quently construct for their pupation. These are often formed on the
debris of the forest floor, but may be attached to the needles or
branches of the tree.

Sawflies, for the most part, complete their life cycle with one gen-
eration a year. With many species the winter is passed in the pre-
pupal stage within the cocoon. In the spring the transformation to
adult takes place. The adults emerge, mate, and deposit eggs in the
new needles, leaves, or shoots. In some species part of the brood
does not emerge from the cocoons until the second spring. The
eggs hatch in about a week, and feeding starts on the foliage. Feed-
ing 1s completed by the middle of summer, and the slugs drop to the
ground to prepare for transformation, usually spinning the tough
papery cocoons. Other species pass the winter in the eggs which
hatch early in the spring, the larvae completing their feeding and
transformation by fall, at which time flight and egg laying again
take place.

The native sawflies are attacked by numerous parasites that play
an important part in holding them in check, but weather conditions
seem to be even more important in determining the number of saw-
flies in different seasons.

Direct control can be effected where it is practical to apply arsen-
ical poisons, such as on shade and ornamental trees, or to forest areas
by means of airplanes. Usually, however, the cost of control is not
justified, because of expense, the difficulty of application of dusts,
and the fact that most outbreaks are rather quickly suppressed by
natural control agencies.

In the forests of western North America there are numerous native
species of sawflies, which, although usually inconspicuous in num-
bers, may periodically become prevalent enough to cause noticeable
damage. So far, although extensive defoliations have occurred, the
actual destruction of timber has been small, and the outbreaks have
quickly subsided.

SAWFLIES ON CONIFERS

A number of species of sawflies belonging to several genera attack
the needles of pines and other conifers. The adults are colored vari-
ously, often black or brown, and with yellowish appendages. ‘They
are usually from one-fourth to one-half inch in length. The males
frequently have large, feathery antennae while those of the females
are threadlike. Eggs are laid singly, in slits made in the needles.

The young hairless larvae first feed in clusters on the nearest
needles, then as they grow they scatter out over the fohage and feed
singly. Upon reaching full growth, about the first of September,
they are from one-half to 1 inch in length, usually greenish, with
black or brown heads, and have eight pairs of prolegs. Upon com-
pleting their feeding they usually drop to the ground and form
brown, papery cocoons in the forest debris, but some may form co-
coons on the needles or in crevices of the bark, while still others do
not construct cocoons. The winter is usually passed in the prepupal,
larval, or egg stage, and the new adults emerge the following spring.
These sawflies are easily controlled where trees can be sprayed with
lead arsenate or other stomach poisons.

Se 6 OEE ar O MMi ad, a . - ~~

90 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

The lodgepole sawfly (WMeodiprion burkei Midd.) (fig. 45), in
the adult stage, is about one-third of an inch long. The males are
black and the females brownish. The hairless, wrinkled bodies of
the larvae are greenish or grayish, with lighter lateral and dorsal
stripes, brown heads, and black eyes, and are about 1 inch long when
mature. ‘This species developed a severe outbreak in 1921 over a
large area of lodgepole pine at West Yellowstone, Mont. In the
next few years a tremendous acreage of lodgepole pine was defoliated
and a large percentage of the trees died. This outbreak was further
complicated by a contemporary outbreak of the lodgepole pine needle
tier (see p. 82). Control of both species along highways was effected
by spraying with lead arsenate.

FIGURE 45.—Lodgepole sawfly (Neodiprion burkei): A, Egg pockets in needle and
very young caterpillars feeding, X 1.5; B, larvae at_work, natural size; C, hibernating
prepupa, X 5; D, pupa, X 5; H, adult female, X 7; F, adult male, xX 7

Other species of the genus Veodiprion which feed on the needles
of western pines include the following:

Species of Neodiprion Host and distribution
INE falicen s ‘Cress. St seat eee Ponderosa pine. California.
Ne ouilette: MEGill2 = 22s eas Ponderosa pine. Colorado.
Needwardsi Norton: 2. 22s aes Sugar pine, western white pine. California.
No Goniwert. Midd=. 2 = ee Pinon and _ singleleaf pine. New Mexico

and California.

INSECT ENEMIES OF WESTERN FORESTS QO]

The Monterey pine sawfly (/tycorsia sp.) attacks only the Monterey
pine in its native habitat, near Pacific Grove, Calif. The larvae are so
prevalent at times as to completely defoliate the trees, either killing
or seriously weakening large numbers of them. The larvae are dark
green or brownish, with black heads. A characteristic of their work
is that the needles are sawed off or chewed into a mass, and these
broken needles and brownish excrement pellets are webbed together
with silken threads. |

The hemlock sawfly (Weodiprion tsugae Midd.) occasionally be-
comes epidemic and defoliates extensive areas of western hemlock
in Oregon and northward into Alaska. The adults are small, about
one-fourth inch in length. The males are dark brown to black, and
the females are larger and green to yellowish brown. The larvae
are green and about 1 inch in length when full grown. The papery
cocoons are attached to the needles and to debris on the ground.

In the northwestern part of the United States there are two species
of sawflies that feed on the foliage of western larch. So far they
have not caused damage of any great economic importance. In 1921
an outbreak of these two insects occurred throughout the larch stands
of northern Idaho and western Montana. This is the first and last
record of their appearance, and although they occurred in countless
numbers in 1921, it was practically impossible to find a single larva
in 1922. This isa marked example of how rapidly an outbreak can
disappear.

The larvae did their heaviest feeding from the middle of July to
the last of August, and either devoured the foliage or killed it by
chewing on the fleshy portion of the needles anywhere between the
tip and base. ‘The larvae leave the trees when they are mature
and spin small silken cocoons under the duff, in which they pupate.
Small pebbles and grains of sand adhere to these cocoons, giving
them the appearance of small lumps of dirt. The winter is passed
in the cocoon, and the new adults emerge the following spring about
the time the larch foliage appears.

Adults of the two-lined larch sawfly (Platycampus laricis Roh. and
Midd.) are small, black, wasplike insects, a little less than one-
fourth inch in length. The folded wings have a blue-green metallic
sheen. The larvae are rather slender, about three-eighths inch in
length when full grown, with eight pairs of prolegs on the abdomen
and are brownish-green with two narrow dark-green stripes along
the sides, dark-brown heads, and black, shiny eyes. The western
larch sawfly (Platycampus laricivorus Roh. and Midd.) closely re-
sembles the foregoing in the adult stage, but the larvae have a single
green line down the center of the back.

The larch sawfly (Nematus (Lygaeonematus) erichsonii Hartig)
which is a native of Europe and was first found in New England
about 1880, has spread westward through the Lake States and Canada
into northern British Columbia. Its progress has been disastrous
imasmuch as it kills trees rapidly, and has left vast areas of dead
and dying larch in its wake. Only recently it has been reported at-
tacking western larch in southern British Columbia and in the north-
western part of the United States.

The cypress sawfly (Susana cupressi Roh. and Midd.) feeds on
the foliage of Monterey cypress in California.

eS ee ee

92 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

SAWFLIES ON BROADLEAVED TREES

There are a large number of sawflies that feed on the leaves of
broadleaved trees. Some of these produce galls, and many others
feed externally on the leaves and cause a varying amount of damage. |
Only a few will be mentioned here.

The elm sawfly (Cimbex americana Leach) is commonly found in
the Middle West as well as in the Eastern States, but ranges west
into Colorado and British Columbia. These sawflies are active feeders
on the leaves of willow and elm, and also attack poplar, alder, maple,
and other trees. The adults are large, steel blue to black, broad-
waisted sawflies about three-fourths of an inch in length with three
or four yellow, oval spots on each side of the body, short knobbed
antennae, and smoky wings. They girdle the bark on twigs and kill
many of them, especially in the tops of trees. The larvae are naked,
wrinkled, and pale yellowish with a median black stripe down the
back, and have eight pairs of prolegs. They usually he coiled and are
from 1 to 2 inches long when full grown. The adults fiy in May
and insert their oval eggs in the leaves. The larvae reach full
growth in July or August, and overwinter 1n cocoons in the debris on
the ground or just below the surface. Pupation occurs in the spring,
only a few days before emergence and flight.

At least three other sawflies attack willow in the West. Cimbex
pacifica Cress., which has similar habits to the preceding, is found
in Oregon and Washington, where the larvae feed on willow leaves.
The adults are large, about 1 inch in length, and are brownish red.
It is known as the Pacific sawfly. Cimbea rubida Cress. is found
in the sierras of California and Nevada and along the coast, feed- |
ing on various species of willow. The adults are about three-fourths |
of an inch in length, reddish brown, with black stripes on the abdo-
men and wings of metallic blue or smoky brown. Another species,
Lrichiosoma lanuginosa Norton, also feeds on willow in the Cali-
fornia and Nevada sierras. The adults, which are velvety or shiny
bluish black, with dense pale-yellow hairs on head, thorax, and base
of abdomen, look very much lke large bumblebees. They are about
three-eighths of an inch in length and have short knobbed antennae
and smoky brown wings.

The cottonwood sawfly (Pteronidea sp.) although common, has
not been identified specifically as yet. The larvae, which are slender,
about one-half inch in length, green, with brown head and black
eyes, and six pairs of prolegs on the abdomen, feed on the leaves
of black cottonwood in northern Idaho. During the early feeding
period the larvae skeletonize the leaves, eating only the fleshy part,
but in the later stages of larval development the entire leaf is con-
sumed. When mature the larvae construct small, parchmentlike
cocoons that are attached to the leaves. The complete seasonal his-
tory of this insect has not been determined, but it appears to have
one generation a year.

LEAF BEETLES

There are a number of beetles that are leaf eaters in the larval
or adult stage or in both. None of these have been responsible for
any noticeable injury to western coniferous forest trees, but the
skeletonizing and defoliation of broadleaved trees by beetles is a

INSECT ENEMIES OF WESTERN FORESTS 93

common occurrence. Most of these beetles belong to the family Chry-
somelidae. The adults of this large family of destructive beetles are
small, rather short, somewhat oval in outline, and of variegated
colors, some with bright metallic green or blue and others dull brown
or black. The larvae are rather stout, humpbacked grubs. Some
are armed with spines, while others partially cover themselves with
excrement. In western forests the alder flea beetle is probably the
most common repre-
sentative of this
family.

No control, appears
practical or war-
ranted, under forest
conditions, but on
park and shade trees
leaf beetles can be
controlled by spray-
ing with powdered
acid lead arsenate at
the rate of 4 pounds
to 100 gallons of
water. The spray
should be applied as
soon as the leaves
unfold in the spring.

The alder flea bee-
tle (A ltica bimar-
ginata Say) (fig. 46)
is a native species
found throughout
the Pacific Coast
States, where it feeds
on and _ skeletonizes
the fohage of alder,
poplar, and willow,
both as larvae and as
adults. The adults
are small, dark shiny ieee
blue, and about one- ie
fourth inch long. Ficurw 46—Alder flea beetle (Altica bimarginata) : A, Adult
vitomminamie larvae! Net crciecénizel iat 2? PUPA SS
are a trifle over one-
fourth inch in length, dull brown to black, with shining black head
and thorax and three pairs of short legs. The adults hibernate dur-
ing the winter in debris beneath the trees and other sheltered places,
appearing early in the spring to resume feeding. Clusters of yellow
egos are deposited sometime after the spring appearance of the
adults. The larvae, which appear a few days later, reach maturity in
August, and pupation occurs on the ground in the duff. New adults
appear in a week or 10 days and feed voraciously on the foliage until
the close of the season, when they hibernate for the winter, to appear
the following spring, completing the cycle of one generation a year.

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The elm leaf beetle (Galerucella xanthomelaena Schrank) (G4.
luteola Mull.) is an introduced pest which has proved to be very
destructive to elms. Since 1834 it has gradually extended its range
to include nearly all parts of the country where elms are grown.
Trees are weakened and subject to attack by various boring insects
or are killed outright by repeated defoliations. The adults are one-
fourth inch in length and dull olive green with a black stripe on each
elytron. The larvae are blackish yellow and about one-half inch long
when full grown. Park and shade trees can be protected by spraying
with arsenicals soon
after the new leaves
open in the spring.

The western wil-
low leaf beetle (Ga-
lerucelladecoraSay )
1s a dull, yellow-
brown to black na-
tive species that feeds
on the leaves of wil-
low and poplar
throughout the
country.

The cottonwood
leaf beetle (Lina
scripta F.) (fig. 47)
is found throughout
the country, feeding
on the leaves of wil-
low and poplar. In
New York it is very
destructive to wil-
lows raised for bas-
ketwork, and often
heavily defolhates
these trees in the
West. The adults
are yellowish marked

Piet 7 Chee a lenpipectie: (id ne with black spots and
IGURE 47.—Cottonwood leaf beetle (Lina scripta): A, Fe- ‘
male beetle, X 5; B; male bectle. < G:C, larval’ B:. are ADOUL One Lourtn

ee pune a . 5; H, eggs on cottonwood leaf; F, skeletonized jneh in length. : They
appear early in the
spring and feed on the tender shoots. The eggs are yellowish or
reddish and are deposited in clusters on the under surface of the
leaves, and it is here that the black grubs feed as soon as hatched.
The period of growth to the mature larval stage is about 15 days in
hot weather. Five generations a year are reported in the West. -
L. tremulae F. feeds on aspen and poplars in the Pacific Northwest.
The willow leaf beetle (Lina interrupta F.) is similar to the above,
but smaller. It feeds on willow and ranges from California to
Alaska. Another species, Z. californica Rogers, is black to bluish
“green and feeds on willow in California.
The spotted willow leaf beetle (Lina lapponica L.) is sometimes
as prevalent and just as injurious to willows and poplars in the

INSECT ENEMIES OF WESTERN FORESTS 95

Northwest as the cottonwood leaf beetle, which it closely resembles
in appearance and habits. The adults are reddish, one-fourth inch
in length, and spotted with black.

MINERS IN THE INNER BARK AND PHLOEM —

Many different species and families of insects are represented
among those that select the cambium region of the main trunk of
trees as a suitable place to feed. All of these are chewing insects
that bore under the bark and feed in the soft layers of bark and
wood. As feeding progresses the channels may penetrate deeply
into the sapwood or be extended into the outer bark.

The insects of this habit that are capable of attacking living,
healthy trees are among the most destructive species with which the
forester must deal. By far the greatest number of the cambium
feeders, however, are capable of attacking only unhealthy, weakened,
dying, or felled trees and cannot resist the copious flow of sap or
resin which in the normal tree serves as a defense against attacking
bark borers. At times, when a tree’s resistance is low, even these
normally secondary species may kill trees, if they attack in sufficient
numbers.

It is easy to recognize the work of bark-feeding insects. Usually
a close inspection of the trunk of an infested tree will reveal boring
dust in the crevices of the bark or pitch exuding from small holes
in the bark. These may or may not indicate bark-mining insects.
Positive evidence of infestation can be obtained only by removing a
small chip of bark and determining whether the phloem is fresh and
white or discolored with the mines of some boring insects. If such
mines are found, a larger piece of bark can be removed, and the
species responsible for the damage usually can be identified by the
character of its work.

A few species of inner-bark miners, such as the pitch moths, may
work in the phloem from the edge of wounds without threatening
the life of the tree, and no attempt need be made to control such
species under forest conditions. Nor is. it necessary to attempt
any control of the vast number of inner-bark-feeding insects that
confine their attack to weakened, sickly, or felled trees. Only those
species that are capable of attacking and killing living trees need
cause any concern, and fortunately the number of ‘such species 1s very
limited. It is not difficult for the forester to learn to recognize the
comparatively few phloem-mining insects that are aggressive killers
of the trees in his region. Such species are discussed in detail in the
following pages.

KEY TO THE DIAGNOSIS OF INSECT INJURY TO THE INNER BARK

A. Entire tree or a large part sickly, dying, or dead; foliage fading,
turning yellow or red. Inner bark of main trunk and sometimes
roots attacked and killed.
1. Outside of bark showing boring dust collected in crevices, or
small pitch tubes. Small egg tunnels under bark usually
of uniform width, from which extend diverging tunnels
usually packed with fine borings. The egg tunnels are
made by small beetles while the diverging mines are made
by small, white, curled, legless larvae______ bark beetles, page 96.

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2. Bark showing no outward sign of insect attack. Tunnels
under bark and sometimes entering wood; these increase
in size with the growth of the white, often legless grubs
which make them.
a. Mines flattened, oval in cross section, usually packed
with arc-like layers of boring dust made by
slender grubs shaped like horseshoe nails; first
thoracic segment greatly enlarged and flattened,
with a horny plate on both top and _ bottom
flatheaded borers, page 182.
b. Mines broadly oval in cross section, made by elongate
grubs which are thick in front with tapering
bodies, thoracic segments enlarged, with horny
plate on top only_______- roundheaded borers, page 154.
c. Mines round in cross section ending in pupal cells
partly in the wood, often lined with shredded wood
fibers. Usually at base, root collar, or roots of
weakened trees. Sometimes in terminals and
GW Sele eae eet anes A pero teetts bark weevils, page 138.
B. Tree apparently healthy or in some cases top-killed. Large masses
of pitch exuding from wounds on trunk or with the bark, on a
dying top, appearing pitchy and dry, and separating from the
wood as though scorched. Slender caterpillars with three pairs
of legs found working in the pitech_______________ pitch moths, page 139.

BARK BEETLES

The common term “bark beetle” (79) is applied to a group of
small beetles belonging to the family Scolytidae. They are the most
destructive group of insects to be found associated with western
coniferous forests. Recent estimates place the annual loss of timber
in the Western States as a result of their activities at 2 billion board
feet. The bulk of this destruction is caused by three species of
Dendroctonus, the western pine beetle, the mountain pine beetle,
and the Black Hills beetle. :

The bark-beetle adults are small, cylindrical insects, ranging in
size from the tiny Crypturgus, about one-twentieth of an inch in
length, to the larger species of the genus Dendroctonus, that attain a
length of approximately three-eighths of an inch. Most species are
unicolored, dark brown, reddish brown, or black, and are either
shining or dull, though a few species have variegated markings.
The head, which is more or less hidden by the thorax, has chewing
mouth parts, with well developed mandibles.

The adults of cambium-mining bark beetles have the very dis-
tinctive habit of boring through the bark and making a tunnel
between bark and wood in which to lay their eggs. The complete
work or engraving of the bark beetles is therefore characterized by
having two types of tunnels—egg galleries, made by parent adults,
and larval mines, formed by the growing larvae. These tunnels
form a particular pattern on the inner surface of the bark, which is
distinctive for each species and usually very similar for each genus.

In starting an attack the male or female beetle bores an entrance
tunnel through the bark, usually at a slightly upward angle. An
egg tunnel is then constructed along the surface of the wood, cutting
through the inner bark and often slightly or deeply scoring the
sapwood. As the work progresses, fine boring dust and excrement
are extruded through the entrance hole and collect in the bark
crevices. In some cases pitch and sap exude from the entrance hole

INSECT ENEMIES OF WESTERN FORESTS O7

and harden on the bark in various forms of pitch or resin tubes.
Some species construct ventilation tunnels at intervals along the ege
galleries. These are perpendicular to the egg galleries and extend
through the bark to the surface or may end before the surface is
reached. Boring dust is pushed out of those that are open at the
surface of the bark, and they all are probably used as turning
niches as well as for ventilation of egg tunnels. Later, as the mine
progresses, these are sometimes plugged with boring dust.

The eggs, which are very small, are oval, round, or slightly elon-
gate, and clear or chalky white. They are deposited in small cup-
shaped cavities along the sides of the egg galleries. Usually a single
ege@ is placed in each cavity or egg niche, which is closed with a plug
of “boring dust in such a way that the smooth cylindrical egg gallery
is but little altered. Some species cut larger cavities or egg pockets
and deposit from two to eight eggs in each. Others cut an elon-

gated groove on one or both ‘sides of the ege gallery and deposit the
egos in layers or rows.

“The larvae or grubs are thick-bodied, always legless, cylindrical
and curved, white or cream colored, with a distinct head and promi-
nent dark-colored mandibles. At first the larvae and their mines are
very small, but both increase in size as feeding progresses. The
larval mines start away from the egg gallery more or less at right
angles and may continue nearly straight or turn and run parallel to
the egg tunnel. They are always packed with excrement and boring
dust.

Transformation to the pupal stage takes place at the end of the
larval mine in a specially constructed pupal cell. The pupae are
soft, white, and unprotected. The antennae, mandibles, legs, and
wing pads are clearly visible, and hairs and spines are often ‘present
on the various regions of the body. Gradually the pupae darken,
turning light yellow and then brown, as the adult form is reached.

The adults, after a short hardening period, emerge and fly t
attack new host trees, or congregate in cavities under the bark of the
old host tree, or drop to the ground to hibernate. Some adults do
a certain amount of feeding under the bark before emerging, and
food tunnels made in this way are quite distinct in character from
the regular egg galleries. Others upon emerging feed upon twigs
or buds of other trees before again attacking the bark of a new
host.

Normal or endemic infestations of bark beetles are present in
practicaliy all mature forests (S/), causing an annual ioss of a frac-
tion of 1 percent of the timber on the area. Under conditions favor-
able to the insects, serious epidemics develop from these normal
infestations in a very few years. Such outbreaks may be of short
duration, or they may continue for many years, destroying large
volumes of merchantable timber over extensive acreages.

If bark-beetle attacks are to be successful, the attacking insects
must be present in suificient numbers to overcome the resistance of
the tree. Dead and dying trees offer little resistance to attack and
for this reason they are usually chosen by the secondary species that
are not capable of coping with a vigorous pitch flow. Light attacks
by primary species on living trees often fail because the flow of
pitch is so copious that the attacking beetles are overcome or driven

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from their galleries. The oleoresins are known to be repellent and
toxic to the beetles and so aid in resisting light attacks.

In the following discussion the bark beetles attacking western
forest trees will be treated under their principal host trees.

PINE BARK BEETLES

No group of commercially valuable trees in western forests
has more insect enemies than the pines, and of these, bark beetles
are the most numerous and destructive. The most aggressive bark
beetles attacking western pines are the so-called “pine beetles” which
belong to the genus Dendroctonus. Several species in this group are

capable of attacking and killing normal healthy trees. The damage.

they do in western pine forests runs into millions of dollars annually.

The next most important group comprises the pine engraver
beetles belonging to Ips, Pityogenes, and related genera. ‘These
beetles usually work under thinner bark and make very striking and
distinctive forked or star-shaped gallery patterns. While they
normally breed in weakened, dying, or felled trees, or in broken
branches and slash, and are to that extent beneficial in hastening the
disintegration of forest debris, they occasionally develop in sufficient
numbers to become primary enemies of young trees and of the tops
of older ones.

There is also a third group of bark beetles comprising a large
number of species that are secondary in their attack and are seldom
responsible for the death of any trees. Many of these are found
feeding under the dying bark of pines that are being killed by other
bark beetles, fire, or other causes and sometimes are confused with
primary species. Space will not be taken for a description of all the
bark beetles that may be encountered, for it is usually sufficient for
all practical purposes if the forester learns to recognize those species
of chief importance.

PINE BEETLES OR DENDROCTONUS BEETLES

The pine beetles which are members of the genus Dendroctonus
(meaning tree killers) (46) make up by far the most destructive
group of bark beetles attacking pine trees in North America. All
species breed under the thick bark of the trunk of living or dying
trees or in fresh stumps or logs of various pines. Some species prefer
felled, weak, or dying pines, whereas others apparently prefer normal,
healthy pines for their attack.

The adults are stout, cylindrical, dark reddish-brown to black
bark beetles ranging from one-eighth inch to about three-eighths
inch in length. The eggs, larvae, and pupae are similar to those
of other bark beetles. These beetles are monogamous in habit and
each pair constructs a single egg gallery, which, starting from the
outside, penetrates to the cambium and is extended between the bark
and wood. Egg galleries differ in that some wind in a tortuous
manner, crossing and recrossing the galleries made by other pairs
of beetles, while others are straight and parallel to the grain of the
wood. In all cases Dendroctonus egg galleries are always packed
with boring dust, except for an inch or two at the end where the
beetles are working. This will distinguish the work of the Dendroc-
tonus beetles from that of other groups of bark beetles.

——

INSECT ENEMIES OF WESTERN FORESTS 99

Trees attacked by Dendroctonus beetles can first be distinguished
by reddish boring dust caught in bark flakes or crevices and around
the base of the tree, or by pitch tubes that form on the bark at the
mouth of the entrance tunnels, but in the case of heavily attacked
or decadent trees pitch tubes are often either missing or are so small
that they can be seen only from a short distance. Later, discoloration
of the foliage furnishes a more noticeable evidence of attack. It is
difficult, however, accurately to correlate the degree of discoloration
with the status of brood development, as this varies with different
tree species, regions, and seasons. The most conclusive evidences of
attack are the egg and larval galleries on the inner surface of the
bark. These form a pattern which is so characteristic for the work
of each species that, when considered with locality and host. tree, the
identification of the species responsible for the attack is relatively
simple.

The western pine beetle (Dendroctonus brevicomis Lec.) (20) is
the most important insect enemy of ponderosa and Coulter pine
within the range of these trees from Baja California, north into
Oregon, Washington, Idaho, Montana, and western Canada. Other
pines may be attacked under exceptional conditions. Normally it
breeds in a few overmature trees, in windfalls, unhealthy trees, or
in trees weakened by drought, stand stagnation, or fires. Under
epidemic conditions it becomes aggressive and kills apparently vig-
orous trees of all age classes having bark sufficiently thick to protect
it in its development. Trees under 6 inches in diameter are seldom
attacked by this beetle nor does it breed in hmbs. The heaviest losses
of mature merchantable ponderosa pine have resulted from outbreaks
of this insect in California, Oregon, and Washington. It is less
important in the more northern limits of its range. Losses as high
as 50 percent of the timber in 5 years have been recorded, and many
large blocks of pine timber have been commercially ruined by its
depredations (fig. 48).

The adult beetles are about the smallest of the western species of
Dendroctonus and measure from one-eighth to about one-fifth of an
inch in length. The larvae found in the outer bark are white, curved,
and about the size of a grain of rice. Their work is distinguished
from that of other bark beetles within the same range by the winding
egg galleries which cross and recross each other, forming a network
of irregular markings on the inner surface of the bark and on the
surface of the sapwood (fig. 49). The larvae feed in the inner bark,
working away from the egg gallery for about half an inch and then
turn into the outer bark, where their development is completed.
Flight and attacks start late in spring or early in the summer and
continue until stopped by cold weather. There are from one to two
generations annually in the northern part of the range and from
two and one-half to four generations in the southern portion, where
its activity continues almost without interruption throughout the
year.

Woodpeckers, clerid beetles, and ostomatid beetles are important
natural enemies of this insect, though its abundance is more often
determined by climatic influences and the resistance of the host tree.
Prolonged winter temperatures of —20° F. and lower have been
found to cause heavy brood mortality. Rapid, vigorous tree growth
increases host resistance and discourages epidemics.

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100 MISC. PUBLICATION 273, U. 8. DEPT. OF AGRICULTURE

Direct control is recommended, particularly during developing epi-
demic conditions. The control measures consist in felling the infested
trees; peeling and burning the bark late in the fall, or in winter or
early spring; or peeling and spreading the bark for destruction of

Figure 48.—Work of the western pine beetle (Dendroctonus brevicomis): A, Egg galler-
ies on inner bark (half size) ; B, an infested tree trunk with bark removed (drawing
by DeYoung) ; C, 1 year’s loss in a ponderosa pine stand in California.

the broods by solar heat during the summer months. Control work
has been successful in reducing infestations during critical periods,
but cannot be relied on to eliminate them, and must be repeated until
natural control factors become operative.

The southwestern pine beetle (Dentroctonus barberi Hopk.) attacks
ponderosa pines in southern Colorado, southern Utah, Arizona, and
New Mexico. A preference is shown for trees over 6 inches in diam-

INSECT ENEMIES OF WESTERN FORESTS 101

eter and for those that, owing to drought or other causes, are in
a weakened condition. It is most frequently found attacking mature,
slow-growing trees on the lower fringe of pine growth and trees

FicurE 49.—Typical winding egg galleries of western pine beetle marking the surface
of the wood.

exposed on rocky ridges and dry southern slopes. This insect and the

pattern of its galleries can scarcely be distinguished from those of

the western pine beetle, but as methods of control are also the same,

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more detailed descriptions are unnecessary. Since this beetle is less
ageressive than the western pine beetle, however, control measures
are seldom required.

The roundheaded pine beetle (Dendroctonus convexifrons Hopk.)
attacks ponderosa pine throughout the same range as the south-
western pine beetle and often in company with it. This species
usually enters the lower portion of trees previously infested by other
bark beetles, but is sometimes primary in its attack upon decadent
or weakened trees. The adults are about one-fourth inch in length
and are a dark, shiny brown or black. The egg galleries are mostly
vertical, long, shghtly to markedly sinuous. The larval mines are
usually in the cambium; pupation may take place either in the
inner bark or concealed in the outer corky bark. Normally there
is but one generation a year, and since the emergence is extended
throughout most of the season there are never any great numbers
of beetles attacking at any one time. The species is usually second-
ary and relatively unimportant.

The Arizona pine beetle (Vendroctonus arizonicus Hopk.) attacks
and kills ponderosa pine and Arizona pine in central Arizona and
probably other parts of the Southwest. Its appearance and habits
are very similar to those of the southwestern pine beetle, and the
methods of control are the same.

The Colorado pine beetle (Dendroctonus approximatus Dieta)
attacks ponderosa, limber, Arizona, Chihuahua, and probably other
pines in its range from northern Colorado and southern Utah south
through Arizona and New Mexico. The dark-brown, elongate adults
are from one-eighth to about one-fifth inch in length. They exca-
vate a network of long, anastomosing, longitudinal, diagonal, and
sometimes transverse galleries between the bark and wood of dying,
felled, or occasionally healthy trees. The brood gaileries are dis-
tinguished from those of most other species by the fact that the eggs
are deposited in large niches on the side of the gallery farthest
from the wood, rather than on. the other sides of the gallery. Its
work is therefore characterized by the absence of exposed larval
mines on the inner surface of the bark. There is only one genera-
tion annually, and as a consequence it is not an aggressive species or
of economic importance.

The mountain pine beetle (Dendroctonus monticolae Hopk.) (30)
is very destructive to forest trees in the high mountains of Cali-
fornia, Oregon, Washington, western Nevada, Idaho, western Mon-
tana, northwestern Wyoming, and British Columbia. In many -
places it has all but wiped out thousands of acres of lodgepole and
western white pine (fig. 50), taken a heavy toll of valuable sugar
pine, and attacked and killed ponderosa pines, whitebark pines, and
other pines, mountain hemlock, and Engelmann spruce. Trees from
4 or 5 inches in diameter up to those of the largest size may be
attacked. Attacks are usually heaviest along the main trunk of a
tree from within a few feet of the ground up to the middle branches
but may extend from the root collar very nearly to the top and
into the larger limbs. During endemic infestations there is a tend-
ency for the beetles to select the weaker, less vigorous trees for
attack, but no such selection is apparent during epidemic conditions.
Infested trees are recognized first by pitch tubes on the trunks of

INSECT ENEMIES OF WESTERN FORESTS 1038

trees and red boring dust in crevices and on the ground at the roots;
later, by discoloration of the foliage, as 1t changes from normal
green to hight greenish yellow and then to red.

The adults are rather stout, black, cylindrical beetles from one-
eighth to one-fifth inch in length. They excavate very long, per-
pendicular egg galleries (figs. 51 and 52) through the inner living
bark, engraving both bark and wood. The ealleries may be nearly
straight or slightly sinuous, and sometimes, particularly in sugar
pine, ~ decidedly winding, and at the bottom of these galleries there
is a short crook, or bend, 1 or 2 inches in length. The } perpendicular
portion of the gallery ranges in length from 12 to 36 inches and
nearly always follows the grain of the wood.

FIGURE 50.—Lodgepole pine stand killed by the mountain pine beetle.

Kggs are deposited singly in cells or egg niches on alternate sides
during the construction of the egg gallery. These hatch in a few
days, and the small white larvae excavate short feeding tunnels at
right angles to the egg gallery. These feeding tunnels vary in
length and are exposed on the inner bark surface. When full grown,
the larvae construct small pupal cells at the ends of the larval mines
and in these transform to pupae and then to new adults. These
pupal cells are usually exposed when the bark is removed, but in
thick-bark trees they may be concealed in the inner bark. The new
adults may bore away the intervening bark between pupal cells and
congregate beneath the bark, prior to emergence, or individual emer-
gence holes may be constructed directly from the pupal cells. Two
or more insects often use the same emergence hole, and the emerging
beetles often take advantage of cracks in the bark or holes resulting
from woodpecker work.

The winter is passed in all stages of development except that of
the pupa. These overwintering broods emerge in three well-defined

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groups, (1) in June, (2) late in July and early in August, and (3)
in September. New attacks are made immediately after emergence,
and the resultant broods develop to new adults, mature larvae, or

small larvae before the cold winter weather again stops develop-

FIGURE 51.—Stages and typical work of the mountain pine beetle (Dendroctionus monti-
colae). Adults, larvae, and pupae, at lower right. Natural size.

ment. Normally there is only one generation a year, but owing to
the uneven development there is considerable overlapping of the
various broods, so insects in all stages may be found at any one time
during the summer. Late fall, winter, or early spring is therefore
the best time to carry on control work.

INSECT ENEMIES OF WESTERN FORESTS 105

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FicurE 52.—Long vertical egg galleries are characteristic of mountain pine beetle work.

A clerid beetle (noc sclerus) , a fly (Medeterus), and a parasitic
wasp (Coeloides) are the most active insect enemies. Woodpeckers
also prey upon the species, and climatic conditions often are impor-
tant as natural control agencies.

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106 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

Direct control methods consist in felling the infested trees and
either peeling the bark from the trunk or burning the bark either
on or off the trunk. In the southern part of ‘its range effective
destruction of the broods in thin-bark lodgepole pine can be secured |
by felling the trees, trimming off the branches, and exposing the
trunks to the sun’s rays. Under certain conditions spraying the
standing trees with fuel oil and burning them without felling has
been found to be inexpensive and effective. Control operations are
usually undertaken in the spring of the year. Peeling must be dis-
continued when the broods pupate. Burning can be continued until
the start of emergence or until the fire hazard becomes too great.

FIGURD 53.—Severe damage to ponderosa pine in the Kaibab National Forest, Ariz., from
attack by the Black Hills beetle. (Blackman.)

The Black Hills beetle (Dendroctonus ponderosae Hopk.) (6) is
the most aggressive and destructive insect enemy of ponderosa pine
in the Rocky Mountain region. It is distributed from the Black
Hills of South Dakota (whence it received its name) to eastern
Montana and south through eastern Wyoming, Colorado, Utah,
Arizona, and New Mexico. Under normal conditions it 1s compara-
tively rare and found only in weakened, decadent trees. Period-
ically, however, its numbers increase to epidemic proportions and
these sweep through the ponderosa pine stands, killing small to large
groups in ever-increasing numbers, until as much as 50 to 90 per-

INSECT ENEMIES OF WESTERN FORESTS 107

cent of the stand may be killed over large areas (fig. 53). Under
such conditions it shows little discrimination and will attack and
kill trees of all sizes, except the very smallest, apparently without
regard for their health or vigor. Infested groups may contain from
2 or 3 to as many as 350 or more trees, and the size of the groups
is a good indication of the severity of the infestation. On the edge
of large groups there will nearly always be “pitched-out” attacks,
indicating insufficient numbers in the attacking force. While pon-
derosa pine is the favored host, the beetles, particularly when epi-
demic, will attack ali other pines within their range, such as lodge-
pole, limber, bristlecone, Mexican white, and pifion pine, and occa-
sionally spruce. This beetle is so similar to the mountain pine
beetle in appearance, habits, and the character of work as to be
scarcely distinguishable from it.

The Black Hills beetle passes the winter as young to full-grown
larvae and parent adults under the bark of trees attacked the pre-
vious season. The new brood of mature adults emerges late in July
and in August, with some stragglers emerging in September. There
is but one generation a year.

Direct control methods consist in felling the infested trees and
peeling the bark or decking trees into piles and burning them. This
work is usually done late in the spring and early in the summer.
Peeling becomes ineffective as soon as the pupae have formed.
Burning can be carried on later, but it will be halted by the approach
of fire weather. ;

The Jeffrey pine beetle (Dendroctonus jeffreyi Hopk.) is an
ageressive and at times very destructive enemy of Jeffrey pine in
California. Although it often attacks trees that are apparently in
a healthy condition it seems to prefer trees that are retarded in
growth by droughts or defoliations. It rarely attacks felled trees,
so does not breed in slash or windfalls to any extent. It confines
its attacks to Jeffrey pine, and its distribution is therefore limited
to that of its host tree.

The work of this beetle (fig. 54) 1s very similar to that of the
mountain pine beetle. Reddish pitch tubes form at the mouth of
the entrance holes, which are usually in crevices of the bark. There
is usually a shght turn at the bottom of the egg gallery, which
then proceeds up the tree in nearly a straight line following the
grain of the wood. These galleries are usually 2 or 3 feet in length
and are packed with boring dust. The eggs are placed in niches
along the sides of the galleries, and the larvae work out from the
egg gallery across the grain of the wood. The pupal cells are
formed in the inner bark and are exposed to view when the bark is
removed. The adults are black and about one-fourth of an inch
in length, similar to, but considerably larger than the mountain
pine beetle.

Trees are attacked most frequently in July or August. Eggs are
laid, and some of the insects reach the new adult stage by winter.
Parent adults, larvae, and new adults spend the winter under the
bark. In the spring, development continues, and most of the new
broods emerge during July and August. Thus there is ordinarily
only one generation a year.

PA. Cee wee ee

108 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

|
i

FIGURE 04,.—Tunnels of the Jeffrey pine beetle on the inner bark surface of Jeffrey pine.

INSECT ENEMIES OF WESTERN FORESTS 109

Either peeling the bark from infested trees before new adults
form, or burning it, will kill the Jeffrey pine beetle. Methods used
for the control of the western pine beetle are usually employed for
this species also.

The lodgepole pine beetle (Dendroctonus murrayanae Hopk.)
develops in large numbers in freshly cut stumps and attacks the
base of old, weakened lodgepole pine in eastern Washington, Idaho,
Montana, Wyoming, and Colorado. Ordinarily it is not an agegres-
sive enemy, but it occasionally does kill overmature lodgepole pine
left standing following tie operations, timber sales, or other cuttings.
Fortunately such outbreaks die down at the close of the operation.
In some instances trees are killed during the first year by the basal
attacks of the lodgepole pine beetle, or it may require 3 or 4 suc-
cessive years of attack before the resistance of the trees is sufficiently
lowered to render them attractive to other bark beetles. In other
cases they are abandoned by the insects before the attacks prove
fatal. In any case, this basal damage to the tree may be considered
as primary, as it is the first weakening influence.

The adults, which are about one-fourth of an inch in length, have
reddish wing covers, while the prothorax and head are a dark
brown or black. Their attacks, which are made on stumps or on
the boles of the trees, usually within 4 or 5 feet of the ground, are
easily recognized by the large pitch tubes, an inch or more in diam-
eter, which form at the entrance holes. On reaching the cambium
the attacking beetles construct short egg galleries, ranging from 5 to
12 inches or more in length, directly between the bark and wood.
Eggs are deposited along the sides of these galleries and are sepa-
rated from one another by boring dust. The larvae feed away from
the egg gallery, keeping together in a common excavation or brood
chamber. There are no separate or individual larval mines. Trans-
formation to pupae and new adults takes place in cells constructed
in the uneaten part of the inner bark or in cocoonlike structures com-
posed of excrement in the brood chamber. The seasonal history has
not been thoroughly worked out, but there appears to be one genera-
tion a year. Outbreaks of this insect are seldom of sufficient economic
importance to warrant control measures.

The red turpentine beetle (Dendroctonus valens Lec.) (36) attacks
the base of either injured, dying, or healthy trees, or freshly cut logs
and stumps of all pines and occasionally spruce, larch, and fir
throughout the western and northeastern part of the United States
and southern Canada. Ordinarily it is not considered an aggressive
tree killer but it does do considerable primary damage and so weak-
ens trees as to make them more susceptible to attack by other bark
beetles. In some cases, such as with Monterey pine in California, it
causes sufficient damage to result in the death of the tree. It is par-
ticularly active around logging operations, where it not only works
in the stumps, but will often produce catfaces on the bases of trees
left in the reserve stand.

The adults are the largest bark beetles of this genus, measuring
from one-fourth to three-eighths of an inch in length, and are dis-
tinctly reddish in color. They are often called barber beetles by
woodsmen, on account of their ability to clip hairs, and are com-
monly, though erroneously, thought to be the bark beetles responsible

110 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

for the destruction of pes. Their attacks are characterized by large
reddish pitch tubes that form at the point of attack. On burrowing
under the bark the beetles excavate an irregular longitudinal ege
gallery between the bark and the wood. These galleries range from
a few inches to several feet in length, as Patterson reports finding
one gallery extending underground along a root for 15 feet from the
point of entrance. The gallery is more or less packed with frass,
and eggs are laid in groups or masses at intervals along the sides.
The larvae feed out through the inner bark in mass formation, pro-
ducing a cavity between the bark and wood which ranges from a few
square inches to a square foot or more in area. These chambers are
often filled with a resinous hquid that apparently has no injurious
effect upon the developing broods. Transformation to the adult.
stage occurs within pupal cells constructed in the boring dust of the
brood chamber or in short mines along its margin.

There are one or more overlapping generations annually, depending
on the locality and season. In the more southern range of the beetles
it can be found in all stages of development at nearly any season of
the year. The heaviest attacks occur in midsummer, and the winter
is passed as larvae, new adults, and parent adults, in trees and stumps
attacked the previous season.

Though this beetle is seldom of serious importance in commercial
timber stands, should control measures become necessary, the broods
could be destroyed by removing the bark from fresh stumps and from
the base of infested trees. For the protection of individual park or
shade trees, the damage can be halted by cutting out the attacking
beetles with a knife or chisel as soon as pitch exudations indicate their
presence. Successful control also has been obtained by injecting
carbon disulphide into the galleries.

THE PINE ENGRAVER BEETLES

Smaller species of bark beetles which work in the trunks and
larger branches of pines, and construct egg galleries which radiate
from a central nuptial chamber and form distinctive patterns, are
frequently referred to as the pine engraver beetles. These belong to
Ips, Pityogenes, Orthotomicus, and other related genera.

These bark beetles normally feed on the cambium of weakened,
dying, or recently felled coniferous trees and are capable of develop-
ing in large numbers in such material as windfalls, snowbreak,
logging and road slash, and also the tops of trees killed by Dendroc-
tonus or other beetles. They are beneficial insofar as they help in the
reduction of forest debris, but if large quantities of favorable host
material are available they frequently develop and emerge in such
numbers as to attack and seriously injure or kill adjacent groups of
healthy trees. Under such conditions they are often exceedingly
destructive to seedlings, saplings, and young second-growth poles,
and the tops of older trees. While Dendroctonus beetles prefer to
attack the thick bark of the main trunk and are, therefore, more
destructive to mature trees, the engraver beetles usually select thin-
bark trees for attack, thereby qualifying as primary enemies of
younger trees. Some species are frequently found working in associ-
ation with Dendroctonus beetles, in which case their attack is usually
of a secondary nature, although in some cases, top-killing of trees

INSECT ENEMIES OF WESTERN FORESTS ale

by these engraver beetles precedes and possibly attracts subsequent
infestation by Dendroctonus beetles. With the removal of mature
forests, to some it seems quite likely that this group of bark beetles
will uranic the Dendroctonus beetles in destructiveness to the second
crop of pines.

The Ips or engraver beetles

The first evidence of attack by this genus is yellow or reddish
boring dust in bark crevices or little piles of such dust around the
entrance holes or on the ground beneath. Pitch tubes are seldom
formed, and the boring dust is usually dry and free from pitch.
Soon after a tree has been attacked the foneee fades and turns from
green to yellow, sorrel, and red. Upon removing the infested bark
the tunnels of the engraver beetles will be found | grooving the inner
bark surface and slightly marking the sapwood. “The egg galleries
differ from those of the Dendroctonus beetles in that instead of being
tightly packed with boring dust they are open runways in which the
adult beetles are free to travel the entire length. A second difference
is their polygamous social habit of constructing a central nuptial
chamber from which fork or radiate several egg ‘galleries. In many
cases the pattern of the completed work is sufficiently distinctive to
identify the species responsible. However, some species cannot be
recognized in this way and can be distinguished only by characters
in the adult beetles.

The adults are small, reddish brown to black, often shiny, cylin-
drical bark beetles ranging from one-eighth to ‘approximately one-
fifth of an inch in length. A distinguishing feature is the pro-
nounced concavity on the posterior end, which is margined with from
one to six pairs of toothlike spines. The small, white, legless larvae
differ slightly from Dendroctonus larvae in that the body is more
tapering and is thicker at the forward end than toward the rear.

Attacks are made by these bark beetles with the coming of warm
weather in the spring. An adult male bores through the bark and
constructs a small cell or nuptial chamber in the inner bark. Several
females then join in the work and each constructs an egg gallery in
which eggs are laid in niches along the sides. The larvae, upon
hatching, feed in the inner bark and work away from the egg galler-
ies, leaving gradually widening, excrement-packed tunnels behind
them. When their feeding is completed oval pupal cells are formed,
in which the transformations from larvae to pupae and then to adults
take place. From the time of attack until the emergence of the first
of the new brood ordinarily requires from 42 to 68 days. From two
to five generations of these beetles may develop during the summer,
depending on the altitude, latitude, and species, there being consid-
erable overlapping of generations. The winter is usually spent in the
adult stage, although occasionally i in the egg or larval stage. Some
species congregate in large groups under the bark of standing trees
killed the previous year and feed to a limited extent on the dry, dead,
inner bark. Others emerge and hibernate under the bark of old
stumps, among the bark scales, or in crevices and litter at the base
of old brood trees.

Engraver beetles have a number of predacious and parasitic ene-
mies but it appears that these do not affect the numbers of the beetles

112 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

so much as does the lack of suitable host material. Given a quantity
of freshly cut slash or windfalls, a large beetle population is
almost certain to be produced but it will not long survive after
the supply of this material is exhausted.

Since outbreaks in standing, healthy trees are sporadic and of short
duration, the destruction of the broods in these trees, through the
application of control methods, seldom contributes a great deal
toward reducing the damage. Efforts should be directed toward
preventing outbreaks by eliminating all situations favorable to the
development of excessive progeny. Thus, slash should be piled and
burned before the /ps beetles emerge, or scattered in the open where
the sun will dry it out and make it unsuitable as a breeding medium.
If it should be necessary to destroy broods in standing trees, the most
economical and effective method is to fell the trees and burn or scorch
the infested bark. A large number of species of this genus are
recorded from western pines, all very similar in appearance and
naps, so only a few of the more common species need be mentioned
1ere.

The western six-spined engraver (/ps ponderosae Sw.) is a second-
ary enemy of ponderosa pine, which for the most part attacks trees
that have been felled or those dying from attacks of more primary
species of bark beetles. The adults are about one-fourth inch in
length, reddish brown to black, with six spines on each side of the
elytral declivity. The gallery pattern consists of from two to five
ege@ galleries extending up and down the tree from the central nuptial
chamber. Though the pattern is similar to that of 7. oregoni, the
galleries are distinctly wider. This beetle has been recorded from
Arizona, California, Montana, and South Dakota, and undoubtedly is
present in other Western States.

The California five-spined engraver (/ps confusus Lec.) is destruc-
tive to tops of mature trees, small poles, and the saplings of various
pines in California and southern Oregon west of the Cascade and
Sierra Nevada ranges. It breeds readily in slash and felled logs, and
the broods from such material often cause extensive damage to the
young pine growth in the vicinity. It commonly attacks ponderosa
pine, sugar pine, western white pine, Coulter pine, Monterey pine,
and less frequently other pines within its range.

The adults are reddish brown to pitch black, about one-eighth inch
long and with five spines on the margin of each side of the elytral
declivity. The egg galleries usually comprise from three to five
nearly straight tunnels radiating from a central entrance chamber.
The typical form has three galleries in the shape of an inverted Y.
These galleries are not packed with boring dust and are usually from
5 to 10 inches long. Attacks are started early in the spring and from
two to five generations of beetles may develop during the summer.
In the northern part of the range, at an elevation of about 3,000 feet,
there are usually two summer generations which develop in fallen
logs and a third, or overwintering generation, which develops in
standing trees. At lower altitudes and in the southern part of the
range there are from three to five summer generations. The beetles
overwinter mostly in the adult stage, under the bark of recently killed
trees and probably in crevices and under litter on the ground.

INSECT ENEMIES OF WESTERN FORESTS 113

Some attempts have been made in California to control outbreaks
of this beetle in young pine stands by felling the trees and burning
the infested bark much as is done for the control of the western pine
beetle. Usually such methods are not warranted, as outbreaks are
sporadic and can be avoided if roadway, line, or other slash is burned
before the beetles emerge, or in logging oper ations 1f a continuous
supply of fresh mater ial is provided to absorb developing broods.

The Arizona five-spined engraver (/ps lecontei Sw.) 1s the south-
western form of /. confusus. It attacks ponderosa and other pines in
the southern Rocky Mountain region and at times is exceedingly
destructive. Its characteristics and habits are very similar to those
of its near relative, and the methods of control are the same. Re-
cently some rather extensive operations have been carried on in
Arizona to control this beetle.

The Vancouver ips (/. vancouveri Sw.) is also closely allied in
character and habits to 7. confusus, but is slightly larger. The adult
beetles are reddish brown to black, about one-fourth inch in length,
and with five spinelike teeth on the margins at each side of the
concave elytral declivity, which is densely clothed with long, slender
hairs. These beetles usually attack decadent or weakened western
white pine, sugar pine, foxtail pine, lodgepole pine, and Sitka spruce
throughout the Northwest, but under favorable conditions will attack
apparently healthy trees. The gallery pattern is of a radiating,
longitudinal type with three to five short eg@ galleries extending up
and down the tree from the nuptial chamber. There are apparently
two but possibly three generations a year.

The Cloudcroft ips (/ . cloudcrofis Sw.) 1s a secondary enemy of
pines in the high mountains of New Mexico. It is a slender species
with five pairs of spines on the elytral declivity and is closely related
to I. confusus in character and habits.

The emarginate ips (/. emarginatus Lec.) is most frequently found
associated with the mountain pine beetle in its attacks on ponderosa
pine, lodgepole pine, and sugar pine, and with the Jeffrey pine beetle
in Jeffrey pine, but is quite capable of and occasionally does kill trees
on its own account. This is the largest western species of /ps. Its
range extends through California, north to southern British Colum-
bia, and east through Idaho to western Montana. The adults are
dark-brown, cylindrical bark beetles about one-fourth inch in length,
with three prominent spines along each side of the elytral declivity,
and a fourth nearly obsolete spine. Their work is characterized by
the long, straight, nearly parallel egg galleries from 2 to 4 feet in
length, which run up and down the tree and connect at different
points (fig. 55). Owing to the similarity in length and width of the
egg galleries, its work is often confused with that of the mountain
pine beetle with which it is so often associated. However, the pres-
ence of a nuptial chamber and the absence of packed boring dust in
the Zps galleries will distinguish their work. In the northern part
of its range this species has two complete generations a year, while
in the southern part there are a number of summer generations with
considerable overlapping of broods. Control work has included this
species when in association with more aggressive bark beetles, but no
separate control ever has been required.

136650°—38——_8

114 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

Knaus’ ips (/. knaust Sw.) attacks lodgepole pine, ponderosa pine,
and Arizona pine through the pine belt of Arizona, New Mexico,
and Colorado. It is ustially a secondary enemy. In its habits, char-

FIGURE 55.—Galleries and pupal cells of the emarginate ips (J. emarginatus) on the inner
bark surface of ponderosa pine.

acter of work, and appearance it closely resembles its near relative,
T. emarginatus, and may be considered the southern Rocky } Mountain
form of this beetle.

INSECT ENEMIES OF WESTERN FORESTS 115

The smaller western pine engraver (/ps latidens Lec.) usually
confines its attacks to the tops and limbs of dying or weakened
pines and seldom causes any primary injury. Under favorable con-
ditions, however, it has demonstrated its ability to kill trees, par-
ticularly those weakened by mistletoe or drought, and in some
instances even healthy trees of small diameter. It is quite common
in the tops of lodgepole pines killed by Dendroctonus beetles, and
during severe epidemics of the mountain pine beetle it often de-
velops in such numbers as to attack and destroy many small trees
throughout the area. The adults are the smallest of the western
species and are about one-eighth inch in length. They are distin-
guished by having three small, spinelike teeth along the margin of
the elytral declivity, which is nearly vertical. Its typical work
consists of from two to five rather short, sometimes curved, egg
galleries radiating from the central nuptial chamber. It is distrib-
uted throughout most of the Western States, where it attacks pon-
derosa, sugar, digger, lodgepole, western white, and probably other
species of pine. J/. guiéldi Blkm. is a closely related form which
attacks lodgepole and probably other pines in Colorado and the
central Rocky Mountain region.

The sawtooth pine engraver (/ps integer Eichh.) 1s distributed
throughout the Western States, but is found most commonly in the
Rocky Mountain region. It generally breeds in weakened or felled
ponderosa pine, lodgepole pine, western white pine, and western
larch, but under favorable conditions 1t may become primary. The
stout, brownish-black adults are about one-fifth of an inch in length
and have four spinelike teeth along the margin on each side of the
concave elytral declivity. This species constructs three or four straight
longitudinal egg galleries that fork from the common entrance or
nuptial chamber. The egg niches are so thickly and evenly spaced
along the sides of the egg galleries as to give these a sawtoothed
appearance—a distinctive feature of this species’ work.

The California pine engraver (/ps plastographus Lec.) is a species,
closely related to J. ¢nteger, which prefers to attack the trunks and
branches of felled Monterey, Bishop, and lodgepole pine, but at
times also attacks weakened or dying standing trees. It is not often
primary in its attacks, but is usually associated with the Monterey
pine engraver and the red turpentine beetle in the killing of living
trees or trees injured by fire or other causes. It is found through
the range of its host trees in the coastal belt of middle California
and in the Sierras. The adults are about one-fifth of an inch in
length, with four pairs of spines on the posterior margin of the
wing covers. The work pattern is very similar to that of 7. confusus,
the typical form having three egg galleries from 5 to 15 inches in
length, issuing from each entrance chamber. There are from three
to five generations annually, depending on the locality and season.

The Oregon pine engraver (/ps oregont Eichh.) is probably the
most common /ps beetle found throughout the Western States, where
it attacks ponderosa pine, lodgepole pine, sugar pine, Jeffrey pine,
digger pine, and probably other species (fig. 56). Large numbers
develop in such host material as windfalls, freshly cut logs, pieces
of slash over 2 inches in diameter, and in the tops and limbs of
trees killed by Dendroctonus beetles. When conditions are favor-
able and suitable host material is plentiful, they frequently develop

116 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

in such numbers as to become aggressive in their attacks on health
living trees. However, such outbreaks are usually of short duration
and seldom last more than one season. The most frequent damage

FIGURE 56.—The typical galleries of the Oregon pine engraver score the sapwood.

is in the killing of young replacement trees from 2 to 8 inches in
diameter and the top-killing of older trees.

The adults are reddish brown to nearly black, about one-sixth of
an inch in Jength, and with four small teeth along the margins on
each side of the elytral declivity. A typical sample of their work

eo eee Se = ee SS ore ————_ ~—

INSECT ENEMIES OF WESTERN FORESTS cy,

shows three or four egg galleries forking from a central nuptial
chamber and running more or less longitudinally with the grain
of the wood for a distance of 5 to 10 inches. There may be any-
where from one to seven females to each male, with as many egg
galleries radiating from the one nuptial chamber. There are from
two to four generations of this species a year, depending on the
locality and the length of season. The parent adults often emerge
and make a second and even a third attack that results in a con-
fusing overlapping of
broods. Preventing U4:
these beetles from be- Ny Vaal
coming too numerous NUN
through timely slash
disposal will do more
to prevent damage
than the application of
control measures after
damage has occurred.
The Monterey pine
eneraver (Jps radiatae |I%
Hopk.) attacks living, | Swag
injured, dying, and re- ie
cently felled Monterey, ne
Bishop, knobcone, Jef- ia q
frey, lodgepole, and tie

Nati
tl

whitebark pines from | Pee
central California |f 15 DY”

northward to British &fity:/¢ Ail k

Columbia and east- || ee bi

ward to Tdaho and “WHR Wy pay Z ‘fh
Wyoming.. It is usu- Hi Wie ae ial it :
ally a secondary enemy [HIN )3, 2400 UG :

and associated with Z snk ae . ey
. TIGURE 57.—Monterey pine engraver (Ips radiatae) :
other bark beetles in Adult (X 8) and pattern of work on sapwood.

its attack, but at times

may become primary, especially in plantations of Monterey pine.
The adult beetles are about one-fifth of an inch in length, dark brown
and shining, with parallel sides and one very prominent spine on the
end of each wing cover. The egg galleries are curved or S-shaped,
with three or four larval mines issuing from each egg pocket (fig. 57).
The rapidity of development and the number of generations will
vary with different seasons and localities. Usually there are one or
two summer generations and an overwintering generation. The
beetles overwinter beneath the bark of trees killed during the pre-
vious summer, mostly as adults, but also as larvae and pupae. Some
extensive control operations have been undertaken in California to
suppress outbreaks of this beetle that developed from roadway
slashings.

Pityogenes and other wood engraver beetles
The small bark beetles belonging to the genus Pétyogenes are

sometimes referred to as “wood engravers.” They usually are of
secondary importance and attack the tops, limbs, and twigs, of

AS MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

weakened, dying, and newly felled trees; but, like other secondary
species, under favorable conditions they may develop in sufficiently
large numbers to attack and kill small trees growing in the vicin-
ity of their breeding place. The adults are small, dark-brown
beetles, with small, spinelike teeth along the margin of a slightly
concave elytral declivity. They are polygamous and excavate nu-
merous galleries under the bark, which radiate from a central, more
or less circular, nuptial chamber.

Pityogenes carinulatus Lec. breeds in ponderosa, lodgepele, white-
bark, Jeffrey, and probably other pines and is distributed over
nearly all of the Western States. The adults are slender, reddish-
brown bark beetles about one-eighth inch in length. The females
have three small, spinelike teeth along each margin of the elytral
declivity, whereas the males have only two declivital teeth on each
side, the first pair strongly developed into prominently curved spines.
Their gallery pattern consists of from 8 to 10 or more rather slender
egg galleries from 1 to 2 inches in length, radiating from a circular
entrance chamber.

Pityogenes knechteli Sw. is a stout species about one-eighth inch
long, commonly found associated with 7ps and Dendroctonus beetles
under the thin bark of lodgepole pines in the Western States and in
British Columbia, and is sometimes responsible for the destruction
of small patches of lodgepole pine in reproductions. The work
consists of from three to five egg galleries 114 to 3 inches in length,
radiating from the central nuptial chamber.

Pityogenes fossifrons Lec. is a species occasionally found working
in the tops and limbs of weakened or dying western white pine and
lodgepole pine from California northward to British Columbia
and eastward to Idaho. Its attacks are seldom primary, though it
sometimes attacks western white pine reproduction. The adults are
small, brownish-black bark beetles approximately one-eighth inch
in length with three very small spines along each margin of the
elytral declivity. Their gallery pattern consists of four or five egg
tunnels 1 to 114 inches in length, radiating from the entrance or
nuptial chamber (fig. 58).

Several other species of small engraver beetles may be encountered
under the bark of pines. Ovthotomicus ornatus Sw. is a very small
species about one-eighth inch in length. The elytral declivity is
shghtly concave, with three pairs of small teeth, the second and third
pairs of teeth larger on the males. Their work is similar to that
of Pityogenes, and they frequently are found under the thick bark
of ponderosa, Jeffrey, and lodgepole pines in small mines inter-
mingling their work with that of the pine beetles. Some species of
the genus Pityophthorus are occasionally found under the thick
bark of dying pines, and may be responsible for the death of
weakened trees (p. 31).

Fir Bark BEETLES

The balsam firs (Abzes spp.) and Douglas fir (Pseudotsuga taai-
Folia), as well as pines, have their full share of bark-beetle enemies
(19). In general the destructive species are different from those
attacking pines, though many of the secondary species may be the
same. Douglas fir growing under favorable conditions in the com-

INSECT ENEMIES OF WESTERN FORESTS He)

mercial stands of western Oregon and Washington seems to be quite
resistant to bark-beetle attack, and serious damage is rarely found.
At times, however, this tree suffers from bark beetles, even in this)
region of favorable growth. In the eastern portion of the Douglas
fir range, where growth conditions are less favorable and the timber
is of inferior quality, bark-beetle outbreaks of disastrous proportions

Ficurp 58.—Typical galleries and egg niches of Pityogenes fossifrons.

are not an uncommon occurrence. The Douglas fir beetle (Dendroc-
tonus pseudotsugae) is the most common offender and causes the
bulk of the damage. Small Douglas firs are frequently killed by
the fir engraver beetles, particularly in situations where large num-
bers of these small beetles have developed in windfalls or slash. The
engravers usually responsible for this type of damage are Scolytus
unispinosus or Pseudohylesinus nebulosus.

120 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

The balsam firs are very susceptible to bark-beetle damage, and.
in certain years outbreaks sweep through fir stands and kill a high
percentage of the trees. In such cases if 1s not uncommon to see
entire hillsides turn red with the discolored foliage of dying trees.
Since balsam firs are not of great commercial ‘value within our
western forests, no estimates have been made as to the extent of
such damage.

In addition to aggressive tree-killing fir bark beetles, there are
also a large number of secondary species that breed in dying or
dead trees, slash, and broken tops. These, under exceptionally fa-
vorable circumstances, may become destructive to living trees.

The Douglas fir beetle (Dendroctonus pseudotsugae Hopk. ) is the
most important bark-beetle enemy of Douglas fir throughout its
range in the Western States. It also attacks western larch, western
hemlock, and bigcone spruce. Normally it confines its attacks to
felled, injured, or weakened trees and is not of great importance.
At times, however, it becomes aggressive and kills apparently
healthy, mature trees, singly and in groups, over extensive areas.
Some serious epidemics have occurred in the Rocky Mountain region,
particularly where trees were weakened by drought, fires, or detolia-
tions. In the commercial Douglas fir region of Oregon and Wash-
ington outbreaks are of less frequent occurrence, although the kill-
ing of groups of mature trees in second- erowth stands is not
uncommon.

Reddish or yellow boring dust caught in bark crevices or around
the base of trees gives the first evidence of attack by the Douglas fir
beetle, as no pitch tubes are formed. The adults are reddish to dark
brown, often black, beetles about one-fifth of an inch long and very
sunilar to other Dendroctonus beetles (p. 98) except for their reddish
color and their covering of conspicuous long hairs. These beetles
work in pairs and construct egg galleries which are mostly in the
inner bark, though they also shghtly etch the sapwood. Typical
galleries are perpendicular, usually straight or shghtly sinuous (fig.
59) and average about a foot in length, though they may range from
6 to 30 inches. The eggs are laid in masses of from 10 to 36. These
masses are in grooves at alternate intervals along the sides of the
gallery. The larval mines diverge from the egg groups and are
extended through the inner bark close to the wood. They expand
as the larvae grow, so the completed work from each group of eggs
is somewhat fan- shaped. The pupal cells, which are constructed
at the ends of the larval mines, may be exposed when the bark is
removed from the tree, or they may be concealed in it, depending on
the thickness of the bark. Im these cells the transformation from
larvae to pupae and then to new adults takes place. The new
adults bore away the intervening bark between pupal cells and con-
gregate, sometimes for rather long periods, beneath the bark. Fi-
nally they bore through the bark to the surface, emerge, and fly
to make their attack on other trees.

Ordinarily the Douglas fir beetle passes the winter in the adult
stage. although small to mature larvae also may be found. The over-
wintering adults emerge rather early in the spring, but the delayed
broods mature and emerge at any time throughout the summer
months. It is also possible that some of the young overwintering

INSECT ENEMIES OF WESTERN FORESTS lead

larvae do not have time to complete their development before cold
weather overtakes them in the fall, and consequently they are obliged

to spend another winter in the host tree.’ One generation of beetles

ee ee error _ecct[.CO_ EOL Ow OO Ea____ ea

FIcuRP 59.—Galleries of the Douglas fir beetle on inner bark surface.

a year is probably the normal rate of development, but there are
considerable overlapping and retardation of broods, somewhat obscur- |
ing the demarkation between generations.

1:22 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

The usual method of direct control is to fell the tree and cut the
infested bole into logs, which are then decked and burned. As a
large percentage of these insects overwinter as adults and emerge
early in spring, fall control is the most effective.

THE FIR-ENGRAVER BEETLES

There are a number of small species of bark beetles, belonging to
Scolytus, Pseudohylesinus, and other related genera, which commonly
work under the bark and score the sapwood of dying, broken, or felled
firs, but which at times may become so abundant and aggressive as to
attack and killsmalltrees. This
entire group may be referred to
as “fir engraver beetles.”

Members of the genus Scoly-
tus, are small, shiny, dark, or
nearly black bark beetles, which
are easily recognized by the con-
cave appearance of the posterior
ventral surface of the abdomen.
The adults feed for some time
by making feeding pits in the
twigs and later attack in pairs
and construct short egg gal-
leries, usually from a central en-
trance chamber. The larvae
work out at right angles from
the egg gallery and bore through
the phloem and inner bark, usu-
ally deeply scoring the sapwood.
Some members of the genus are
exceedingly destructive to bal-
sam firs. Others work in Doug-
las fir, hemlock, spruce, or even
in broadleaved trees.

The Douglas fir engraver
(Scolytus unispinosus Lec.) is
re ee ee COOL ome UU ele Lay

graver (Scolytus wnispinosus). weakened, injured, dying, OL re-
cently killed Douglas fir in the
Pacific Coast and Rocky Mountain States and southwestern Canada.
Sometimes it 1s a primary enemy of young Douglas firs. The
adults are small, black, cylindrical, shining bark beetles about one-
eighth inch in length, with a long spine projecting from the middle
of the nearly perpendicular face of the ventral declivity. The
typical ege gallery follows the grain of the wood and may range
in length from 114 to 3 inches. A short entrance tunnel leads into
the main gallery, at an angle of 45°, and a small nuptial chamber
is constructed at the juncture (fig. 60). The larvae work out at
more or less of a right angle from the ege gallery, and then work
up or down the tree so that the mines will not cross one another. The
winter is spent in the egg and young larval stages. Emergence of
adults takes place late in April, in May, June, and July. There
appear to be two generations annually.

INSECT ENEMIES OF WESTERN FORESTS 123

The fir engraver (Scolytus ventralis Lec.) is found attacking
the balsam firs in all the Western States and in British Columbia,
and at times has been exceedingly destructive to white fir stands in
California and Oregon. The adult is a short, black bark beetle
about one-eighth inch in length, without a prominent spine on the
ventral declivity. The egg galleries are excavated in the inner bark
and cut transversely across the grain of the wood, which they score
rather deeply for a
distance of from 2
to 6 inches on both
sides of a central
entrance chamber.

Eggs are laid in
niches along both
sides of these galler-
ies and the larvae,
on hatching, work
up and down the
bole (fig. 61), ex-
tending their indi-
vidual larval mines
for a distance of 5
to 7 inches. A brown
stain of the cambium
caused by: a fungus
is always found in
the area in which the
larvae feed. Pupa-.
tion occurs in the in-
ner bark at the end
of the larval mines,
and the new adults
bore directly to the
surface of the bark
when ready to
emerge. Frequently
green trees are at- graver (Scolytus ventralis).
tacked and new
broods develop and emerge without destroying enough of the cam-
bium to cause the death of the tree. The patch of “dead cambium
heals over and leaves only a brown pitch pocket in the wood to mark
where the injury occurred. Some wood sections have shown as many
as seven such attacks during the life of the tree, which indicates that
a certain amount of activity by this beetle is constantly going on in
the forest. Trees are attacked during the summer months, and the
eggs hatch and larvae develop before winter. The winter usually is
passed in the larval stage, and the new broods emerge the following
year. There is normally but one generation of these beetles annually.
Because of the sporadic character of outbreaks and the possible pres-
ence of healthy broods in living trees no methods of control appear
practical.

Other species of Scolytus which may be found in western firs
include S. subscaber Lec., a large species which makes E-shaped

Figure 61.—Egg galleries and larval mines of the fir en-

ae es a eee 2 ee ee le a! SS ee

124 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

galleries in the limbs of balsam firs: S. praeceps Lec., a small species
about one-eighth inch in jength, which attacks the limbs and small
tops of white fir and other firs in the Western States; and S. mon#i-
colae Sw., about one-eighth inch in length, which is recorded by
Swaine as attacking western white pine and Douglas fir in British
Columbia. rs

Some of the species of the genus Pseudohylesinus are also quite
frequently found in various firs. They usually are secondary in
habit but at times
some species are de-
structive. Their work
is very similar to that -
of Scolytus in that the
typical egg gallery
consists of two short,
straight branches from
a central entrance tun-
nel. The work usu-
ally can be distin-
guished from Scolytus
in that no enlarged
nuptial chamber, scor-
ing the sapwood or
visible on the inner
surface of the bark, is
constructed, as is the
case with Scolytus.
Another distinguish-
ing feature between
these two genera is
that the wing covers
of Pseudohylesinus are
densely covered with
scales, and therefore
are dull in appearance
instead of shiny.
Moreover, the beetles
are nearly oval in out-
line and do not have
the concavity at the rear of the abdomen which is such a distinctive
feature of Scolytus.

The Douglas fir hylesinus (Pseudohylesinus nebulosus Lec.) is fre-
quently found attacking recently felled or injured small Douglas
firs through the range of this tree from British Columbia to central
California. It seems to prefer the thin bark of saplings, or poles,
or limbs of larger trees, and frequently kills trees of small diameter.
The adults are small, grayish to yellowish-brown, variegated bark
beetles about one-eighth inch in length. Usually a short longi-
tudinal egg gallery is constructed in the cambium layer, often with
two branches, originating from a central entrance tunnel, one up
and one down the trunk, parallel with the grain of the wood (fig.
62). Their work is very similar to and easily confused with that
of Scolytus unispinosus, but is distinctive in that no well-defined

FIGURE 62.—Adults and galleries of the Douglas fir hylesi-
nus (Pseudohylesinus nebulosus), natural size.

INSECT ENEMIES OF WESTERN FORESTS 125

nuptial chamber is visible on the inner surface of the bark. The
larval mines diverge from the egg gallery and end in pupal cells
in the inner bark. There appear to be two generations a year.

The grand fir bark beetle (Pseudoh ylesinus grandis Sw.) attacks
the trunks or limbs of w eakened or dying Douglas fir, lowland
white fir, and white fir, and is usually of. secondary importance.
The adult beetles are about one- -eighth inch in length, rather stout,
elongate-oval, densely covered with brown and gray scales w hich
sometimes form V- shaped markings on the wing covers. ea work
in pairs and each pair constructs a short, transverse ege gallery
for 2 or 8 inches, sometimes on only one side but more frequently
on both sides of the entrance tunnel. The work is very similar to
that of Scolytus ventralis except that the egg gallery 1s narrower,
not so uniformly straight, and without the well defined entrance
chamber. There are one or two generations a year, depending on
the locality.

The fir root bark beetle (Pseudohylesinus granulatus Lec.) is a
larger, very dark reddish to black species about one-fifth of an
inch in length, with very rough elytra and prominent striae. It
1s a secondary enemy of grand fir and white fir, working under the
bark of dying or dead trees, particularly at the base and in the
roots of small trees. It is distributed from Califorma to British
Columbia.

The noble fir bark beetle (Pseudohylesinus nobilis Sw.) 1s similar
to P. grandis, approximately one-eighth inch in length, and is found
breeding in dying noble fir.

Some of the species of Dryocoetes are found working under the
bark of firs. While they are usually secondary enemies, they at
times attack and kill apparently healthy trees.

The western balsam bark beetle Dryocoetes confusus Sw. is prob-
ably the most destructive member of the group and is quite often
found attacking alpine fir and sometimes other species of fir and
spruce. The adults are rather short, reddish-brown bark beetles
about one-eighth inch in length. They construct a small, circular
nuptial chamber under or in the bark, with several radiating egg
galleries which may score the sapwood (fig. 63). There is probably
only one generation a year. The species is distributed throughout
the Northwestern States from British Columbia southward in Oregon
and eastward to Colorado.

Dryocoetes pseudotsugae Sw. is a secondary enemy of Douglas
fir. The adults are reddish brown and are about three-sixteenths
of an inch in length. They construct short, irregular galleries in
the inner bark of wind-thrown and dying trees ‘throughout Cali-
fornia and northward to British Columbia. The young adults gather
in galleries in the outer or inner bark, not in the cambium, to pass
the winter. Emergence occurs early in the spring. Trees attacked
in the spring produce mature beetles by August. There probably
are one and a partial second generation each year.

SPRUCE BARK BEETLES

Spruce trees are attacked by a large number of bark beetles,
most of which are secondary enemies, bre eeding only in dying, felled,
or weakened trees. A few species, however, such as the Englemann

126 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

spruce beetle, become exceedingly destructive at times. Young trees
are sometimes killed by species of Zps, Pseudohylesinus, and Dry-
ocoetes, and by other ena engraver beetles.

FIGURE 63.—Galleries of the western balsam bark beetle, Dryocoetes confusus.

The Englemann spruce beetle (Dendroctonus englemanni Hopk.)
has caused widespread destruction of mature Englemann spruce in |
the Rocky Mountain region and is considered a very important

INSECT ENEMIES OF WESTERN FORESTS lei

insect enemy of this tree. It will also attack other species of spruce
within its range, which covers Oregon, Washington, Idaho, Montana,
Wyoming, the Black Hills of South Dakota, Utah, Colorado, Ari-
zona, and new Mexico. Lar ge, overmature trees are preferred
for attack, as are also trees weakened by mechanical injuries, logs,
and windfalls. With large standing trees the base is seldom at-
tacked, and examinations “must be made at a height of 6 feet or
more from the ground if the insects responsible for the injury are
to be found.

The adult beetles are about one-fourth inch in length, reddish
brown, with the body sparsely clothed with long hairs. They exca-
vate a short, nearly straight, longitudinal egg gallery in the inner
bark, slightly scoring the sapwood. The gallery is much wider
than the beetles and is packed with boring dust, through which the
adults keep a passageway open. LEggs are laid side by side in elon-
gate cavities alternating from side to side of the egg gallery. The
larvae at first bore out en masse, transversely from “the ege gallery,
but later make separate mines. The pupal cells are usually con-
structed in the inner bark, being exposed when the bark is removed,
but are sometimes deeper in the bark, and quite concealed in thick-
bark trees.

There is only one complete generation annually, but it shows con-
siderable overlapping of broods. ‘The winter is passed in all stages
of development, except the pupal stage, with new adults predomi-
nating, in trees attacked the preceding summer. The overwintering
adults emerge rather early in the season, but the emergence from the
overwintering larvae 1s spread over a rather long period, owing to
variations in individual development. The time of emergence and
attack will vary materially, according to differences in elevation
and exposure, but the period of heaviest attack is in June and July.

Since the developing larvae and pupae of this species are exposed
when the infested bark is removed, such removal through peeling of
infested trees will result in their destruction if the broods are in the
larval or early pupal stage. The burning or severe scorching of
infested logs is also an effective method of destroying the broods,
especially when the beetles are in the adult stage. Owing to dense
forest cover in most forests of Engelmann spruce the use Pof fire in
beetle control will often be impractical because of the danger
involved. As with the Douglas fir beetle, fall control is to be pre-
ferred to spring control.

The Alaska spruce beetle (Dendroctonus borealis Hopk.) attacks
white and Engelmann spruce in Alaska and northwestern Canada.
In appearance and habits it is very similar to the Engelmann spruce
beetle, to which it is closely related.

The Sitka spruce beetle (Dendroctonus obesus Mann.) is usually
considered as a secondary enemy of the Sitka spruce, but it has the
potentiality of becoming destructive. At times it has killed a con-
siderable volume of Sitka spruce along the coast of Oregon, Wash-
ington, and British Columbia.

Many species of small engraver beetles which breed in the dying
bark of felled or weakened trees sometimes become so plentiful as
to become dangerous to small spruce trees and the tops of older

128 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

trees. These belong to the same genera that are met with in pines
and firs. |
The Sitka spruce engraver (/ps concinnus Mann.) attacks the |
bark of living, dying, or felled Sitka spruce along the coast of
Oregon and northward to Alaska. No reports have been received
of its having done more than nominal damage. The adults are about
one-eighth inch long, with three teeth, one very prominent and two
smaller, on each side of the concave elytral declivity. They excavate
an irregular central nuptial chamber, with three or four short curved
or S-shaped galleries radiating therefrom. Four eggs are laid in
each egg pocket and the four laval mines issuing from each pocket are
a characteristic feature of its work. (See p. 111 for a general discus-
sion of the work and habits of the /ps beetles. )
Other species of 7ps which attack spruce include the following:
Species of Ips Host and distribution
. perturbatus Eichh__ yee _ White spruce. Northern Canada and
Alaska.
ater PUnClus Wich Sse ee White spruce and Engelmann spruce.

a
I

Alaska, Yukon, and British Columbia.
T_interrupris, Manns» 252) 32s Sitka spruce, white spruce. Oregon to
I

Alaska and eastward.

SOLOS. SS Was Oe Pee Be Engelmann spruce. British Columbia
and Rocky Mountain region.

LE inidens Mann) 2 oa a ee Engelmann spruce, Sitka spruce, and
probably white spruce. Canadian
Rockies and British Columbia.

I. engelmanni Sw__------------------. Engelmann spruce and white spruce in
Same region.

TT. YOoheensis “SW a __.. Engelmann spruce and probably white
spruce. British Columbia.

The Sitka spruce hylesinus (Pseudohylesinus sitchensis Sw.) is a
small, densely scaly, suboval bark beetle which is found attacking
felled or dying Sitka spruce in British Columbia, Washington, and
Oregon.

Scierus annectens Lec., a small reddish-brown bark beetle about
one-eighth inch long, attacks white spruce, Engelmann spruce, lodge-
pole pine, and probably Sitka spruce in western Canada and the
Northwestern States.

Dryocoetes affaber Mann. attacks the tops of felled and dying
Sitka spruce, Engelmann spruce, and Douglas fir from Alaska south-
ward into the Northwestern States. The adults, which are less than
one-eighth inch in length, construct irregular, short egg galleries.

Dryocoetes confusus Sw. (p. 125) may also be found attacking and
sometimes killing Engelmann and other spruces.

HEMLOGK BARK BEETLES

While hemlocks have a number of bark-beetle enemies, these are
mostly of secondary importance, and seldom are any large number
of trees killed.

Western hemlocks (Tsuga heterophylla) are sometimes attacked
and killed by the Douglas fir beetle (p. 120) when associated with
Douglas fir. At times weakened trees are attacked by species of
Scolytus and Pseudohylesinus.

Mountain hemlocks, when in mixture with lodgepole pine, are
sometimes killed by the mountain pine beetle (p. 102), but are most
frequently attacked by a species of Scolytus.

INSECT ENEMIES OF WESTERN FORESTS 129

The hemlock engraver (Scolytus tsugae Sw.) is a small, dark,
shiny bark beetle about one-eighth inch in length, with the wing
covers projecting over the concave abdomen. It constructs a short,
straight ege tunnel across the grain, from one or both sides of a
small entrance chamber. Both mountain and western hemlocks are
attacked, and at times, as recently in Crater Lake National Park,
the species is very destructive. It is distributed from British
Columbia southward to California.

The hemlock hylesinus (Pseudohylesinus tsugae Sw.) 1s a stout,
oval bark beetle about one-eighth inch long, reddish brown and
sparsely clothed with scales and short stout hairs. It breeds pro-
lifically in felled and dying western hemlock and also is known to
attack and kill apparently healthy trees. It is reported from
British Columbia and Washington, but will probabiy be found
throughout the range of the host tree.

BarkK BEETLES AFFECTING LARCH

Western larch is quite resistant to insect enemies, but it some-
times is killed by species of bark beetles that work in various other
coniferous trees. Probably its most serious bark-beetle enemy is the
Douglas fir beetle (p. 120). Dying and felled trees may be attacked
by Ips integer or other small engraver beetles.

The larch engraver (Scolytus laricis Blkm.), which is very similar
to S. wnispinosus in appearance and habits (p. 122), has recently
been described by Blackman from specimens found breeding in this
tree:

CEDAR BARK BEETLES

All the closely related trees belonging to the families Taxodiaceae
and Cupressaceae, such as the various cypresses, incense cedar, Port
Orford cedar, Alaska cedar, western red cedar, redwood, and the
various junipers, are attacked by diverse species of one genus of
bark beetles, Phloeosinus. Not only is this genus practically con-
fined to this group of trees (one species has been doubtfully re-
corded from pine), but as these trees have almost no other bark-
beetle enemies, any species found working in the inner bark of
cedarlike trees is almost certain to be a species of Phloeosinus. As
a general rule these small oval beetles are not aggressive in their
attack and are found working under the bark of trunks, tops, and
limbs of weakened, dying, or felled trees, or of broken branches.
Occasionally, however, they become sufficiently numerous and ag-
gressive to attack and kill apparently healthy trees. Usually the
ereatest injury by these bark beetles is due to their habit, as newly
emerged adults, of feeding on the twigs of healthy trees, often caus-
ing these to break or die. This habit is similar to that of most
species of Scolytus. In constructing their brood burrows the beetles
work in pairs, and, while there is some variation in the work pat-
tern, the typical egg gallery consists of one short, longitudinal gal-
lery arising from an enlarged entrance chamber, with the eggs very
uniformly spaced along the sides and the larval mines extending
laterally in a very regular pattern (fig. 64). Trees are attacked in
the spring and summer, and there are one or one and one-half gen-
erations a year. The only method of artificial control is to fell

136650°—38——9

130 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

and burn the infested trees or severely scorch the bark. No control
work has been attempted in the West except in California for the
control of a species affecting ornamental Monterey cypress. Ap-

Figure 64.—Smali redwood scored by galleries of the redwood bark beetle (Phloesinus
sequoiae) and a roundheaded horer (Semanotus ligneus var. sequoide).

proximately 20 species have been described from western cedars

and related trees. Many of these are rare and of little economic
importance,

INSECT ENEMIES OF WESTERN FORESTS 131

The western cedar bark beetle (Phloeosinus punctatus Lec.) at-
tacks the trunk and larger limbs of western red cedar, incense cedar,
Alaska cedar, and Port Orford cedar in the mountains of the Pacific
Coast States and eastward through the range of western red cedar.
It is a common species and at times quite injurious to living trees.
The galleries consist of either one short tunnel, not over an inch
in length, or two short tunnels in the form of a V. The beetles
are dark red to black and about one-eighth inch long.

The juniper bark beetle (Phloesinus juniperit Sw.) is dark brown
and about one-eighth inch in length. It attacks the trunks of west-
ern juniper in California and Oregon. P. scopulorum Sw. breeds in
Juniperus scopulorum in British Columbia and southward into
Washington. P. utahensis Sw. breeds in J. monosperma in Colorado
and Utah.

The redwood bark beetle (Phloeosinus sequoiae Hopk.) (44) is
one-eighth inch long and the largest of the genus. It attacks weak-
ened, felled, or fire-scorched redwocd (fig. 64), western red cedar,
and Port Orford cedar along the coast from British Columbia to
central California.

The bigtree bark beetle (Phlocosinus rubicundulus Sw.) works in
broken branches of big trees (Sequoia washingtoniana) in their
native groves in California.

The cypress bark beetles, Phlocosinus cupressi Hopk. and P. cris-
tatus Lec., are at times very destructive to the various species of
cypress in California. Besides killing many trees outright, they
mine and kill the twigs of ornamentals, making the trees very un-
sightly. The Sargent cypress bark beetle (Phloeosinus variolatus
Bruck) is a large species which works in Sargent cypress in Califor-
nia. Other small species of cedar bark beetles which work mainly
in twigs are discussed on page 32.

BARK BEETLES AFFECTING BROADLEAVED TREES

Certain species and genera of bark beetles confine their attacks to
various broadleaved forest trees. Some of these are important
enemies of shade trees, park trees, and ornamentals. Some of the
more common are mentioned in the following paragraphs:

The alder bark beetle (Alniphagus aspericollis Lec.) 18 a common,
and often quite destructive enemy of western alders from British
Columbia southward through California. The beetles usually at-
tack weakened, dying, or felled trees. The adults are small,
robust bark beetles about one-eighth inch long. They bore through
the bark in pairs, usually at the base of branches, and construct a
longitudinal egg gallery from 2 to 5 inches long, with no apparent
nuptial cell. Eggs are placed close together along both walls of
the gallery, with as many as 50 eggs to the inch. The larvae work
out from the egg gallery and pupate in the soft inner bark. There
appear to be two generations a year, with attacks occurring through-
out the growing season.

The ash bark beetle (Leperisinus californicus Sw.) breeds in felled
or dying ash trees in California and Oregon, and under certain con-
ditions may be injurious to living trees. The adults are small bark
beetles covered with scales. They construct egg galleries beneath

8S,
the bark, with two transverse branches starting from a central en-

132 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURD

trance chamber. In the smaller limbs the galleries extend obliquely
around the limbs and may completely encircle them. They are
frequently very abundant in ash cordwood.

The oak bark beetles (Pseudopityophthorus spp.) 1m some instances
attack so heavily as to cause the death of weakened oak trees.
Usually, however, these beetles confine themselves to injured, felled,
or recently killed trees or to the dead branches and twigs of other-
wise healthy trees. The adults are tiny, cylindrical, brown bark
beetles. Their typical work consists of transverse egg galleries ex-
tending for a short distance on either side of the central entrance
tunnel and diverging larval mines running longitudinally with the
trunk or limb.

The mountain mahogany bark beetle (Renocis heterodoxwus Csy.)
is a small brown bark beetle that mines the limbs and trunks of
mountain mahogany in Oregon, Nevada, and California.

The shrub bark beetle (Micracis hirtellus Lec.) is a secondary
species which mines the hard, dry wood of many flowering shrubs
and broadleaved trees including willow, alder, and laurel in Cali-
fornia. The adults are dark reddish brown and about one-eighth
inch long. They have been found boring into lead telephone cables.

The birch bark beetle (Dryocoetes betulae Hopk.) is a secondary
enemy of birch throughout British Columbia, Canada, and the
northern part of the United States.

FLATHEADED BORERS

(Buprestidae)

The flatheaded or metallic wood borers (7/2) comprise a large
family of beetles the larvae of which mine in the inner bark and
wood of many species of forest trees. Their activities are diversified.
A few species attack and kill healthy trees by mining under the bark;
others bore into the inner bark and sapwood of trunks, branches, and
twigs of weakened and dying trees; while others breed only in dead
or recently felled trees and make flattened, winding wormholes
through the wood. A few species are leaf miners. In general, the
group is a destructive one in that they sometimes kill living trees
and often reduce the value of lumber by their attacks. Others assist
materially in the natural process of disintegrating deadwood in the
forest, and these are decidedly beneficial.

The adults are flattened, frequently brightly colored beetles with
a metallic luster. They fly and mate and then lay their eggs in bark
crevices or on the outer surface of the bark, early in the spring or in
summer. When the eggs hatch the young grubs construct long,
winding, oval mines in either the bark or the wood, or in both (fig.
65). These mines gradually widen as the grubs increase in size
and end in elongated, oval pupal cells. The slender white grubs are
the stage usually found in trees, and they can be recognized by their
long, legless bodies, shaped like a horseshoe nail. The head is small,
and the first segment back of the head is much broader than the fol-
lowing body segments and has horny plates on the top and bottom.
Growth of the larvae continues until fall, when activity ceases with
the advent of cold weather. The winter usually is passed in the
larval stage, although some larvae may pupate in the fall and pass

INSECT ENEMIES OF WESTERN FORESTS 133

the winter as adults. Some species require 2 or even 3 or more years
to complete their growth.

Since the beetles of this family have very diverse habits, only those
species which attack and mine the inner bark of living trees will be
considered in this section. Those species that work itn the wood are
more important from the standpoint of forest products and will be
discussed in that section.

FIGURE 65.—Flatheaded borers (Melanophila sp.) : A, Frass-packed channeis in inner
bark; B, full-grown larvae; GC, adults; B and (, natural size.

For the control of flatheaded borers that mine in the inner bark,
the same methods are used as for bark beetles. Infested trees usually
are felled, peeled, and burned, and this work is frequently carried on
in connection with the control of bark beetles.

The pine flatheaded borer (Melanophila gentilis Lec.) (13) 1s com-
monly found throughout the Western States, working beneath the
bark of sugar pine, ponderosa pine, and Jeffrey pine. It is the
species usually found infesting felled trees and logs, windfalls, and
injured trees or occurring as a secondary species in the bole of
standing trees. The adults are about one-half inch in length and are
a bright, bluish green. The larvae are white, legless erubs about 1

134 MISC. PUBLICATION 273, U. 8. DEPT. OF AGRICULTURE

inch in length. They are primarily bark-boring in habit and rarely
enter the wood. On reaching maturity the larvae work out into the
outer bark and pupate in oval cells close to the surface. There
appears to be one generation annually.

The California melanophila (Melanophila californica Van D.) is
similar in habits to the foregoing but has been found very destruc-
tive to various pines throughout California, Oregon, and Idaho. It
is also reported from Douglas fir and bigcone spruce. Pines grow-
ing on rocky slopes, in fringe type stands, or in other situations
where soil moisture is insufficient for normal tree growth, and old
decadent trees are most frequently subject to attack. The larvae
bore under the bark of the main trunk and scar the sapwood of
apparently healthy trees, and it is the species of flatheaded borer
most frequently found killing the tops of ponderosa pines. The
adults are a greenish bronze and about one-half inch in length.

The fir flatheaded borer (Melanophila drummondi Kirby) is the
species of this group most frequently found attacking Douglas fir,
balsam firs, and hemlock. It also attacks western larch, spruce, and
possibly other conifers. Though preferring trees that are dying or
recently felled, the beetles sometimes attack and kill apparently
healthy trees. The adults are from three-eighths to one-half inch
in length and are metallic bronze or dull shining black and have an
iridescent sheen. Some of the beetles have bright golden spots on
the wing covers. Jf. pini-edulis Burke works in dying or dead pifion
pine in Colorado, Utah, and Arizona.

Certain small, flat, nearly black metallic beetles called “firebugs”
are well known to fire fighters in the pine region on account of their
prevalence around forest fires, where they gather in large numbers on
the men’s backs or bite them on the neck, arms, and hands. They
appear to be strongly attracted by the smoke of forest fires; and
during conflagrations, owing to some peculiar instinct, they try
frantically to lay their eggs on the still smouldering trees.
Several species of Melanophila have this habit, the most common
offenders being M/. acuminata DeG. and M. consputa Lec., which
attack badly fire-scorched or weakened pines, spruces, firs, and other
conifers, and even some hardwoods. The larvae feed in the inner
bark.

There are many other species of flatheaded borers that feed in
and under the bark and do more or less damage to forest trees, but
so far none of the western species have become of sufficient impor-
tance to require the application of control measures, and space does
not permit sting them here.

ROUNDHEADED BORERS OR LONG-HORNED BEETLES

(Cerambycidae)

The roundheaded borers, or long-horned beetles (24), are an im-
portant group of forest insects, and include some very destructive
species of tree-killing and wood-boring forms. Few of the western
species, however, are serious enemies of living trees, although many
species are injurious to forest products.

The adults are medium- to large-sized, oblong to cylindrical beetles,
with antennae often longer than the entire body. These long anten-
nae, or feelers, are their most characteristic feature and give them the

INSECT ENEMIES OF WESTERN FORESTS 135

name of “long-horned beetles.” The name “roundheaded borers”
comes from the structure of the larvae, which are white, long, slender,
usually legless grubs with enlarged thoracic segments, and with a
horny plate on the top surface of the first segment near the head,
but with no plate on the under side of this segment. This distin-
euishes them from the flatheaded larvae, which in most species have
a plate both above and below.

While many of the species are characteristically wood-boring in
habit, one group confines its work to boring beneath the bark. Some
of these bark-boring
species are injurious
LO iv Meo sb Ie eS,
whereas others work
in the bark of trees
killed by other in-
sects, or breed in the
bark of felled, fire-
killed, or wind-
thrown trees. Some
are beneficial in that
they feed so vora-
ciously on the bark as
to rob the primary
bark beetles of their
food and thus reduce
their progeny.

The adults deposit
their eggs in bark
crevices, and the
young larvae bore
through the bark
and construct long,
irregular mines in
the bark and wood.
These are increased
In size with the
growth of the larvae Figure 66.—Roundheaded_ fir borer (Tetropium abictis) :

A, Adult, x 3; B, detail of adult head, side view, x 4;
and are . usua l ! aye C, larva, X 2; D, dorsal view of last abdominal segments
packed with the bark of larvae x 2; B. pupa, x Pap Hy, cochon of parasitized

% arva in pupal cell, natural size; G, Ichneumon parasite,
or wood fibers of the natural size. (Drawing by Edmonston.)

larval borings.

So far no attempt has been made to control these species in west-
ern forests, and few are ever aggressive enough to warrant such
measures.

The roundheaded fir borer (Vetropium abietis Fall) is probably
the most injurious roundheaded bark-boring species in western conif-
erous trees. The grubs are commonly found working under the bark
of felled balsam firs and are sometimes suspected of being respon-
sible for the death of standing trees. In the adult stage this insect
tae oe brown beetle about three-fourths of an inch in length

g. 66).

The western larch roundheaded borer (Z'etropiuwm velutinum Lec.)
works between the bark and the wood of weakened larch and hem-

136 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

lock and is sometimes suspected of killing such trees. It is distributed
through the Rocky Mountain and Pacific coast regions, where it also
is found breeding in Douglas fir, balsam firs, and sometimes in pines.
The adults are elongated, velvety brown beetles about one-half inch
in length and are in flight from May to August. The larvae feed in
the bark, where they
construct irregular,
winding mines which
sometimes complete-
ly encircle the tree.
During the later
stages of larval de-
velopment they may.
enter the wood to
pupate, or pupate in
the bark.

The ponderosa
pine bark borer
(Acanthocinus spec-
tabilis Lec.) (fig
67), in the larval
stage is the large
white grub so com-
monly found in pon-
derosa pines killed
by the western pine
beetle, and is some-
times mistakenly
supposed to be the
insect responsible
for the death of the
trees. It also occurs
in other pines. These
insects are more ben-
eficial than _ other-
wise, in that they rob
FicuRE 67.—Larva and work of the ponderosa pine bark the bark beetles of

borer (Acanthocinus spectabilis). The borings are shown t h (oad Ha af (ome) d. The

crossing those of the western pine beetle. Insert: A. .
Male beetle; B, female beetle. All natural size. adults are Lat oe,

speckled, gray bee-
tles with extremely long feelers, and the female has a long, hornlike
ovipositor extending from the end of the abdomen.

The locust borer (Cyllene robiniae Forst.) (22, 34, 45) (fig. 68)
is well known as an economically important insect pest of locust in
the Eastern States and has spread as far west as Colorado and east-
ern Washington. The adults are somewhat slender, one-half to two-
thirds of an inch in length, black, heavily marked with yellow, and
with reddish legs. The markings on the wing covers or elytra con-
sist of zigzagged and broken lines, and on the thorax and body are
narrow yellow bands. The adults appear late in summer and lay
their eggs in the crevices of the bark. The larvae bore irregular,
winding galleries into the sapwood and heartwood of locust and

INSECT ENEMIES OF WESTERN FORESTS 137

often bring about the death of the trees. Trees may harbor succes-
sive broods of these insects for a number of years before being killed.
Much damage is caused by the wind breaking off the infested stems
of young trees within 3 feet of the ground. The winter is passed by
the very young larvae in the bark, and pupation occurs the following
July. Damage in plantations can best be reduced by growing trees
on good sites.

The poplar borer (Saperda calcarata Say) (42) breeds in felled and
weakened aspen and poplar throughout most of the United States,
The adults are elongate, robust, ‘erayish beetles about 1 inch in
length, with faint yellowish spots on the elytra, and the antennae are
as long or longer than the
body. Emergence of the
adults occurs late in July
andin August. The female
chews a slit in the bark, in
which one or two eggs are
deposited. The young lar-
vae mine into the bark and
remain there over winter.
They enter the sapwood
and heartwood the follow-
ing spring, where they feed
for 2 years. During this
time an opening is main-
tained through the bark
where the eggs were laid,
and through this boring
dust is expelled. When
mature the larvae construct
pupal cells near the lower
end of the larval mines,
and in these they remain
inactive until the follow-
ing spring. In July of the
third year the adults =
emerge through the holes Ficure 68.—Locust borer (Cyllene [oviniae) : A,
TeeoMovgiuemlanyae torex-: halt “natural size) “(Drawing by ‘Edmouston.)
pelling frass.

The amethyst cedar borer, (Hylotrupes) Hemicallidium amethysti-
num Lec., attacks western red cedar, incense cedar, and juniper; and
although ‘it usually selects injured or dying trees, it sometimes ap-
pears responsible for killing healthy trees. The adults are black,

over 1 inch in length, and have violet or bright-blue wing covers.

Other species of bark-boring roundheaded ‘beetles are as follows:

Species Hosts and distribution
Aime, WorsaluismMuees-. Ha Cypress, juniper, and incense cedar. Western
States.
Semanonismioneus, FE. var == Juniper, cedar, big tree, redwood, hemlock,

spruce, Douglas fir, balsam firs, larch, cy-

press, and pines. North America.
Phymatodes tidus Lec 2-2. Cypress, redwood, and cedar. Pacific coast.
Leptostylus nebulosus Horn__—~-_- Balsam firs. Oregon.

Phymatodes decussatus Lec_____-. Oak. Washington.

Acanthocinus obliquus Lee _--_____ Pines and spruce. Western States.

138 MISC. PUBLICATION 278, U. S. DEPT. OF AGRICULTURE

BARE WEEVILS

Some bark weevils of the genus Pissodes (48) are particularly im-
portant as enemies of terminal shoots (p. 33) ; others attack the basal
portion of the trunk of small trees and may extend their work into the
roots. Weakened, suppressed, and decadent trees are usually preferred,
but under some conditions these insects may attack healthy trees.
Usually they breed under
the bark of logs, in stumps,
or under the bark of dying,
standing trees and hence
are of little economic im-
portance.

The adults are stout bee-
tles with uniform or varie-
gated markings of yellow,
brown, or black. The head
is prolonged into a snout
or break, which is used to
puncture buds and tender
bark of terminal or lateral
branches for feeding pur-
poses, and in the case of the
female to make a hole for
the reception of the eggs.
The larvae are small, white,
legless grubs, with curved
cylindrical bodies. The
larvae mine under the bark
and form winding galler-
ies, gradually increasing in
size, which extend through
the inner bark and some-
times score the sapwood.
Each mine ends in a pupal
cell constructed partly in
anne ee the bark but mostly in the
FIGURE 69. Yosemite bark weevil (Pissodes yosem- sapwood, This cell is oval

a ODk) Typical work and adults. Natural in outline and is lined with

excelsiorike shreds of
wood fiber. The nearly round larval mines and the “chip cocoons”
are characteristic features of their work.

The adults are long lived and may deposit their eggs over a con-
siderable period of time. The larvae, which reach maturity rapidly,
usually within 2 or 3 months, may overwinter in the galleries or
transform to adults that either overwinter under the bark or emerge
and hibernate in the ground. There usually is but one generation
annually.

Artificial control of the species in western forests has never been
found necessary, as they are usually held in check by natural enemies
and the limitation of suitable breeding material.

Bark weevils of the genus Pissodes that are most commonly found
breeding under the thick bark at the base of small conifers, and the
hosts in which they breed are as follows:

INSECT ENEMIES OF WESTERN FORESTS 139

Species of Pissodes Hosts and distribution

P. yosemite Hopk. (fig. 69) _______ Ponderosa pine, sugar pine, and western
white pine. California, Oregon, and
Washington.

PSCC OTNIGhsS Hopke = 2l a. Saas Ponderosa pine. California.

aU CU DIRE O [) Keke tents SEE Ey Ponderosa pine, Mexican white pine, and -
lodgepole pine. Southern Rocky Moun-
tains.

PTC LUCHELOD Kee 2 ta es See Monterey pine, Bishop pine, knobcone pine,
and lodgepole pine. California and Wash-
ington.

Pamurravancie Hopk=—-—--—-— = - = = Lodgepole pine. Eastern Oregon, Washing-
ton, and the northern Rocky Mountain
region.

PP eCUUELCT bel OK sees = a Western white pine. Northern Rocky
Mountains and northward into Canada.

eRe GSCLOLAUS AuCG = ee Oe oS Douglas fir. Oregon, Washington, and Brit-
ish Columbia.

Pepper weloOpke <2) | 2k es ee Balsam firs. Oregon, Washington, Idaho,
and British Columbia.

PREOUPIGCULELO kts et es eta Alpine fir. Rocky Mountains.

iP costatuseMannh= = Sitka spruce. Oregon to Alaska.

Pcoloradensis Hopk.—-___--_=__ Spruces. Rocky Mountains.

IPAMaSCENSISTELOP ket S22 Engelmann spruce and probably’ other
spruces. Montana and northward into
Alaska.

(Also see terminal-feeding Pissodes, p. 338.)
PITCH MOTHS

There are several species of moths, belonging to different families,
that attack the bole and larger limbs of living forest trees. Eggs are
laid on wounds or on the bark surface, and the caterpillars which
hatch therefrom mine into the inner bark and feed upon the exuda-
tion of pitch. These larval galleries are filled with a thick, gummy
pitch, and a large mass of pitch accumulates on the outside of the
bark at the point of attack. Because of the character of their work
they are called pitch moths. Some species are very injurious to the
tops of trees, but the majority simply extend local wounds and do
not threaten the life of the trees.

One large group of these pitch moths belongs to the family
Aegeriidae, called clear-winged moths owing to the absence of scales
on the wings and the general resemblance to wasps.

The sequoia pitch moth (Vespamima sequoia (Hy. Edw.)) (7)
attacks various coniferous trees throughout the Western States, in-
cluding pine, Douglas fir, and redwood. Although the caterpillars
of this moth are frequently found working in large pitchy masses on
wounds of forest trees, the species is not a serious enemy. Sometimes
breakage follows the attacks on small trees, or the pitchy, healed-over
galleries cause defects in the lumber.

The adults are clear-winged moths about two-thirds of an inch in
length, somewhat resembling a wasp or yellow jacket, as the body is
marked with yellow lines. The caterpillars are dirty white or yel-
lowish and about three-fourths of an inch long when full grown.

The adults appear in the latter part of June and in July and
lay eggs in bark crevices or in mechanical wounds on the trees.
The larvae start the construction of mines from the place where
the eggs are laid and bore winding mines through the inner bark
and the outer layers of wood. A large mass of gummy, sticky
pitch, mixed with boring dust, exudes from the point of entrance.

’
|
'
:

140 MISC. PUBLICATION 273, U. 8. DEPT. OF AGRICULTURE

Two years are required to complete the life cycle, and both winters
are passed by the larvae in their galleries. When mature the
larvae transform to pupae within the pitch mass, and just prior to
emergence the pupae push their way partially out so as to permit
the moths to emer ge without coming in contact with the pitch mass.

The Douglas fir pitch moth (Aegerza novaroensis Hy. Edw.) (8)
attacks Douglas fir throughout the range of this tree and has also
been recorded from weakened larch. As in the case of the sequoia
pitch moth, its economic importance lies primarily in the subsequent
lumber: defects.

The adults are clear-winged moths with a wing expanse of 114
inches. They have spots of orange red on the thorax and bands of
the same color on all the body segments except the last. The males
are distinctly smaller than the females. The larvae are slender
white caterpillars with brown heads, and when full grown range
in length from 1 to 14% inches. The larval skin is quite transparent,
and in this respect the larvae differ from those of the sequoia pitch
moth,

Brunner reports the appearance of the adults during the latter
part of May and in June. The habits are comparable to those of
the sequoia pitch moth, except that 4 years are required for develop-
ment. Winters are passed by the larvae in their galleries, which are
covered with large accumulations of pitch.

The spruce pitch moth (Parharmonia piceae Dyar) is a shining
black species with a red spot on the under side of the abdomen, T he

caterpillars work in Sitka spruce along the coast of Oregon and
Washington.

There are many other species of clear-winged pitch moths that
work in various ‘coniferous and broadleaved forest trees, though
they are rarely found and are of little economic importance. Some
of the species of the family Pyralidae, or snout moths, work in the
inner bark of various coniferous trees, causing a heavy exudation
of pitch, and cause injury very similar to that of the clear-winged
moths. Most of these do more serious damage to young trees than
to older ones and therefore were discussed in the section dealing
with younger trees (p. 37).

Many species of clearwing moths or pitch moths belonging to the
family Aegeriidae work in the inner bark and bore into the wood
of various forest trees. An exceptionally large number of these
work in the wood of broadleaved trees and at times so riddle the
interior that the limb or tree dies or is broken off by the wind,
and the products derived from the wood show serious injuries. The
adults of this group are very pretty moths with clear wings, and
resemble hornets. The caterpillars are naked or have only” a few
prominent hairs. There are so many species that are seldom seen
by the forester that no attempt will be made to list the western
species here. The alder borer (Aegeria americana Beut.) 1s some-
times found working in alder. The locust clearwing (Paranthrene
robiniae Hy. Edw.) is sometimes very injurious to locust and poplar.
The cottonwood crown borer (Aegeria tibialis Harr.) infests poplar
and willow, as does also A. pacifica Hy. Edw. and Alcathoe api-
formis Clerck. Aegeria mellinipennis Bdvy. attacks sycamore and
oak in California.

INSECT ENEMIES OF WESTERN FORESTS 141

INSECTS INJURIOUS TO WOOD AND FOREST
PRODUCTS

Insects lay a heavy toll on crude and finished forest products (26,
47, 72, 76), a loss that has been variously estimated to be from 1
to 5 percent of the annual cut. The principal damage to forest
products is caused by insects that feed on or bore into the wood.
Some damage is done to wood while still in living trees, but a great
deal occurs after trees have been killed or felled, ‘and before utiliza-
tion; and the green or seasoned lumber, and even the final utilized
products are fed on by insects.

After a tree has been killed by fire, insects, or other causes, or
felled by wind, snow, or cutting operations, it becomes particularly
attractive to a ‘large ‘variety of insects. Ambrosia beetles find the
dying wood with fermenting sap an especially suitable medium for
the growth of their fungi. Horntail wasps, or wood wasps, settle on
freshly felled trees, sometimes before the woodsmen have finished
cutting them into logs, and on fire-killed trees before the fire is out,
and insert their long slender ovipositors deeply into the wood to lay
their eggs. Many of the flatheaded and roundheaded borers,
weevils, “and larvae of carpenter moths and clear-winged moths are
wood boring i in habit. The larvae usually feed for a time in the cam-
bium layer “and then penetrate the wood. Fresh, unseasoned wood
still containing sap, pitch, or other essential food elements is re-
quired for them. In short, so many different species of wood-boring
insects start their work on killed or felled trees that it is important
that such timber be peeled or promptly removed from the woods
to avoid heavy damage.

After lumber has been kiln dried it becomes reasonably safe from
insect attack. There are, however, a few important groups which
still persist in their attacks unless the wood is properly handled.
The seasoned sapwood of hardwoods is particularly susceptible to
damage by powder-post beetles and must be carefully managed in
the lumber yard or in storage to avoid becoming infested. ~ Even.
after timbers are in place they are subject to attack by these insects,
by carpenter ants, by certain roundheaded wood borers, flatheaded
borers, and by termites unless precautions are taken to provide
proper insulation from the ground or protection is secured through
the impregnation of the wood with creosote or other chemicals.

As has been indicated, the control of insects injurious to forest
products is largely a matter of prevention of damage through cutting
at the proper season, prompt removal of logs, poles, and stulls from
the woods, proper handling in the mills, and certain precautions in
utilization. Logs that are to be used for poles or in rustic work
should be peeled before wood borers have had an opportunity to enter
the wood. Some success has been obtained in repelling attacks of
wood borers by spraying logs with coal-tar creosote diluted with 3
parts of kerosene (23). In cases where logs have been attacked, the
insects can be killed by spraying with crude orthodichlor obenzene at
full strength or paradichlorobenzene dissolved in 3 parts, by weight,
of kerosene (72). All such treatments, however, give only a tem-
porary immunity. More specific methods are discussed for each of
the different insect groups.

——— 2 at

Se ea a oo oo ee) a ee

Bf? SOLA 9 Ore) te

AT NSP A Died

142 MISC. PUBLICATION 273 U. S. DEPT. OF AGRICULTURE

KEY TO DIAGNOSIS OF INSECT INJURY TO WOOD AND WOOD
PRODUCTS

A. Insects attacking green, unseasoned, or seasoning wood, living or dying
trees, or freshly felled trees or logs, and projecting their tunnels
directly into and through the wood... -

1. Small, circular, open pinholes, often surrounded by dark
stains; diameter uniform and less than one-eighth
inch; made by small, brown, shining, cylindrical
beetlescs 20 se i ae ee ambrosia beetles, page 148.

2. Large, more or less circular holes in wood; diameter more than
one-eighth inch; lightly filled with ee wood stained
or not.

a. Nearly circular holes of medium size in wood of broad-
leaved trees made by caterpillers
clear-wing moths, page 1389.
b. Very large irregular holes one-half to 1 inch in
diameter in broadleaved trees, usually lined with
a silky yellowish-brown web__ carpenter moths, page 154.

3. Circular, oval, or irregularly shaped tunnels of varying width
gradually increasing to more than one-eighth inch in size;
usually tightly packed with fine boring dust or coarse
frass, except at ends occupied by larvae or pupae.

a. Tunnels flatly oval, usually lightly packed with arc-
like layers of sawdust-like borings and pellets of
woody excrement, and surface of wood marked by
fine, transverse, crescentric lines; made _ by
slender, white, legless grubs shaped like horseshoe
nails with very wide, flat segments back of head;
first segment with a well developed plate on both
upper and lower surfaces, upper plate marked
with a central line, groove, V or Y
flatheaded borers, page 147.
b. Tunnels broadly oval to nearly circular, tightly packed
with sawdustlike borings and pellets of wood ex-°
crement; made by long, thick, white, apparently
legless grubs, with horny plate on top of first
thoracic segment, which is somewhat enlarged
; roundheaded borers, page 150.
c. Perfectly circular holes in wood, not evident in cam-
bium, made by long, white, cylindrical grubs with
small heads, fleshy lobes for thoracic legs, and
the abdomen terminating rearwards with a sharp
horny prong_-- horntails and certain Coleoptera, page 155.
B. Insects attacking living trees and causing black checks, pitch pockets,
pitch flecks, gum spots, or ring distortion, but not causing pinholes
or wormhboles.

1. Black checks showing in wood of conifers, Surrounded by
curled or distorted wood____.__________ bark maggots, page 158.

2. Birdseye pitch flecks in pine________________ pitch midges, page 54.

3. Double rings, distorted rings, retarded growth’_ defoliators, page 58.

4, Pitch pockets, gum spots, and pitch streaks in coniferous
WV OCS 2 Sitti hie eet cms De Me eer bark beetles, page 96.

Cas SU Seka eke 2 tance ee ce flatheaded borers, page 182.
Se A Sail Maine Al Se Shere SUR Re pitch moths, page 139.
IGOR Th RBIS Ae tt eeeea see ta terminal-feeding insects, page 29.
C. Insects attacking sawed lumber, seasoned wood, or utilized wood
products.

1. Small wormholes in wood, tightly packed with a very fine
powder, powder sometimes pushed out through holes in
wood. Usually working in very dry wood.

a. Small, nearly round tunnels in various hardwoods
powder-post beetles, page 159.
db. Irregulariy shaped tunnels in softwoods and hard-
woods (see above under A, 3).

7 Aiso from causes other than insects.

INSECT ENEMIES OF WESTERN FORESTS 148

2. Large cavities, lightly filled with excrement pellets or frass,
not tightly packed with boring dust. Insects working in
either dry or moist wood.

a. Made by big black ants which leave only chewed
wood fibers in cavities or push these out of the
tunnels, leaving the same quite clean

carpenter ants, page 161.

b. Made by soft, antlike insects with white bodies and
brown heads which usually leave many oblong im-
pressed excrement pellets___________ termites, page 162.

INSECTS WORKING IN UNSEASONED LOGS OR LUMBER
THE AMBROSIA BEETLES OR PINHOLE BORERS

Ambrosia beetles (52) are important enemies of forest products
because of their ability to riddle the sapwood and even the heart-
wood of unseasoned logs or poles with small round pinholes or shot
holes. These holes become surrounded with a dark-brown or black
stain. The beetles of this destructive group belong to the families
Scolytidae and Platypodidae, and although related to the bark
beetles, they have very distinctive habits.

The adults are small, reddish-brown to nearly black, cylindrical
beetles that select for their attack dying or freshly felled trees, saw-
logs, green lumber, or other unseasoned or moist wood such as stave
bolts, or wine, beer, or vinegar casks. Small round tunnels are
bored directly into the sapwood or heartwood, and since the beetles
do not feed on the wood the borings are cast out of the tunnels and
collect on the surface of the bark or wood as a fine light-colored
powder. The character of the tunnels varies with different species.
Some construct an open, simple cavity; others a long, winding, cir-
cular gallery; while ‘still others construct what is called a com-
pound tunnel in that small pockets or larval cradles are gnawed
along the main channel. Into the tunnels, either intentionally or
not, ‘the adults carry the spores of certain fungi. These become
detached, and, if moisture conditions are suitable, the fungi begin
to grow along the walls of the galleries. Each species of beetle has
its own specific ambrosial fungus, and the selection of trees for at-
tack probably depends largely upon the requirements of the fungi.
Some beetles specialize on certain species of trees, while others are
more general in their attacks. As the fungi orow they are fed
upon by the beetles and the developing larvae. The living require-
ments of these insects are very exacting. If moisture conditions
are not suitable the fungi fail to grow, “and the beetles starve, or
if the fungi grow too abundantly, the beetles are unable to cope
with them and are smothered in their own food. For this reason
only moist, unseasoned wood is suitable for attack, and dried
seasoned lumber is immune.

The shot holes and the accompanying stain are serious defects of
lumber and often render it worthless. In some seasons 30 percent
or more of the lumber from Douglas fir logs on the Pacific coast
has been ruined by the attacks of these beetles. Spruce airplane
stock has been badly damaged in this same region. Damage is
usually the greatest in the South or along the coast where mild
winters give favorable temperature and moisture conditions for a
long period of beetle activity. Where the winters are severe the

——— a

SSS ee ee SO ee Oo

ee eS. ER <> & eee

144. MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

beetles become inactive and thus a longer period may elapse be-
tween the time of cutting and the removal of logs, before damage
becomes important.

The control of ambrosia beetles is largely a matter of prevention
of damage through the regulation of woods practice and proper
handling of the products from the mill. Logs cut in the summer
or fall should be removed from the woods within a week or two
after cutting and either placed in water or run through the mill
(56a). Logs cut late in the fall, in widwinter, or early in the spring
will be reasonably safe until the approach of warm weather but often

FicurE 70.—Tunnels in fir made by ambrosia beetles: Long winding tunnel made by
Platypus wilsoni; branching tunnels made by Gnathotrichus sulcatus.

cannot be removed before damage has occurred. Freshly sawed
lumber. will be safe from attack if it 1s dried quickly, but some
damage may occur in storage if the lumber is piled so as to re-
main or become moist. Logs or wood either heavily soaked with
water or quite dry are not suitable for attack, but the exposed parts
of logs left floating in ponds are very apt to become infested. In
general, the control of these beetles 1s very difficult, and prompt
utilization or kiln drying of the lumber is about the only satis-
factory solution (49c). A small amount of parasitism has been noted

INSECT ENEMIES OF WESTERN FORESTS 145

in studies connected with the work of these beetles in seasoned prod-
ucts, but it is of insufficient importance to reduce appreciably the
number of beetles and the injury they cause.

Wilson’s wide-headed ambrosia beetle (Platypus wilsonit Sw.) is
very different from the other species in that the adults are long,
slender, somewhat flattened, reddish-brown, shining beetles about
one-fourth inch in length, with a few long yellow hairs, projecting
wing covers, and broad heads. They construct round, winding
tunnels, of a few inches to a foot in length (fig. 70), into the sap-
wood and heartwood of
dying, weakened, injured,
or recently dead or felled
balsam firs, Douglas fir,
spruce, and hemlock, and
sometimes other conifers.
At intervals along the
main tunnel secondary
tunnels branch horizon-
tally. Kggs are deposited
loosely in small clusters
in the tunnels, each female
laying 100 or more. The
young larvae wander
freely about in the mines,
feeding on the ambrosial
fungus, and reach matur-
ity In 5 or 6 weeks. When
full grown they excavate
cells at right angles to the
main gallery in which to
transform to pupae and
adults. These eells are
parallel to the grain of
the wood and are often
arranged in groups of 8
to 10 or more. The insect
is distributed over the en-
tire Pacific Northwest,

where it is the only repre- = Ficure 71.—Damage to sapwood of western white
sentative o f the family pine. Riya by an ambrosia beetle (Trypoden-

. Platypodidae.

The wood stainers of the genus Gnathotrichus are small, cylindri-
eal, dark-brown or black beetles of the size and appearance of a short
piece of pencil lead. They attack nearly all species of conifers in the
Western States, and one species works in alder. Their work is dis-
tinguishable from that of other western ambrosia beetles in that a
primary tunnel penetrates the sapwood, and at intervals along this
tunnel secondary tunnels branch horizontally, the branches more or
less following the annual rings. The tunnels are of the compound
type, in that larval cradles are constructed at regular intervals, both
above and below the primary and secondary galleries. ‘The species
so far recorded in the West are as follows:

136650°—38——10

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Qn 7 & + |» sR 38

4) at

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146 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

Species of Gnathotrichus Hosts and distribution

Gu retusus Leese e 2 a) Sea a Pines, hemlock, Douglas fir, and balsam firs.
Western States and Canada.
G:. sulcatus Veet see ee Spruce, hemlock, Douglas fir, and balsam firs,

and sometimes also pines, redwood, cedar,
and other conifers. Western States.

Ge aciculatus 7 Bikim 2) eee ae Ponderosa pine, Mexican white pine, Douglas
fir, and white fir. Rocky Mountain region.

Gdenticuiatis Bikm=_ 222 oes k: Pines and white fir. New Mexico, Arizona,
and Texas.

Gonainiibikmes. 220s See ie re ornien Alder. Western Oregon and Washington.

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FiGurE 72.—Tunnels of the oak timber beetle (Pterocyclon scutellare) and adults: Male
above, female below, x 8

The ambrosia beetles of the genus Trypodendron are small, stubby,
dark-colored beetles, with a roundish prothorax and a smooth, more
or less shining body, often with lighter colored longitudinal stripes.

They attack the wood of many species of coniferous and broad- .

leaved trees and are distributed throughout the greater part of the
United States and Canada. Their galleries (fig. 71) are of the
compound type with larval cradles arranged in series both above
and below the main tunnels, which branch in a horizontal plane
and cut across the grain of the wood.

The species most frequently encountered in the Western States are
as follows:

Species of Trypodendron Hosts and distribution
TS TOtuintalim, Kirby a aes ae Nearly all conifers. North America.
TP UT OTSUS IAT DY 2h eee me Lodgepole pine. Idaho, Montana, Oregon,
and Washington.
TD COG motse Mian = esses Pine, spruce, alder, birch, and cedar. Pacific
Northwest,

INSECT ENEMIES OF WESTERN FORESTS 147
Species of Trypodendron Hosts and distribution
TEM UOKRCHLUS BS Wee see et Engelmann spruce and _ white-bark pine.
Idaho and Montana.
Te pon aderosae ISwee- 2-22 = Ponderosa pine, Engelmann spruce, Douglas

fir, and mountain hemlock. British Colum-
bia and south to Oregon.

me ROLILS ILS) wliG Gas ee ee Bee Poplar and aspen. Western States and
Canada.

The oak timber beetles of the genus Pterocyclon (Monarthrum)
are small, elongate, cylindrical, dark-brown ambrosia beetles which
work in the wood of oak and various other hardwoods and deciduous
trees. After the beetles have entered into the wood they excavate
a central nuptial chamber from which secondary tunnels branch in
three or four directions. From the secondary branches the larval
cradles are excavated at right angles and parallel to the grain of the
wood. Pterocyclon scutellare Lec. (fig. 72), about one-eighth inch
in length, works in various species of oak from Oregon to southern
California. P. dentiger Lec. is a smaller species, about. one-sixteenth
inch in length, which works in the same trees in California.

Species of Xyleborus make very small pinholes in the dying or
dead wood of a wide assortment of fruit, shade, and forest trees.
Larval cradles are not formed, and the tunnels are either plain or
enlarged into cavities where the larvae feed. Most frequently their
work is found in dying or recently dead wood. Xyleborus scopu-
lorum Hopk. works in the dead woed of ponderosa pine and Coulter
pine in California, Oregon, and South Dakota. X. arbuti Hopk.
works in madrona in California. X. xwylographus Say is the very
common eastern species which attacks a large variety of hardwoods.
Similar species in the Western States have been referred to this spe-
cies. The galleries consist of simple branching tunnels in which the
larvae live and feed upon ambrosial fungus without constructing an
enlarged cavity or larval cradle.

THE FLATHEADED WOOD BORERS
(Buprestidae)

The flatheaded borers have been previously discussed under the
section on cambium or inner-bark miners (p. 132). By far the larger
number of species, however, are of more economic importance as
wood borers than as killers of living trees. Many species work first
in the inner bark of dying trees, then extend their tunnels into the
sapwood and even into the heartwood. The flattened oval wormholes
that are made by the horseshoe-nail-shaped grubs are usually tightly
packed with boring dust and may wind in a tortuous fashion back
and forth through the wood so as to riddle it completely. Even a
few such wormholes greatly lower the quality of the lumber, and a
large number make it unfit for any but the roughest use. Some of
these wood borers attack the pitchy fire scars on living trees and
gradually extend their mines into the sounder portions. Many others
attack trees that have been killed or felled and do most of their
damage while the wood is still unseasoned. Others will attack wood
after 1t has been run through the mill and is placed in storage, or
even after it has been put into use.

The prevention of fire scars and other injuries to standing trees
and the prompt utilization of dead or felled trees will reduce this

= @& /; | + ee eR 6JS

Sees 1) oe COP

—~

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ee

148 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

damage to a low point. In wood that has become infested after being
put into place, the grubs usually can be reached and killed by liberal
applications of crude orthodichlorobenzene or kerosene.

The sculptured pine borer (Chalcophora angulicollis Lec.) (fig.
73) 1s the largest of the western species of flatheaded borers and the
only western representative of this genus. The adults are over 1
inch long and dark brown to black, with an iridescent bronze luster,
especially on the under side. The upper surface is marked with ir-
regularly sculptured areas. Many a woodsman has been startled on a
warm summer day to have one of these large beetles suddenly take
flight with the noise of a small airplane from its quiet resting place
on a hearby tree trunk. The larvae feed in the wood of dead pines
and firs throughout the Western States.

FIGURE 73.—Flatheaded wood borers: A, Chalcophora angulicollis, larva and adult, * 1.5
(drawing by Edmonston); B, the same, natural size; @, Dicerca tenebrosa, natural
size. _

The golden buprestid (Buprestis aurulenta L.) is one of the most
destructive species in this group. The adults are beautifully colored
beetles one-half to three-fourths of an inch in length, with a flattened
oval body and an iridescent green or bluish color, with all margins
bordered with copper. They are particularly attracted to pitchy
wood and lay their eggs on fire scars or the expesed pitchy wood of
pines, firs, and other conifers. Flooring and woodwork of Douglas
fir that is not heavily covered with paint or varnish is sometimes re-
peatedly attacked until the interior is completely riddled and
destroyed. If the wood is very dry, it takes several years for the
larvae to complete their development.

There are about 12 other species in this genus of highly colored
beetles that do similar damage to the wood of western forest trees.
Some of the more common are as follows:

INSECT ENEMIES OF WESTERN FORESTS 149

Species of Buprestis Hosts and distribution
BRO CCLUMLC Ce ee Seer Dios OD. Jeffrey, lodgepole, and other pines. West-
ern States.
EPRCOMRECLG LON ss see Jeffrey pine and ponderosa pine. California,
Oregon, Idaho, and Montana.
Beiacvvuentirs Week sens so oes. Ponderosa pine and other pines and Douglas

fir. California, Oregon, Washington, Idaho,
and Arizona.
B. maculativentris var. subornata

Lee. Safe, asf iene eae Pines. Western States.

BeeRUSCUCOTULTH SGU DV eee Douglas fir and balsam firs. Throughout the
Western States.

1B) TAGI UO ea CW 0 0 a es Douglas fir and ponderosa pine. All Western
States.

B. viridisuturalis N. and W____- Poplar, cottonwood, and white alder. Cali-
fornia and Oregon.

ECONTLCWECR SA ee ee Poplar and aspen. Throughout the United
States.

AO UO Stale Cente timc ek Se Oak and cottonwood. California, Oregon,

Washington, and Colorado.

The dicerca beetles, members of the genus Dicerca, are medium-
sized, robust, roughly sculptured, metallic, wood-boring beetles of a
dull bronze color, with the tips of the wing covers prolonged into
narrow points. The larvae work under the bark and into the wood
of various species of trees that are sickly, dying, or dead. Of the 10
species recorded from the Western States, those most frequently
found breeding in the wood of forest trees are the following:

Species of Dicerca Hosts and distribution
D. tenebrosa Kirby (fig. 73) —------. Pines, balsam firs, Douglas fir, and Engel-

mann spruce. California, Oregon, and
Eastern States.

DaSCLUMlusaerotehees “oe Se en eo. Douglas fir, ponderosa pine, Jeffrey pine,
and knobecone pine. New Mexico, Ari-
zona, California, Oregon, and Washington.

DuGEUSSIGONL IS mle Cee ee 2 Lodgepole pine and Douglas fir. California,
Oregon, and Washington.

IDS FN AOUOMO UGE \UN CE aS See aes ere Aspen, cottonwood, poplars, alder, and other
broadleaved trees. All Western States.

ID (CR, (CrOKe l= 32 ae ee ee Alder, madrofia, oak, sycamore, and other

broadleaved trees and shrubs. Montana,
Idaho, Washington, Oregon, and Cali-
fornia.

DD OVaGTIGOLOASAYS 2 = Sis ste Alder, birch, and other broadleaved trees.
Colorado.

The western cedar borer (7’rachykele blondeli Mars.) (14) (49a)
mines in the sapwood and heartwood of living, injured, dying, or
dead trees of western red cedar, cypress, and related species and is
very destructive to trees used for poles, shingles, cooperage, ship-
building, or other purposes where sound wood is required. The
adults, which are roughly sculptured beetles about five-eighths of
an inch,.in length, of a very beautiful, bright emerald green with

a golden sheen, lay their eggs on the wood of scars on the trunk or
ee of standing trees, and the flatheaded larvae mine about in
the wood for a period of 2 or 3 years before reaching maturity.
The newly formed beetles remain in the wood for about 6 months,
from September to May, before they emerge and start a new genera-
tion. There is no practical means of control under present. forest
conditions. The variety 7. blondelt juniperit Burke is found in
junipers in California.

150 MISC. PUBLICATION 2738, U. S. DEPT. OF AGRICULTURE

Three other species of this genus are found in the Western States
doing similar work in various cedarlike trees.

Species of Trachykele ws Hosts and distribution
EOD Ulenta aera eee Incense cedar, big tree, western red cedar,
and related trees. California, Oregon,
and Washington.

TT RiMbOsSd2 Wallies eke ae ais Balsam firs and mountain hemlock. Cali-
fornia, Oregon, Washington, and British
Columbia.

TP Snhartimant burkel-=3 2s es Sargent cypress. California.

Below are listed other western species of wood-boring. buprestids
that may cause damage of some economic importance:

Species Hosts

iPOCCILONOUG ‘Spp)=e2 2224-6 See About 5 species which breed in willows and
poplars.

Chrysobothris- spp eS aes About 26 species in both conifers and
broadleaved trees.

ACMOGCOGCrAASPD2 se eee About 18 species in various broadieaved
trees and shrubs.

Polycesita spp 232 e a eee Three species in broadleaved trees and
shrubs.

(Also see bark-, twig-, or cone-bearing buprestids, pp. 21, 35, 132.)

THE ROUNDHEADED WOOD BORERS

(Cerambycidae)

The roundheaded borers or long-horned beetles (27) have been
previously discussed (p. 184) under the section of miners of the inner
bark and cambium region. The western members of this family,
however, are much more important from the standpoint of damage
to forest products than in the role of killers of living trees. Most
of the species are typically cambium-wood insects, in that the larvae
first mine in the cambium region of dying or dead trees and then
extend their tunnels into the sapwood and in some cases into the
heartwood. The large, broadly oval wormholes are a serious defect
in lumber, and if these are numerous the wood becomes worthless
for lumber purposes. Dying or dead trees, those killed by insects
or fire, or trees felled in cutting or by windstorms are most fre-
quently selected for attack; and if such timber is not promptly
removed from the woods, it may soon be completely ruined for
commercial purposes. The salvage of fire-killed trees frequently
depends upon the rapidity with which they can be removed from
the danger of attack by these borers. Unpeeled logs left in the
woods during certain seasons of the year are often seriously
damaged.

There is no way, in which these insects can be controlled in the
woods, and there seems little likelihood that practical methods will
be developed that will prevent attack on dead or dying trees or
recently felled logs. As with other insects that attack unseasoned
wood, about the only thing that can be done is to remove the logs
from the woods as quickly as possible and place them in water or
run them through the mill and kiln-drying process. A few of these
insects, however, are of importance even after the lumber is placed
in storage.

INSECT ENEMIES OF WESTERN FORESTS 151

The ponderous borer (H'rgates spiculatus Lec.) is very destruc-
tive to the wood of recently killed or felled coniferous trees, to
fallen logs and stumps, and even to power and telephone poles. Re-
cently it has been found to be a most important determining factor
in the salvage of fire-killed Douglas fir. The heartwood of this tree
is very resistant to deterioration until penetrated by the large mines
of this wood-boring species. The adults are the largest of our
western beetles, measuring from 11% to 214 inches in length (fig. 74).

Figure 74.—Larvae and adult of the ponderous borer (HLrgates spiculatus). Natural size.

The color is uniformly dark brown, with the head and thorax some-
what darker than the elytra. The sides of the prothorax are armed
with a few large or many small teeth or spines. They are often
found flying around lights early in the summer. Eggs usually are
Jaid in crevices of the bark of dead trees or stumps, and the larvae
excavate large channels, packed with coarsely chewed wood fiber,
in the sapwood and then into the heartwood. When full grown the
large, thick-bodied larvae are often 214 inches in length, creamy
white, with reddish heads bearing plates armed with four spines just
above the mandibles. The species is found throughout the Western
States, commonly attacking Douglas fir and pines but also other
conifers.

The California prionus (Prionus californicus Mots.) is another
large species very similar to the foregoing. The larvae feed in the
wood of oak, alder, poplar, and other hardwoods, sometimes boring
into the roots of living trees. The adults usually have three promi-
nent spines on the lateral margins of the prothorax. The larvae are
very similar to those of Lrgates.

152 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

SAWYERS

The larvae of the genus Monochamus, known as sawyers, are re-
sponsible for extensive damage to dying and recently killed and
felled trees throughout the United States. The females chew irreg-
ular pits in the bark, and in these from one to six eggs are placed.
The larvae, which are elongated, footless, whitish grubs, feed from
4 to 8 weeks between the bark and wood, loosening the bark and
filling the space between bark and wood with long fibrous borings.
Later the larvae enter the wood, forming small oval holes, that
become nearly round as the larvae mature. These tunnels extend
through the sapwood, often into the heartwood, and then turn out-
ward to the bark several inches from the point of entrance, thus
making U-shaped burrows in the wood. During the early stages of
larval development
the borings are
dropped from the
galleries and form
small piles of saw-
dust. As the larva
nears maturity the
borings are no longer
ejected, and the gal-
leries are packed
solid, with the ex-
ception of a small
cell at the end of the
gallery in which pu-
pation occurs. The
mature adult emerges
by gnawing a round
FIGURE 75.—Spotted pine sawyers (Monochamus maculosus) pole aie tas ulm

2 XS. ’ layer of wood and

bark which separates

the pupal cell from the surface. Though the life cycle of these insects

is usually completed in 1 year, in the northern portion of the range

two seasons are often required. The adult beetles, during flight and

egg laying, feed upon the needles of conifers, and some species gnaw
the bark from young twigs, many of which are killed.

The spotted pine sawyer (Monochamus maculosus Hald.) (fig. 75)
is from one-half to 1 inch in length, drab brown, with grayish,
irregular-shaped markings. The prothorax is of the same width as
the head and has a prominent toothlike projection on each side. The
larvae, which range from 1 to 134 inches in length, are destructive
to fire-scorched, dying, or recently felled pines and Douglas fir
throughout the Western States.

The Oregon fir sawyer (Monochamus oregonensis Lec.) is a stout,
black beetle, approximately one-half to 114 inches in length, with
gray markings, antennae about twice as long as the boay, and a
toothlike projection on each side of the prothorax. The larvae range
from 1 to 134 inches in length and are destructive to fire-scorched,
injured, dying, or recently felled Douglas fir, balsam firs, and other
coniferous trees of the Western States. This is the western variety
of the eastern black pine sawyer (JZ, scutellatus Say).

INSECT ENEMIES OF WESTERN FORESTS 153

The obtuse sawyer (Jlonochamus obtusus Csy.) is a small brown
beetle with gray markings, measuring from one-half to three-fourths
of an inch in length. The antennae are over twice as long as the
body, and the prothorax has a toothlike projection on each side.
The larvae are from 1 to 114 inches in length and are destructive to
pine and Douglas fir in Idaho, Montana, California, and probably
other Western States.

The black-horned pine borer (Callidium antennatum Newm.) (fig.
76) 1s a common species in western forests which attacks the logs
and limbs of dead ponderosa pine and sugar pine. It has recently

FIGURE 76.—The black-horned pine borer (Callidium antennatum) : A, Larvae; B, pupa;
C, adult; D, larva making tunnels on edging of pine board. A, B, C, natural size.

attracted attention as a destructive borer in lumber stored in mill,
yards in northeastern California, where it attacks strips of bark left
on the edges of lumber stock. The larvae work under this bark and
score the surface of the wood, then extend their mines into the sap-
wood for a depth of 2 or 3 inches. They also injure seasoned rustic
work by mining out the cambium layer and causing the bark to
loosen from the log. The larvae are yellowish-white, apparently
legless grubs about three-fourths inch in length when full grown.
The adults are flat, shining, bluish-black beetles about one-half inch
in length, with antennae about half the length of the body. Other
closely related species are found in the various firs, pines, cedars,
and redwood.

Other species of wood-boring cerambycids which may be en-
countered damaging the wood of western forest trees are the follow-

1S

Species Hosts and distribution
Tragosoma harrisi Lec______--___. Pines. Western States.
Asemum atrum Wsch 222 Pines, firs, and spruce. Western States.
Liasemum nitidum Lee _-----_- Pines, firs, and Douglas fir. Pacific coast.
Criocephalus productus Lec______-_ Pines, firs, and Douglas fir. Western States.
Criocephalus asperatus Lec__-_-_--. Pines. Oregon and California.

oh, ah tie ee

154 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

Species Hosts and distribution

Northorhina aspera Lee_________- Douglas fir. Western States.

Xylotrechus undulatus Say__---_- Pines, firs. Douglas fir, hemlock, and spruce.
Western States.

Xylotrechus nubilus Linsley_—--~- White fir. California.

Ulochaetes leoninus Lee____-___-__ Ponderosa pine, Douglas fir, and spruce.
California to British Columbia.

Aylotrechus nauticus Mann_-___~_. Oak, madrona, and eucalyptus. California
and Oregon.

Neoclytus conjunctus Lee____----~- Oak, ash, and madrofia. Western States.

Neoclytus caprea Say-_---_--__-~- Oak and mesquite. Arizona, Colorado, and
Utah.

Brothylus gemmulatus Lee______- Oak. Colorado and California.

Synaphoeta guexi Lee___________- Oak, maple, and willow. Pacific coast.

Rosalia funebris Mots__---____--- Ash, California laurel, willow and alder.
New Mexico and California to Alaska.

Necydalis cavipennis Lec________- Alder and eucalyptus. Arizona and Califor-
nia.

Xylotrechus obliteratus Lec_____-. Aspen. Rocky Mountains.

Xylotrechus insignis Lec____-_--~-- Willow. California.

Malacopterus tenellus F________-- Willow and poplar. Arizona.

Cyllene antennata White_____-__-. Mesquite. Southwestern States.

WOOD-BORING WEEVILS

(Curculionidae)

Some of the weevils belonging to the genera Rhyncolus, Cossonus,
Pissodes, and Cryptorhynchus are found at times working in wood.
The work of Pzssodes has been previously mentioned (pp. 33 and 138).
The Rhyncolus and Cossonus weevils are small brown or black
weevils less than one-fourth inch in length, with the head produced
into a snout. The larvae are white, legless, and comma-shaped.
Both adults and larvae may be found boring into and destroying
wood, but as the wood is usually in a decaying condition, they are
seldom of any economic importance. :

The popiar and willow borer (Cryptorhynchus lapathi L.) (57)
bores under the bark and into the wood of poplars and willows mak-
ing irregular more or less cylindrical tunnels which often so riddle
the wood as to cause heavy breakage. The adults are rough, dark-
colored weevils about one-fourth inch in length, with a band of
bright pink across the tip of the wing covers. This is an introduced
species which is gradually becoming widely distributed throughout
the country. It has recently been found causing serious damage to
willows along the Columbia River in Oregon.

CARPENTER MOTHS

(Cossidae)

The larvae or caterpillars of some families of moths (Lepidoptera)
are wood boring in habit and mine directly into the wood of injured
or weakened trees, where they may cause additional injury which
may result in the tree’s death. These injuries to the living tree often
appear as serious defects when the tree is converted into lumber.
The carpenter moths, belonging to the family Cossidae, principally
attack broadleaved forest, shade, and fruit trees. The adults are
large, mottled-gray moths, with spindle-shaped bodies and narrow,
strong wings of medium to large size. They are night flyers and lay
their eggs in bark crevices or on old wounds. The caterpillars,
which are nearly hairless, have both true legs and abdominal pro-

INSECT ENEMIES OF WESTERN FORESTS 155

legs but are somewhat grublike in form. Pupation occurs within
the larval gallery, and when about ready to change to the adult the
pupa works partially out of the burrow, so after emergence the
empty pupal skin is found protruding from the tunnel.

The carpenter worm (Prionoxystus robiniae Peck) (fig. 77) is the
most common representative of this group. It attacks oak, elm,
poplar, cottonwood, locust, ash, maple, willow, and other ornamentals
and also fruit trees and is distributed generally throughout the
United States. As is the case with the carpenter moths, these moths
cause injuries that show up later as defects in the lumber, since they
mine in the sapwood and heartwood of trunks and limbs. It is prob-
ably the most destructive insect enemy of oaks in California. The
adult females are gray moths with a wing expanse of from 2 to 3
inches. The males are smaller, with the front wings dark gray and
the hind wings yellowish red lined with black (fig. 77). The mature
larvae are about 214 inches in length, somewhat pinkish, with a dark
head and with scattered hairs arising from small brown spots on the
body. Eggs are laid in June and July, each female depositing from
200 to 300. Three years are required to complete the life cycle.

Another species, Acossus populi Walk., does similar work in pop-
lars and cottonwood. Givira lotta B. and McD. works in the outer
heavy bark at the base of ponderosa pines in Colorado.

HORNTAILS OR WOOD WASPS
(Siricidae)

The horntails, or wood wasps, are injurious to the green, un-
seasoned or moist wood of practically all western conifers. Fre-
quently serious damage is done, especially to the wood of fire-killed
trees. Sometimes redwood lumber is attacked and injured, even
after it is cured and placed in storage yards.

The adult females are thick-waisted, cylindrical wasps, with two
pairs of wings and a hornlike ovipositor, which resembles a stinger,
at the rear of the abdomen. They are usually of metallic colors—
dark blue, black, or marked with orange and red. The females
alight on freshly felled injured or dying trees and with great dex-
terity insert their long flexible ovipositors deeply into the wood,
often for an inch or more, and lay their eggs. Sometimes they
are unable to extract their ovipositors from the wood and die in
this position. The larvae which hatch from the eggs are cylin-
drical and yellowish white, with a small spine at the posterior end
of the body, and they sometimes hold their bodies in the shape of a
shallow letter S. They are truly wood-eating in habit and work
in the solid wood without any opening extending to the outside.
As they feed they make perfectly circular holes in the wood and
pack their boring dust in the tunnels behind them. It takes one
or two seasons for them to complete their development. Pupal cells
are constructed near the surface of the wood, and when the adults
mature, they cut round, clean-cut emergence holes to the surface
through which to escape.

Prompt. utilization of unseasoned wood exposed to attack by
these insects is the best means of avoiding damage. Logs placed
in mill ponds and frequently rolled will not suffer from attacks.
Kiln-drying gives complete control, destroying the infesting larvae,

156 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

Re Lee |

Wow
Wb! BBE j
% I,

FIGURE 77.—Carpenter worm (Priono«rystus robiniae) : A, Pupa in wood tunnel; B, adult
moths, male above: OC, egg, larva and pupae; D, borings in trunk of tree. (Drawings
by Edmonston.) A, B, and C, excepting the eggs, one-half natural size; eggs X 3.

INSECT ENEMIES OF WESTERN FORESTS 157

and there is little danger of these insects attacking dry, finished
lumber products.

The different species of horntails are very difficult to distinguish,
and many of the species have not been named or satisfactorily sep-
arated. In many cases the males and the females of the same species
have been given different names, since the sexes are markedly dif-
ferent in appearance. Only a few of the more common ones need
be mentioned.

rs
$

5

i

§

bi

|

’

_

1 4 44 ad vs

Figure 78.—Western horntail (Sirex aerolatus): A, Adult male, &* 1.5; B, female,
xX 1.5; C, larva, X 3; D, pupa, xX 3; EH, exit holes; Ff, larval mines. (EHEdmonston.)

Urocerus californicus Nort. is the largest of the western species.
The females are dangerous-looking wasps with black bodies and
legs, yellow antennae, yellow bands on legs, patches of yellow on
sides of head, and amber wings. They measure from 114, to 2 inches
in length, and the ovipositors are slightly shorter than the body.
The males are smaller and have yellow bodies. The larvae infest
balsam firs and Douglas fir and sometimes pine. Uvocerus flavicornis
F. is a somewhat smaller species, 1 to 114 inches long, and black,
marked with yellow or red. It breeds in various coniferous trees,
including the firs and pines.

Sirex californicus Ashm., a dark, metallic, blue-bodied species
with buff-colored wings and black legs, is commonly found infesting
pines. S. juvencus L. is also metallic blue, but the legs are dark

158 MISC. PUBLICATION 278, U. 8S. DEPT. OF AGRICULTURE

red or marked with yellow. It is found in pines, firs, and spruce
throughout the West. S. aerolatus Cress. is another metallic-blue
species (fig. 78), with black legs and smoky wings. This species
commonly attacks redwood, cypress, and cedars, but it is also found
in pines, firs, and other conifers. S. behrensti Cress. is a smaller
species, five eighths of an inch in length, with head and thorax blue
black and the apical segment of the abdomen reddish brown. The
larvae infest ponderosa pine and sugar pine and have been found
also in Monterey cypress.

Z
Za
ji
Z
ig:
Ze
q
H
y

ae PEN

TO

.

ANWWARUAAININNNNNNUNN

FIGURE 79.—Hemlock bark maggot (Cheilosia alaskensis) : m, Resin mass with exit hole,
adult fly having emerged; n, longitudinal section of similar mass, showing wound in
inner bark and outer sapwood, pupal chamber and exit hole in outer pitch mass, and
original beetle entrance connecting them; o, healing wound in inner bark beneath mass
like that shown at m; q, longitudinal section of wound p; r, maggot; s, puparium; f,
pupa; uw, adult male; v, head of female; w, head of larva; £, antenna. 17, s, t, u, and
WF XD De 20a XS 455 a CBurkes)

Xeris caudatus Cress. is a very long, slim species, with an ovi-
positor as long as, or longer than, the body. The abdomen is wholly
black and the legs yellow. The favorite host apears to be lodgepole
pine. X. morrisoni Cress. is similar but has a reddish abdomen.
It attacks firs and lodgepole pine and probably other conifers.

BARK MAGGOTS

Pecular defects in the lumber of certain coniferous trees, con-
sisting of dark-brown or blackish resinous scars, with the wood
thickened and curled, are made by bark maggots of the genus

INSECT ENEMIES OF WESTERN FORESTS 159

Cheilosia (11). This type of defect is very prevalent in western
hemlock growing in western Washington and Oregon at elevations
below 1,800 feet and is called the “black check” of hemlock. These
defects do not impair the wood for structural purposes but render
a high percentage worthless for finishing wood, staves, or other
special purposes.

The adults are small two-winged flies which lay their eggs on the
bark of the trees, probably on the resin which exudes from feeding
punctures made by the hemlock hylesinus. The maggots enter the
bark, making a small wound, and feed on the sap and inner bark.
The larvae when full grown are white maggots three-fourths of an
inch in length, with the fore part of the body thickened and with a
long, telescopic, protractile tail. Feeding continues for several years,
then in the spring puparia are formed in the resin mass at the en-
trance to the wound, and the adult flies emerge in April and May.

Two species have been recognized as important in the West.
Cheilosia alaskensis Hunter makes the black check in western hem-
lock (fig. 79) and is distributed from Oregon to Alaska. C. hoodi-
ana Bigot does similar work in white and lowland fir in the same
region and also has been reported from New Mexico. There are
several other species whose habits are not fully known, which cause
similar wounds in other western conifers.

INSECTS WORKING IN SEASONED OR DECAYING WOOD

POWDER-POST BEETLES

A group of beetles belonging to the families Ptinidae, Anobiidae,
Bostrichidae, and Lyctidae are called powder-post beetles because
the larvae burrow into hard, dry wood and reduce it to fine powder.
There are hundreds of species in this group, many of which confine
their attack to deadwood in the forest and are of lttle economic
importance. Most of this group confine their attacks to the sapwood
of the hardwoods, but a few species attack pine and Douglas fir and
occasionally do some damage. A few work in finished products and
are extremely destructive on account of their ability to reinfest wood
repeatedly until it is completely destroyed and to attack any
exposed surfaces of furniture, flooring, and sills, and thus establish
themselves in utilized wood products.

Great care needs to be taken in storage yards to prevent infestation
from developing before the sapwood of hardwoods is treated with a
filler, painted, or varnished and thus protected. Badly infested
stocks of tool handles, oars, or building material should be burned.
If lightly infested they can be treated by soaking in kerosene or by
applying liberal doses of crude liquid orthodichlorobenzene.

The Lyctus beetles (49, 74) are probably the most dangerous and
destructive members of this group (fig. 80). The adults are small,
flat, slender, dark-brown beetles about one-eighth to three-sixteenths
of an inch long. Eggs are laid in the pores of the wood, and the
larvae bore only in the sapwood of various hardwoods, reducing it to
a flourlike powder. The insects pass the winter as larvae. Pupa-
tion occurs in the spring, and the new adults appear early in the
summer. In heated buildings development is hastened, and under
such conditions adults may appear much earlier. Small round holes

169 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

in the wood from which fine powder exudes are a good indication of
their presence.

Favorable conditions for attack are made when the sapwood of
fine-quality hardwoods, especially of hickory, ash, and oak, is
allowed to season for 2 or 3 years in endieeurier piles. Accumula-
tions of old stock, refuse, and useless material greatly increase the
hazard of infestation. Species of hardwood ordinarily not subject
to the attack of these insects will, if piled with more favorable host
species, share the damage of infestation. It is, therefore, evident

FIGURE 80.—Wood showing holes made by Lyctus beetles.

that proper methods of handling will do much to prevent these de-
structive pests from becoming established. Material should be
inspected and rehandled annually, and all sapwood refuse, as well
as stock showing signs of infestation, should be burned. Woods of
different species should be piled separately and should be classified
according to age of seasoning, in order that a constant turn-over in
yard s tocks may be maintained | by utilizing or disposing of the long-
est-seasoned stock first. The use of heartwood instead of sapwood
for piling sticks in the yard also helps to reduce the breeding ground.
Kiln drying and steaming under pressure have produced gratifying
control. An undesirable feature of the steam- -pressure methods is
that it is hable to lower the structural strength of the wood, and also
there is danger of causing discoloration.

Stout’s bostrichid (Polycaon stouti Lec.) is a large black beetle
about three-fourths of an inch long, with prominent mandibles. The
larvae bore in the wood of various hardwoods such as oak, eucalyp-
tus, maple, California laurel, madrofia, sycamore, and other trees in
California. In several cases these large beetles have emerged from

INSECT ENEMIES OF WESTERN FORESTS 161

polished table tops where these native woods were used as a base
for veneer. A smaller brown species, Polycaon confertus Lec., also
mines in the wood of these and other broadleaved shade and fruit
trees in California and is sometimes responsible for the extensive
killing of twigs and branches.

The lead cable borer (Scobicia declivis Lec.) (17) is an omnivo-
rous feeder in all sorts of seasoned hardwoods, and has been par-
ticularly destructive by boring into alcohol or wine casks and into
lead telephone cables. The adults are cylindrical dark brown or
black beetles about one-fourth of an inch in length and have the
head retracted under the thorax, giving them the appearance of bark

beetles.
CARPENTER ANTS

Large black ants belonging to the genus Camponotus are called
“carpenter ants” because of their habit of tunneling into the wood
of stumps, logs, dead standing trees, or the dead interior of living
trees, and even into
the framework of
houses, where they
excavate large cavi-
ties that they use for
nests in which to rear
their young. The
wood is not eaten by
the ants, but cast
out in order to make
room for the nests,
causing little piles of
wood fibers to collect
below the entrance
holes. Their excava-
tions in wood are
frequently so exten-
sive as seriously to
impair its structural
value (fig. 81). In
the Pacific North-
west carpenter ant
damage greatly ex-
ceeds and to a large
extent supplants that
done by termites—
the termite damage
being much more
prevalent farther
south. These ants
are general feeders, FIGURE 81. —Carpenter gust cen their work. (Natural
including in their
fare both animal food and sweets, their preferred items of food ap-
pearing to be the honeydew excreted by aphids and the caterpillars of
certain lycaenid butterflies. They have even been known to shelter
the aphid eggs in their nest during the winter and carry them out
and place them on plants to develop in the spring.

136650°—38——11

162 MISC. PUBLICATION 273, U. 8. DEPT. OF AGRICULTURE

These species differ from some of the other ant species in that the
queen of the carpenter ant works alone in founding a colony. An
interesting feature is that, from the time the queen builds her cell
and begins to lay eggs until a brood of workers mature, no food
is taken into the cell. This covers a period of about 10 days from
the laying of the egg to the larval stage and perhaps 30 days more
before the workers are mature and begin to carry in food. It is
generally supposed that the queen carries enough food within her
body to feed the growing workers, apparently by the process of
regurgitation.

Carpenter ants are difficult to control, and at times all remedies
seem to fail. The first precaution is to prevent the ants from gaining
access to foundation timbers. Where timbers are placed on solid
foundations away from contact with the ground, the chance of
carpenter ant attack is greatly minimized but not always prevented.
The best preventitive is to impregnate foundation timbers thoroughly
with creosote.

After a piece of timber has become infested, the colonies of car-
penter ants can be destroyed by injecting sodium fluoride, arsenical
dusts, carbon disulphide, kerosene, or orthodichlorobenzene into the
nests. The sodium fluoride is probably the most satisfactory, for
the ants will track through it and carry it to all parts of the nests,
whereas the liquids and gases are often blocked by the tortuous,
partly frass-filled cavities. If house timbers become badly infested,
it is often necessary to tear them out and replace them with timbers
treated with creosote. All decaying wood in the vicinity of the
buildings, such as old logs, etc., should be cleared away.

LARGE CARPENTER BEES
(Xylocopidae)

Certain species of large bees, resembling bumblebees, excavate
large cylindrical tunnels in dry wood in building their nests. These
tunnels, especially where several colonies of bees build nests close
together, may seriously weaken building timbers and telephone
poles. The work differs from that of the carpenter ants in that
the burrows are partitioned into larval cells by chips of wood ce-
mented together to form circular or spiral discs. Several species
of these bees are found in California and the Southwest.

TERMITES OR WHITE ANTS
(Isoptera )

The termites (4, 56, 73, 75, 77) are a very destructive group of
wood-boring insects that excavate large cavities in wood, and at
times so mine the interior as to leave only a paper-thin shell. In
the forest they are commonly found in the wood of felled trees,
in snags killed by bark beetles or fire, and in stumps or other sec-
tions of dead or decaying wood. Insofar as they reduce forest
debris they are beneficial, but they are exceedingly destructive when
they turn their attention to fences, telephone poles, buildings, furni-
ture, or other utilized cellulose products. The group as a whole
finds its greatest development in the Tropics, and in the United
States does the most serious damage in the warmer southern lati-

ee ee

INSECT ENEMIES OF WESTERN FORESTS 163

tudes. A large number of species are found in the Southwest and
southern California, but only a few extend their range into the
Pacific Northwest, and northern Rocky Mountain region.

Termites are dirty-white, soft-bodied insects that live in colonies
in the wood or in the ground and expose themselves to the light
only when in the mature winged adult form. Each colony is made
up of several specialized forms, such as workers, soldiers, king, and
queen or else secondary sexual forms (fig. 82). They look like soft,
fleshy ants but are distinguished from ants in having weakly chitin-
ized body parts, except the head; and the winged forms have four
wings of quite similar size and shape, while the true ants have
hind wings smaller than the forewings.

FIGURE 82.—One of the largest termites, Zootermopsis angusticollis Hagen, and examples
of its work: A, Winged adult, x 1.5; B, second reproductive caste, X 1.5; C, worker,
x 2; D, soldier, x 4; #, tunnels in wood. (Edmonston.)

The social life of these insects is very interesting and quite com-
plicated. Their excavations in wood are characteristically hollow,
completely enclosed, more or less longitudinal cavities, in which
some species (moist-wood and dry-wood forms) deposit peculiar,
small, impressed excrement pellets. The destructive subterranean
form deposits its feces in the form of liquid drops, which make
only characteristic spottings in their galleries.

The control of termites consists in isolating wood material from
contact with the ground, or impregnating it with creosote or other
termite-repellent materials. Very detailed methods of contro] have
been devised, and it 1s recommended that the reader interested in
this specialized subject consult one of the bulletins or publications
devoted to the prevention of damage and control of these insects
(56, 73, 75).

164 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

INSECTS INJURIOUS TO FOREST RANGE PLANTS

Grasses, herbage, and browse, which furnish feed to range ani-
mals, comprise a forest product sometimes of greater economic
importance or value than the trees that grow on the area. These
grazing plants may also suffer from insect attack and at times
are so completely destroyed in certain localities that cattle and
sheep have to be moved to other ranges. Moreover, the damage
to browse plants may carry over from year to year and reduce the
available feed for several years. Fortunately there are compara-
tively few insects that cause serious damage to range plants.

The damage which grasshoppers may ‘do to the erazing areas
is well known to everyone, and the insects themselves are such
common pests as to require no description. They are often par-
ticularly abundant in grassy meadows, where the females lay their
egos in the ground. usually during the fall of Me year, and new
broods emerge each spring to feed on all kinds of green and dry
vegetable matter. The nonmigratory grasshoppers remain in a given
locality and produce a new brood each year, under favorable con-
ditions becoming excessively abundant and destructive. Others are
migratory in habit and, after breeding to enormous numbers, and
having developed ene travel across the country devouring every
growing thing in their path.

Much attention has been given to the control of grasshoppers,
and effective methods have been devised, the most satisfactory con-
sisting in spreading poisoned baits broadcast over the breeding
areas at about the time the young hoppers first come out and begin
feeding. A good bait consists of a mixture of 1 pound | of white
arsenic, sodium arsenite, or paris green to 25 pounds of bran or
middlings, 2 quarts of blackstrap, and enough water to make a
thin mash.

Periodically armyworms, which are caterpillars of certain noctuid
moths, appear in countless numbers and advance over grazing areas,
devouring everything in their path. These also can be controlled
to some extent by the application of poisoned baits similar to those
used for grasshoppers, or by plowing trenches in front of the
traveling army of worms and ‘killing them in the trenches by drag-
ging a log over them. Fortunately armyworm invasions on forest

ranges are not of very frequent occurrence.

The Great Basin tent caterpillar (Malacosoma fragilis Stretch)
appears from time to time in the Great Basin area between the Rocky
Mountains and the Cascades and defoliates the bitterbrush (Purshia
tridentata), which is a most important browse plant for sheep in this
area. From 1928 to 1930 an invasion of this caterpillar swept over
the range country of eastern Oregon and northern California and so
seriously damaged the bitterbr ush that it took several seasons for it
to recover, and the carrying capacity of the ranges was greatly
reduced. No practical control for this pest has been suggested, but
fortunately outbreaks are brought under control by natural enemies
after a few seasons of heavy feeding.

The range caterpillar (Hemileuca oliviae Cxkll.) (86) feeds on
wild grasses and sometimes on cultivated crops, and at intervals of 10
or 12 years is a serious range pest from Colorado southward into

INSECT ENEMIES OF WESTERN FORESTS 165

Mexico. The adults are large moths with reddish, brown, or black
bodies and buff or clay-colored wings. The caterpillars are yellow,
eray, or black and have numerous coarse, poisonous spines.

The California tortoise-shell butterfly ’ (Aglais californica Bdv.)
(fig 83) is found throughout all the Western States and often ap-
pears 1n such numbers as sto attract public attention. The caterpillars

é Woy a a a

aa Wf
Ze, es ys ae (G ee Fed Heed

FicureE 83.—California tortoise-shell butterfly (Aglais californica) : A, Adults; B, cater-
pillar; and ©, pendulous chrysalids. (Above) about natural size; (below) about half
size. (Drawings by Hdmonston.)

feed on different species of Ceanothus, and during severe epidemics
other shrubs and: trees may be attacked. The adults are medium-
sized butterflies with a wing expanse of 2 to 214 inches. The wings
are brown, with orange above, marked with black spots and black
borders, with a single black spot and a marginal row of purple spots

166 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

on the hind wings. The caterpillars are 1 to 114 inches in length,
black with fine-branched spines on each segment, the middle row
being bright yellow. The adults are in flight during midsummer.

The peppergrass beetle (Galeruca externa Say) is a black oval beetle
about one-fourth inch in length, with a narrow yellow border on the
elytra, which feeds on lupine in the Great Basin area. In 1934 it
destroyed the lupines over hundreds of acres in eastern Oregon and
also fed on the grasses.

The range crane fly (Zipula simplex Doane) (65) at intervals is
very destructive to grasslands in California. It is also a serious
pest of grains, barley, and alfalfa. The adults are grayish brown,
long-legged flies about one-half to three-fourths of an inch long.
The females are wingless. The larvae, which are pale brown and
somewhat roughened, live in small round holes in the ground, from
which they emerge during the night or on dull days to feed upon any
green vegetation nearby. During mild or wet seasons vast areas
of range land may be almost denuded. The spreading of poisoned-
bran mash, such as is used for grasshoppers, 1s an effective control
measure.

NATURAL CONTROL FACTORS

The question is frequently asked, “Where did these destructive
forest insects come from?” The answer is that in most cases they
have been here as long as the forest trees on which they feed. Nearly
all species of western forest insects, both injurious and beneficial, are
native to these forests and are distributed throughout the range of
their favorite host. Occasionally foreign pests are introduced and
become established where food and climatic conditions are favorable.
So far, no introduced forest insects of major importance have found
their way into the forests of the West. The destructive species were
already here and widely established when the forests were first ex-
amined. Given favorable conditions for their increase, they can
suddenly build up their numbers from the few parents which are
normally present and develop epidemics.

In the insect world a constant struggle is going on for survival.
On the one hand, the insects themselves are provided with potential-
ities for tremendous increase. Some females lay hundreds of eggs
and some species produce many generations a year, so if all individ-
uals survived the world would soon be overrun with the progeny. On
the other hand, the insects must contend with many adverse condi-
tions that serve to hold their progeny in check. Weather conditions,
food supply, prevalence of natural enemies, and many other environ-
mental factors influence their abundance. Some of the more
important of these factors will be considered.

CLIMATIC AND ENVIRONMENTAL INFLUENCES

Climatic factors, such as temperature, moisture, and weather con-
ditions in general, have an important bearing on the abundance,
activity, and distribution of insects.

TEMPERATURE

Insects as a rule have a very small range of temperatures (50°—
95° F.) within which they are the most active; and the optimum for

INSECT ENEMIES OF WESTERN FORESTS 167

many of the Temperate Zone species appears to be about 77°. Tem-
peratures either above or below this optimum range limit activity
and extremes cause death (62, 63). Few insects can withstand tem-
peratures above 120° and this makes possible the control of many
species of bark- and wood-boring insects by raising the temperature
of their environment to fatal heights. Low temperatures also are
fatal. It has been found that larvae of the western pine beetle are
killed when exposed to a temperature of —10° and extremely cold
winters with air temperatures below —20° have proved fatal to a
high percentage of this and other bark-beetle broods (4a) (45a).
Moreover, elevation and exposure modify temperature and limit the
distribution of insect species, regulate their activity, and govern the
number of generations per year. _

MOISTURE

Moisture has an important bearing on insect abundance, both
through its direct effect upon the insects and indirectly through its
influence upon the host. Some insects require very moist conditions
under which to work to best advantage and are killed by dryness;
others require very dry conditions and are killed by moisture. More-
over, moisture through precipitation has an important influence upon
the growth and resistance of trees to bark-beetle attack; and periods
of drought are frequently followed by serious consequences in
supplying insects with an abundance of weakened host material.

FOOD SUPPLY

The abundance or scarcity of the food supply is an important
consideration in determining the distribution and successful develop-
ment of insect progeny. Most of the insects which prey upon living
forest trees are limited in their distribution to that of their favorite
host, whereas those which feed upon dying or dead trees are apt to
be widely distributed throughout forest regions.

Insects, such as the defoliators, that attack healthy forest trees
always have an abundant food supply at their disposal, and their
numbers are controlled primarily by biological and climatic factors.
On the other hand, a great many insects, such as most of the bark
beetles, can develop in large numbers only when a sufficient quantity
of their food material in a suitable condition for attack is available.
Thus the development of certain destructive bark-beetle outbreaks
is dependent to a large degree upon a supply of overmature or deca-
dent trees, fire-weakened trees, slash, windfalls (67), snow-broken
or lightning-struck trees, or trees weakened by drought, smelter
smoke, disease, or other causes. Under favorable conditions, however,
a few species of bark beetles can develop in epidemic numbers
without such contributing factors.

In the virgin pine forests of the West, a high percentage of the
trees are mature or decadent. They grow more slowly, and resistance
to beetle attack is lessened in other ways during periods of drought.
Such conditions present a highly favorable field for bark-beetle
activity, and the heavy losses that have been sustained in the pine
regions during the past few years indicate very clearly that the bark
beetles have not neglected this opportunity.

168 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

Trees that have been felled by wind or snow and those struck by
lightning furnish favorable breeding places for a great many destruc-
tive bark and wood borers. Such material is probably the natural
habitat for many species that at times become excessively abundant
and attack living trees. Many severe bark-beetle epidemics are
known to have originated in areas of wind-blown timber.

SLASH

The debris left from the cutting of trees in the forest is a suitable
and attractive breeding ground for a great many forest insects, some
beneficial and some harmful (37, 67, 84). When slash is freshly
produced, the dying inner bark is attractive to many species of bark
beetles that are commonly found breeding in standing trees. Usually
these bark beetles select in the slash or stumps the type and size in
which they normally breed. Thus the limb- and twig-feeding bark
beetles go into the brush and smaller pieces of slash, trunk-breed-
ing bark beetles go into the cull logs and butts, and those that nor-
mally work at the base of the tree attack the stumps. The abundance
of the progeny depends a great deal upon the moisture and temper-
ature conditions within the slash and the requirements of the differ-
ent species of beetles. The red turpentine beetle, which breeds readily
in pine stumps, frequently develops in such numbers as to do serious
injury to adjacent forest trees. The trunk-breeding pine beetles
rarely find suitable conditions in the cull logs and butts, and the
progeny which they produce under such circumstances seldom cause
any trouble in neighboring forests or to the reserve stand, especially
where logging operations are continuous. The engraver and twig
beetles, which breed in the smaller pieces of slash, frequently emerge
in such enormous numbers as to kill patches of young trees and
sometimes the tops of older trees.

The wood-boring species that breed in slash must be considered
generally beneficial, in that they help to decompose the wood and
reduce the slash with its accompanying fire hazard.

They may become injurious, however, and in order to avoid or reduce
a possible menace from slash-breeding insects special considerations
in slash disposal are frequently necessary. When a logging operation
is continuous, and a fresh supply of slash is furnished throughout
the flight period, the emerging progeny is repeatedly absorbed in the
slash and in the logs removed to the mill, and no special precautions
need be taken. But if a cutting operation ceases or is intermittent,
as in the case of road and power-line development, then some damage
from slash-breeding insects may be expected and should be avoided
if possible. Burning the slash is beneficial provided the large limbs,
cull logs, and stumps are included and the burning done before the
insects emerge. In many cases this would mean that the burning
would have to be done in the middle of summer or early in fall, and
this would not be safe from the standpoint of fire hazard. Spreading
the slash so as to receive the direct rays of the sun is effective in
disposing of a high percentage of the insects in the more southern
latitudes where high temperatures can be attained in and under the
bark in this way.

INSECT ENEMIES OF WESTERN FORESTS 169

FIRE

Trees scorched or killed by forest fires are particularly attractive
to a large number of forest insects, which may be drawn to them
from a radius of several miles (64). Subsequent insect damage
augments the fire losses, as bark beetles often kill many trees which
otherwise might have survived. Wood-boring species then enter the
wood and so riddle the interior that within a few years it becomes
valueless for lumber purposes.

Forest fires are not of any benefit in destroying injurious bark
beetles, as is sometimes supposed. Sometimes hght burning has
been advocated as a means of controlling bark beetles, but’ studies
have shown that such fires are more apt to have the opposite effect.
Destructive, tree-killing bark beetles never breed in and seldom
inhabit the forest litter and duff and hence are seldom killed by
light ground fires, and can only be killed in the trees by a fire severe
enough to kill the bark on the trunks. Such a fire obviously would
do more harm than good.

NATURAL ENEMIES

Insects, like other living things, have natural enemies that prey
upon them and tend to hold them in check. Three of the most im-
portant of these are birds, disease, and other insects.

BIRDS

Many species of birds are insectivorous. Nuthatches, chickadees,
creepers, warblers, kinglets, and many other species search for insects
on tree trunks and folhage, while woodpeckers dig through the bark
and feed on larvae of bark beetles and wood borers. Counts have
shown that fully 75 percent of the western pine beetle population
in patches of pine bark worked over by woodpeckers have been
destroyed by these industrious workers. But not all birds are bene-
ficial in this respect. Some are as destructive to beneficial insects
as to the harmful species, and their feeding has ultimately little effect
in reducing the injurious forms.

DISEASE

insects are subject to many fatal diseases, that sometimes are a
potent factor in suppressing an outbreak of some harmful pest.
These diseases are represented by many different micro-organisms,
including bacteria, fungi, and the causes of polyhedral bodies. Few
of these have been adequately studied. One of the most common
examples is a wilt disease that spreads rapidly through outbreaks
of various caterpillars when these are excessively numerous. The
caterpillars suddenly sicken and die and are seen hanging from leaves
and twigs in a blackened, shriveled condition.

BENEFICIAL INSECTS

Many species of insects belonging to different orders and families
are distinctly beneficial in that they devote their lives to preying
upon certain harmful species (57). These beneficial forms may be

170 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

divided into two large groups, (1) the parasites, which live in, on,
or with some particular host and gradually consume it, and (2)
the predators, which feed externally and devour their prey. The
line of demarcation between a parasite and a predator is not a rigid
one, since both live at the expense of their host. A parasite is usually
considered as one capable of completing its life history in or upon
the body of one host, whereas a predator feeds on a succession of
individuals. Often both the immature and adult forms of predacious
insects feed directly on all stages of their insect hosts.

Most of the parasites belong to two or three families of wasps
(Hymenoptera) and one family of flies (Diptera). The wasps
frequently have long ovipositors with which they deposit their eggs,
often within the body of their insect hosts. Here the egg hatches
and the young parasite grows to maturity, feeding on and finally
killing its victim. Fbhes lay their eggs on the surface of the host, and
the maggots burrow within. Native forest insects are plentifully
supplied with parasitic enemies. Unfortunately, even the beneficial
insects are not immune from attacks of other parasites, called hyper-
parasites. -Hyperparasitism is occasionally carried to the third and
fourth degrees, making parasitism an extremely complex relationship.

The most active predacious insects are beetles belonging to the
families Cleridae, Ostomatidae, Carabidae, and Coccinellidae; lace-
wing flies of the family Chrysopidae; and several families of true
bugs belonging to the order Hemiptera. Other important predators
include such small mammals as chipmunks, mice, and shrews (7Ja).

The larvae of some of the roundheaded borers are very voracious
bark feeders and'‘are often unwittingly beneficial in that they devour
the inner bark so rapidly as to rob the bark beetles of their food.
This is a case of competition between two species of insects, one
of which is capable of killing trees and the other harmless in this
respect, with the harmless species depriving the destructive one of
necessary food material.

Under normal conditions, the operation of these physical, nutri-
tional, and biological forces counteracts the enormous reproductive
capacity of the insects and tends tc keep the destructive and beneficial
insects more or less in balance. The few harmful individuals which
escape their enemies live and feed on their hosts without doing
conspicuous injury. The defoliating insects feed on a few leaves
or needles, but the damage is so small as to escape notice. The bark
beetles kill an occasional tree or breed in down logs and broken tops.
The aggregate damage is negligible, and the annual growth which
the trees acquire exceeds the drain, so that there is a net accretion
of volume in the stand. Insect infestations which continue under
these conditions are termed “endemic.” This is the normal cond1i-
tion in nature and it is a hopeless and unwise undertaking to try
to exterminate native insects under such conditions. The result of
an effort in this direction would be more apt to disrupt the delicate
balance than to accomplish the objective.

Under certain conditions, the natural balance may be broken by any
one of a number of factors. For example, the beneficial insects or
other enemies of harmful species may become reduced in numbers;
the resistance of the trees may be lowered through drought, fire, or
stagnation; large quantities of slash or other breeding material may

INSECT ENEMIES OF WESTERN FORESTS vil

become available; or climatic factors may become especially favorable.
Under any such ‘condition the injurious species will breed rapidly
and in excessive numbers, and a sudden destructive outbreak soon
develops. Within a few seasons a high percentage of a timber stand
may be killed by bark beetles. Such epidemics may continue for
years and spread over large areas. Defoliators may suddenly appear
within an area and, after destroying the foliage of valuable timber
over large acreages, "disappear with equal suddenness. Many factors
come into play in bringing about these sudden changes, and it is
often difficult to isolate the responsible causes. Outbreaks of such a
character are called “epidemic” infestations and require immediate
attention and drastic control.

CONTROL OF INJURIOUS FOREST INSECTS

The objective 1 in forest-insect control, in areas not under intensive
management, is to prevent or suppress epidemic outbreaks of in-
jurious insects and to prevent their spread. As has just been indi-
cated, it is best not to disturb normal infestations of native insects,
for there is small hope of exterminating them, and the complicated
factors that hold the species in balance may be unfortunately dis-
rupted. Control of native pests is therefore confined to the prevent-
ing of threatened outbreaks and the suppression of those that have
attained some proportions. In the case of defoliators, the object,
is to hold down the injury to as low a point as possible until natural
factors suppress the epidemic. In bark-beetle control the objective
is to prevent or suppress the development of a large beetle popula-
tion, at the same time giving every encour agement to the natural
control agencies, so that the natural balance may be restored.

The control of forest insects, scattered as they are over vast forest
areas, May seem an insuperable undertaking, and yet certain methods
are available that make this not so hopeless a task as it might appear.
Control problems my be approached in at least three different ways:
(1) Through such direct remedial methods as destroying the insects
by burning, drowning, or poisoning; (2) by silvicultural methods
that modify the physical or nutritional forest conditions so as to
change temperature, moisture, or food supply; and (3) by biological
methods that alter conditions so as to increase the numbers of
natural parasitic or predacious enemies. Though these are distinct
methods of approach, it is often necessary to utilize more than one
of them in the solution of some forest-insect problems.

Forest-insect control in the Western States is, at the present time,
largely a matter of protecting mature timber stands from the ravages
of insects through the application of direct remedial control meas-
ures. But as mature timber stands are cut and brought under man-
agement, there will be more and more opportunity “to apply silvi-
cultural measures in the solution of forest-insect problems. The
‘application of biological methods will depend largely upon what is
discovered through ‘further research work as to the various inter-
relationships of the insects concerned.

The control of introduced or foreign pests presents quite different
problems. In the first place, every ‘effort is made to prevent their
introduction into this country through rigid quarantine inspections
made at all ports of entry. Such pests as escape detection and become

72 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

established in the country are hedged about with domestic quarantines
for the prevention of their further spread, while every effort is
made to exterminate them before they have become so firmly en-
trenched as to make such efforts impractical. If these efforts fail, a
search is made in their native homes for the specific parasites and
predators which normally hold them in check there, and these are in-
troduced and their establishment attempted in this country. Work
of this sort has been highly successful in controlling many foreign
pests that have been inadvertently introduced.

SILVICULTURAL CONTROL

When timber stands are brought under management, it becomes
possible so to regulate conditions as to make forests less vulnerable
to insect attack; or 1f insect damage does occur, to salvage the timber
without undue loss. The underlying aim is to maintain a biological
balance throughout the period of rotation. This task is hardly as
simple as it sounds and cannot be accomplished without a thorough
understanding of all the factors contributing to insect abundance
and the resistance of forest stands. The possibilities in this direc-
tion have not as yet been fully investigated, and there is still much
to be learned about the management of western forest types before
thoroughly sound methods of procedure can be recommended with
complete assurance of success,

It is apparent, however, that this field of silvicultural control
offers almost unlimited possibilities. In the older forests much can
be done to lessen insect: damage by avoiding injury to the trees from
forest fires and other weakening influences; by keeping forests .in a
healthful condition through disposal of windfalls, slash, and other
insect-breeding places; and by selective cutting operations to remove
the trees most susceptible to insect attack, and through these cuttings
to regulate forest composition and density. In new plantations con-
sideration should be given to the selection of the site and the plant-
ing of species and varieties of trees best adapted to it, to their proper
spacing, and to the regulation of drainage, temperature conditions,
and stand density. Mixed stands are also less susceptible to serious
injury than pure stands. These are just a few of the possibilities
that suggest themselves in which insect activity can be modified
through silvicultural practices.

In the overmature virgin forests of ponderosa pine, bark beetles
are not indiscriminate in their attacks but make a selection of certain
trees or groups of trees scattered through the stand (70). <A study
of the types of trees selected has shown that in general the more
slowly growing trees, the codominants and intermediates in the stand,
and the older age classes are selected in preference to the thrifty,
dominant, young trees (55). The damage in these pine forests also
becomes more acute when the stands are suffering from stagnation
or are subjected to periods of drought, and the soil moisture is not -
sufficient to keep all of the trees in a thrifty, growing condition. A
selective cutting to remove the more beetle-susceptible trees, to release
the stand from stagnation, and to give the more thrifty dominant
trees first chance for such moisture as may be available is the most,
obvious solution. Instead of cutting heavily on small logging units
forest management is looking toward a light selective system where-

INSECT ENEMIES OF WESTERN FORESTS 17:

by large areas will be opened up so that insect-killed trees can be
quickly salvaged and stands improved from the standpoints of both
growth and insect resistance.

Under management, the age at which certain stands become
susceptible to beetle attack will necessarily be taken into considera-
tion, and a cutting rotation adopted that will permit the timber crop
to be harvested before the beetle hazard becomes too great. Lodge-
pole pine is a good example of a tree whose short life is largely a
result of periodic, devastating outbreaks of the mountain pine beetle.

In some cases stand composition and density will have to be regu-
lated to avoid serious damage from insect attack. Pure stands,
which are those composed of a single tree species, are particularly
susceptible to disastrous outbreaks. For instance, outbreaks of the
hemlock looper have been especially destructive only in stands com-
posed of a high percentage of hemlock. Where a heavy mixture of
other species occurs the infestation soon thins out and loses its
destructive power. Attacks of the spruce budworm also have been
most destructive in stands composed of a high percentage of balsam
and Douglas firs. It is particularly important that cuttings, in
stands that normally grow as mixed types, should not favor the
leaving of a single species. This is not so important in stands that
normally occur in nature as pure types, for in such cases there is
usually a natural balance between the tree species, the vegetative |
ground cover, and the insects that are associated in this type of
forest. :

The stand density has an important bearing upon temperature
and moisture conditions and in many cases must be regulated so as
to improve growth rates and discourage the attacks of certain insects.

Many of these problems of silvicultural control become increas-
ingly important when new plantations are established. Sites must
be selected which are adapted to the growing of trees, or growth
will be so poor and the trees so weak that insects will have a fertile
field for their activities. Here, too, there is the opportunity to select
varieties of trees that are not only adapted to the particular site
but are insect-resistant or capable of making such rapid growth as to’
overcome any set-backs from insect attack. Drainage, the mixture
of species, and the spacing of the trees also must be given special
consideration.

BIOLOGICAL CONTROL

174 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE

these native insect enemies through artificial propagation presents
seemingly insurmountable difficulties with little hope of any lasting
benefit.

Another possibility is the introduction of a new parasitic or pre-
dacious enemy. To do this, it is first necessary to find an insect
not already present within the infested area that will prey upon the
harmful species. Even though such an enemy may be found, there
are many complex factors which will influence the success of the
introduction and its ultimate effectiveness. The life history of the
new enemy must synchronize with that of its host if it is to be on
hand at the proper time for attack. If a parasitic enemy has more
generations annually than the host, other insects must be present for
it to attack at other periods during the season, The parasite must
be capable of wide distribution and have a greater reproductive
capacity than that of its host if it is to succeed. Moreover, its ability
to adapt itself to the change in climatic conditions in its new
environment may be an important factor in determining its ability to
succeed. So far, no introduction of a foreign parasite or predator
has been outstandingly successful in the control of any of our native
forest insects.

The introduction of parasites and predators has been confined
largely to cases where injurious insects have been accidentally im-
ported into new regions while their natural enemies have been left
behind. Under such conditions the introduction of parasites from
the original home of the pest have, in several instances, been entirely
successful, although the continuation of artificial control has fre-
quently been necessary. In only a few instances have introduced
beneficial insects been able to control destructive epidemics completely
without other assistance.

In view of the fact that the application of biological control meas-
ures often presents almost insuperable difficulties, a thorough knowl-
edge of all associated insects is of vital importance, in order that the
more direct control methods may be applied so as to take full
advantage of any aid from parasites and predators,

DIRECT ARTIFICIAL OR REMEDIAL CONTROL

When nature fails to keep an injurious insect in check, and valu-
able forest crops are threatened with destruction or serious injury,
direct remedial or artificial control measures are called for. These
consist in such mechanical methods as the application of insecticides,
as in spraying, dusting, fumigating, or baiting; felling or burning in-
fested trees; or the use of trap trees or solar heat. In brief, these
artificial control measures are employed to destroy the harmful
insects directly in one way or another.

The control measures applicable to the control of cone and seed
insects, root-feeding nursery pests, terminal or twig insects, and in-
sects injurious to forest products have already been considered in
connection with the discussion of these special groups. The control
of defoliating insects and bark beetles affecting mature forest trees
has been given special attention in western forests, and, since spe-
cialized methods have been developed, these will be given detailed
consideration,

y
|

INSECT ENEMIES OF WESTERN FORESTS 175

CONTROL OF DEFOLIATING INSECTS

Defoliating insects can be controlled through the use of chemical
poisons. Chemical control has been in use for many years, but until
recently the control of tree defoliators by such methods has been lim-
ited to orchard, park, and shade trees. However, the application of
these methods is gradually being extended to forest trees. In general,
two types of poisons are used in this work, (1) the stomach “insecti-
cides and (2) contact insecticides. These may be applied in the form
of either dusts or liquid sprays (fig. 84).

FIGURE 84.—High-pressure spraying outfit used along highways of the Shoshone National
Forest, Wyo.

The stomach poisons are used against insects that chew their food,
such as the leaf-eating caterpillars, sawflies, and beetles, and when
applied directly to the foliage become effective against the insect
through its mouth and digestive tract. The most useful poisons for
this purpose are various arsenical compounds such as lead arsenate
and calcium arsenate. Lead arsenate and calcium arsenate are not

only toxic to the insects but contain comparatively little free arsenic

and hence are not harmful to the foliage of many trees when used
with discretion. Calcium arsenate is the cheaper of the two, but
lead arsenate is somewhat more effective and less injurious. A
spreader is usually added to the hquid sprays in order to make them
spread evenly over the surface of the foliage and to adhere well.
Fish-oil soap, linseed oil, glucose, resin stickers, and similar sub-
stances are frequently used for this purpose.

The stomach-poison spray most frequently used for the control of
leaf-chewing defoliators consists of the following:
Lead arsenate, paste (or lead arsenate, powder, 3 to 5 pounds)__ 5 to 6 pounds.

WAY GN EGTE’ (EQ. Taian en ag RR POP SN a ce ea 100 gallons.
JENISIE Gil Oe Oe Ses gy te a 14%, to1% pints.

176 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

Contact insecticides are used against small sucking insects such as
the aphids, scales, and bugs, and sometimes against small caterpillars
and leaf miners, and are applied in the form of liquid sprays or dusts
so as to come in direct contact with the insects. These poisons kill
the insects by entering the respiratory system, or by penetrating
through the thin body membranes, or they may destroy them by
plugging their breathing tubes, paralyzing the nerve centers, or
actually burning the insects through the caustic properties of the
chemicals. The young insects are much more easily killed by such
treatment than the older forms, which often become protected or
more or less resistant.

There are a large number of contact sprays and dusts, each with
certain advantages and special fields of usefulness. Only a few will
be mentioned here, since the contact sprays, while very useful in the
control of shade-tree pests, have not as yet been used in the forests
of the West.

One of the most useful contact sprays is 40-percent nicotine sul-
phate diluted with water in the-ratio of 1 to 800 or 1 to 1,000, to
which is added about 1 ounce of soap to each gallon of spray in order
to give good spread and adhesion. This spray is particularly useful
in the control of aphids and other soft-bodied insects. A typical
formula 1s—

Nicotine ‘sulphate; 40-percem teas se ee eat ee ee eee 1 pint
Fish-oil soap_—-—-- Ia pg pe Ry et Yee Reo ane eS he 5 pounds
Water lo make 2esos 202 eek eee DS Sa TES Toe 2 se ae ee 100 gallons

Miscible oils, or oils that will mix with water, have come into
prominence in recent years as effective contact sprays for shade and
orchard trees, and are useful in nurseries and plantations against
such forest pests as the spruce bark louse, the green spruce aphid,
and various scales. These oils are proprietary products, sold under
a variety of names, and varv somewhat in strength. The winter oils
are used as dormant sprays and will injure foliage if apphed when
the trees are in leaf. Lighter or summer oils are also available that
can be applied to the folage without injury. Instructions as to
dilution of the oils come with the product. Fish-oil soap is usually
used as a spreader.

Soap and kerosene emulsion have been used in the past, but
results from their use are uncertain, and they are no longer recom-
mended for shade-tree sprays.

Lime sulphur is a very effective and inexpensive spray which is
used in the control of the armored scales. It is applied during the
winter or early in the spring as a dormant spray. ‘The concentrated
preparation should have a density of about 30° Baumé and should
be diluted with eight parts of water.

Many other insecticides are available, and various combinations
of ingredients are used for special purposes. Some of these may be
very harmful to plants and dangerous to use. If special problems
come up requiring the use of chemical inseeticides, it is best to con-
sult an entomologist before entering on any extensive control project.

SPRAYING

_ Liquid insecticides, either stomach or contact poisons, when used
in the control of tree-defoliating insects, are applied in the form of a

INSECT ENEMIES OF WESTERN FORESTS 177

spray by means of power spraying apparatus. Such methods are
commonly used in the control of park- and shade-tree defoliators,
but under forest conditions can be used only along roads or at camp
sites and resorts where it is possible to tr ansport the heavy equip-
ment. Because of the height of forest trees, high-power spraying
pumps are a necessity. Even the largest spr aying equipment so far
developed is not adequate for the tallest trees.

Ficurp 85.—A long hose permits reaching out for distances of 1,500 to 5,000 feet from the
spray pump.

Spraying for the control of the spruce budworm has been carried
on for several years in the Shoshone National Forest, Wyo., along
highways and around summer resorts. One of the largest spraying
outfits so far developed has been used in this work. "This consists
of a three-cylinder power sprayer with a capacity of 25 gallons per
minute through 14-1nch tip under a nozzle pressure of 300 to 1,000
pounds. This pump is mounted on a motor truck that carries from
1,500 to 5,000 feet of hose to reach out on either side of the road
(fig. 85). This equipment can shoot a stream to a height of 90 feet
when a %%,-inch tip is used. But even this powerful equipment

136650°—38——_12

178 MISC. PUBLICATION 273, U. 8. DEPT. OF AGRICULTURE

would not be adequate for the spraying of trees over 90 feet in
height or for reaching out into inaccessible forest areas.

AIRPLANE DUSTING

Although most defoliating insects, can be easily killed by properly

apphed insecticides, their control is not a simple one owing to the
great difficulty of application, (33, 57). Outbreaks of forest defolia-
tors often cover large areas in inaccessible terrain and affect some
of the tallest forest ‘trees that cannot possibly be reached with any
dusting or spraying apparatus operated from the ground. For
these reasons the only fea-
sible means of applying
insecticides to large forest
areas 1s from the air and
in recent years the airplane
has come into use for this
purpose. Dry dusts are
best adapted for this pur-
pose, but in some recent
orchard work liquid sprays
have been used. Calcium
arsenate is the dust most
frequently used as a stom-
ach poison for airplane
dusting against leaf-eating
insects.

Airplanes for dusting are
equipped with a hopper to
carry up to 1,000 pounds of
dust (fig. 86). Inside of
the hopper is an agitator to
keep the dust stirred up,
and at the bottom of the
Figure 86.—Loading hopper and airplane used in hopper IS 4a shding gate

forest-dusting operations in Washington in 1931. that can be opened and

closed from the pilot’s seat.
This opening allows the dust to be discharged into the air stream,
which catches it and whirls it groundward in a vast cloud. The
airplane is required to fly very low (fig. 87), and when it is flying
at a height of 40 feet above the tree tops the dust cloud settles
over a width of about 150 feet. The airplane fiies back and forth
letting the strips of dust overlap slightly. The flying must be done
when wind movement is neghgible and preferably when there is
dew on the foliage that will help to hold the dust. In some recent
dusting for the hemlock looper (54) (fig. 87) the dust was applied
at the rate of 20 pounds per acre, but in heavy forest stands the
dosage must be increased up to about 60 pounds per acre. The cost
of the work ranges from $3 to $6 per acre and this expense is justi-
fiable only for the protection of particularly valuable timber.

Airplane dusting has certain disadvantages that prevent its general
adoption as a satisfactory method of controlling forest defoliators.
It is expensive and very dangerous, since the airplane must fly
so close to the tree tops. Even under ood conditions. an even distri-

INSECT ENEMIES OF WESTERN FORESTS 179

bution of dust is extremely difficult to obtain, owing to slight wind
movements and irregular topography, and in order that dosages on the
foliage may be lethal, a great deal more dust must be applied than
would ordinarily be required in the ground-dusting of small trees.

FiGURD 87.—Spreading calcium arsenate dust from an airplane in dusting operations
against the hemlock looper in Washington.

Furthermore, the question as to the effect of heavy applications of
arsenicals to large forest areas has not been fully answered. In
its present stage of development airplane dusting cannot be recom-
mended for general use in the control of forest defoliators.

BARK-BEETLE CONTROL

A tree in which bark beetles have successfully established them-
selves cannot be saved, and the best that can be done is to destroy
the infesting insects before they are able to emerge and attack other
trees (50). Bark-beetle broods can be destroyed by several methods
of artificial control,® the method and time of application varying for
different species and different regions. ‘Though bark-beetle out-
breaks can be reduced, these insects cannot be exterminated, so con-
trol measures must not be considered as a panacea or cure for all
time. The results of a sucecssful bark-beetle control project may
last for years or they may be of extremely short duration.

In justifying the application of measures for the control of bark
beetles, such factors as the value and merchantability of the timber,
the destruction of the forest cover in its relation to watershed pro-
tection, the creation of fire hazards, and the danger of the epidemic
spreading into more valuable stands of timber must be considered.
The proper evaluation of these factors, balanced against the cost
of the operation, will determine the economic justification of the
project. However, it is difficult to foresee the extent of the probable

8 KEEN, F. P. MANUAL OF BARKBEETLE CONTROL IN WESTERN PINE FORESTS. U.S. Dept.
Agr., Forest Serv. 58 pp., illus. 1927. [Muimeographed. ]

180 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

damage or the course the epidemic may take if no control is under-
taken, and conclusions as to the success of a bark-beetle project
can only be deduced on the basis of an estimate of what would
have happened if no control work had been undertaken. Control
measures applied during the decline of an outbreak often tend to
place an inflated value upon the results obtained. On the other
hand, control undertaken during the time an outbreak is building
to an epidemic may show little reduction in damage and give the
appearance of failure. The best that can be done is to compare the
trend of the epidemic on the treated area subsequent to control with
that on a similar neighboring area where no work was done.

To protect valuable forest areas from bark-beetle outbreaks cer-
tain steps should be taken. These may be summarized as follows:

(1) A general reconnaissance or detection survey of valuable
forest types subject to bark beetle epidemics should be made each
year. to detect the beginning of any outbreak. If an outbreak is
indicated, a decision should be reached by the owners or those respon-
sible for forest protection as to whether timber values in or adja-
cent to the site of a detected outbreak warrant the probable expense
of a control operation. If so—

(2) An extensive bark-beetle survey should be undertaken, usually
under the supervision of a competent forest entomologist, to deter-
mine (@) the trend of the outbreak and the possibilities of natural
control; (6) The area involved in the infestation and threatened
by it; (¢) what areas must be included in the control program; (d)
the number of trees that will require treatment, and the area that
must be covered in the first season; and (e) the probable cost and
results to be expected. In the light of the complete information
furnished by the extensive survey, a decision can be reached as to
the need and justification for applying artificial control measures,
and whether or not the necessary cooperation of all affected owners
can be obtained and the work adequately financed. If control work
is decided upon, then—

(3) A control campaign should be outlined and prompt and thor-
ough control measures should be applied to all units showing epi-
demic trend within the project area. This should be followed by
treatment of such outlying areas as may jeopardize results in the
cleaned units.

(4) A maintenance control program should be continued until a
natural balance has been restored.

DETECTION OF BARK-BEETLE OUTBREAKS

If forests are to be protected from serious damage or destruction
by bark beetles, incipient outbreaks must be promptly discovered and
reported. If such asystem is consistently carried out, it will greatly
reduce the ultimate cost of protection and prevent the building up
of disastrous and uncontrollable infestations.

The first reporting of outbreaks devolves upon the timber owners,
the State or Federal forest rangers, or others who are primarily
responsible for the protection of forests. Such work is analogous
to that of the forest-fire detection system.

This detection work should be so planned that all valuable forest
types subject to bark-beetle outbreaks are given some measure of

INSECT ENEMIES OF WESTERN FORESTS 181

inspection for insects each year. This work does not need to be
intensive, but at least it should disclose whether trees are dying
through any forests tract, and, if so, the probable cause of death,
and the extent of the trouble.

If trees are observed to be dying either singly or in groups, they
should be examined and the cause of the trouble determined. If
there is no evidence of recent forest fires, insects may be suspected
as the responsible agents. If so, a closer examination of foliage,
twigs, or bark should show what primary insect is involved. The
keys and accompanying discussions in the early part of this manual
(pp. 28, 58, 60, 95) should be helpful in making this diagnosis. If
the cause of death cannot be satisfactorily determined, an expert
should be called in or samples of the work and the insects present
sent to an entomologist for his study. Samples taken from the mid-
dle height of the stem are more apt to include the primary destruc-
tive bark beetles than if taken near the ground or in the tops where
secondary insects are often most abundant.

Information as to the extent of the damage can be determined by a
red-top survey or by strip counts made along roads or trails. The
methods to be discussed under “Extensive bark-beetle surveys” are
applicable to this preliminary work, but the field work need be only
in sufficient detail to give a rough approximation of the location,
extent, and intensity of the infestation.

The prompt reporting of the first signs of a bark-beetle outbreak
will greatly reduce the ultimate cost of suppression. On most
national forests the rangers are required to make at least one annual
reconnaissance of their districts and report the conditions as to insect
infestations. In this way bark-beetle outbreaks are promptly
brought to the attention of the forest officers and a decision can be
made as to whether a more extensive survey or immediate control
operations are required.

EXTENSIVE BARK-BEETLE SURVEYS

After an infestation has been reported by the men on the ground,
and before control operations are started, there is usually need
for a more complete field examination or extensive survey to deter-
mine the intensity, size, and character of the infestation, whether or
not control operations are justified, and how large an area must be
included to make such work effective.

The importance of obtaining all possible information as to the
extent and severity of a bark-beetle outbreak before control
measures are started can hardly be overemphasized. Without this
information the need and feasibility of control and the magnitude
and probable cost of the proposed operation cannot be determined.
No project should be undertaken without fairly accurate knowledge
of conditions in all surrounding watersheds. Furthermore, the
actual operation of control projects cannot be efficiently planned
unless such data are available.

One of the first things to be done is to determine the trend of the
infestation—whether normal, increasing, or decreasing—and the
possibility that natural-control factors will soon become operative.
This is done by a thorough study of brood conditions and a compari-
son of past with current losses. Control measures need not be

182 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

applied to normal or rapidly dechning infestations, as the operation
of natural-control factors in such cases is more effective than artificial
measures.

The next step is to make an extensive survey of the area to deter-
mine what parts must be included in the control program, the num-
ber of trees that will require treatment, and the probable cost of
the work. This extensive survey is usually made by experts in
forest-insect control who have had experience in estimating bark-
beetle losses and planning control campaigns.

The methods to be used in such work will depend on the character
of the country, the size of the area involved, the degree of accuracy
desired in the results, and the time and money available for the
work. The simplest and least expensive type of survey is made by
viewing the country from lookout points and making counts along
roads. Sample strips run at intervals back and forth across infested
areas give a very comprehensive estimate of the amount and distri-
bution of infestation, and where time and money are available these
unquestionably furnish the most satisfactory basis of estimates. The
cruising of sample plots has its place as a supplement to topographic
viewing, and with small units it is often possible actually to survey a
rather large percentage of the area in this way. Where large areas
of diverse topography include a number of different forest types,
several different estimation methods or combinations of methods may
be used. In fact, every source of information should be utilized in
arriving at the final estimate, and the more survey data at hand the
more accurate will be the final result.

The topographic method

The topographic method, or red-top survey, is particularly well
adapted to estimating bark-beetle losses over large forested areas of
rough topography, where a large part of the forest can be viewed
from open valleys, ridges, or lookout points. It is the cheapest and
quickest method but is subject to a high degree of error unless sup-
plemented by intensive examinations of sample plots or strips, in
which case fairly reliable results can be obtained.

In using this method, the estimator, equipped with binoculars and
a topographic map of the area, travels through the area visiting all
of the ridges, valleys, or lookout points that can be found. At each
selected point the opposite slopes and visible areas are viewed, the
red, sorrel, or fading trees counted, and an estimate placed on the
map as to the total number of dying or dead trees per acre. Then
strips or plots are actually cruised and a ratio determined between
the number viewed and the total number acutally found. Also, the
relative proportion between newly infested and abandoned trees, all
of which have been counted in the general red-top survey, is deter-
mined. ‘The total estimate is then corrected by these ratios.

The sample-strip method

The sample-strip method is adapted to estimating bark-beetle
losses on flat or gently rolling areas where viewing from a distance is
impossible. it is also a more efficient and accurate method and can

INSECT ENEMIES OF WESTERN FORESTS 183

be used by inexperienced estimators with a fair degree of accuracy.
In order to cover any large area, however, a great many strips must
be run, which makes the method more laborious and consequently
more time-consuming and expensive.

In using this method, the observer travels through the forest along
some routes of known position and length, such as a forest road or
trail, but preferably along a section line or compass line, so as to
obtain an impartial cross section of the area uninfluenced by the
special types of trees which might be encountered along ridges or
canyon bottoms. Distances are determined by pacing, or using the
known distances between. fixed points, such as section corners or topo-
eraphic features located on accurate maps. Without attempting to
blaze or mark the trees, the numbers of fading, sorrel, or red-top
trees are counted within a specified distance on either side of the
line of travel.

The width of the strip will depend on the density of the forest
stand, and should be so chosen that the outer edges will correspond
approximately with the average limit of vision within the stand.
For open ponderosa pine stands a 10-chain strip (330 feet on each
side of the center line) has been found generally satisfactory, but
in the heavier stands this often needs to be reduced to an 8-, 5-, or
even a 4-chain strip. In lodge pole and western white pine stands,
red-top surveys usually are limited to 5-, 4-, 2-, and even 1-chain
strips. However, in these types extensive surveys are usually con-
ducted in the fall of the year to determine the number of new attacks,
and the old loss represented by the red-top trees is ignored. Since
the newly attacked trees are not discolored and can be found only
by sighting the pitch tubes, very narrow strips are necessary, and
a 1-chain strip (33 feet on each side of the compass line) has been
adopted as standard for this work in the northern Rocky Mountain
region.

When a red-top strip count includes several ages of infested and
recently abandoned trees, it 1s necessary to examine a representative
series of trees, either on a sample strip or on a sample plot, to deter-
mine the proportion of the different classes of insect attack and
years of infestation which may be represented. A limited amount
_ of intensive work is also necessary to determine the average diameters,
heights, and volumes represented by the infested trees. The number
of trees counted on the strips multiplied by the number of times
the acreage of the strip would be contained in the acreage of the
entire area will give the approximate number of trees for the entire
unit.

No fixed rule can be given as to the percentage of an infested
area that should be covered during an extensive insect survey to
obtain a reasonable degree of accuracy. The exactness of the survey
will depend on the time and money available and the value of the
timber stand under examination. Small units of valuable timber
should be covered with a greater refinement of methods and a higher
degree of accuracy than an extensive area of heavily infested lodge-
pole pine. Ordinarily a 5-percent sample of an area should give a
reasonably good estimate for control purposes, and on large areas
a 1-percent sample is often sufficient.

184 MISC. PUBLICATION 278, U. S. DEPT. OF AGRICULTURE

BARK-BEETLE CONTROL PROJECTS

The objective of bark-beetle control is to destroy such a high
percentage of the destructive beetles that the aggressive character
of an outbreak will be broken and the remaining infestation will be
held in check by natural control factors. This involves the treat-
ment of as nearly all of the infested trees within the natural bounda-
ries of an affected area as is feasible within physical limitations;
and if migrations threaten from neighboring areas these areas also
should be included in the control campaign. Beetle outbreaks, like
torest fires, if not promptly taken in hand, are soon apt to increase
beyond the practical limitations of artificial control measures.

THE CONTROL UNIT

The size of the area that must be included in any control project
in order to obtain satisfactory results is an important point that
must be given consideration in making the control plans. The feasi-
bility of a project will frequently depend on the possibility of limit-
ing the control area to a unit that can be covered in a single season
with the available man power.

First consideration must be given to the flight habits of the
beetles, and the control area should be made large enough to reduce
to a minimum the possibility of any large number of beetles flying
in from neighboring infested tracts. As far as possible, control
units should be bounded by natural barriers, such as high ridges,
open valleys, or broad strips of timber of a different type. If these
are lacking, then the control area must include all infestation within
the flight range of the beetles. This range for practical purposes
depends on the intensity of the beetle population in any neighboring
area. For instance, in cases where a treated unit is surrounded by
scattered infestations of the western pine beetle, reinfestation, in the
first year following treatment, has been limited to a zone within a
mile of the boundaries. On the other hand, heavy concentrated
infestations of the mountain pine beetle have in some cases appar-
ently migrated across 30 miles of open country to reinfest control

units.
SPOTTING

The first step in connection with any control project is to locate
and mark all infested trees requiring treatment. This is referred
to as “spotting” and is one of the most important phases of the
work, since the success of any control project depends primarily on
finding a high percentage of the infested trees. To accomplish this
the forest must be thoroughly and systematically searched by men
who know an infested tree when they see one. The work should
be begun several days before the treating and should be planned so
as to keep it well ahead of the treating work (fig. 88).

The strip method of spotting is the one best adapted to obtaining
a systematic 100-percent coverage of the area and is the one now
used on nearly ali western bark-beetle projects. According to this
method, a compass man and from two to four spotters run strips
of uniform width back and forth across the area, locate the infested
trees, blaze them or mark them, and map their location so that they
can be found by the treating crews. With a three-man crew the

INSECT ENEMIES OF WESTERN FORESTS 185

compass man, who is usually the chief of the party, runs an accurate
compass line, paces the distances traveled, records data relative to
trees marked for tre atment, constructs a map showing their location,
and assists the spotters in the selection of the proper “trees for treat-
ment. The two spotters cover strips on the sides of, and parallel to,
the course of the compass line, find, blaze, and number the infested
trees, and record whatever data are pertinent in regard to them.
With a six-man crew there are two spotters on each side of the
compass man, and the chief of the party follows behind the crew,
working from side to side to assist in the proper marking of the

Ficurb 88.—Ponderosa pines spotted for treatment in Black Hills beetle control, Kaibab
National TYorest, Ariz.

trees and to prevent any from being missed. Regardless of the or-
ganization, the chief spotter is always responsible for the character
of the work performed by his crew.

The width of the strip and the number of men in the spotting
crew are usually adjusted to the timber type, topography, and
density of the infestation. In typical ponderosa pine stands a
three-man crew, with each spotter covering a five-chain strip, is
the standard practice. This width of strip in the open timber stands
of this type permits the spotters to visit and closely examine not
only the fading trees but all of those which look suspicious and a
high percentage of the green trees as well. On the other hand, in
dense lodgepole and white pine stands a one-chain strip is all that a
spotter can efficiently cover, since it is necessary to look at the base
of every tree, and a six- man crew has been found advantageous in

186 MISC. PUBLICATION 278, U. S. DEPT. OF AGRICULTURE

such timber. When large groups of infested trees are encountered,
all spotters assist in marking all trees within the group, even though
it extends over into the next strip. The spotter who has had the
outside course should always be on the inside during the return
trip, as he is familiar with the boundaries of his strip.

The trees selected for treatment are marked in different ways,
varying from a blaze to a cloth or card tag tacked upon the tree.
When fags are used, it is a good plan to blaze and number the tree
on the opposite side, as this permits the relocation of trees in case
tags are destroyed. ‘The data placed upon tags will vary for each
project, depending on what information is desired. Each tree should
be numbered regardless of the type of mark used, so that a check

can be maintained on the trees treated. After a tree has been
treated the tag is removed, and ali tags are turned over to the project
superintendent at the close of the day’s work and checked against
the serial numbers of the trees marked within the area.

BARK-BEETLE SUPPRESSION METHODS

Methods of bark-beetle control must take into consideration the
varying habits of the insect species, the trees affected, the locality,
and the environmental conditions encountered. Methods effective
in one area cannot be used in other areas even against the same in-
sect because of differences in local conditions. Methods suitable for
the control of an insect in a tree with thin bark cannot be used in
cases where the same species is infesting a tree with thick bark.
Differences in latitude and altitude have an important bearing on
the success of the sun-curing method, and the differences of type and
forest cover will often be a determining factor in the selection of
a suitable control measure. It is often necessary to use two or
more methods, even on a single project, because of differences in ex-
posure or site conditions, the size of trees infested, or the height
of the infestation in the trunk.

Some of the methods that have been of greatest usefulness in the
past are the following:

(1) Burning methods; in which the trees are felled, partly peeled, and
burned; felled and rolled into decks and burned; or burned standing.

(2) Peeling methods; in which the bark is removed from the tree, and
be Boa exposed to predators or left to die through exposure to the sun’s
1eat.

(3) Solar-heat method; in which the trees are felled and the insects killed
by the sun’s heat without peeling the bark from the logs.

(4) Submerging infested logs in water and drowning the insects.

(5) Removing the infested trees from the woods through logging opera-
tions before the insects have had time to emerge and escape.

Since most of the destructive bark beetles confine their attacks
to a few species of trees, control can be carried out by treating just
the affected host trees.

The fell-peel-burn method

The fell-peel-burn method is one of the oldest for bark-beetle con-
trol, yet one which is still used in the suppression of outbreaks of
the western pine beetle and related species, the larvae of which
burrow into the outer bark and are not exposed when the bark is
peeled from the tree.

INSECT ENEMIES OF WESTERN FORESTS 187

Ficure 89.—Felling bark-beetle-infested ponderosa pines is the first step in their treatment.

In this method the infested trees are first felled (fig. 89), either
up or down hill but away from new growth or heavy patches of
brush—never across the slope of the hill, if this can be avoided,
since a broad flame is more difficult to control than a narrow one.
Then the bark is peeled from the top half of the fallen trunk for
as far as the infestation extends, piled along the sides, and set on

188 MISC. PUBLICATION 2738, U. S. DEPT. OF AGRICULTURE

fire (fig. 90). The flames creep under the log and scorch the un-
peeled bark. If it is desired to dispose of the brush at the same time,
the hmbs and top are cut off and piled back over the trunk. If this
would make too large and dangerous a fire, this material can be left
out and burned at a later time or spread on the ground to decay. As
a fire precaution, a fire line is constructed by scraping away all
the litter and duff down to the mineral soil for a width of about
3 feet and completely encircling the tree. In treating a tree in-
fested with the western pine beetle it is desirable to leave the stump

eo

FIGURE 90.—After partial peeling, trees infested by the western pine beetle are burned.

and the duff around it unburned in order to protect the beneficial
clerids in their pupal cells, which are usually concentrated around
the base of the tree.

The fire should be allowed to consume the infested bark, but
should not be so large as to make it difficult to control. In wet
weather pitch will have to be supplied to burn the bark sufficiently,
while in dry weather all tops, limbs, and even needles will have to
be thrown outside of the fire line in order to keep the fire from
becoming too large. In wet weather the burning should be with
the wind and uphill in order to create enough draft to consume the
bark; but in dry weather this should never be done, but the burn-

INSECT ENEMIES OF WESTERN FORESTS 189

ing should be downhill and against the wind so that the fire can
be controlled. Burning, if done by experienced men, can be han-
dled without injury to the forest. Ordinarily the fire is not hot
enough to burn the logs, and if at all accessible they can be used
for lumber if taken out within a year or two.

The fell-deck-burn method

The fell-deck-burn method is one of the most economical control
methods and is particularly useful in the control of bark beetles
infesting trees of small diameter (fig. 91) such as small ponderosa
pine, lodgepole pine, or western white pine, infested with the moun-
tain pine beetle or Black Hills beetle, especially where large groups
of trees are infested. By using tractors or teams even the larger
trees can be handled for treatment by this method.

FiGuRE 91.—Burning in decks is an economical method of treating bark beetle-infested
trees of small diameter.

The trees are felled usually in one direction, and then by using
peavies, are hand-rolled into piles, or dragged by horses or tractors
into openings where they can be bunched into large decks. No
peeling is necessary, except occasionally on the outer surfaces of the
outer logs. The whole pile is then fired and usually is completely
consumed.

This is a very satisfactory method where it can be used and is not
only more economical than the fell-peel-burn method but leaves the
forest free from the fire hazard of fallen logs and piles of brush.
This method also permits the control work to start before the close
of the fire season in the fall since the piles can be prepared, and the
burning done at a later date. Since the burning of decked logs
throws out a terrific heat, the size of the piles should be adjusted to

190 MISC. PUBLICATION 2738, U. 8. DEPT. OF AGRICULTURE

the amount of space available so that neighboring living trees will
not be injured. If this precaution is not taken, the scorched trees may
draw in additional infestation and more or less nullify the effects of
the control work.

The otl-burning method

Recent control technique has developed an economical method of
killing bark beetles in thin-bark trees, such as lodgepole pine, by
spraying the bark with fuel oil, firing it, and letting the bark be
scorched deeply enough so that the beetles will be killed by the
heat. The trees may be either felled and burned or burned in a
standing position.

A fuel oil is used that has a high caloric content and burns evenly
and without too quick a flash. An explosive oil burns too quickly to
give good heat penetration. For burning standing trees a light oil
of gravity 32° to 34° Baumé and a flash point of 160° F. has given
the best results. For burning trees on the ground ordinary fuel oil
with a gravity of 27°+ Baumé and a flash point of 225° F. has been
found most satisfactory because of its slower burning, greater heat
penetration, and lower cost. In either case from one-half to three-
fourths of a gallon is required to burn the average lodgepole pine.
The oil is applied with a hand pump through a long nozzle.

With the burning-standing method, the oil is sprayed as high on
the bole of the tree as the equipment will permit, about 30 feet at
present, and the entire top of the tree is “crowned out” with fire.
The treatment is effective only to the height of the burn, and unless
the bole is thoroughly scorched as high as to a 6- or 8-inch diameter,
which is usually the upper limit of infestation, the tree must be
felled and the scorched portion burned with additional oil. When
lodgepole pine bark has been adequately burned to kill the beetles
underneath, the bark flakes will curl and show white on the edges.
Frequently when this method is used, the spotting and treating are
performed at the same time. A pack trdin carrying the pressure
sprayers, oil, and felling tools follows the spotting crew, and in-
fested trees are treated wherever they are found. This method is an
economical one, and costs have averaged between 68 cents and $1.05
per tree. While the method is effective in ordinary weather it can-
not be used on windy or stormy days, and during dry or windy
weather great care must be used to avoid serious conflagrations.
This method is limited to the treatment of thin-barked trees such as
lodgepole pine, to trees of moderate height that can be burned as
high up as the infestation, and to situations where the fire hazard is
not too great.

Lodgepole pine growing in dark woods or in dense thickets of
underbrush where the sun-curing method is not effective, or tall trees
which cannot be successfully treated in the standing position, can
be felled and burned with oil in places where decking and burning
in piles would not be feasible. A slow-burning fuel oil is used, and
the fire is carried along and confined to the bole of the tree by spray-
ing on oil from a hand pump. Two men follow. behind the fireman
and quickly extinguish any fire left on the tree or starting on the
ground. It is surprising in what hazardous areas this method can
be used without difficulty.

INSECT ENEMIES OF WESTERN FORESTS 191

Penetrating oils

Recent experiments in California have developed some petroleum
oils that, when sprayed on. the trunk of pine trees, will penetrate
the bark and kill the pine beetle broods beneath. The most effective
oils developed to date are those of the distillate grade carrying as
much naphthalene as can be taken in solution. These when applied
to infested ponderosa pine bark at the rate of about 4 ounces per
square foot will give mortalities ranging from 50 to 90 percent. Oils
of this type, however, are effective only when temperatures are above
60° F. and cannot be used at all when the bark is wet. This method
of control is still in the experimental stages, with the possibility that
it may be useful in treating infested trees during the summer months
on recreational areas or late in the spring and early in the fall when
the fire hazard is too great to permit burning.

The peeling method

The peeling method can be used in the control of those bark beetles
that, in the immature stages, work between the bark and the wood
and die of exposure when the bark is removed, and is especially ap-
plicable to moderately thick-barked trees that are easily peeled. It
has been used extensively in the control of the Black Hills beetle in
ponderosa pine of the Rocky Mountain region and in the control of
the mountain pine beetle in western white pine. It has the impor-
tant advantage of involving no immediate fire risk and is cheaper
than the burning method for the treatment of isolated trees less than
30 inches in diameter. If the bark tends to adhere to the wood,
however, peeling is a very slow, tedious process and in the spring
will not destroy overwintering adults, new adults, or pupae in the
last stages of development. In general, it is more expensive than the
burning method, especially for the treatment of trees in groups.
Moreover, it leaves a mass of slash and crisscrossed logs in the woods
that seriously increases the fire hazard.

In carrying out this method, the infested trees are felled across logs
or other felled trees to hold them off the ground, and then all of the
infested bark is peeled with an ax or barking spud and allowed to
drop to the ground where ants, rodents, and exposure dispose of the
immature bark beetles (fig. 92). In some rare cases, where all of
the infestation is within 20 feet of the ground, the barking has been
done with long-handled barking spuds without felling the trees. In
such cases, of course, the work can be done more cheaply than where
felling the trees becomes necessary.

Peeling and spreading bark

A modification of the peeling method, involving the spreading
of the bark where it will receive the direct rays of the sun, has been
used with a fair degree of success in the control of the western pine
beetle and is applicable to the treatment of ponderosa pines infested
with broods of this species late in the spring or in the summer in
places where burning would be dangerous.

In this method the tree is felled across a log so as to keep a large
part of the trunk off the ground, and the bark is peeled and spread

192 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

out in the open where it will receive the direct rays of the sun.
To be effective it is necessary to have summer air temperatures of
85° F’. or more in order to produce fatal temperatures of 115° to 120°
in the bark. The bark must be very carefully spread and must not
be left in the shade of other slabs or trees. On north slopes or in.
canyons it must be carried out to an opening or propped against
rocks or trees in order that the sun’s rays may strike it at an “angle
of not less than 45°.

FIGURE 92.—Peeling western white pines infested by bark beetles by means of spuds.

It can be readily seen that the method is tedious and expensive and
of limited application. Effective temperatures do not always pre-
vail during the control season, especially at high altitudes and on
northern exposures. The method also requires a greater attention
to detail than can ordinarily be expected from the average work-
man. Summer control work in which this method is used has not
proved very effective, and the method has lost favor in recent years.

The solar-heat method

The solar heat or sun-curing method (69) is particularly appli-
cable to the control of bark beetles, other than the engraver beetles
or flatheaded borers, that attack thin-barked trees of small diameter,
such as lodgepole pine, especially those growing in open stands and
and in areas where the deck- burning method is objectionable.

In this method, trees are felled in a north-and-south direction
parallel to one another and never crisscross as in the peeling method.

INSECT ENEMIES OF WESTERN FORESTS 193

They are completely limbed and the brush cleared away so that the
logs will receive direct sunlight. After a few day’s exposure with
air temperatures of 80° F. or more all of the bark beetles on the
top half of the logs will have been killed. Then the men return and
with peavies turn the logs completely over so that the other side
will be exposed.

This method has been very effectively used for several years in
control of the mountain pine beetle in Crater Lake National Park.
It has the advantage of being much cheaper than either the peeling
or burning methods; and in crowded stands it avoids the scorching
of adjacent trees, and thus does not set up influences attractive to the
beetles which would favor reinfestation, as so often happens when.
the logs are burned. The disadvantages are that considerable slash
is left in the woods, and the method cannot be used in the shade
of dense stands, on cold north slopes, or in localities where air tem-
peratures during the control season are less than 80° F.

Submerging the infested logs

Many years ago A. D. Hopkins advocated the submerging of in-
fested logs as a means of destroying bark beetles where the infested
trees could be cut and placed in a mill pond. Recent experiments
have shown that infested logs must be submerged for at least 6
weeks in order to destroy the broods of the western pine beetle. In
any shorter period than this the beetle’s development is simply
retarded. Also, the beetles in the portion of the logs not covered by
water are unhampered in their development and are free to emerge
and escape. So far this method has been tried only in an experi-
mental way, but it has possibilities, where applicable, and some-
time may be of value in connection with a control project.

The trap-tree method

A method of bark-beetle control that has been used in Europe
with apparent success consists in felling injured, weakened, or sup-
pressed, noncommercial trees in accessible locations as attractive
baits for bark-beetle broods, and then destroying them after the
beetles have entered the bark. The method has been tried on numer-
ous projects and on rather an extensive scale in California and
southern Oregon in the control of the western pine beetle, but with
little success. Although beetles are attracted to the traps, these
fail to protect the standing trees in the vicinity, and frequently
the trap tree acts as a source of attraction to bring in bark beetles)
that kill groups of adjacent standing trees. Moreover, the trap
trees have always failed to absorb any large proportion of the beetles
in their area, and hence the method has lost favor as an effective or
economical control measure. It may, however, prove of value in the
control of other species, particularly in cases where the trap logs
can be removed and utilized.

Bark-beetle control by logging

Where the infestations are in accessible tracts of valuable timber,
the cutting and salvage of the infested trees through logging opera-
tions is an effective and economical method of control. This method

136650° —38——_13

194 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE

was first advocated by Hopkins for the control of Dendroctonus
beetles. He proposed that the infested logs be removed from 20 to
50 miles from the forest so that the beetles emerging from them
would find no trees to attack. Often this method has been followed
unwittingly by logging operators who have cut infested trees and
sent them to distant mills or burned the slabs; and this, together
with the removal of beetles in recently felled green logs, explains the
absence of insect-killed trees around many going logging operations.
Of late years this method has come more and more into favor with
the opening up of forest tracts and the development of truck log-
ging, which has made possible the removal of scattered infested
trees at comparatively low costs (53a).

This method serves the dual purpose of controlling the bark
beetles and salvaging timber that otherwise would be completely
worthless within a short time. Where the method can be used it
is economical and sometimes can be carried out with a small imme-
diate profit from the operation in addition to suppressing the beetle
outbreak. Even if the logging operation is carried out at a loss of
from $1 to $2 per thousand board feet of timber, it is better than
spending $3 or $4 a thousand feet to fell the trees and burn them or
leave them in the woods, as is the case with the usual control opera-
tions. The reduction of infestation by either method will be the
same,

In inaccessible areas the method cannot be applied except at a cost
in excess of that of the ordinary control methods, and of course
cannot be used in the control of bark beetles attacking unmerchant-
able species of trees whose chief value lies in the protection of water-
sheds or as a forest cover in parks and recreational areas. Moreover,
bark beetles introduce blue stains which discolor the sapwood before
there is any possibility of salvage, and thus reduce the value of the
material. In ponderosa pine areas it rarely pays to salvage tops or
trees less than 22 inches in diameter, and such unmerchantable mate-
rial must be burned to complete the control operation. Because of
immediate blue staining the value of the logs taken out of the woods
is reduced approximately 50 percent below that of green logs, so
returns from the operation must be computed on that basis. If the
method is to be effective, the beetles on an entire unit must be de-
stroyed in a single season, which means that the logging operation
must frequently be extended over a very large area. This is often
difficult, so logging must be supplemented in many cases by the
ordinary control methods.

MAINTENANCE CONTROL

One season’s treatment of an area will rarely be sufficient to bring
an outbreak under control. Even with the most careful spotting and
treatment some infestation will be missed that will give rise to new
infestation the following year. A follow-up program, or mainte-
nance control, is therefore necessary ‘until the normal balance is
restored and the bark beetles reduced to an endemic status.

With infestations of the mountain pine beetle, unless migrations
occur, a 75-percent reduction is usually obtained following the first
season’s work, and one or two seasons of maintenance work will
usually bring the epidemic under complete control. In western pine

INSECT ENEMIES OF WESTERN FORESTS 195

beetle control, reductions of more than 50 percent are rarely obtained
in one season, and the work has to be repeated for several seasons
until the resistance of the stand has improved through removal of
beetle-susceptible trees or until the trees are better able to resist
attacks. In fact, during long periods of drought and lowered tree
resistance, almost continuous work may be necessary to hold the
beetle population down to reasonable limits.

In this work special consideration must be given to the natural-
control factors and an effort made to favor their effectiveness while
reducing the population of the destructive species. The avoidance
of burning around stumps where predators congregate, the saving
of certain infested trees to permit multiplication of the beneficial
parasitic insects present, and the improvement of stand resistance
are some of the ways in which natural control may be encouraged
(pp. 169, 172, 173).

WHEN CONTROL MEASURES ARE ADVISABLE

When the natural balance in a forest is disturbed and an outbreak
of bark beetles threatens to destroy a large number of valuable trees,
the application of direct control measures (27) is advisable provided
effective methods are available and the value of the timber that can
be protected will justify the expense of the work. Control measures
are expensive and unless the timber is valuable enough from the
commercial, watershed-protection, or aesthetic standpoints to war-
rant the cost of control measures, it is best to allow Nature to bring
the epidemic under control in her own way.

To reach a decision certain data must be obtained. In the first
place, the primary agency responsible for the death of the trees
should be determined. If trees are dying because of drought, fire
injury, flooding, or other causes, there is obviously little use to dis-
pose of the insects, which may be only the final cause of their death.
Nor is it wise to attempt to exterminate native bark beetles present on
an area under normal conditions. Only when the natural-control
factors have been disturbed and an outbreak threatens should arti-
ficial measures be taken.

In the second place, it must be determined whether effective and
economical control measures are available. In some cases, because
of the habits of the beetles, no satisfactory methods of control have
been devised. For instance, the control of the white fir engraver
beetles through burning the bark of dying trees is of little value
since a large number of these insects may continue to breed in
perfectly green trees, causing only local damage. Moreover, the
control measures must not be so expensive as to exceed the value of
timber that might be saved. 3

And lastly, it 1s most important that cooperation be secured from
all owners in the infested area so that the control campaign can
cover all of the contiguous infested territory in a single season.
Small tracts cannot be successfully cleaned up if neighboring or
intermingled tracts are left untreated.

ConTROL COSTS AND PROBABLE RESULTS

The cost of control work varies with the size and type of timber,
the method of treatment, the intensity of the infestation, the rough-

196 MISC. PUBLICATION 2738, U. S. DEPT. OF AGRICULTURE

ness of the terrain, the accessibility of the area, the current cost of
labor, and so many other factors that it 1s impossible to give any
specific costs which might apply to a given situation. Some idea
of the approximate cost of the work, however, may be obtained from
experience gained during the decade from 1921 to 1930.

In the ponderosa pine region of California, Oregon, and Washing-
ton the control of the western pine beetle cost on an average about $4
per treated tree, with the cost In some cases dropping as low as $1.75
per tree. In the control of the Black Hills beetle in ponderosa pine
of the Rocky Mountain region the cost per tree averaged about $1.50
with some costs as low as 75 cents per tree.

The control of the mountain pine beetle in lodgepole pine forests,
where either the solar-heat method or the fell-deck-burn method was
used, cost on the average from 50 cents to $1 per treated tree, de-
pending largely on the intensity of the infestation. Under similar
conditions the solar-heat method is the cheaper of the two.

The control of mountain pine beetle infestations in western white
pine cost about $4.50 per tree, and in sugar pine, on account of its
very large size, the costs sometimes amounted to as much as $16 per
tree.

For the treatment of a few scattered trees around summer homes
or in inaccessible areas the costs will run higher than on large-scale
projects.

Bark-beetle control work has been in progress in western forests
since 1911, and the results of this work have indicated rather
definitely what can be expected in the control of some of the more
important species (27).

Wherever bark beetles have been primarily responsible for the
death of trees, the application of control measures has resulted in
reducing the infestation or in restoring the natural balance so as
to bring the outbreak under control. With such aggressive tree-
killing species as the mountain pine beetle and the Black Hills beetle,
control work has been very effective in quickly suppressing outbreaks
wherever a high percentage of the infested territory could be covered
in a single season and the results were not nullified by migrations
from distant areas. Western pine beetle epidemics have so fre-
quently been partly dependent upon a weakened condition of the
host tree that the results from control have not been so clear-cut.
Infestations have been reduced, but unless the work is continued
or conditions bring about improved tree resistance, the reductions
brought about by control efforts are difficult to maintain,

At best, remedial bark-beetle control is only a temporary expedient,
or a method of suppressing outbreaks that have been brought about
through some interruption, disturbance, or failure of the biological
balance. The only permanent protection is through the management
of forest properties so as to maintain the natural balance, or if this
is broken by forces beyond man’s control, to be able to salvage the
killed timber quickly enough to prevent excessive loss.

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1926. PREVENTING DAMAGE BY TERMITES OR WHITE ANTS. U.S. Dept. Agr.
Farmers’ Bull. 1472, 22 pp., illus.
(76)
1927. DEFECTS IN TIMBER CAUSED By INSECTS. U.S. Dept. Agr. Bull. 1490,
47 pp., illus.
(77)

1933. INJURY TO BUILDINGS BY TERMITES. U. S. Dept. Agr. Leaflet 101,
8 pp., illus.
(78) SwaIngn, J. M.
1913. TENT CATERPILLARS. Canada Dept. Agr., Div. Ent. Cire. 1, 14 pp.,
illus.
(79)

1918. CANADIAN BARK-BEETLES, PART II. A PRELIMINARY CLASSIFICATION,
WITH AN ACCOUNT OF THE HABITS AND MEANS OF CONTROL.
Canada Dept. Agr., Ent. Branch Bull. 14, 148 pp., illus.
(80)

1925. THE FACTORS DETERMINING THE DISTRIBUTION OF NORTH AMERICAN
BARK-BEETLES. Canada Ent. 57: [261]—266.

(81)
1930. AIRPLANE DUSTING OPERATIONS FOR THE CONTROL OF DEFOLIATING
INSECTS. Canada Dept. Natl. Defense, Civil Aviation and Civil
Govt. Air Oper. Rept. 1929, 16 pp., illus.
CRAIGHEAD, F.. C., and BaiLery, I. W.
1924, STUDIES ON THE SPRUCE BUDWORM (CACOECIA FUMIFERANA CLEM.).
Canada Dept. Agr. Bull. (n. s.) 37, 91 pp., illus.
(88) SwENK, M. H.
1927. THE PINE TIPMOTH IN THE NEBRASKA NATIONAL FOREST. Nebr. Agr.
Expt. Sta. Research Bull. 40, 50 pp., illus.
(84) UNITED STATES DEPARTMENT OF AGRICULTURE, BUREAU OF ENTOMOLOGY.
1927. THE RELATION OF INSECTS TO SLASH DISPOSAL. U. S. Dept. Agr.
Dept. Cire. 411, 12 pp.
(85) Watson, E. B. :
1931. THE HEMLOCK LOOPER INFESTING BALSAM IN THE PROVINCE OF
QUEBEC. Quebec Soc. Protect. Plants (1929-80) Ann. Rept.
22: 89-91.
(86) WILDERMUTH, V. L., and CarFrey, D. J.
1916. THE NEW MEXICO RANGE CATERPILLAR AND ITS CONTROL. U. S. Dept.
Agr. Bull. 448, 12 pp., illus.

(82)

INDEX OF HOST TREES

a)

Alder (Alnus spp.)— Fir (Abies spp.)—
bark or cambium, 131, 140. bark or cambium, 56, 109, 118, 120, 122, 123, 124, 125,
leaves, 59, 68, 71, 73, 87, 92, 93. 134, 135, 136, 137, 139.
twigs or branches, 35, 36. cones or seeds, 18, 19, 20, 21.
wood, 132, 145, 146, 149, 151, 154. general, 4, 9, 173.

Alpine fir. See Fir, alpine. needles, 67, 70, 75, 78, 79, 80, 81.

Arbutus. See Madrona. roots, 27.

Ash, Oregon (Frazinus oregona)— twigs, 28, 32, 36, 37, 38, 39.
bark or cambium, 131. wood, 145, 146, 148, 149, 150, 152, 153, 154, 157, 158.
leaves, 71, 73. Alpine (Abies lasiocarpa)—
twigs or branches, 36. bark or cambium, 125, 139.
wood, 154, 155, 160. cones or seeds, 22.

Aspen (Populus tremuloides)— twigs or branches, 40.
bark or cambium, 36, 137. Bristlecone (Abies venusta), cones or seeds, 22.
leaves, 71, 73, 86, 87, 94. Douglas. See Douglas fir.
twigs or branches, 36. lowland white (Abies grandis)—
wood, 137, 147, 149, 154. bark or cambium, 125, 159.

Bay. See Laurel. cones or seeds, 22.

Bigcone spruce (Pseudotsuga macrocarpa), bark or roots, 125.
cambium, 120, 134. twigs or branches, 47.

Bigtree (Sequoia washingtoniana)— wood, 159.
bark or cambium, 131, 137. Noble (Abies nobilis) —
needles, 51. bark or cambium, 125.
wood, 150. twigs or branches, 48.

Birch (Betula spp.)— red (Abies magnifica), cones or seeds, 19, 20, 22.
bark or cambium, 132. Shasta (Abies shastensis), cones or seeds, 19, 22.
leaves, 73. silver (Abies amabilis), cones or seeds, 19, 22.
twigs or branches, 36. white (Abies concolor)—
wood, 146, 149. bark or cambium, 123, 124, 125, 159.

Cedar— cones or seeds, 19, 20, 21, 22.
bark or cambium, 56, 129, 130, 137. needles, 51, 71.
general, 4. roots, 28, 125.
leaves, 33, 50. twigs or branches, 40, 47, 48.
twigs, 32, 36, 37, 42, 43, 47. wood, 146, 154, 159.
wood, 146, 158, 158. Hemlock (Tsuga spp.)—

Alaska (Chamaecyparis nootkatensis)— bark or cambium, 56, 102, 122, 128, 134, 135, 137.
bark or cambium, 129, 131. cones or seeds, 22.
twigs, 32. general, 4, 9.
Incense (Libocedrus decurrens)— needles, 50, 59, 75, 80, 81, 173.
bark or eambium, 129, 131, 137. twigs or branches, 32, 36, 37.
cones or seeds, 20. wood, 145, 146, 154.
leaves, 51, 52. mountain (Tsuga mertensiana)—
twigs or branches, 32, 43. bark or cambium, 102, 128, 129.
wood, 150. cones or seeds, 19, 22.
Port Orford (Chamaecyparis lawsoniana)— wood, 147, 150.
bark or cambium, 129, 131. western (Tsuga heterophylla)—
cones or seeds, 20. bark or cambium, 120, 128, 129.
western red (Thuja plicata)— losses, 7.
bark or eambium, 129, 131, 137. needles, 48, 76, 80, 81, 91.
leaves, 76. roots, 27.
wood, 149, 150. wood, 159.

Cottonwood. See Poplar. Juniper (Juniperus spp.)—

Cypress (Cupressus spp.)— bark or cambium, 56, 131, 137.
bark or cambium, 42, 56, 129, 130, 131, 137. cones or seeds, 54.
cones or seeds, 20. twigs or branches, 37, 47, 54.
general, 4. wood, 137 149.
leaves, 33, 44, 91. Larch, western (Larix occidentalis)—
twigs or branches, 32, 36, 37, 42, 48, 47, 51. bark or cambium, 41, 109, 115, 120, 129, 134, 135, 137,
wood, 149, 150, 158. 140.

Douglas fir (Pseudotsuga taxifolia)— general, 4.
bark or cambium, 38, 41, 51, 56, 118, 119, 120, 122, needles, 48, 71, 80, 81, 91.

124, 125, 128, 134, 136, 137, 139, 140. twigs or branches, 37, 48.
cones or seeds, 18, 19, 22. Laurel, California (Umbellularia californica).
losses, 7, 9, 173. leaves, 87.
needles, 46, 47, 50, 52, 59, 62, 67, 70, 75, 76, 78, 79, 30, wood, 132, 154, 160.
81. Locust (Robinia spp.)—
roots, 27. bark or cambium, 140.
twigs or branches, 32, 36, 37, 38, 47, 48. wood, 136, 155. :
wood, 143, 145, 146, 147, 148, 149, 151, 152, 153, 154, | Lodgepole pine. See Pine, lodgepole.
157, 159. Madrona (Arbutus menziesit)—

Elm (Ulmus spp.)— leaves, 68, 73, 86, 87.
leaves, 92, 94. wood, 147, 149, 154, 160.
wood, 155. Mahogany, mountain (Cercocarpus spp.), bark or

Engelmann spruce. See Spruce, Engelmann. cambium, 132.

203

204 MISC. PUBLICATION 273, U.

Maple ee spp.)—
leaves, Ye.
twigs, "36.
wood, 154, 155, 160.
Mesquite (Prosopis spp.)—
twigs, 37.
wood, 154.
Oak (Quercus spp.)—
acorns, 23.
bark or cambium, 132, 137,
general, 4, 53.
leaves, 59, 68, 71, 73, 77, 87.
twigs or branches, 36, 37.
wood, 147, 149, 151, 154, 155, 160.
Pine (Pinus spp.)—
bark or cambium, 8, 38, 56, 98, 102, 107, 109, 110,
112, 113, 115, 118, 134, 136, 137, 139, 168.
cones or seeds, 16, 18, 19, 38.
needles, 46, 50, 51, 53, 64, 67, 71.
roots, 27.
twigs or branches, 31, 35, 36, 37, 38, 39, 40, 46, 47, 49.
wood, 146, 148, 149, 151, 152, 153, 154, 157, 158, 159.
Apache (Pinus apacheca), cones or seeds, 16.
Arizona (Pinus arizonica), bark or cambium, 102,
114.
Bishop (Pinus muricata), bark or cambium, 115,
117, 139.
bristlecone (Pinus aristata), bark or cambium, 107.
Coulter (Pinus coulteri)—
bark or cambium, 99, 112.
wood, 147.
Chihuahua (Pinus leiophylla), bark or cambium,
102.
Digger (Pinus sabiniana)—
bark or cambium, 115.
needles, 51.
twigs or branches, 40, 46.
Foxtail (Pinus balfouriana), bark or ecambium, 113.
Jefirey (Pinus jeffreyi)—
bark or cambium, 107, 113, 115, 117, 118, 133.
cones or seeds, 16, 18, 41.
needles, 52, 64.
twigs, 35, 46.
wood, 149.
knobcone (Pinus attenuata)—
bark or cambium, 117, 139.
cones or seeds, 18, 21, 38, 41.
twigs or branches, 21, 38, 39.
wood, 149.
limber (Pinus flezilis)\—
bark or cambium, 102, 107.
cones or seeds, 16.
lodgepole (Pinus contorta)—
bark or cambium, 41, 102, 107, 109, 113, 114, 115,
117, 118, 128, 139.
cones or seeds, 16, 18, 39, 41.
general, 7, 8, 9, 173, 183, 185, 189, 190, 192, 196.
needles, 62, 64, 80, 82, 83, 85, 86, 90.
roots, 27.
twigs or branches, 34, 35, 39, 40, 49.
wood, 146, 149, 158.
Mexican white (Pinus strobiformis)—
bark or cambium, 107, 139.
wood, 146.
Monterey (Pinus radiata)—
bark or cambium, 109, 112, 115, 117, 139.
cones or seeds, 16.
needles, 46, 49, 51, 52, 53, 68, 84, 91.
twigs or branches, 35, 40, 49, 56.
pifion (Pinus edulis)—
bark or cambium, 107, 134.
cones or seeds, 16.
needles, 53, 68, 90.
twigs or branches, 37, 46, 49.
Ponderosa (Pinus ponderosa)—
bark or cambium, 38, 99, 100, 102, 106, 107, 112,
113, 114, 115, 118, 133, 134, 136, 139, 155.
cones or seeds, 16, 18, 21, 22, 38, 39, 41.
general, 5, 7, 8, 9, 59, 172, 183, 185, 189, 191, 194, 196.
needles, 46, 49, 51, 62, 64, 68, 80, 86, 90.
roots, 27.

140.

S. DEPT. OF AGRICULTURE

Pine (Pinus spp.)
Ponderosa (Pinus ponderosa.)
twigs or branches, 34, 35, 37, 38, 39, 40, 41, 46, 47,
49, 54, 55, 153.
wood, 146, 147, 149, 153, 154, 155, 158.
singleleaf (Pinus monophylla)—
cones or seeds, 16.
needles, 90.
twigs or branches, 40, 49.
sugar (Pinus lambertiana)—
bark or cambium, ate 112, 113, 115, 133, 139.
cones or seeds, 16, 3
needles, 82, 90.
twigs or branches, 34, 39, 49.
wood, 153, 158.
Torrey (Pinus torreyana), needles, 52.
western white (Pinus monticola)—
bark or cambium, 48, 49, 102, 112, 113, 115, 118,
124, 139.
cones or seeds, 16, 39.
general, 7, 8, 183, 185, 189, 191, 196.
needles, 48, 49, 62, 80, 90.
aoe ie
twigs, 34, 39, 49.
western yellow. See Pine, ponderosa.
whitebark (Pinus albicaulis)—
bark or cambium, 102, 117, 118.
wood, 147.
Ponderosa pine. See Pine, ponderosa.
Poplar (Populus spp.)—
bark or cambium, 42, 137, 140.

general, 52.

leaves, 68, 71, 72, 73, 86, 87, 92, 93, 94.
twigs, 36.

wood, 137, 147, 149, 150, 151, 154, 155

Redwood (Sequoia sempervirens) —

bark or cambium, 56, 129, 131, 137, 139.

general, 4.

leaves, 51.

twigs, 36.

wood, 146, 153, 155, 158.

Sequoia. See Bigtree; Redwood.
Spruce (Picea spp.)—

bark or cambium, 56, 107, 109, 122, 125, 126, 127, 128,
134, 137, 139, 140.

cones or seeds, 18, 19, 20.

general, 4.

needles, 50, 67, 75, 78, 79, 81.

twigs, 32, 35, 37, 38, 47.

wood, 143, 145, 146, 153, 154, 158.

Bigcone. See Bigcone spruce.

Colorado blue (Picea pungens)—
cones or seeds, 2
needles, 51.
twigs, 47, 48, 49.

Engelmann (Picea engelmannii)—
bark or cambium, 41, 102, 126, 127, 128, 139.
cones or seeds, 22.
needles, 80, 86.
roots, 27.
twigs, 34, 40, 41, 47, 48, 49.
wood, 147, 149.

Sitka (Picea sitchensis)—
bark or cambium, 113, 127, 128, 139, 140.
cones or seeds, 22.
needles, 45, 76, 84. ‘
twigs, 33, 40, 45, 47, 48.

Sycamore (Platanus sp.)—

bark or cambium, 140.

leaves, 87.

wood, 149, 160.

Western white pine. See Pine, western white.
White fir. See Fir, white.
Willow (Saliz spp.)—

bark or cambium, 140.

general], 52.

leaves; 68, 71, 72, 73, 87, 92, 93, 94.

twigs, 36, 37.

wood, 132, 150, 154, 155.

Yew, Pacific (Tarus brevifolia), 4.

GENERAL INDEX

[Exclusive of host references listed on pp. 203-204.

Abebaea, 87.
Acanthocinus, 186, 137.
Acmaeodera, 150.
Acorn moth, 23.
Acorn weevils, 22.
Acossus, 155.
Adelges, 47, 48.
Aegeria, 140.
Aegeriidae 139, 140.
Aglais, 165.
Agrilus, 36.
Airplane dusting.
Alcathoe, 140.
Allomyia, 54.
Alniphagus, 131.
Altica, 93.
Ambrosia beetles, 141, 143-147.
Anobiidae, 159.
Anthazia, 36.
Ants—

carpenter, 28, 141, 161.

white, 162.
Aonida, 51.
Apanteles, 72.
Aphids—

bark, 46.

gall, 52.

general, 24, 29, 44, 45, 161, 176.

Monterey pine, 46.

root, 23, 28.

spruce, 45.
Arachnida, 12, 44.
Arctiidae, 66.
Argyresthia, 42, 43.
Argyrotaenia, 82, 84.
Armyworms, 164.
Asemum, 153.
Aspidiotus, 50, 51.
Atimia, 137.
Augomonoctenus, 20.
Bacteria, 11, 169.
Balaninus, 22.
Barbara, 19.
Bark aphids, 46.
Bark beetles—

alder, 131.

ash, 131.

bigtree, 131.

birch, 132.

broadleaf, 131.

cedar, 129.

control of, 179.

cypress, 131.

detection of, 180.

fir, 118, 120.

fir root, 1265.

penetal, 4, 5, 8, 27, 56, 57, 58, 96, 133, 167, 168, 169, 171,

172

grand fir, 125.
hemlock, 128.
juniper, 131.

larch, 129.

losses, 5, 97, 99.
mountain mahogany, 132.
noble fir, 125.

oak, 132.

pine, 98.

redwood, 131.

root, 23, 27.

Sargent cypress, 131.
shrub, 132.

spruce, 125.
suppression, 186.
surveys, 181.
western cedar, 131.

See Dusting.

Italic type denotes principal reference. ]

Bark lice, 47.
Bark maggots, 158.
Bark scorch, 11.
Bees, carpenter, 162.
Beetles—
Alaska spruce, 127.
alder flea, 93.
ambrosia, 141, 143-147.
Arizona pine, 102.
barber, 109.
bark. See Bark beetles.
Black Hills, 96, 106, 196.
clerid, 105.
Colorado pine, 102.
cone, 4, 16.
cottonwood leaf, 94.
dendroctonus, 98.
dicerea, 149.
Douglas fir, 119, 120, 127, 128.
elm leaf, 94.
Engelmann spruce, 126.
engraver—
fir, 122.
general, 110-117, 127, 168.
pine, 56, 110, 111.
spruce, 127.
ips, 111.
Jeffrey pine, 107, 113.
June, 24
leaf, 92.
lodgepole pine, 109.
long-horned, 36, 134, 125, 150.
lyctus, 159.
mountain pine, 7, 96, 192, 107, 113, 128, 194, 196.
oak timber, 147.
ostomid, 99.
pepper grass, 166.
pine, 98, 168.
pityogenes, 117.
powder post, 141, 159.
red turpentine, 109. 115, 168.
roundheaded pine, 102.
Sitka spruce, 127.
southwestern pine, 109, 102.
spotted willow leaf, 94.
twig, 8, 29, 30-33, 168.
western cedar bark, 131.
western pine, 5, 96, 99, 102, 167, 169, 196.
western willow leaf, 94.
willow leaf, 94.
Wilson’s wide-headed ambrosia, 146.
wood engraver, 117.
Beneficial insects, 169.
Birds, 169.
Blight, parch, 11.
Borers—
alder, 140.
amethyst cedar, 137.
bark, 56.
black-horned pine, 153.
cone, 21
cottonwood crown, 140.
Ergates wood, 161.
fir flatheaded, 134.
flatheaded, 29, 35, 37, 132-134, 141.
flatheaded cone, 2/.
flatheaded wood, 147.
lead cable, 16/.
locust, 136.
metalic wood, 132.
pine flatheaded, 133.
pinhole, 143.
ponderosa pine bark, 136.
ponderous, 141.
poplar, 137.

205

206 MISC. PUBLICATION 2738, U. S. DEPT. OF AGRICULTURE

Borers—C ontinued.
poplar and willow, 154.

roundheaded, 29, 36, 134-135, 141, 170.

roundheaded cone, 2/.

roundheaded fir, 135.

roundheaded wood, 150.

sculptured pine, 148.

twig, 36.

western cedar, 149.

western larch roundheaded, 136.

willow, 154.

wood, 141.
Bostrichid, Stout’s, 160.
Bostrichidae, 159.
Brachyrhinus, 26.
Brothylus, 154.
Bucculatriz, 87.
Bud insects, 29.
Budmoth, spruce, 84.
Budmoths, 8, 44, 78-86.
Budworm—

black-headed, 8/7.

hemlock, 44, 60.

spruce, 7, 9, 44, 79, 177.
Budworms, 78.
Bug, spined soldier, 68.
Bugs, 24, 44, 170, 176.
Buprestid, golden, 148.
Buprestidae, 35, 132, 147.
Buprestids, wood-boring, 150.
Buprestis, 148, 149.
Burning, light, 66, 169.
Butterflies, lycaenid, 161.
Butterfly—

California tortoise-shell, 165.

pine, 7, 60, 62.
Callidium, 37, 153.
Cameraria, 87.
Camponotus, 28, 161.
Carabidae, 170.
Carpenter ants, 28, 141, 161.
Carpenter bees, 162.
Carphoborus, 31, 32.
Caterpillars—

blue-sided tent, 73.

California tent, 73.

eastern tent, 73.

false, 87.

forest tent, 73.

Great Basin tent, 73, 164.

range, 1/64.

tent, 72-74, 164.

twig-boring, 29.

western tent, 73.
Cecidomyiidae, 20, 53.
Centipedes, 12.
Cerambycidae, 35, 36, 134, 150.
Chalcids, seed, 2/.
Chalcophora, 148.
Check, black, 159.
Cheilosia, 158, 159.
Chermes, 47, 48.
Chilopoda, 12.
Chionaspis, 50.
Chipmunks, 66, 170.
Chrysobothris, 36, 150.
Chrysomelidae, 93.
Chrysophana, 21, 36.
Chrysopidae, 170.
Cimbex, 87, 92.
Cinara, 28, 46.
Clearwing, locust, 140.
Clearwing moths, 139, 140.
Clerid, 99, 105.
Cleridae, 170.
Climatic influences, 166.
Coccidae, 49.
Coccinellidae, 170
Coeloides, 105.
Coleoptera, 12, 86.
Coloradia, 64.
Cone insects, 15-22.
Conophthorus, 16.
Contarinia, 54.
Control—

advisability of, 195.

barkbeetle, 179.

methods of, 186-194.
biological, 173.

Control—Continued.
chemical, 175.
costs of, 195.
defoliator, 59, 175.
direct, 171.
introduced pests, 176.
maintenance, 194.
natural, 166.
projects, 184.
results, 195.
silvicultural, 172.
See also Dusting, spraying.
Control unit, 184.
Coptodisca, 86.
Coryneum, 42.
Cossidae, 164.
Cossonus, 154.
Criocephalus, 153.
Cryphalus, 32.
Cryptorhynchus, 154.
Crypturgus, 32, 96.
Curculionidae, 33, 154.
Cutworms, 7, 23, 26.
Cyllene, 136, 154.
Cynipidae, 53.
Cynipids, 52.
Damping-off, 23.
Decay, 11.
Defoliation, 9, 58, 120.
Defoliators—
control of, 175.
general mention of, 4, 8, 56, 57, 58, 59, 62, 167, 178.
losses from, 7, 58.
Dendroctonus, 96, 98-110, 111, 115, 118, 119, 120, 126,
127, 194.
Detection surveys, 180.
Dicerca, 149.
Dicrodiplosis, 54.
Dilachnus, 46.
Dioryctria, 18, 19, 37, 38, 39.
Diplopoda, 12.
Diptera, 12, 86, 170. |
Diseases— |
insect, 169. |
tree, 2, 10, 1/7.
wilt, 66, 68, 82.
Drought, 2, 58, 120, 167.
Dryocoetes, 125, 128, 182.
Dusting, airplane, 59, 64, 66, 71, 77, 81, 89, 178.
Dusts, 175, 176, 178.
Ehrhornia, 51.
Elateridae, 26.
Ellopia, 75, 77.
Endemic, 170.
Enemies, natural, 66, 169.
Engravers—
Arizona five-spined, 173.
beetles. See Beetles, engraver.
California five-spined, 112.
California pine, 116.
Douglas fir, 122.
fir, 122, 128. |
hemlock, 129.
larch, 129.
Monterey pine, 115, 117.
Oregon pine, 116.
pine, 110.
sawtooth pine, 115.
Sitka spruce, 128.
smaller western pine, 116.
western six-spined, 112
wood, /1?.
Finoclerus, 105.
Epinotia, 43.
Ergates, 161.
Hriophyes, 62.
Eriophyidae, 52.
Essigella, 46.
Eucosma, 18, 37, 40, 41.
Eucosmidae, 37.
Eucymatoge, 19.
Eulia, 82.
Evetria, 19, 40.
Feeders—inner bark, 46, 95.
leaf, 56, 58.
root, 23.
twig, 29.
Fire, 2, 9, 10, 11, 58, 120, 167, 169, 170.
Firebugs, 134.

INSECT ENEMIES OF WESTERN FORESTS 207

Flatheaded borers, 132, 183, 141, 147. Laspeyresia, 18, 20, 37, 41, 42.
Flea beetle, 93. Leaf chewers, 4, 59, 60, 87.
Flies, lace-wing, 170. Leaf feeders, 68, 60.
ly— Leafhoppers, 23.
range crane, 166. Leaf miners, 59, 86.
tachinid, 68, 71. Leaf rollers, 78, 85.
Food supply, 167. Leaf skeletonizers, 59.
Forest management, 8, 9, 172. Leperisinus, 131.
Forest plantations, losses in, 7. Lepidoptera, 12, 60, 86, 154.
Forest-products insects, 8, 741. Leptostylus, 137.
Fungi, 2, 11, 52, 169. Liasemum, 153.
Galenara, 78. Lice—
Galeruca, 166. Cooley’s gall, 47.
Galerucella, 94. plant, 46.

Gallflies, 53.

Gall louse, Cooley’s, 47
Gallmakers, 42, 87.
Gall midges, 52, 63.
Galls, juniper, 54.
Geometrid, fir cone, 19.
Geometridae, 74.
Girdlers, twig, 35.
Givira, 156.
Gnathotrichus, 145, 146.
Grasshoppers, 23, 164, 166.

spruce gall bark, 47.

wooly pine, 48.
Lightning, 5, 167.
Dina, 94.

Logging, bark-beetle-control, 193.

Lonchaea, 21.
Long-horned beetles, 36.
Loopers—
hemlock, 7, 60, 75, 81, 178.
New Mexico fir, 78.
oak, 77.

Grubs, white, 7, 23, 24. Losses, 4, 5, 8.
Halisidota, 67, 68. Lyctidae, 159.
Harmologa, 79. Lyctus, 159.

Hedulia, 18.
Hemerocampa, 69, 70, 71.

Lygaeonematus, 91.
Magdalis, 33, 36.

Hemicallidium, 137. =
Hemileuca, 164. Dee
Hemiptera, 12, 44, 170. cone, 20.
Hexapoda, 12. root, 7, 23.

Homoptera, 12, 44.
Horntails, 155, 157.
Hylastes, 27.
Hylesinus—
Douglas fir, 724.
Hemlock, 129.
Sitka spruce, 128.
Hylotrupes, 137.
Hylurgops, 27.

Hymenoptera, 12, 60, 86, 87, 170.

Hyperparasitism, 170.
Hyphantria, 68.
Infestations—
endemic, 97, 170.
epidemic, 171.
Influences, climatic, 166.
Injuries, mechanical, 11.

white fir cone, 27.
Malacopterus, 154.
Malacosoma, 72, 73, 164.
Marmara, 86.
Matsucoccus, 51.
Mealybugs, 51.
Measuring worms, 74.
Medeterus, 105.
Megastigmus, 21.
Melanophila, 3€, 133, 134.

Melanophila, California, 134.

Melissopus, 23.
Metamorphosis, 12, 14.
Mice. 170.

Micracinae, 33.
Micracis, 182.

Midges—
ieee oe bird’s-eye pine, 54.

bark, 167. one A eg
beneficial, 169. ae , 52, 63.
bud, 29. onterey pine, 53.
cone, 15. Monterey pine resin, 56.
decaying wood, 159. pe ae 54.
defoliating, 7. seed, <U.
forest-products, 141. Millipedes, 12.

Miners—

leaf-eating, 58-95.
mature-tree, 57.
nursery, 23.
parasitic, 170.
predacious, 170.

aspen leaf, 87.

inner bark, 95.

leaf, 86, 87, 176.
lodgepole needle, 85.

primary, 4. needle, 84.
range-plant, 164. poplar leaf-blotch, 86.
root, 23-28. spruce needle, 86.
sap-sucking, 44. Mistletoe, 11.

seale, 49. - Mite, pine needle, 52.
secondary, 4. Mites, 12, 44, 51, 52.
seed, 15. Moisture, 167.
seedling, 23. Monarthrum, 147.
twig, 29. Monochamus, 152, 153.

wood-boring, 167.

Moths—

young-tree, 28. acorn, 23.
Ips— bark, 41.
Cloudcroft, 113. bud, 44, 78, 85.

emarginate, 773.

general mention of, 31, 32, 56, 98, 110, 111-117, 118,

126, 128, 129.
Knaus’, 114.
Vancouver, 173.

Isoptera, 12, 162.
Itycorsia, 91.
Janetiella, 20, 53.
Kiln drying, 160.
Lachnus, 28:
Larvae, 12.

carpenter, 141, 154.
clear-winged, 139, 140, 141.
cone, 16, 18, 19.

cedar tip, 42.

cypress tip, 43.
cypress twig, 42.
Douglas fir pitch, 740.

Douglas fir tussock, 7, 60, 70.

incense cedar tip, 43.
noctuid, 164.
Pandora, 7, 9, 64.

208 MISC. PUBLICATION 278, U. 8. DEPT. OF AGRICULTURE

M oths—Continued. Rhyncolus, 154.

pine tip, 29, 39. Rollers, leaf, 78.

pine tube, 82. Roots insects, 23-28.

pitch, 4, 38, 40, 139. Rosalia, 154.

pitch nodule, 40. Rots, wood, 11.

satin, 72. Salvage, 193.

sequoia pitch, 139. Saperda, 137.

spruce bud, 84. Saplings, 28.

spruce pitch, 140. Sap-sucking insects, 44.

tiger, 66. Satin moth, 72.

tip, 4, 8, 37. Sawflies—

tussock, 69. broadleaf, 92.

twig, 8, 37. conifer, 89.

wood-boring, 154. cottonwood, 92.

Zimmerman pine, 38. cypress, 91.
Myeloborus, 31, 82. elm, 92.
Necydalis, 154. general mention of, 23, 52, 60, 87, 89, 92.
Needle miners, 88. hemlock, 91.
Needle tier, lodgepole, 82. larch, 91.
Nematus, 91. lodgepole pine, 90.
Neoclytus, 37, 154. Monterey pine, 9/.
Neodiprion, 82, 90, 91. two-lined larch, 97.
Neophasia, 62. western larch, 91.
Niches, egg, 97. willow, 92.
WNorthorhina, 154. Sawyers—
Notolophus, 71. obtuse, 153.
Nursery insects, 23. Oregon fir, 162.
Oberea, 37. spotted pine, 162.
Oeme, 37. Scales—
Oligonychus, 62. California pine, 50.
Oligotrophus, 54. insects, 24, 29, 44, 49, 176.
Oncideres, 37. pine needle, 50.
Opsimus, 37. Scarabaeidae, 24.
Orthotomicus, 31, 110, 118. Schnizolachnus, 46.
Ostomatidae, 170. Scierus, 128.
Ostomid, 99. Scobicia, 161.
Pandora moth, 9, 64. Scolytidae, 27, 30, 56, 96, 143. |
Paranthrene, 140. Scolytus, 32, 56, 119, 122, 123, 124, 125, 128, 129.
Parasites, 170. Secondary insects, 4.
Paratimia, 21. Seed insects, 16-23. |
Parharmonia, 140. Seed midges, 20.
Peronea, 81. Seedling insects, 28.
Petrova, 37, 40. Semanotus, 137.
Phloeosinus, 32, 33, 56, 129, 131. Shrews, 170.
Phryganidia, 68. Sirex, 187.
Phyllocnistis, 87. Siricidae, 166.
Phyllonorycter, 86, 87. Slash, 110, 119, 167, 168, 170.
Phy matodes, 137. Slugs, 87.
Physokermes, 51. Smelter smoke, 11, 167.
Pine, ‘‘birdseye,”’ 54. Snags, 9.
Pineus, 47, 48, 49. Snowbreak, 110, 167.
Pinipestis, 37, 89. Spanworms, 74.
Pissodes, 33, 34, 35, 138, 139, 154. Spider mites, 51.
Pitch moths, 38, 40, 139. Spider, red, 44, 52.
Pityoborus, 31. Spiders, 12.
Pityogenes, 31, 56, 98, 110, 717, 118. Spotting, 184. |
Pityokteines, 32, 56. Spraying, 52, 59, 60, 66, 72, 90, 176, 177. |
Pityophilus, 31. Sprays, 44, 45, 50, 81, 175, 176.
Pityophthorus, 31, 32, 56, 118. Squirrels, 66.
Plantations, 7, 23, 28. Stagnation, forest, 170. |
Platycampus, 91. Stilpnotia, 72. |
Platypodidae, 148. Sun seald, 11. |
Platypus, 146. Suppression methods, bark beetle, 186.
Poecilonota, 150. Survey methods, 182.
Pogonocherus, 37. Surveys, barkbeetle, 180, 181, 182.
Poles, 28. Susana, 91
Polycaon, 160,161. Synaphoeta, 154. |
Polycesta, 150. Taniva, 86.
Polyhedral bodies, 169. Temperature, 166. : |
Polyphylla, 25. Tent caterpillars, 72, 164.
Predators, 170. Terminal insects, 29. |
Prionozystus, 166. Termites, 72, 141, 161, 162.
Prionus, 151. Tetranychus, 52. |
Projects, bark-beetle-control, 184. Tetropium, 135.
Pseudococcus, 51. Thecodiplosis, 53. |
Pseudohylesinus, 27, 32, 56, 119, 122, 124, 125, 126, 128, 129. | Theronia, 63.
Pseudopityophthorus, 33, 132. Tier, lodgepole needle, 44, 82, 90. |
Pterocyclon, 147. Tiger moths, 66. ||
Pteronidea, 92. Tip moths, 39, 42. |
Ptinidae, 159. Tipula, 166. ||
Pyralid, cone, 19. Tortricidae, 44, 78. |
Pyralidae, 37, 140. Tortriz, 82. |
Recurvaria, 85, 86. Toumeyella, 51. |
Renocis, 132. Trachykele, 149, 150.
Retinodiplosis, 54, 56. Tragasoma, 153. |
Rhopalomyia, 54. Trichiosoma, 92. |
Rhyacionia, 29, 37, 39, 40. Trichogramma, 71. i

|

INSECT ENEMIES OF WESTERN FORESTS

Trypedendron, 146, 147
Twig—

beetles, 29

borers, 35.

girdlers, 35.

insects, 29-44.

moths, 87.

weevils, 33.
Ulochaetes, 154.
Urocerus, 167.
Vespamima, 139.
Walshomyia, 54.
Wasps—

eynipid, 53.

horntail, 141, 155.

wood, 141, 155.
Webber, cypress, 43.
Webworm, fall, 68.
Weevils—

acorn, 22.

bark, 56, 138.

nut, 22.

root, 23, 26.

terminal, 33.

tip, 8.
twig, 29, 33.

136650 °—38——14

| Weevils—Continued.

wood-boring, 154.
White grubs, 7, 28, 24.
Windfalls, 110, 119, 133, 167.
Winter injury, 11.
Wireworms, 7, 23, 26.
Witches’ brooms, 11.
Wood borers—

flatheaded, 147.

metallic, 132.

roundheaded, 150.
Woodpeckers, 99, 105, 169.
Wood stainers, 145.
Woodwasps, 166.
Woolly bears, 67.
Worms—

California oak, 68.

carpenter, 155.

measuring, 74.
Xeris, 168.

Xyleborus, 147.
Xylococcus, 51.
Xylocopidae, 162.
Xylotrechus, 154.
Zeiraphera, 84.
Zootermopsis, 163.

209

ORGANIZATION OF THE UNITED STATES DEPARTMENT OF AGRI-
CULTURE WHEN THIS PUBLICATION WAS LAST PRINTED

SECKELATY_Of AQT CULL tITe eee een rs a Henry A. WALLACE.

Under Secretaria Se ee ee r ees SMe oes OWitsone

SASsistant iS cr eLanyae 2 oss eee eee jee Harry L. Brown.

Director of Extension Work... = 22=_.-_= ©: W. WaRBURTON.

Director ojo ina nees am = No Sei Spee erat pee ae W. A. Jump.

Directorsor Jajormaiton 22% Sse hens M. 8S. EISENHOWER.

Dene Ctor ofc CnSONME | Sees a ey Gk ares eee OP W. W. StTocKBERGER.
Darectowofeli esearch == epee ee! See JAMES T. JARDINE.

WOUCHONE. Ske. aan, pee eet eer ee Pe Mastin G. WHITE.
Agricultural Adjustment Administration ____- H. R. Tourer, Administrator.
Bureau of Agricultural Economics____-_-_-- £ A. Gz Buack, Chief.

Bureau of Agricultural Engineering________- S. H. McCrory, Chief.
Bureau-of Animal Industry ss se JoHun R. Moutuer, Chief.
Bureau of Biological Survey. ___._____-__-- Ira N. Gaprrevson, Chief.
Bureau of Chemisiry and Soils-_=-_-=-2---- Henry G. Kniaut, Chief.
Commodity Exchange Administration___-_- ~~~ J. We dt Duyn; Cheer
Bureauw-o- Dairy Indusizy=__ = > ae O. E. Reep, Chief.

Bureau of Entomology and Plant Quarantine. Lez A. Strona, Chief.

Office of Experiment Stations__-__________-- JAMES T. JARDINE, Chief.

Food and Drug Administration_______----~- WALTER G. CAMPBELL, Chief.
Forest Seroiees sa oi Deen ae ee ee FERDINAND A. Siucox, Chief.
Bureau of-HomesHconomics. =. = eee Lovu1sE STANLEY, Chief.

EAD EOS Sea ee ee ee Oe LE eee ae CLARIBEL R. Barnett, Librarian.
Bureau of Plant nausiry 22. | 3 E. C. AUCHTER, Chief.
Buréeauroj Publis oadss = S25 fa eee THomas H. MacDona.tp, Chief.
Farm Security Administration__ 22-22 222 W. W. ALEXANDER, Adminisirator.
Sotl Conservation, Service... = _ - -82 22-2 H. H. Bennett, Chief.

W CQther 21S Ur. 60.1 es ne ce yes I Se Wiis R. Greac, Chief.

This publication is a contribution from

Bureau of Entomology and Plant Quarantine. Lez A. Strrone, Chief.
Division of Forest Insect Investigations-. F. C. CraiGHEab, Principal
Entomologist, in Charge.

210

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