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UNITED STATES
{“ DEPARTMENT OF AGRICULTURE
Miscellaneous Publication No. 273
° Issued February 1938
Washington, D.C. Slightly revised April 1939
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Bureau of Entomology and Plant Dee
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UNITED STATES
DEPARTMENT OF AGRICULTURE
Miscellaneous Publication No. 273
Issued February 1938
Washington, D.C. Slightly revised April 1939
INSECT ENEMIES OF WESTERN
FORESTS |
Compiled by F. P. KEEN, senior entomologist, Division of Forest Insect Investiga-
tions, Bureau of Entomology and Plant Quarantine
CONTENTS
Page Page
Introductions ae-es === aa Nea ss ie 2 Key to diagnosis of insect injury to young
Kinds of forest insects and the losses they bRe@S see ee renee Moot cae Stace nie
CAUSE emer a ae eet rk Teen Ne 2 Insects affecting twigs, terminal shoots,
IDIREGE WOSSS Se at N Sa a aei 5 NOVO ONG Bes Rae oe ae ee ees See 29
Imdirocolossest tt fob Lo) 8 Sap-sucking insects_____.----_.-..-------- 44
Relation of insects to forest management___ 9 poeders on ue nner Dale of young trees-_- oe
ar ay efoliators of young trees________________-
Pe sae damage-___-- W Insects injurious to mature forest trees________ 57
nsects allecting seed production. _-__--------- 15 Key to recognition of insect injury to ma-
Key to diagnosis of insect injury to cones TIT ORCL COS er ee oe Pk Su ans ieee 58
GUNG! SECO Ss See See ee ees 15 Leaf feeders and defoliators____._________- 58
Wonebec tlesteaies wl aes Sa need oe sk 16 Miners in the inner bark and phloem____- 95
GONE OLS Meee eee EW 16 | Insects injurious to wood and forest products__ 141
C@OnNeMNAT OTS ase en Se ey Se es 20 Key to diagnosis of insect injury to wood
WOME DORE S ey ees eee oi 21 and: wood products: 22-2 2525 2.) 142
Syaegl GRAIG IR SE ieee ae ee 21 Insects working in unseasoned logs or lum-
Nut and acorn weevils__...._.-.-.-------- 22 ber_------- Se as ata thal tee oe ee =-- 188
Neormmoth 23 ee working in seasoned or decaying
oa CENA ek Eee PEE RMON Bh Mert VA OL OYO barat eS TSI eek ee Us Ear NN ie es 159
Bases OU. te. ees oS ee ea ae 23 Insects injurious to forest range plants____-__- 164
Key to diagnosis of insect injury to seed- Natural control factors_________- eR T EER EET 166
Wie! aoe 2.15 ik SR ois alge Ae ea 24 Climatic and environmental influences_-_ 166
VULGAR UTE = ato 7 coal I 24 Naturalienemies: 2! Ssc) Ves aaseae ee as 169
ROO GRWICC Wil S eee ee i IE 9¢ | Control of injurious forest insects_______------- 171
VAT CWOLITIGH meen tins Wan in GN Te) 26 Silviculturalicontrolas{ 222k ese. eee oe eases 172
Wily, ORI S meee ee te ae a PE 6 Biologicalicombrol: saa w se we eee aye 173
oo tbanlabectles meme wie eo See 27 Direct artificial or remedial control_-__---- 174
TRYOOU DY OMG GE et eRe os Qe Mviteracunre;Clbeda stews a 5e) a ames eee ye 197
Insects injurious to young trees (saplings and Indextof hostatreessa. 20 ee ee 202
OXON) os Sees el Po a D8 aN (Grete Tali Tn ClO ett cem a abat se talenss Sus alse ee te eee 205
1FKor 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 ae 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 tke instruction and education of
these men and of their leaders and has erystallized 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.
130643 °—39 1 1
2 MISC. PUBLICATION 273, U. S. 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 supphes. 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 pr otection of utilized wood prod-
ucts, and ev en 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 is 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
FIGURE 1.—Insect control is one of a forest ranger’s many routine tasks.
infested tree.
Marking
an
4 MISC. PUBLICATION 2738, U. 8S. 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 fohage 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 oreen trees, often
with serious results. In spite of the large number of insect species
which prey upon the forests, compar atively 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 1s primary or secondary in its attack, as it is wasted
effort to proceed against an insect, even if 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 1s 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 ace 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, however, 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)
n 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, includ-
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 lightning or
windstorms. On the
other hand, much of
it can be prevented
through silvicultural
practices, proper for-
est management, and
direct control meas-
FicurE 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 westerr 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 1n%1921, lost 3,875,000 board feet through bark-
beetle attack’ during the 11-year period 1921-31. Growth during the
same period, which, owing to drought and to defoliation by the
MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE
6
$
&
to fecaggrss Shacy
Mae
en a Ome 5
DA ae
ious
f commercial ponderosa pine stands by bark beetles is a ser
FIGURE 38.—Destruction o
problem in many Western States.
INSECT ENEMIES OF WESTERN FORESTS 7
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 1923-82 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 (380 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 defohators 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.
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 is
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 1s 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 lines would alone justify large expenditures for
insect control. i
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 1s 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
growth 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-
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 1s 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 ial
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 impor-
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 is
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
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 is 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
FIGURE 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; F, adult male; G, grub.
Flies (Diptera): H and K, maggots; J and L, puparia; J, adult fly. Scale insects
(Homoptera) (drawings by Edmonston): M, adult male; N and QO, scales on pine
foliage. P, termites (Isoptera). All natural size; except H. I, J, K, L, X23; NM, O,
greatly enlarged.
14 ' MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE
called caterpillars; those of flies with two clear wings are called mag-
gots; and those of wasplike 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
ego, 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 1s 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, bliighting,
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
welbed-ADOTINgS= 2a eee 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
IMASSOS OL Olt = ee es 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.
C. Injuries to nuts or seeds of broad-leaved trees.
1. Acorn showing no injury externally but mined by small,
white cum] ed sorbose ce ss Seb he 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.
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. (59).
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,
od ae
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2() 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. Pe.
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 (Cecidomyilidae) 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 Dea
The white fir cone maggot (Lonchaea viridana Meig.) is 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
length.
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 ovipositors 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 countries, 1n-
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
pues against. Calcium cyanide may prove to be a more satis-
actory 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.
29 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 _~___. Silver fir, lowland white fir, white fir,
Shasta fir, and bristlecone fir.
Megastigmus tsugae Crosby____— Mountain hemlock.
Megastigmus spermotrophus
Wachtl (60) ___________________ 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
gnaw 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- yext spring, and the
cid (Megastigmus albifrons) laying eggs through small :
green cones into seeds (drawings by Edmonston). En- adults emerge 1n the
larged. OC, Larvae, pupae, and adults of same species of
Megastigmus, X 8. Female above, male below. summer, Several
INSECT ENEMIES OF WESTERN FORESTS De
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.
Batamnus ,caryae, Horn 22.8 Hickory, pecans. Eastern States and west-
ward into Colorado.
BOUGRURAUS a GECUUS: ) SAY ts Chestnuts, acorns. Eastern States and
westward into Arizona.
BALaninws NASICUS Say. 2 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 (JZ elissopus latiferranus Ws. ), 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 i in southern California and may likewise be found
in the large green cynipid galls formed on various oaks. There 1s
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 1t 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 varl-
D4 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 owithout dees === 2s root weevils, page 26.
c. Long, slender, hard-shelled, yellow or brown “worms”
with feebly developed legs eae ss oe wireworms, page 26.
d. Nearly hairless, soft, sluggish, dark-colored caterpil-
lars working below surface of ground *
cutworms, page 26.
2. 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
WAS fst oat ce Ps cs ee 2 eae cutworms, page 26.
0. Grasshoppers s22 2 228 2 ee grasshoppers, page 164.
2. Borings under bark of larger seedlings________ bark beetles, page 96.
C. Leaves of seedlings either chewed, skeletonized, mined, discolored, or
attacked by leaf-sucking insects_________--____-__~_ 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. : ; at SLE ee
*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,
INSECT ENEMIES OF WESTDRN FORESTS DAS,
The large, shining, brown “June bugs” (fig. 10) often lay their
eggs in grassy places or where the ground vegetation is 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 FES SAE ot ea seal Se
erubs 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
26 MISC. PUBLICATION 273, U. S. 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 hght 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—rachyrhinus ovatus L., B.
pugosostriatus 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-
erown larvae pupate in the soil and emerge as new adults the follow-
ing summer. |
Seedbeds can be protected from infestation by encirchng 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 hghts 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-
eround 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 1s 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:
AV VALSNENEY 6 | Onc si A SO AiR le eA St ite Hee I s . 25 pounds.
Wihitevarsenicior paris. 2reen—o_ = 2 - nije BERLE Bane eee 1 pound.
BIACKSE AD MOlASSeS sess ase! 8 ae Eee alive Near OP KO 8 Ee
BV Vea Weer eee ne ee Ee Pe 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
Hylastes nigrinus Mann_-____~-~-. Douglas fir, western white pine, western
hemlock, and probably other conifers.
TULGOSCESINUAGCCT WueCC ears i Engelmann spruce, ponderosa pine, and
lodgepole pine.
Hylurgops leconteti Sw____---- --- Lodgepole pine, ponderosa pine.
Hylurgops porosus Lec____------ . Lodgepole pine, western white pine, and
probably other pines.
Pseudohylesinus granulatus Lee. Balsam firs.
The general habits of bark beetles are more fully discussed in a
later section (page 96).
a8 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 term1-
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. ret Ly:
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
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 (Lriophyes pint 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 (ZV'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
applcation 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 53.
b. Needles blistered within the sheaths, causing pre-
mature shedding__—-__ 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-
LOMVeSCCre WON 2 aGe eee ee 2 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
JIS VVEN BY Cc a 2 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
4
gall aphids, page 47.
. 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 i m shape and
splny, 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
ie in the Western States. Only a few, however, do any appre-
ciable damage.
GALL MIDGES
The gall midges belonging to the family Cecidomyiidae 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 (V’hecodiplosis 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,
54 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE
Apical, budlike swellings are formed on ponderosa pines in Colo-
rado by Contarinia coloradensis Felt and Dicrodiplosis gilletter Felt.
Several of the Juniper galls are caused by species of gall midges.
Walshomyia juniperina Felt causes a shghtly enlarged fruit of
Juniperus californica, also a purplish, apical bud gall with three or
four diverging lobes. Oligotrophus betheli Felt forms reddish, api-
eal, conical galis 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
pitchy 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
areas (Thecodiplosis pini-radiatae). Insert, adult have not been named
as yet.
The birdseye pine midge (Retinodiplosis sp. near inopis O. 8.) isa
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 EN
IMIES OF WESTERN FOREST
ay)
bright-red maggots. If the pockets are not numerous enough to kill
nes 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; C, 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. 8. DEPT. OF AGRICULTURE
The Monterey pine resin midge (Retinodiplosis 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 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 other wise, 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 Pityoktemes. 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 greater 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. 8. 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. scconseyy and only attack
trees already in a weakened or dying condition. A few species, how-
ever, are aggressive 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 is 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 cLwnk, DrANChes, OF WOOtS= ee a= ee ee defoliators, page 58.
B. Terminal shoots, laterals, or tips deformed or killed. Remainder of
tree appearing: health yos-2o 32-2 See oe 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 Mmsects and killed [eee 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
(SE), Gr owth 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 defoliation 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 foliage 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 1s 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.
60 MISC. PUBLICATION 273, U. 8S. 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
defoliated trees. Tor instance, Jarge forest areas in Washington,
Canada, and Alaska have been badly defolated 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
young caterpillars are more easily killed by poison than older ones,
early detection and control are important.
As these leaf chewers actually swallow and digest their leafy food,
the method of artificial control is to spray or dust the folhlage 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 apphcation 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.
cee. 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 caterpillars 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.
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, ieathery 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
ATL CLS STG SS Sans ee ees a giant silk moths.
(4) Yellow and black caterpillars with branched
spines; feeding on willow, popular, and
other broadleaved trees and_ shrubs
i 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.
Oa Workinie: in, broad leaves.) 220.2 leaf miners, page S6.
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
peetles Wes yess ks See eatoheeties: page 92:
B. Trees sickly, leaves not chewed but yellowing or covered with a sticky
Ox Gd alioneoreblacks Smuts oe es sap-sucking insects, page 44.
C. Leaves stunted, galled, or swollen_____.______.___ | ___ gall makers, page 52.
_°Similar work is done on broadleaved trees by a great variety of caterpillars, saw-
Hie CL, 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.) (37) is potentially
one of the most dangerous enemies of ponderosa pine in the North-
western States. One of the earhest 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-
fohated thousands of
acres of ponderosa
pine along the Little
Salmon and Payette
Rivers in Idaho in
1922 and 1923. Old,
mature ponderosa
pihes are more sus-
ceptible to injury
than the younger,
thriftier trees. West-
ern white pine and
lodgepole pine, when
FIGURE 27.—The pine butterfly (Neophasia menapia) : Eggs, 1 mixture with pon-
alee pape’ Coes 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 134 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, 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 (Theronia 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 lving caterpillar or butterfly within the de-
folhated 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 defohator is brought under
control by natural means. Even if only 50 percent of the foliage
of 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 the 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 defoliated 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
30 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
Figure 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, « 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 21% to 3 inches in length, with each segment sup-
porting a few stout branched spines.
130643°—39——_5
66 MISC. PUBLICATION 273, U. 8S. 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 defoliator 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 is 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 ight 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. 8. 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 pihon pine in Colorado. HT. 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 Monter ey pine
in California.
The fall webworm (//yphantria 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 foliage. 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 ground 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. 3]
t-4
{ 4 i
\ ft.
i A ay
— s
x
} /
4 -, o> a
\B TS SRA 2
\ eye |
DS
ae t
= ae
Y oy, S
7 *
>
FicurRE 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; £#, adult female, X 7; F, adult male, X 7
Other species of the genus Veodiprion which feed on the needles
of western pines include the following:
Species of Neodiprion Host and distribution
IN. SUUUICEDS .CrOSS = = ee tee Ponderosa pine. California.
N= gitlette: McGill 22-2 2e = = Ponderosa pine. Colorado.
N. edwardsiu- Nortona__=— = _ =: Sugar pine, western white pine. California.
N > -vrohwer, Nh = 2 ee Pifon and singleleaf pine. New Mexico
and California.
INSECT ENEMIES OF WESTERN FORESTS QO]
The Monterey pine sawfly (Ztycorsia 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 (Meodiprion 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 (Vematus (Lygaeconematus) 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
inasmuch 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.
O2 MISC. PUBLICATION 2738, U. S. 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 lie 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 in 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 like 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 (Altica 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
blue, and about one-
fourth inch long. — Fievre 46.—Alder flea beetle (Altica bimarginata) : A, Adult
hee mature larvae eee nate eags, x 4 55C, larva, About 26 species in both conifers and
broadleaved trees.
Acmacodera spp------------------ About 18 species in various broadleaved
trees and shrubs.
Polycesta-spp2==--2- = 22 _.__ 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 L5l
The ponderous borer (Hvrgates 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 114 to 214 inches in length (fig. 74).
Figure 74.—Larvae and adult of the ponderous borer (Hrgates 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
laid 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 prom1-
nent spines on the lateral margins of the prothorax. The larvae are
very similar to those of Hrgates.
152 MISC. PUBLICATION 273, U. 8. 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
ee eet ort ei ee aa hole through the thin
GURE (¢0.—sSpotted pine See ONOCNAMNUS MACULOSUS), 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
ege 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 (Alonochamus 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.) 1s a stout,
black beetle, approximately one-half to 114 inches in length, with
gray markings, antennae about twice as long as the body, 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,
mjured, 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 (MZ, scutellatus Say).
INSECT ENEMIES OF WESTERN FORESTS 153
The obtuse sawyer (J/onochamus obtusus Csy.) 1s 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 11% 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-
ing:
Species Hosts and distribution
Tragosoma:harrisi Lecs—___=_-__- Pines. Western States.
Asemum atrum Esch__-__________. Pines, firs, and spruce. Western States.
Asemum nitidum Lec _- Pines, firs, and Douglas fir. Pacific coast.
Criocephalus productus Lec_______. Pines, firs, and Douglas fir. Western States.
Criocephalus asperatus Lec____-~-- Pines. Oregon and California,
154 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE
Species Hosts and distribution
Nothorhina aspera Lec___--_---_-_- Douglas fir. Western States.
Xylotrechus undulatus Say_-_--__- Pines, firs. Douglas fir, hemlock, and spruce.
Western States.
Xylotrechus nubilus Linsley__--~- White fir. California.
Ulochaetes leoninus Lec____--__--- Ponderosa pine, Douglas fir, and spruce.
California to British Columbia.
Xylotrechus nauticus Mann_-___~_-. Oak, madrona, and eucalyptus. California
and Oregon.
Neoclytus conjunctus Lec____---_- 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 Phyncolus 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 (Prionowystus 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 hmbs. 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
900 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,
MISC. PUBLICATION 2738, U. 8. DEPT. OF AGRICULTURE
adult
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