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Issued November 25, 1910.

US) DEPAR EMENTD «OF SAG RIGUE TURE,
BUREAU OF ENTOMOLOGY—CIRCULAR No. 129.

L. O. HOWARD, Entomologist and Chief of Bureau.

INSECTS IN THEIR RELATION TO THE REDUCTION
OF FUTURE SUPPLIES OF TIMBER, AND
GENERAL PRINCIPLES OF CONTROL.

BY

A. D. HOPKINS,
In Charge of Forest Insect Investigations.

64130°—Cir. 129—10 WASHINGTON : GOVERNMENT PRINTING OFFICE : 1910

215AS*%

BUREAU OF ENTOMOLOGY.

. O. Howarp, Entomologist and Chief of Bureau.
Ge: ec Gewvnnk Entomologist and Acting Chief in Absence of Chief.
R. S. Crirron, Hxrecutive Assistant.
W. EF. Taster, Chief Clerk.

FP. H. CHITTENDEN, in charge of truck crop and stored product insect investigations.
A. D. HopxKINs, in charge of forest insect investigations.

W. D. Hunter, in charge of southern field crop insect investigations.

FE’. M. WEBSTER, in charge of cereal and forage insect investigations.

A. L. QUAINTANCE, in charge of deciduous fruit insect investigations.

E. F’. PHivuirs, in charge of bee culture.

D. M. Rocers, in charge of preventing spread of moths, field work.

Roiyia P. Currig, in charge of editorial work.

MABEL CoLcorD, librarian.

Forest INSECT INVESTIGATIONS.
A. D. HopxKrINns, in charge.

H. EH. Burke, J. L. WEBB, JOSEF BRUNNER, S. A. ROHWER, T. H. SNYDER, W. D.
EDMONSTON, agents and experts.

Mary E. FAUNCE, preparator.

WILLIAM MIDDLETON, Mary C. JOHNSON, student assistants.

II

CiRCULAR No. 129. Issued November 25, 1910.

United States Department of Agriculture,

BUREAU OF ENTOMOLOGY.

L. O. HOWARD, Entomologist and Chief of Bureau.

INSECTS IN THEIR RELATION TO THE REDUCTION OF
FUTURE SUPPLIES OF TIMBER, AND GENERAL PRIN-
CIPLES OF CONTROL.

By A. D. HoPKINs,
In Charge of Forest Insect Investigations.

Insects not only reduce future supplies of timber by killing the ma-
ture trees and destroying the wood of timber that is inaccessible for
utilization, but through injuries inflicted upon trees during the flow-
ering, fruiting, germinating, seedling, and sapling periods. of early
growth they prevent normal reproduction and development.

INTERRELATIONS OF FOREST INSECTS AND FOREST FIRES.

Investigations conducted by the writer and assistants in all sections
of the country during the past ten years indicate to them quite con-
clusively that the average percentage of loss of merchantable timber
in the forests of the entire country to be charged to insects during a
five or ten year period is infinitely greater than most people realize.

Losses from forest insects —The writer estimates that for a ten-
year period the average amount of timber in the forests of the entire
country killed and reduced in value by insects would represent an
average loss of $62,500,000 annually.?

It has been estimated that the Black Hills beetle killed approxi-
mately 1,000,000,000 feet B. M. of timber during a period of ten years,
which at $2.50 per thousand would amount to an average of $250,000
annually. This is merely one example of very destructive depreda-
tions by a single species of barkbeetle in a single National Forest.¢

“Revised extracts from Bulletin No. 58, Part V, Bureau of Entomology,
United States Department of Agriculture.

+ Losses from forest fires.—It has been estimated that ‘on the average, since
1870, forest fires have yearly cost $50,000,000 in timber.” (Cleveland, T., jr.,
Circular 167, Forest Service, United States Department of Agriculture, p. 3.)

¢It has been estimated that the losses of timber from forest fires on all of
the National Forests of the United States from 1905 to 1908, inclusive, average
only $165,062 annually. (Cleveland, T., jr.. Yearbook United States Department
of Agriculture for 1908, p. 541.)

bo

INSECTS AND REDUCED TIMBER SUPPLY.

Prof. Lawrence Bruner, state entomologist of Nebraska, at a meet-
ing of the American Association of Economie Entomologists, held at
Baltimore, Md., in December, 1908, spoke as follows: “I can agree
with Doctor Hopkins that the insects are far more important in
destroying our forests than fires.”

Insect-killed timber as fuel for fires—It has often happened that
after insects have killed the timber over extensive areas the standing
and fallen dead trees furnished fuel for great forest fires which have
not only destroyed or charred the dead timber but killed the living
timber and reproduction and swept on into adjacent areas of healthy
timber. Indeed, abundant evidence has been found during recent in-
vestigations to indicate that some of the vast denuded areas in the
Rocky Mountains and other sections of the country are primarily due
to widespread devastation by insects, and that subsequent fires de-
stroyed the timber and prevented reproduction.

It is also evident that a considerable percentage of dead timber, and
especially that found in coniferous forest regions, which has generally
been believed to have been fire-killed is a result of primary attack by
insects. This has been demonstrated in many cases by the pitch-
marked galleries of the destructive barkbeetles on the surface of the
wood of the old dead trees which had escaped subsequent fires.

Fire-killed timber injured by insects.—It is true that a vast amount
of timber has been killed outright or has died as the direct result of
forest fires, but in almost every case observed insects have contributed
to a greater or less extent to the death of recently fire-injured trees
which might otherwise have recovered, and especially to the rapid
deterioration of the wood of a large percentage of the injured and
killed trees. It is evident that in some cases fire-scorched and fire-
killed timber has contributed to the multiplication of one or more of
the insect enemies destructive to living timber, and thus the injury
started by the fire may have resulted in a destructive outbreak of
beetles. However, it is evident that this has happened only when the
destructive beetle was already present in abnormal numbers in the
forest surrounding the fire-swept area. Therefore, i is believed
that injuries by fire are not as a rule an important factor in contrib-
uting to subsequent depredations by barkbeetles. Such fires, how-
ever, contribute to the multiplication of the insects which depredate
on the bark and wood of dying and dead trees, so that in forested
areas where fires are frequent the damage to the wood of such trees
is more severe, and fewer injured trees recover on account of the
abundance of secondary barkbeetle enemies which do not, as a rule,
attack and kill hving timber.

Destruction of insects by fire—There is another important feature
in the relation of insects and fire, in which the fire contributes to the
destruction of the principal barkbeetle enemies of the living timber.

[Cir. 129]

INSECTS AND REDUCED TIMBER SUPPLY. 3

This happens when the fire burns the timber while it is infested, thus
effectually destroying the broods of the insects. It is perfectly plain
that the dying and dead foliage of the beetle-infested trees and the
dead bark on the trunks would contribute to the spreading of crown
fires and thus the bark on the entire infested trunks would be suffi-
ciently scorched to kill the insects. Therefore, complete fire control
may easily contribute to more extended depredations by insects on the
living timber, thus increasing, rather than diminishing, the need for
insect control. However, the setting of fires or permitting them to
burn for the purpose of combating insects should never be undertaken
or permitted.

Durability of insect-killed timber—Some of the matured larch
trees which evidently died as a result of defoliation by the larch
worm between 1881 and 1885, and which had escaped subsequent
depredations by fire and wood-boring insects, were found by the
writer in 1908 to be standing and sound enough to be utilized for
railroad ties and many other purposes. Under similar conditions the
heartwood of red spruce and white pine in the East, of Engelmann
spruce in the Rocky Mountains, and of Douglas fir in the Northwest
coast region have been found by the writer to be sound enough for
profitable utilization for pulp wood, lumber, fuel, and other pur-
poses from twenty to thirty years after it had been killed by insects
or fire. Thus it is shown that timber killed by insects and fire would
be available for utilization for many years were it not for injuries
through the secondary attacks of wood-boring insects and the de-
struction of insect-killed timber by forest fires.

INTERRELATION OF FOREST INSECTS AND FOREST FUNGI.

Decay following injury by insects.—It is well known that the bur-
rows in the bark and wood of living and dead trees and in the crude
and finished products often contribute to the entrance of bark and
wood decaying fungi. Deterioration and decay are thus far more
rapid than would otherwise be possible. It is also known that trees
injured and dying from primary attack by parasitic fungi are attrac-
tive to certain insects which breed in the bark and wood of sickly and
dying trees, and that certain other complicated troubles affecting for-
est trees are the result of an intimate interrelation and interdepend-
ence of insects and fungi. There can be no doubt, however, that cer-
tain species and groups of both insects and fungi are independently
capable of attacking and killing perfectly vigorous and healthy trees.

SUMMARY AND ESTIMATES RELATING TO CHARACTER AND EXTENT OF
; INSECT DAMAGE.

The killing of trees by insects; the damage by them to the wood
of living, dying, and dead timber; the destruction of insect-killed
timber by subsequent forest fires; the damage to fire-killed timber

[Cir. 129]

4 , INSECTS AND REDUCED TIMBER SUPPLY.

by insects; and the damage from decay resulting from insect injuries
to the wood, have all been more or less continuous for centuries and
are still going on in the forest and woodland areas of this country.

While these depredations are not always evident or important in
all forests or localities, yet almost every year, somewhere in the
forests of the country, there are widespread depredations.

In every forest and woodland there is an ever present but incon-
spicuous army of insects which require the bark, wood, foliage, and
seeds of the various tree species for their breeding places or food.
Thus, the accumulated but inconspicuous injuries wrought during
the period required for the growth of a tree to commercial size go
far toward reducing the average annual increment below the point
of profitable investments.

The accumulated damage to crude, finished, and utilized products
reduces the profits of the mgunebadtnne’s increases the price of the
higher grades to the consumer, and results in an increased drain on
the natural resources.

In any attempt to estimate in feet, board measure, or dollars, the
extent of losses or waste of timber supplies caused by insects there
are many conflicting factors which contribute to the difficulty of ar-
riving at accurate conclusions. The published information concern-
ing the amount in board feet of standing timber in the country is
admittedly only an estimate, as are also the published data relating
to average stumpage value. The published statistics relating to the
amount and value of forest products are of course more accurate, but
until more complete data can be furnished by the forest experts on
the various complicated phases of forest statistics any figures given
by the forest entomologist relating to the value of timber and com-
mercial products destroyed or reduced in value by insects must be
considered on the same basis as the other estimates, and as the best
that can be presented on available evidence.

Standing timber killed and damaged by insects—When we con-
sider the amount of standing merchantable timber killed by insects
and the amount of standing timber, living, dying, and dead, which
has been reduced in quantity and value through their agency during
a ten-year period, we would estimate that such timber represents an
equivalent of more than 10 per cent of the quantity and stumpage
value of the total stand of merchantable timber in the United States
at any given time.* A certain percentage of such timber is a total

*The estimate of the area and stand of the present forests of the United
States, as given in Circular 166 of the Forest Service, page 6, is two trillion
five hundred billion feet (2,500,000,000,000) board measure. The average
stumpage value has been given as $2.50 per one thousand feet b. m., making a
total value of the standing merchantable timber of $6,250,000,000. Ten per
eent of this amount would be $625,000,000, as the amount to be charged to in-

[Cir. 129]

INSECTS AND REDUCED TIMBER SUPPLY. 5

loss because of the impossibility of utilization; but in some cases a
greater or less percentage can be, and in some cases is, utilized within
the period in which it is of sufficient value to yield a profitable return
on the cost of logging and manufacture, although its value is greatly
reduced.

Reduction in the Nation’s wealth—When we consider the forest
resources both in merchantable timber and young growth as an im-
portant asset of the Nation’s wealth; as representing a given value
to the people for direct utilization; as a cover to the soil for protec-
tion of the land from erosion; as protection of headwater streams and
of game; and as contributing to the esthetic value of health and
pleasure resorts, it would be difficult indeed to estimate the amount
or percentage of loss of timber or the reduction in the land values, in
each case, chargeable to insects. It is plain, however, that in the
ageregate it is considerably greater than when estimated on stumpage
values alone.

Reduction in cash revenue-—When we consider the problem from
the standpoint of direct utilization we can estimate the annual loss
on a basis of mill values; but here again we meet with complications,
since much of the damaged material is left standing or is discarded
in the woods or at the mill without measurement. Therefore we are
left to judge from our observations and knowledge of the general
conditions as regards dead and damaged timber found in the forests
of the country, and the information from lumbermen in different sec-
tions, as to the percentage of loss from defective timber. On this
basis we can estimate that the amount of insect-killed and damaged
timber left in the woods, plus the reduction in value of that utilized,
to be charged to insects is not far from an equivalent of 10 per cent
of the value of the annual output of forest products of all kinds, in
the rough. The total value of the forest products of the United
States in 1907 is given as $1,280,000,000; the losses from insect depre-
dations would therefore represent an annual loss in a cash value of
more than $100,000,000.

Reduction in value of finished and commercial products—When
we consider the aggregate loss to the manufacturers of the finished
products, to the trade, and to the consumer from insect injuries to
the wood, it is evident that it amounts to many millions of dollars in
addition to the estimated loss of crude products, or at least 3 per
cent of the mill value.

sects for a ten-year period, or an average of $62,500,000 annually. As an ex-
ample, it has been estimated that over 1,000,000,000 feet b. m. of timber was
killed by the Black Hills beetle in the Blacks Hills National Forest within a
period of ten years. This, at $2.50 per one thousand feet stumpage, would be
an average of $250,000 annually in a single forest of 1,294,440 acres.

(Cir. 129]

6 INSECTS AND REDUCED TIMBER SUPPLY.
METHODS OF PREVENTION AND CONTROL.

The results of extensive investigations and of practical applications
of the knowledge gained during recent years have demonstrated that
some of the most destructive insect enemies of American forests and
ef the manufactured and utilized products can be controlled. and
serious damage prevented, with little or no ultimate cost over that
involved in forest management and business methods.

There are, of course, certain insects and certain injuries which,
under present conditions and available information, can not be con-
trolled or prevented, but it is very evident that if the :aformation
now available through the publications of the Department of Agri-
culture and through direct correspondence with its experts is properly
utilized in the future it will result in the prevention of at least 30
per cent of the estimated annual waste of forest resources that has
been caused by insects within recent years, and thus contribute greatly
to the conservation of forest resources.

GENERAL PRINCIPLES OF CONTROL.

The ordinary spraying and similar methods employed in dealing
with fruit and shade tree insects are, of course, not available for
practical application in the case of forest trees. But there are other
and less expensive methods of accomplishing the desired results.

In all efforts to control an outbreak or prevent excessive loss from
forest insects it should be remembered that as a rule it is useless to
attempt the complete extermination of a given insect enemy of a
forest tree or forest product. Experience has demonstrated that it
is only necessary to reduce and weaken its forces 75 per cent or more.
It can not then continue an aggressive attack, but must occupy a
defensive position against its own enemies until conditions resulting
from avoidable negligence and mismanagement by the owners of the
forests and manufacturers of forest products favor its again becom-
ing destructive. Forest insects can thus be easily kept under control
by good management.

The desired control or prevention of loss can often be brought about
by the adoption or adjustment of those requisite details in forest
management and in lumbering and manufacturing operations, stor-
ing, transportation, and utilization of the products which at the
least expenditure will cause the necessary reduction of the injurious
insects and establish unfavorable conditions for their future multipli-
cation or continuance of destructive work.

It is, however, of the utmost importance that any adjustment or
modification in management or business methods should be based on

[Cir. 129]

INSECTS AND REDUCED TIMBER SUPPLY. 7

expert technical knowledge or advice relating to the species, habits,
life history, and natural enemies of the insects involved and the
essential features of the methods for their control. This should be
supplemented by expert knowledge or advice on the principles of
technical and applied forestry in the proper management, care, and
utilization of the forest and its resources, and still further supple-
mented by practical knowledge and experience relating to local con-
ditions and facilities favorable and unfavorable for success in prac-
tical applications according to the recommended method or policy of
control.

As has been shown, the mature or merchantable timber is the most
susceptible to injury or death from the ravages of insects. There-
fore, considered from the standpoint of insect control and the pre-
vention of one of the greatest items of loss, it is important that such
matured timber should be utilized before it begins to deteriorate, or
before it reaches the stage of unprofitable growth.

For the greatest success in dealing with forest insects, it must be
recognized that there are certain features in the habits and seasonal
history of each species which differ to a greater or less extent from
those of all other species, even of the same genus; that there are cer-
tain features in the characteristics of the various species of trees
which differ from those of all other species; and that as a rule it is the
technical knowledge of these peculiar features or characteristics of
the trees and their enemies which furnishes the clew to successful
methods of control. ,

There are also many peculiar features in the prevailing conditions
in different localities, some of them favorable, others unfavorable, for
the practical application according to a given method, so that while
certain general advice may apply in a broad sense and be available
for utilization by the practical man, whether owner, manager, or
forester, without further advice, it is often necessary to diagnose a
given case before specific expert advice can be given as to the exact
cause and the most effective method or policy to be adopted, just as a
physician must diagnose a case of illness or injury before prescribing
the required treatment for his patient.

Therefore, in a consideration of the problem as to how far the
waste of forest resources caused by insects can be prevented and how
far the damaged timber can be utilized, we will attempt to give only
general statements based on the results of our observations relating to
some of the principal kinds of loss discussed in Circulars 125 to 128,
inclusive, of this Bureau. In addition, we will consider in this cir-
cular the utilization of natural enemies of injurious insects and the
utilization of waste caused by insects.

[Cir. 129]

8 INSECTS AND REDUCED TIMBER SUPPLY.

UTILIZATION OF NATURAL ENEMIES AND FACTORS IN THE CONTROL OF INJURIOUS
INSECTS.

Were it not for the natural checks and natural factors of control
of some of the more destructive insect enemies of forest trees and
forest products, artificial control would in many cases be impossible,
and the depredations would evidently be far more continuous and
complete. These natural factors in the control of the depredating
insects consist of parasitic and predatory insects, diseases of insects,
birds, adverse climatic conditions, etc. While one or more of these
beneficial factors exert a continuous and powerful influence toward
the prevention of a much greater waste of forest resources, it has
been repeatedly demonstrated that they can not be depended on to
prevent widespread devastations or to otherwise work for the best
interests of the private or public owner by protecting the best trees
and the best tree species. The insects and birds which prey upon the
depredating insects also have factors to contend against, consisting
of insects, birds, diseases, and climatic conditions. Therefore under
normal conditions the tendency is toward the preservation of a bal-
ance between the warring factors, but frequently the enemies of the
trees get the ascendancy and take on the character of an invasion,
which may continue for two or three or even ten years before the bal-
ance is again adjusted through the influence of the natural enemies
or diminished food supply. Thus a vast amount of timber or of a
given forest product may be destroyed before the factors of natural
control can prevail.

It is evident that the most effective utilization of the agencies of
natural control will be through the alliance with them of the owner of
the forest by his efforts toward an artificial reduction of the enemies
of the trees rather than by efforts to make the natural enemies of the
injurious insects his allies through artificial introduction or dissemina-
tion. The former is accomplished by the adoption of methods of com-
bating the invaders which will reduce and weaken their forces below
their power of prosecuting aggressive movements and attacks, or, as
previously stated, to reduce their numbers to the point where they
must occupy a defensive position against their natural enemies and be
dependent for their supplies of food and breeding places upon that
furnished through avoidable mismanagement of the forests and manu-
facturing operations. Thus the owner of the forest can contribute
greatly toward the preservation of a balance which will be to his
material benefit. On the other hand, he may in the future, as in the
past, contribute greatly to the multiplication of the depredating
insects and to greatly increased losses caused by them through neglect
or a disregard of available information on the fundamental prin-
ciples of insect control in the management of forests and manufac-
turing enterprises.

[Cir. 129]

INSECTS AND REDUCED TIMBER SUPPLY. 9
BENEFICIAL INSECTS.

The beneficial insects comprise those which are internal or external
parasites of the immature or mature stages of the injurious insects,
and predators which feed on the young or adults of insects either
before or after they make their attack on the trees or products. These
two beneficial factors are doubtless far more effective in the long run
than any other agencies of natural control. Yet they, in combination
with all other factors, can not be relied upon to render continued and
efficient control. They can, however, be relied upon to respond to
artificial assistance in reducing the numbers of the depredators.

BENEFICIAL DISEASES OF INSECTS.

It is very evident that the parasitic fungi and bacteria which some-
times cause epidemics among injurious insects often exert a powerful
influence toward the control of extensive outbreaks or invasions of
insect enemies of forests. Indeed, it appears that the greatest serv-
ice rendered by this class of natural enemies is in the frequent sudden
appearance of an epidemic which kills off a destructive species of
insects after the latter has increased to such numbers and extended
its depredations over such vast areas as to be far beyond the control
of man or his insect and bird allies. Numerous examples of this kind
of natural control are found in the sudden ending of widespread
depredations by various species of caterpillars and sawfly larve which
defoliate deciduous and coniferous trees. As a rule, however, the
beneficial effects of the diseases of insects prevail only after the
injurious insects have increased to excessive numbers. Therefore this
factor of insect control can not be depended upon to hold the insects
in check or prevent outbreaks. The fact, however, that it operates on
a class of insect enemies of the forest (defoliators) which at present
can not be controlled by any known artificial methods renders the
services of the diseases all the more valuable.

It is believed that with further knowledge of nature’s method of
propagating, perpetuating, and disseminating the diseases which
cause epidemics among insects they may be utilized more or less suc-
cessfully through artificial propagation and dissemination to prevent
threatened invasions of defoliating insects.

BENEFICIAL BIRDS.

It is very evident that certain kinds of birds, such as woodpeckers,
render valuable service toward the natural control of destructive
bark and wood boring insects. They appear to render the greatest
service, however, where but few trees are being killed or injured,
because their concentrated work on such trees may contribute toward
the prevention of an abnormal increase of the insects. They also

[Cir. 129]

10 INSECTS AND REDUCED TIMBER SUPPLY.

render some service as allies of the other beneficial factors which assist
in artificial control. It is evident, however, that where many hun-
dreds or thousands of trees are being killed the comparatively limited
number of birds in any forest under the most favorable conditions
could have little or no beneficial effect. Therefore, while the birds
should be classed among the valuable friends of the forest, and should
be protected, it is plain that they can not, even with the utmost pro-
tection, be relied upon to protect the forest against destructive ravages
of insects.

We must remember, in this connection, that there are complicated
interrelations between birds, injurious insects, and beneficial insects
which do not necessarily operate to the benefit of the forest. In
fact, it may sometimes be quite the reverse. Therefore, in order to
derive the greatest benefit from the conflict between the birds, the
insect enemies of the trees, and the insect friends of the trees, we
must utilize our knowledge of the factors which are contributing
toward the preservation of a balance, so that whenever the enemies
of the forest threaten to get beyond natural control we may enter the
field through artificial means and endeavor to force them back to
their normal defensive position.

BENEFICIAL CLIMATIC CONDITIONS.

The benefits to be derived from climatic conditions which are detri-
mental or destructive to insect enemies of the forest, while some-
times very great; are necessarily unreliable, and thus can not be
depended upon to assist in artificial control. In fact, the very condi-
tion which may contribute to the destruction of one depredator may
favor the multiplication of another.

UTILIZATION OF WASTE CAUSED BY INSECTS.

When we come to consider the vast amount of standing timber in
the forests of the country which has been injured or killed by insects,
and will go to waste if it is not utilized within a limited period, we
realize that there are great possibilities in its utilization as a means
of preventing the reduction of future supphes of living healthy tim-
ber. It is all the more important that the insect-infested timber
should be utilized, because in so doing we can contribute more per-
haps than in any other way to the reduction of the insects to or below
their normal numbers, and thus provide against serious injury in the
future, as well as to the maintenance of control.

Approved :

James WILson,
Secretary of Agriculture.

Wasuineton, D. C., October 7, 1910.

[Cir. 129]
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