Insects which kill forest trees


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Insects which kill forest trees
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Hopkins, A. D ( Andrew Delmar ), 1857-1948
United States -- Dept. of Agriculture
United States -- Bureau of Entomology
Govt. print. off. ( Washington )
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aleph - 029686131
oclc - 80338980
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Issued November 25, 1910.

L. 0. HOWARD, Entomologist and Chief of Bureau.




In Charge of Forest Insect Investigations.

64136-Cir. 125-10




L. 0. HOWARD, Entomologist and Chief of Bureau.
C. L. MIARLATT, A-..istant Entomologist and Acting Chief in. Abs.ncc of Chief.
R. S. CLIFTON, Executire Assistant.
W. F. TASTET, Chief Clerk.

F. H. CHITTENDEN, in charge of truck crop and stored product insect investigations.
A. D. HOPKINS, in charge of forest insect investigations.
W. D. HUNTER, in charge of southern field crop insect investigations.
F. M. WEBSTER, in charge of cereal and forage insect investigations.
A. L. QUAINTANCE, in charge of deciduous fruit insect investigations.
E. F. PHILLIPS, in charge of bee culture.
D. M. ROGERS, in charge of preventing spread of moths, field work.
ROLLA P. CURRIE, in charge of editorial work.
MABEL COLCORD, librarian.


A. D. HOPKINS, in. charge.

EDMONSTON, agents and experti.
MARY E. FAUNCE, preparator.
WILLIAM MIDDLETON, MARY C. JOiiNSON, .student assistunIts.
[Cir. 125]

CIRCULAR No. 125. Issued November 25, 1910.
United States Department of Agriculture,

L. 0. HOWARD, Entomologist and Chief of Bureau.

In Charge of Forest In.qcct Inrrstigntiors.
It has been conclusively demonstrated that certain species of insects
are the direct or primary cause of the death of forest trees of all
ages, and that from time to time they multiply to such an alarming
extent that their depredations a-sume the character of a destructive
invasion, which results in the death of a large percentage of the best
timber over thousands of square miles.
There are many species of barkbeetles which prefer to attack
matured and healthy trees, and there are many examples of whole
forests of century-old trees that have perished from the girdling effect
of the mines of the beetles, which are extended in all directions
through the inner living bark on the main trunks of the trees.
Indeed, we find among these bark-boring beetles the most destructive
insect enemies of North American forests. Some notable examples
of the depredations of these barkbeetles are given below.
The southern pine bectle.-In 1890-1892 a destructive invasion of
the southern pine beetle extended from the western border of West
Virginia through Maryland and Virginia into the District of Colum-
bia, northward into southern Pennsylvania, and southward into North
Carolina. In this area, aggregating over 75,000 square miles, a very
large percentage of the mature and small trees of the various species
of pine and spruce was killed by this beetle. In many places in West
Virginia and Virginia nearly all the pine trees of all sizes on thou-
sands of acres were killed, while shade and ornamental trees within
the same area suffered the same as those in the forest. Since 1902
a Revised extracts from Bulletin No. 5S, Part V, Bureau of Entomology, U. S.
Department of Agriculture, 1909.
[Cir. 125] 1


this barkbeetle has been more or less active in the Southern States
from Virginia to Texas. and in some localities and during certain
years it has killed a large amount of timber. Records of extensive
destruction of timber in the Southern States are found dating back
to the early P)art of the nineteenth century. This species may be
considered one of the most dangerous insect enemies of southeastern
conifers and. therefore, a constant menace to the pine forests of the
Southern States.
The c(astern spruce beetle.-During the period between 1818. and
1900 there were several outbreaks of the eastern spruce beetle in the
spruce forests of New York. New England, and southeastern Canada.
This species caused the death of a very large percentage of the ma-
ture spruce over an area of thousands of square miles. In the aggre-
gate many billions of feet of the best timber were destroyed. The
larger areas of this dead timber furnished fuel for devastating for-
est fires, with the result tliat in most cases there was a total loss.
The Engeitmann spruce beetle.-The Engelmann spruce beetle,
with habits similar to the eastern spruce beetle, has from time to time
during the past fifty years caused widespread devastations in the
Rocky Mountain region to forests of Engelminann spruce, in some sec-
tions killing from 75 to 90 per cent of the timber of merchantable size.
The Blark Hills beetle.-One of the most striking examples of the
destructive powers of an insect enemy of forest trees is found in the
Black Hills National Forest of South Dakota, where during the past
ten years a large percentage of the merchantable timber of the entire
forest has been killed by the Black Hills beetle. It is estimated that
more than a billion feet of timber have been destroyed in this forest
as the direct result of the work of thllis beetle. This destructive
enemy of the western pine is distributed throughout the forests of
tlhe middle and(1 southern Rocky Mountains region, where, within
recent years, it has been found that in areas of greater or less extent
from 10 to 80 per cent, of the trees have been killed 1by it.
ThIc' n oUfi/t;n pine bc',tle and the u cster, pine beetlc.-The sugar
pine, silver pine, western yellow pine, and lodgepole pine of the
region north of Colorado and Utah, westward to the Cascades, and
soilithward through tlhe Sierra Nevadas are attacked by the mountain
pine )ietle and the western 1pine beetle, and, as a direct consequence,
billions of feet of the tinilber have died. In one locality in northeast-
eI' Oreg(n,) it is estiliate(1 that. 90 to 9.5 per cent of the timber in a
dense s(- aid of l()(lge)ole pine covering an area of 100.000 acres has
been killed within the past iltree yIears 1by tlhe mountain pine b)eetle.
Through iii:iiny sections of tlie sugar-p)ile districts of Oregon and
('a li foriii; a. s t11 result of attacks by this same dlestructive barkbeetle
a (co(si)liderni l pen''tage of tile largest and best trees is dead.
I r. l2 -'.-I


The Douglas flt beetle.-The Douglas fir throughout the region
of the Rocky Mountains from southern New Mexico to British Co-
lumbia has suffered severely from the ravages of the Douglas fir
beetle, with the result that a large percentage of dead timber is found,
much of which will be a total loss.
Three other species of beetles, having destructive habits similar
to those above mentioned, depredate on the pines of New Mexico and
Arizona, and still another has contributed greatly to the destruction
of the larch throughout the northeastern United States and south-
eastern Canada.
The hickory barkeetle.-Within the past ten years the hickory
barkbeetle has caused the destruction of an enormous amount of
hickory timber throughout the northern tier of States from Wiscon-
sin to Vermont and southward through the eastern Atlantic States
and into the Southern States as far as central Georgia.
The larch worm.-There are alho many examples of widespread
depredations chargeable to insects which defoliate the trees, thus
contributing to their death. Notable among these are the depreda-
tions by the larch worm, which, during -everal extensive outbreaks
since 1880, has killed from 50 to 100 per cent of the mature larch
over vast areas in the northeastern United States and southeastern
Canada. It is evident that the amount of minerchantable-sized timber
that has died as the result of defoliation by this il-nsect will aggregate
many billions of feet.
The barkbeetles which kill trs, attack the bark on the trunk and
destroy the life of the tree by extending their burrows or galleries in
all directions through the inner living bark. The broods of young
grubs or larva, develop within the inner bark, on which they feed.
Those of .sonie species develop to the adult stage within the inner bark
and are exl)osed when the bark is removed, while those of other
species transform to the adults in the outer corky bark and the larva'
are not exposed when the bark is removed. Some species have two
or more generations in a season or annually, while others have 1)ut
one, and in a few species it require, two years for a single generation
to develop.
The barkbeetles of the genws. Dendroctonus represent the most
destructive enemies of the principal coniferous tree species of Ameri-
can forests. and at the same time are among the easiest of control.
The general requisites for succe-s are embodied in the following rules:
(a) Give prompt attention to the first evidence of a destructive
outbreak, as indicated by an abnormal percentage of yellow or red
topped dying trees, and especially when such trees occur in groups of
ten or more or cover large areas; (b) secure authentic determination
[Cir. 125]


(if the particular species of insect responsible for the trouble; and
(c) take prompt action toward its control according to specific expert
advice. published or otherwise, onil the best method for the destruction
of the necessary 7.) per cent or more of the insects in the infested trees.
Some of the methods to be adopted to meet the requirements of
various local conditions are as follows:
(1) Utilize the infested timber and burn the slabs during the
period in which the broods of the destructive beetles are in the imma-
ture stages or before the developed broods emerge from the bark; or
(2) Fell the infested trees and remove the bark from the main
trunk and burn the bark if necessary; a or
(3) Remove the infested bark from the standing timber and burn
the bark when necessa rv: a or
(4) Immerse the unl)arked logs in ponds, lakes, or streams, where
the bark will remain soaked long enough to kill the insects; or
(5) Remove the unbarked logs or products to a locality where
there are no trees liable to attack within a radius of 20 miles or more.


Future trouble of a serious nature from barkbeetles which kill
trees can be prevented within a given forest or area of greater or less
extent if an insect-control policy is adopted in connection with, or
independent of, a fire-control policy by which groups of dying trees
will receive similar prompt attention as that required for the pre-
vention or control of forest fires.
In state awi, national forests.-In all forest reserves in which there
is an organized force of rangers and fire wardens or patrols each
(Officer should be furnished with instructions for the location of
beetle-infested trees, and with equipment and directions for taking
thlle necessary action whenever the conditions demand or warrant it.
In pi';cahtc forests should receive the same atten-
tion as publicc forests, but this is often far more difficult on account
of intervening forests w'lere tlhe owners either can not or will not
give the matter the required attention. While it may be advisable
to have .-omne laws to govern the treatment of timber infested with a
(lall gerolsl. pest \when the owner refuses to take any action, such a
law should apply only to the more extreme cases or as a last resort
(0l autlhoritative advice. It is probable that in most cases legislation
will not bie lecess:irv, and more ultimate good will result without
tIhan witl stlrit laws. especially when it can be made clear to the
a If li In rodls divviop to mid lts in t1he outer bark, it must be Iurned : if they
level(.l4p in the hark antid iare exposed whlien the bI)rk is removed, burning
i.s 1 1t ( e'ssIry. As a rule the burning of the tops to destroy the insects Is
lill li( cssd i ry.
I t'ir-. 1'_-*5]


owner that his personal interests demand that he take the proper
action and that, when necessary, his neighbors will render assistance,
as is done in the case of a forest fire.
Inaccessible areas.-There are yet large inaccessible areas in the
East and West where it is not practicable or possible at present to
control the depredations by these beetles and which must therefore
be left to the sime natural adjustment that has been going on in
all forests from their beginning. While under such natural control
much of the older matured timber will be lost it will usually be re-
placed by young growth, either of the same species of trees or of a
different species, so that under normal conditions the forest will be
perpetuated; but under exceptional conditions and combinations of
detrimental influences, such as secondary insect enemies, fire, and
drought, extensive areas may be completely denuded, never to be
reforested under natural conditions. Therefore it will evidently not
be very long before it will pay to adopt insect-control policies even in
the areas that are inaccessible for profitable limbering.
The practicability of the advice based on the results of recent ento-
mological investigations is demonstrated by a number of examples of
successful control of depredations by destructive barkbeetles.
The control of an alarming outbreak of the eastern spruce beetle
in northeastern Maine in 1900 and 1901 was effected by the concentra-
tion of regular logging operations into the areas of infested timber
and placing the logs in lakes and streams and driving them to the
mills on the Androscoggin River. Thus, with little or no additional
expense, there was a saving to one firm, according to its estimates,
of more than $100,000.

The complete control of the hickory barkbeetle, which threatened
the total destruction of the hickory trees on Belle Isle Park, at Detroit,
Mich., in 1903.0 was effected by felling and removing the infected trees
and converting them into merchantable products, all without cost to
the park commission.

An extensive outbreak of the Black Hills beetle in the vicinity of
Colorado Springs. Colo., in 1905-,;. which was threatening the living
pine timber of the entire section, was brought under control through
the efforts of the private owners, of forests and those of forest offi-
cials in the adjoining National Forests. It was accomplished by
[Cir. 125]1


cutting anld barking about 1.000 beetle-infested and beetle-killed pine
trees. The cost of the operations was largely, if not entirely, cov-
ered by the utilized felled timber, although there was considerable
unnecessary expense involved through the felling and barking of
trees from which the beetles had emerged and from the unnecessary
burning of the bark and tops.
The suc.e-sful control of another serious outbreak' of this beetle, in
1900. on an extensive private estate in southern Colorado. was effected
through the efforts of the owners, who had some 500 infested trees
felled and barked within the necessary period to destroy the broods.
A large percentage, but not all. of the infested timber was thus
treated. These operations were so successful that not a single in-
fested and dying tree could be found when the area was inspected in
11() In this. as in the other case. considerable unnecessary expense
w;is involved in the burning of the bark and tops. but the value of
utilizable timber was probably more than enough to pay all expenses.
It is evidlenit that in this case a destructive invasion was prevented.
The practicability of controlling this most destructive enemy of the
pine timber of the central Rocky Mountain region, not only without
ultimate cost but at a profit on the operations, was demonstrated on
a large private estate and the adjoining Pike National Forest in
north-central Colorado. An examination of the timber on this estate
in the spring of 1907, by a ranger detailed from the Forest Service to
work under instructions from the Bureau of Entomology, showed
that tlhe depredations by the beetle had been going on for the .past ten
vears or more and had resulted in the death of the choicest timber to
the extent of more than 800.000 board feet. About 65.000 board feet
of timber was found to be infested by the beetle at the time of the ex-
animation. The owner was notified by the Bureau of Entomology
of the dangerous character of the infestation and the required action
fir it- (.cntr)l "as, recommended. Ihut ino action was taken. Another
(xaI111iination of thlie property was made in tlhe fall of 1907. when it
wa fotnmd that tlie lie\\ infestation resulting from swarms of beetles
tla;it had bIeen allIvwed to emerge from the old infested trees involved
early folri tinlies as much tiniber, or 240.000 board feet. This alarm-
il g illcrease led to tlie prompt adoption of the recommendations
lv the owner anmid the Forest Service, and by May of tihe following
sj-pri ,r (1 ,'s) tlhe -nl;Iil mer, of trees 4o11 thle National Forest was
cut ;idl harked. to kill thle insects in the inner bark. and the 1.000
I rev, (il tilie private e(.ate were felled, the logs converted into lumber,
;,nd( tlie lalbs builrlied. whichll accon iplished the desired purpose of de-
4- royinig the 1roodl.s (of (lie l eetle. lie owner realized a sufficient
rI.Veeli, fromI tlhe tiiumbier thius involved to cover all expenses and leave
:1et p.roIfit ,of ove1r $l.200. ExanTuiation of tie area in the fall of
l'I.( -liuWe'. that li i p)romlpt ald 1)roperly conducted effort to con-
V -ir. 12",]


trol the beetle was a complete success. Thus the average death rate
of some 100,000 feet of timber annually during the past ten or more
years was reduced to a minimum, at a net profit on the cost of doing it.
In addition to infested trees disposed of by the Forest Service in
timber sales, 165 infested trees in one section of the Las Animas
National Forest were cut and barked in May and June, 1908, at a
direct cost of $177.50, and at the same time a considerable amount of
infested timber was disposed of by sale in the Wet Mountains section
of the San Isabel National Forest. This had a decided effect in
checking the ravages of the beetle in both of these forests and it was
followed up in the latter forest the next spring (1909) by the proper
disposal of over 1,000 infested trees by free use. ranger labor, and
direct expenditure of fund& appropriated by the Forest Service.
According to the forest supervisor's report, 80.7 per cent of the
infested trees were treated, ranging from 70 per cent to 92.5 per cent
on the five units of infestation; 795 trees were treated (535 barked,
and 260 felled and bark scorched) at the expense of the Forest Serv-
ice, including salary and expenses of rangers. The cost per tree was
about 60 cents for felling and barking, and raiiged from 52 to 78
cents for felling and scorching the bark on the infested trunks. The
average cost. per tree was 68.2 cents. Six hundred and twenty-six
trees were treated by temporary labor, at an average cost of 61 cents
per tree under contract at $1.50 to -2 per hundred feet in length of
trunk peeled. The same rate wasi allowed for scorching the infested
bark instead of removing it. Two hundred and seventy-five trees
were treated under administrative u-e without cost to the Forest
In Sepl)tember, 1909, a very thorough examination was made of
the timber in and adjacent to the areas involved in the control opera-
tions. and it was found that the thorough, prompt, and proper manner
in which the instructions of the Bureau of Entomology were carried
out in this case resulted in bringing the beetle under complete control.
Only 7 trees had been -ticce-fully attacked by the beetles which had
emerged from some 400 infested trees which were not cut during the
previous control operations. Over 100 trees were found that had
been attacked by the beetles, bt, owing to the limited number of
the latter, the trees were able to resist them and recover.
It is now evident that the control operations carried on in southern
Colorado during the past three years, on the Trinchera estate near
Fort Garland in 1906, in the Las Animas National Forest and Wet
Mountains section of the San Isabel National Forest in 1908, and
the more extensive work in the latter area in 1909, had a far-reaching
effect in bringing the Black Hills beetle under control within the
forested areas of southern Colorado, and that the loss of timber
[Cir. 125]


from this .-ource. amounting to an average of some 300.000 board feet
annually, has been reduced to a minimum.
These results mark the most important events in the control of
forest insects in this country and serve as striking demonstrations of
what can be accomplished when cooperative efforts are directed along
the proper lines and based on the results of scientific investigation.
The attainment of these results was due to three important factors:
First. a knowledge of the insects on which the recommendations by
the Bureau of Entomology were based; second, a knowledge of local
conditions and requirements and of the habits of the insects in rela-
tion to newly infested trees, which enabled a forest ranger to locate
the infested trees and give instructions to the forest officials in regard
to such locations and the essential details in the recommendations;
third, a prompt and proper practical application by the Forest Serv-
ice of the recommendations according to improved forestry methods
to meet the requirements of a forestry problem.
Ten years ago it would have been absolutely impossible to have
accomplished this result, owing to the utter lack of knowledge of the
first two of these features, and at the present time it would have
been impossible without the assistance of the Forest Service.
A very threatening outbreak of the mountain pine beetle was lo-
cated, in 1909. in the Snowy Mountains section of Montana, adjacent
to and within the Jefferson National Forest, involving, at the time,
more than 1.500 infested and dying trees. The infestation included
timber on the National Forest. public domain, state lands, and private
lands, thus involving a complication of federal, state, and private
interests with which to deal in securing the required action. The
case was so successfully managed that an agent of the Bureau, Mr.
Josef Brunner, was placed in complete charge to carry out the recom-
mendations and instructions of this Bureau. and. through the aid of
the Forest Service, state officials, and private owners, 1.355) infested
trees were cut and barked to kill the broods of beetles. The cutting
was started about June 15. 1909. and( was completed about July 24
of the same year. Four hundred and twenty-two trees were cut at
private expl)ense. 783 at the expense of the Forest Service, and the re-
mainder b)v local owners. Tlhe average cost for felling and removing
thei bark from) thIe infested portion of tihe trunk was 30 cents per tree.
Early ii Dect'iiiber', 1909, a careful examination was made of the
area for evidence of new infestation. It was found that, while some
56 trees hlad lbt'n attacked by the mountain pine beetle, the broods
wenr 1icig le-t roed Iy woodp)eckers and other natural enemies, and
that. tlhert.fore, the efforts to control the beetle depredations were a
('* il ['lt -. i2t'J (ss.
[f ir. 1 ".,


The examples of practical control given above have demonstrated at
least two important facts: One, that extensive outbreaks by two of the
most destructive bark-beetle enemies of the pine timber of the Rocky
Mountain forests can be controlled at moderate expense when the tim-
ber is not accessible for utilization, or at a profit whenever the condi-
tions are favorable for the utilization of the infested timber; the other,
that the essential details of the recommendations and expert advice,
based on the results of scientific research, can be successfully applied by
a manager of a private forest or by the rangers of national and state
forests. Furthermore, these results indicate quite conclusively that
the widespread depredations in the Black Hills National Forest could
have been prevented with very little expense to the Government if the
matter had received prompt attention in 1901, when the first investi-
gations were made and essentially the same recommendations sub-
mitted as in the cases mentioned. Failure to do so w-as through the
lack of public appreciation of the importance of the problem at the
time and the lack of sufficient authority and funds later. Therefore
the outbreak was allowed to extend beyond practical control, and in
consequence a large percentage of the timber of the entire National
Forest has been killed. There were then no forcible examples of the
practical value of recommendations based on scientific research, and
no other argument, was effective in arousing public interest in the
threatening character of the outbreak or confidence in the advice and
methods of control. Now that the practicability of controlling the
most destructive insect enemies of North American forests has been
demonstrated, this should lead to a more general interest in the subject
and confidence in the results of scientific research as a basis for success
in practical application.
Secretary of Agyieblture.
WASHINGTON, D. C., October 7,1910.


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