STATE PLANT BOARD
CIRCULAR NO. 126. Issued November 16,1910.
United States Department of Agriculture,
BUREAU OF ENTOMOLOGY.
L. 0. HOWARD, Entomologist and Chief of Bureau.
INSECT INJURIES TO THE WOOD OF LIVING TREES.a
By A. D. HOPKINS,
In Charge of Forest Insect Inrcstigulionis.
It has been determined that insects of a certain class attack the
wood and bark of living timber and that, while they do not con-
tribute materially to the death of the trees or give much external
evidence of their presence, they produce wounds in the bark and
wormhole and pinhole defects in the wood which result in a depre-
ciation in commercial value amounting to from 5 to 50 per cent.
These defects in the wood are not detected until after the trees have
been felled and the logs transported to the mill and converted into
lumber. Thus to the actual damage to the lumber is added the
expense of logging and manufacture of the defective, low-grade
material, much of which must be discarded as worthless culls.
The oak timber worm.-One of the most destructive of the class of
depredators just mentioned is the oak timber worm. It enters the
wood of the trunks of living trees through wounds in the bark and
at the base of broken or dead branches and extends its "pinhole"
burrows in all directions through the solid heartwood. The losses
occasioned by this insect in the hardwood forests of the eastern United
States are enormous and usually affect the wood of the finest ex-
amples of old trees.
The chestnut timber worm.-The chestnut throughout its range is
damaged in a like manner by the chestnut timber worm. Practically
every tree of merchantable size is more or less affected, and a large
percentage is so seriously damaged that the product is reduced to that
of the lowest grade. It is estimated that the reduction in value of the
average lumber product at any given time is not far from 30 per cent,
a Revised extracts from Bulletin No. 5S, Part V, Bureau of Enitomology, U. S.
Department of Agriculture. 1909.
>() 63707-Cir. 120-10
- 1. a
thus involving extensive waste and an increased drain on the forest
to supply clear lumber. This insect also attacks the oaks, and espe-
cially the red oak, the older trees of which are often as seriously
damaged as are the chestnut.
Carpenter worm s.--The oaks, especially the white oak and the red
oak. are seriously damaged by carpenter worms of the genus Pr.ion-
oxystus. Thie holes made by these insects through the heartwood of
the best part of the trunks are sometimes 1.5 inches in diameter one
way by 0.75 inch the other, thus causing serious damage to the wood.
These, with other large wood-boring beetle larvae, sometimes infest
the top part of the trunk and the larger branches of oak trees, where
their continued work results first in the dead and so-called stag-
horn" top and subsequently in broken, decayed, and worthless trunks.
Ambrosia beetles.-One of the commonest defects in white oak, rock
oak, beech, whitewood or yellow poplar, elm, etc., is that known to the
lumber trade as "grease spots," "patch worm," and "black holes."
This defect is caused by one of the timber beetles or ambrosia beetles,
which makes successive attacks in the living healthy sapwood from
the time the trees are 20 or 30 years old until they reach the maximum
age. Thus the black-hole and stained-wood defect is scattered all
through the wood of the best part of the trunks of the trees. The
average reduction in value of otherwise best-grade lumber amounts,
in many localities, to from 25 to 75 per cent. The defect is commonly
found in oak and elm furniture and in interior hardwood finish in
dwellings and other buildings.
The locust borer.-The locust, as is well known, suffers to such an
extent from the ravages of the locust borer that in many localities the
trees are rendered worthless for commercial purposes or they are
reduced in value below the point of profitable growth as a forest tree;
otherwise this would be one of the most profitable trees in the natural
forest or artificial plantation and would contribute greatly to an in-
creased timber supply.
Turpentine beetles and turpentine borers.-While the softwood
trees, or conifers, suffer far less than the hardwoods from the class
of enemies which cause defects in the living timber, there are a few
notable exampl)les of serious damage. There is a common trouble
affecting the various species of pine throughout the country known
as bamsal wounds or basal fire wounds. It has been found that a large
perc('enItage of this injury to the pine in the States north and west of
the Gulf States and in the Middle and South Atlantic States is
caused ly tlhe red turpentine beetle and in the Southern States by
ltht black turpentine beetle. The.e beetles attack the healthy living
bark ;lat -Ind toward the base of the trunks of medium to large trees
aidl kill :irc:is varying in size from 1 to 10 square feet. These dead
areas are subsequently burned off by surface fires and are then gen-
erally referred to as fire wounds. The further damage to the ex-
posed wood by successive fires, decay, and insects often results in a
total loss of the best portion of the tree, or a reduction in value of the
lower section of the trunk of from 10 to 50 per cent. These and
similar wounds in the bark of trees, including those caused by light-
ning and by the uncovering and exposure of the wood in turpentin-
ing, offer favorable conditions for the attack of the turpentine borer,
the work of which, together with that of two or three others with
similar habits, is very extensive, and causes losses amounting to from
10 to 50 per cent of the value of the wood of the best part of the trees
The white pine weevil.-The abnormal development of white pine
trees as the result of successive attacks on the terminals of the sap-
lings and young trees by the white pine weevil is an element of loss
of considerable importance, especially in mixed stands and in open
pure stands of this timber. The value of such trees is reduced from
20 to 50 per cent below those of normal development, and there is an
additional loss from the effect of their spreading branches or crowns
in the suppression or crowding out of trees which would otherwise
occupy the space thus usurped.
There are many other examples of insects which damage the wood
and bark of living trees, but those mentioned should be sufficient to
demonstrate the importance of insects in this relation.
CONTROL OF INSECTS WHICH CAUSE DEFECTS IN LIVING TIMBER.a
The class of insects which cause defects in the wood of living timber
can be controlled to a greater or less extent, depending upon local con-
ditions, and a large percentage of the losses prevented through the
adoption of certain requisite details in forest management, among
which the following are especially important:
(1) The utilization of all of the defective and infested timber
that will pay expenses for manufacture into merchantable products,
such as lumber, cordwood, etc.
(2) The burning of infested timber and waste material not avail-
able for use, including (lead standing and fallen timber, to remove
the breeding places of insects like the oak timber worm and the
chestnut timber worm, which go from the dead to the living timber.
(3) The prevention of wounds of any kind in the bark of living
SFor methods of cmtrolling the locust bhrer and white pine weevil, see
Circulars 83 and 90, respectively, of the Bureau of Entomology, U. S. Depart-
ment of Agriculture.
(4) The prevention of future losses by the practice of improved
forestry methods to eliminate favorable conditions for injury and con-
tribute to a perpetual supply of vigorous, healthy timber to be utilized
before it passes the stage of profitable increment.
It should be remembered that the different species of insects which
cause defects in the wood of living timber require different details in
the methods of control, and that special cases, special local conditions,
and details in business methods and requirements determine which
one of the available methods should be adopted.
It should also be remembered that in the more important cases much
loss of time and money may be prevented and the best success attained
by first securing some authoritative advice on the insects involved
and the specific requirements for the control work.
Secretary of Agriculture. UNIVERSITY OF FLORIDA
W ASHINGTON, D. C., October 7, 1910. 1111l/ll1illlll 1111l i 11111111111111111111I
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