THE BORERS OF OUR SHADE TREES.
In no way can the good taste and public spirit of our citizens be better
shown than in the planting of shade trees. Regarded simply from a
commercial point of view one cannot make a more paying investment than
setting out an oak, elm, maple or other shade tree about his premises.
To a second generation it becomes a precious heirloom, and the planter
is duly held in remembrance for those finer qualities of heart and head,
and the wise forethought which prompted a deed simple and natural, but a
deed too often undone. What an increased value does a fine avenue of
shade trees give to real estate in a city? And in the country the single
stately elm rising gracefully and benignantly over the wayside cottage,
year after year like a guardian angel sending down its blessings of
shade, moisture and coolness in times of drought, and shelter from the
pitiless storm, recalls the tenderest associations of generation after
generation that go from the old homestead.
Occasionally the tree, or a number of them, sicken and die, or linger
out a miserable existence, and we naturally after failing to ascribe the
cause to bad soil, want of moisture or adverse atmospheric agencies,
conclude that the tree is infested with insects, especially if the bark
in certain places seems diseased. Often the disease is in streets
lighted by gas, attributed to the leakage of the gas. Such a case has
come up recently at Morristown, New Jersey. An elm was killed by the Elm
borer (Compsidea tridentata), and the owner was on the point of suing
the Gas Company for the loss of the tree from the supposed leakage of a
gas pipe. While the matter was in dispute, a gentleman of that city took
the pains to peel off a piece of the bark and found, as he wrote me,
"great numbers of the larvæ of this beetle in the bark and between the
bark and the wood, while the latter is 'tattooed' with sinuous grooves
in every direction and the tree is completely girdled by them in some
places. There are three different sizes of the larvæ, evidently one, two
and three years old, or more properly six, eighteen and thirty months
old." The tree had to be cut down.
Dr. Harris, in his "Treatise on Injurious Insects," gives an account of
the ravages of this insect, which we quote: "On the 19th of June, 1846,
Theophilus Parsons, Esq., sent me some fragments of bark and insects
which were taken by Mr. J. Richardson from the decaying elms on Boston
Common, and among the insects I recognized a pair of these beetles in a
living state. The trees were found to have suffered terribly from the
ravages of these insects. Several of them had already been cut down, as
past recovery; others were in a dying state, and nearly all of them were
more or less affected with disease or premature decay. Their bark was
perforated, to the height of thirty feet from the ground, with numerous
holes, through which insects had escaped; and large pieces had become so
loose, by the undermining of the grubs, as to yield to slight efforts,
and come off in flakes. The inner bark was filled with burrows of the
grubs, great numbers of which, in various stages of growth, together
with some in the pupa state, were found therein; and even the surface of
the wood, in many cases, was furrowed with their irregular tracks. Very
rarely did they seem to have penetrated far into the wood itself; but
their operations were mostly confined to the inner layers of the bark,
which thereby became loosened from the wood beneath. The grubs rarely
exceed three-quarters of an inch in length. They have no feet, and they
resemble the larvæ of other species of Saperda, except in being rather
more flattened. They appear to complete their transformations in the
third year of their existence.
"The beetles probably leave their holes in the bark during the month of
June and in the beginning of July, for, in the course of thirty years, I
have repeatedly taken them at various dates, from the fifth of June to
the tenth of July. It is evident, from the nature and extent of their
depredations, that these insects have alarmingly hastened the decay of
the elm trees on Boston Mall and Common, and that they now threaten
their entire destruction. Other causes, however, have probably
contributed to the same end. It will be remembered that these trees
have greatly suffered, in past times, from the ravages of canker-worms.
Moreover, the impenetrable state of the surface soil, the exhausted
condition of the subsoil, and the deprivation of all benefit from the
decomposition of accumulated leaves, which, in a state of nature, the
trees would have enjoyed, but which a regard for neatness has
industriously removed, have doubtless had no small influence in
diminishing the vigor of the trees, and thus made them fall
unresistingly a prey to insect devourers. The plan of this work
precludes a more full consideration of these and other topics connected
with the growth and decay of these trees; and I can only add, that it
may be prudent to cut down and burn all that are much infested by the
borers."
[Illustration: 101. Elm Tree Beetle.]
The Three-toothed Compsidea (Fig. 101), is a rather flat-bodied, dark
brown beetle, with a rusty red curved line behind the eyes, two stripes
on the thorax, and a three-toothed stripe on the outer edge of each wing
cover. It is about one-half an inch in length.
[Illustration: 102. Elm Tree Borer.]
The larva (Fig. 102) is white, subcylindrical, a little flattened, with
the lateral fold of the body rather prominent; the end of the body is
flattened, obtuse, and nearly as wide at the end as at the first
abdominal ring. The head is one-half as wide as the prothoracic ring,
being rather large. The prothoracic ring, or segment just behind the
head, is transversely oblong, being twice as broad as long; there is a
pale dorsal corneous transversely oblong shield, being about two-thirds
as long as wide, and nearly as long as the four succeeding segments;
this plate is smooth, except on the posterior half, which is rough, with
the front edge irregular and not extending far down the sides. Fine
hairs arise from the front edge and side of the plate, and similar hairs
are scattered over the body and especially around the end. On the upper
side of each segment is a transversely oblong ovate roughened area, with
the front edge slightly convex, and the hinder slightly arcuate. On the
under side of each segment are similar rough horny plates, but arcuate
in front, with the hinder edge straight.
It differs from the larva of the Linden tree borer (Saperda vestita) in
the body being shorter, broader, more hairy, with the tip of the abdomen
flatter and more hairy. The prothoracic segment is broader and flatter,
and the rough portion of the dorsal plates is larger and less
tranversely ovate. The structure of the head shows that its generic
distinctness from Saperda is well founded, as the head is smaller and
flatter, the clypeus being twice as large, and the labrum broad and
short, while in S. vestita it is longer than broad. The mandibles are
much longer and slenderer, and the antennæ are much smaller than in S.
vestita.
[Illustration: 103. Linden Tree Beetle.]
[Illustration: 104. Linden Tree Borer.]
The Linden tree borer (Fig. 103) is a greenish snuff-yellow beetle, with
six black spots near the middle of the back; and it is about
eight-tenths of an inch in length, though often smaller. The beetles,
according to Dr. Paul Swift, as quoted by Dr. Harris, were found (in
Philadelphia) upon the small branches and leaves on the 28th day of May,
and it is said that they come out as early as the first of the month,
and continue to make their way through the back of the trunk and large
branches during the whole of the warm season. They immediately fly into
the top of the tree, and there feed upon the epidermis of the tender
twigs, and the petioles of the leaves, often wholly denuding the latter,
and causing the leaves to fall. They deposit their eggs, two or three in
a place, upon the trunk or branches especially about the forks, making
slight incisions or punctures for their reception with their strong
jaws. As many as ninety eggs have been taken from a single beetle. The
grubs (Fig. 104, _e_; _a_, enlarged view of the head seen from above;
_b_, the under view of the same: _c_, side view, and _d_, two rings of
the body enlarged), hatched from these eggs, undermine the bark to the
extent of six or eight inches, in sinuous channels, or penetrate the
solid wood an equal distance. It is supposed that three years are
required to mature the insect. Various expedients have been tried to
arrest their course, but without effect. A stream, thrown into the tops
of trees from the hydrant, is often used with good success to dislodge
other insects; but the borer-beetles, when thus disturbed, take wing and
hover over the trees till all is quiet, and then alight and go to work
again. The trunks and branches of some of the trees have been washed
over with various preparations without benefit. Boring the trunk near
the ground and putting in sulphur and other drugs, and plugging, have
been tried with as little effect.
[Illustration: 105. Poplar Tree Borer.]
The city of Philadelphia has suffered grievously from this borer.
[Illustration: 106. Broad-necked Prionus.]
Dr. Swift remarks, in 1844, that "the trees in Washington and
Independence Squares were first observed to have been attacked about
seven years ago. Within two years it has been found necessary to cut
down forty-seven European lindens in the former square alone, where
there now remain only a few American lindens, and these a good deal
eaten." In New England this beetle should be looked for during the first
half of June.
[Illustration: 107. Larva of the Plain Saperda.]
The Poplar tree is infested by an other species of Saperda (S.
calcarata). This is a much larger beetle than those above mentioned,
being an inch or a little more in length. It is grey, irregularly
striped, with ochre, and the wing-covers end in a sharp point. The grub
(Fig. 105 _a_; _b_, top view of the head; _e_, under side) is about two
inches long and whitish yellow. It has, with that of the Broad-necked
Prionus (P. laticollis of Drury, Fig. 106, adult and pupa), as Harris
states, "almost entirely destroyed the Lombardy poplar in this vicinity"
(Boston). It bores in the trunks, and the beetle flies by night in
August and September. We also figure the larva of another borer (Fig.
107 _c_; _a_, top view of the head; _b_, under side; _e_, dorsal view of
an abdominal segment; _d_, end of the body, showing its peculiar form),
the Saperda inornata of Say, the beetle of which is black, with ash gray
hairs, and without spines on the wing-covers. It is much smaller than
any of the foregoing species, being nine-twentieths of an inch in
length. Its habits are not known. We also figure the Locust and Hickory
borer (Fig. 108; _a_, larva; _b_, pupa), which has swept off the locust
tree from New England. The beautiful yellow banded beetles are very
abundant on the flowers of the golden rod in September.
[Illustration: 108. Locust Borer.]
FOOTNOTES:
[Footnote 4: The External and Internal Parasites of Man and Domestic
Animals. By Prof. A. E. Verrill, 1870. We are indebted to the author for
the use of this and the figures of the Bot fly of the horse, the turkey,
duck and hog louse, the Cattle tick, the itch insect and mange insect of
the horse.]