SB

818 lo. 61.
578
ENT ited States Department of Agriculture,

BUREAU OF ENTOMOLOGY,

L. O. HOWARD, Entomologist.

BLACK CHECK IN WESTERN HEMLOCK.
By H. E. BurKE, Special Iield Agent.

ECONOMIC IMPORTANCE.

Black check is the lumberman’s name for a common defect, consist-
ing of a dark brown or blackish resinous scar, in the wood of the western
hemlock. A few layers of the wood beneath this scar are slightly
stained for a short distance around, and all
of those above are thickened, curled, or in
some way abnormal. When seen in a
quarter-sawn board (radial section) the
defect appears as a small, thin seam (fig. 1)
from one-half to one inch long, with one
side curly. In a bastard-sawn board (tan-

aoe, = F
SS

gential section) it is an oval or circular
spot (fig. 5, g) that varies in diameter from
one-half to one inch. In both cases it lies
with the grain of the wood.

Hemlock timber growing on lowlands
is often seriously affected, while that on-
higher land, especially above an altitude
of 1,800 feet, appears to be free from the
injury. In a large quantity of box stock
cut from lowland timber, nearly every
board examined by the writer contained
numerous examples of the defect.

Timber badly affected with this defect
is nearly worthless for finishing, turning,

=)? Fig. 1.—Longitudinal section of

staves, and woodenware, for which it would a board approximately quar-
otherwise be excellent. The injury is very pM reee
conspicuous in bastard-sawn lumber, un-
fitting it for finishing or turning, while in that quarter-sawn (fig. 1) or
cut across the grain it is apt to form an open seam which renders it
worthless for staves and woodenware, where tightness is required, but
it would appear that it is not materially detrimental to timber for con-
struction and other purposes.

Taking into consideration the common occurrence and injurious effect
of the blemish in lumber for certain purposes, and the large amount of
timber concerned, the total loss caused by the check must be considerable.

2

This form of injury is due to the attack of the bark maggot (Cheilosia
alaskensis) subsequent to primary injury by the hemlock barkbeetle
(Hylesinus n. sp.).

HISTORICAL.

In 1902 Mr. Edward T. Allen, of the Bureau of Forestry,! described
the defect which he had found to be caused by a maggot or larva of an
unknown fly.

In 1903-4 the writer made special investigations of the trouble, under
instructions from Dr. A. D. Hopkins, to determine: (1) The species
which is responsible for the damage; (2) the life
histories and habits of the principal species and
closely related forms, their natural enemies, etc.;
(3) whether or not the larve are capable of entering
healthy, uninjured bark; and (4) the character
and causes of previous injuries which induce attack.

The principal localities in which the work was
carried on in connection with that on forest insects
in general, were Hoquiam, Aberdeen, Satsop,
Copales, Kent, Puyallup, North Bend, South Bend,
and Seattle, in the State of Washington, and the
vicinity of Portland, Oreg.

The first examination of infested trees was made
in August, 1908, when maggots of various sizes
were found to be quite common in the bark of the
trunks of living trees. Their presence was indi-
cated by small masses of resin on the surface of
the bark. In and beneath each of these a single
Fig: 2-—Box cage fastenea Maggot was at work in a cavity or hole which

to side of tree to catch extended to the surface of the wood, where there
ee}: was a wound, evidently caused by this insect.
Similar wounds, partially healed, and others several years old were

found in the same trees, from near the outer layers of the sapwood to
layers deeply buried in the heartwood. The latter were readily
recognized as the black-check defect and there was no doubt left as to
their being caused by this insect, which should, therefore, be hereafter
known as the hemlock bark maggot.

Experiments with different methods of rearing the adult insect were
at once started. At first the infested resin masses with a portion of the
adjoining wood were cut out and placed in jars and tin boxes, but they
soon dried up or molded. Then cages of netting placed over the resin
masses on the trees were tried. These proved too flimsy and were hard
to examine. Finally, cages were made from small baking-powder and
spice cans, by knocking off the bottoms, cutting the sides into narrow

1 Bur. For., U.S. Dept. Agric., Bul. 33, ‘‘ The Western Hemlock,”’ pp. 19, 20, 23.

strips, and punching holes for tacks in the tips of the strips (fig. 2).
This was found to be admirably adapted to the work; it was durable,
could be readily fitted to any surface, and was easily examined by

simply removing the lid.

The investigations were started
too late in the season to secure the
pup or adults, but many larvee in
various stages of development were
collected and studied, and a num-
ber of the infested wounds were
covered with the tin cages.

The most important result of the
first season’s work was the discovery
that the primary cause of the attack
and subsequent injury by the bark
maggot was the work of the hem-
lock barkbeetle (Hylesinus n. sp.)
(fig. 8, a)! which was found exca-
vating short burrows (fig. 3, b,¢) in
the healthy bark, and through it
to the surface of the wood, where
a small wound was made, causing
a slight flow of resin (fig. 3, f).
These burrows were evidently made
by the beetles for the purpose of
obtaining food, and not for the
purpose of depositing eggs, since
neither eggs nor larvee of the beetle
were found, and the burrows were
soon abandoned. Some of these
food burrows were healed over with-
out further injury to the wood,
while others were open and con-
tained a small amount of resin.
These abandoned galleries, with the
resin, formed ideal places for the
young bark maggots to begin their
work, and were, apparently, utilized
in preference to any other wounds.

The investigations of 1904 were
more successful. Upon the first

Fra. 3.—Development of the black check in west-

ern hemlock: a, the beetle (Hylesinus n. sp.)
that makes the primary injury—natural size: b,
entrance of beetle in outer bark ; ¢, longitudinal
section of a similar entrance: d,
showing wound in inner bark; e, same, showing
wound in outer sapwood; f, resin exuding from
an entrance after beetle has gone: g, fresh resin
mass on outer bark, indicating hemlock bark
maggot at work; h, longitudinal section of simi-
lar mass, showing position of maggot: i, maggot
wound ininner bark; j,same, in outer sapwood:
k, resin mass after maggot work is done and
the pupa is formed; J, longitudinal section of
similar mass, showing pupa, the wound begin-
ning to heal (original).

same as }b,

examination of the breeding cages on April 27 one adult male was found.
On April 30 a female emerged, and May 8 two males were secured from

resin masses placed in cages in the laboratory. Another female was

‘Bul. No. 48, Div. Entom., U. 8. Dep. Agric., p 20.

4

taken on May 10, while it was flying in the sun in a field near the forest.
No adults were found in the cages or collected after May 10, which
would indicate that in this locality the adults emerge during the last of
April and the first of May. Specimens of the fly were sent to Mr. D. W.
Coquillett, who identified them as Cheilosia alaskensis Hunter.

The last examination of the field breeding cages was made on Octo-
ber 10. A number of the resin masses that were caged in October, 19038,
still contained larvee. This would indicate that the insect lives several
years in the larval state. The fact that larvee of various sizes were

iy Weg
mi g

Fia. 4.—Hemlock bark maggot (Cheilosia alaskensis): m, Resin mass with exit hole, adult fly hav-
ing emerged; 7, longitudinal seetion of similar mass, showing wound in inner bark and outer
sapwood, pupal chamber and exit hole in outer piteh mass, and original beetle entrance con-
necting them; o, healing wound in inner bark beneath mass like m; p, healing wound in outer
sapwood beneath mass like m; q, longitudinal section of wound p; r, maggot; s, puparium; ¢,
pupa; uw, adult, male; », head of female—all about twice natural size; w, larval head—enlarged
about 20 times; 2, antenna—enlarged about 45 times (original).

found at all times of the year and adults only in the spring strengthens
this belief.

LIFE HISTORY AND HABITS OF THE HEMLOCK BARK MAGGOT.

The female fly was not observed ovipositing, nor was the egg found,
but young larvee were collected from the barkbeetle wounds. It there-

5

fore seems evident that the egg is laid on or in the slight flow of resin
that exudes from such a wound (fig. 8,7). No evidence was found that
the larva could make an independent entrance through the bark.

DESCRIPTION OF THE STAGES.

The larva.—The larva (fig. 4, 7) is a whitish maggot with a small,
wrinkled head almost buried in the front end of a plump, subcylindrical,
segmented body that terminates behind in a long, telescopic, protractile
tail. The head (fig. 4,w) has a pair of stout, black, forked mandibular
hooks, and is densely clothed with short brown spines. When exam-
ined with a microscope, a pair of small branched feelers (antennze) are
found just above the hooks. The body seems smooth to the naked eye,
but it is quite thickly covered with minute spines. Just back of the
head, upon the dorsal surface of the first segment, is a pair of widely
separated, small, fleshy tubercles. Each bears a dark brown breathing
organ (spiracle). Most of the segments have a pair of fleshy append-
ages, probably false feet, on their ventral surface. Upon the ventral
surtace of the last segment, and surrounding the anus, which opens there,
are often seen five -or six heavily convoluted, bladder-like protrusions.
These are probably the rectal glands.

The tail is about the same length as the body. It bears several pairs
of the fleshy foot-like organs, and terminates in a dark-brown fork, each
branch of which is armed with a whorl of four strong plumose bristles.
It is simply a long breathing tube that may be lengthened or shortened
at will to meet the varying depth of the resin mass covering the body.
The tip, or fork, bears and protects the spiracles, which must always
be kept out to the air. The full-grown larva, including tail, is from
0.6 to 0.8 inch in length, and 0.08 to 0.12 inch in width at its largest
part.

The puparium.—The puparium (fig. 4, s, ¢) is formed within the last
larval skin. The larva lies doubled up with the tail bent over the back
and the head just within the outer surface of the resin mass. The tail
shortens up, appears to lose its breathing function, and the body
becomes more compact and solid. The two spiracle-bearing tubercles
on the back of the first segment become elongated into horns, and form
the breathing tubes. The Jarval skin does not seem to become very
much thickened. nor any darker, as is usually the case in related forms.
It remains quite transparent and the outlines of the puparium can be seen
through it quite plainly. The puparium, including the inclosing larval
skin, is 0.28 to 0.36 inch in length, and 0.12 to 0.16 inch in width.

The adult. —When full development is reached, the head of the larval
skin is pushed out and the adult emerges. This usually takes place
in April or May. The adult (fig. 4, w) is a small black fly, about 0.36
inch in length, 0.12 inch in width, with wings 0.52 inch in length, and
is rather densely covered by medium black hairs. The male is more

6

slender than the female, which has a rather broad pointed abdomen.
The eyes of the male are contiguous on the top of the head, while those
of the female (fig. 4, v) are quite widely separated. Little is known
of the habits of the adults. Though carefully sought for, only one speci-
men was taken in the field. This was flying in the sun in a little
meadow at the edge of a forest. The species was described! from a
single female taken at Cook’s Inlet, Alaska. ‘here is also a female
from Yakutat, Alaska, in the U. 8S. National Museum Collection.

HABITS OF THE LARVA.

The larva is usually found in the wound (fig. 38, #), surrounded by the
soft resin. The head and body lie in the inner part next to the sapwood,
while the tail extends out through the bark and outer resin mass, with the
spiracles opening into the air. The cambium, or growing layer, which is
composed of soft, living, outer sapwood and inner bark, is bruised and
torn by the mandibular hooks until quite a wound is made. This is
enlarged as its occupant grows in size. The resin is pushed out of the
entrance and forms an irregular, globular, reddish-gray mass on the
outer bark (fig. 3, g, k, and fig. 4, m).

Breathing through its tail and feeding on the sap and soft tissues of
the tree, the larva lives in the wound until it becomes full-grown. This
takes, in some cases at least, several years. Some larvee, from eggs
laid, probably, in May, 1903, had not changed to adults in October,
1904. All sizes of larvee are found at all seasons of the vear, but the
adults during April and May only. The wounds (fig. 8, 7,7) show that
as many as five successive layers of new growth may be eaten, although
the usual number seems to be three. These facts seem to indicate that
living representatives of several broods may be found at any time, and
that the length of the larval stage is variable. It is probable that under
unfavorable conditions it may be prolonged to four or five years, while
if the conditions are favorable it may be shortened fo one year.

Although the larva is usually found in the wound as described before,
it sometimes moves around in the outer resin mass and even on the
outer surface of the mass. In the spring the fully developed larva with-
draws to the outer mass to pupate (fig. 3, J).

The primary wound made by the barkbeetle through the bark remains
the same size as the beetle leaves it, and the bark maggot occupies the
chamber between the inner bark and wood. Both entrance and cham-
ber are filled with resin. The completed wound (fig. 4, 0, p, q), there-
fore, consists of the beetle burrow, which is about 0.08 inch in diame-
ter, through the outer and inner bark to the inner chamber, which is
one-half inch to 1 inch in diameter. The external resin mass is 0.6
inch to 1 inch in diameter, and 0.4 to 0.6 inch in depth.

1W. D. Hunter, Can. Ent., Vol. XXIX, p. 124, June, 1897.

As soon as the maggot leaves the inner chamber the irritation ceases
and the wound begins to heal. The cambium grows down into it year
after year, and the annual growth of wood formed there slowly covers
it over until in three or four years it is completely buried (fig. 5)
beneath the new growth and thus forms the black check.

As the wood grows down into the wound in healing it over, a depres-
sion is formed in each new layer, but sometimes the new layer thickens
around the depression and forms an elevation above the surrounding
surface. In both cases an ornamental curl is formed that will show as
a bird’s-eye effect in bastard-sawn or longitudinal sections of the wood.

Fra. 5.—a, Longitudinal section of wood containing a black check; b, the check; ec, the stain in
the wood beneath it; d, the curls in the wood covering it; e, the resin mass on and in the bark;
f, section a split into four sections to show tangential views: g, tangential view of check.
hh, tangential view of curls; 7, black spot or old resin mass (original). :

NATURAL ENEMIES.

Two hymenopterous parasites were bred from the syrphid puparia.
Dr. Wm. H. Ashmead, of the U. S. National Museum, ‘identified one
of these as an ichneumonid (Syrphoctonus maculifrons Cr.) and the
other as a chalcidid (Hutelus flavipes Walk.). Both species are fairly
common, and probably aid greatly in keeping the trouble in check.

Syrphoctonus maculifrons Cr.—This is a small wasp-like ichneumon
fly about 0.86 inch in length. It has a dark body marked by a
few white patches at the bases of the wings and legs. The face is
nearly covered by a square of white, and the legs are reddish brown.
The abdomen of the male is more slender than that of the female, and
the white square on the face is larger. The earlier stages are not known.
Pupation takes place in the body of the maggot in the outer resin mass.
The adult emerges during the latter part of June or the first of July.

ee

Each maggot furnishes subsistence for but a single parasite. Adults
were bred from resin masses of both the hemlock and the lowland fir
bark maggots.

Eutelus flavipes Walk. is one of the small chalcidid flies. The
females have dark metallic-green bodies, cherry eyes, light brown legs,
rather dark antenne, and are about 0.12 inch in length. The males
are smaller, about 0.08 inch long, and have a broad yellow band across
the abdomen. Their bodies are a lighter green and the legs and anten-
ne are yellow. Each maggot supports a number of parasites, usually
about a dozen. The pups are formed in the body of the host in the
outer resin mass. The adults emerge during the latter part of June.
This species was bred only from the hemlock resin masses.

These two parasites were the only natural enemies found. There was
no evidence of any bacterial or fungous disease, and the maggot is so
concealed in the bark and resin that it is well protected from preda-
ceous enemies.

ASSOCIATES.

Two small pill beetles (Amphicyrta simplicipes Mann. and Simplocaria
nitida Mots.) were frequently found on and near the resin masses. Their
relation, if any, to the syrphid was not determined.

METHODS OF PREVENTING LOSSES.

Since the black check is the result of the work of the insects during
past years, or even centuries, and is thus distributed all through the
wood of the trunks of the matured affected trees, the only methods
which appear to be available for preventing losses are:

(1) Where clear stuff is required, select timber which, as indicated
by the absence of the old resin masses on the bark, is free from the
trouble.

(2) Utilize timber from badly affected trees for box material and
other purposes where the checks are not objectionable.

(3) Utilize the bird’s-eye or curled wood for natural-wood finish.

BARK MAGGOTS IN OTHER TREES.

THE LOWLAND FIR BARK MAGGOT.

In 1903, while studying the black check of the hemlock at Satsop,
Wash., a similar trouble was discovered in the white or lowland fir.
The insect causing it was reared and proved to be Chetlosia hoodianus
Bigot, a species closely related to the hemlock fly. The maggot is very
similar in size, appearance, and habits. The adult is a trifle larger and
not so dark in color. The thorax is dark brown, and the abdomen a
light chocolate. The emergence of the adult takes place a little later
in the season than that of the hemlock species. Most of those reared
emerged about the middle of May, but the last one did not come out
of the resin mass until August 12.

9

The work of the two species is very similar. The fir is a more rapidly
growing tree than the hemlock and the wounds under the bark, there-
fore, go deeper into the sapwood. These wounds, also, occur more
often in patches. The primary injury is made by several species of
barkbeetles, viz, the western hemlock barkbeetle (Hylesinus n. sp.),
the larger fir-tree barkbeetle (Hylesinus granulatus Lec.), and prob-
ably other species.

Two specimens of the parasite Syrphoctonus maculifrons Cr. were
bred from the resin masses. No other enemies were seen.

Satsop was the only place where the trouble was noticed. The amount
of damage done and the distribution of the insect causing it are not
known.

THE ALPINE FIR BARK MAGGOT.

On October 24, 1904, a bark maggot was found in a resinous wound
on the trunk of an alpine fir at Smith’s Ferry, Boise County, Idaho.
The wound seemed to have been started from an old limb sear. Only
one specimen was found. It resembled the maggots of the hemlock
and jowland fir, and is probably the larva of another species of Cheilosia.
The amount of damage it causes was not determined.

THE SITKA SPRUCE BARK MAGGOT.,

A maggot closely resembling the other species, except that it has a
short tail, is quite common in the wounds on the trunks of Sitka spruce.
It is usually found in the pitch around the edges of the large resinous
wounds caused by the spruce pitch-worm (Parharmonia picew Dyar).
Several maggots live in the same wound, and the irritation produced
by their feeding keeps it open for so long a time that an ugly scar is
formed in the wood. Several generations may live in the same wound.
Pupation takes place in the drying resin of the wound. This is prob-
ably a species of Cheilosia. Hoquiam, Wash., was the only place where
the trouble was noticed.

THE YELLOW PINE BARK MAGGOT.

A dark, subcylindrical dipterous puparium was very common in pitch
exuding from axe and other wounds in the bark of young yellow pine
(Pinus ponderosa) trees at Moscow Mountain, Idaho, and barkbeetle
(Dendroctonus sp.) and sapsucker wounds in the bark of the young
trees of yellow pine, and the lodgepole pine (Pinus murrayana) at
Smith’s Ferry, Idaho. No adults were reared. The species is probably
a syrphid, possibly a Cheilosia, though the puparium does not resemble
those of Cheilosia alaskensis and hoodianus. The amount of damage
done is unknown.

CONCLUSIONS.

(1) Western hemlock timber growing on low land is often affected by

a defect known as black check, which renders a large percentage of the

‘

10

wood worthless for finishing, staves, and woodenware, but apparently is
not seriously detrimental to timber for other purposes.

(2) The black check is caused in nearly every case by an injury to
the cambium (growing layer) of the trunk by the hemlock bark maggot,
Cheilosia alaskensis Hunter. Somewhat similar defects may be caused
by barkbeetles, bark-borers, sapsuckers, or anything that makes a
wound in the cambium, which afterwards heals.

(3) The maggot enters the bark through an abandoned food burrow
made by the hemlock barkbeetle (Hylesinus n. sp.). It gradually
enlarges the burrow into a small wound, in which it lives for several
years, feeding on the sap and cambium. In the spring, when full
grown, it pupates in the resin mass which has formed on the outer bark
around the entrance to the wound. The puparium soon changes to the
adult, which emerges in April or May. The egg is probably laid on the
resin exuding from the abandoned gallery of the barkbeetle.

(4) A near relative (Cheilosia hoodianus Bigot) of the hemlock
bark maggot causes, in a similar manner, a black check in the timber
of lowland, grand, or white fir (Abies grandis). It enters the bark
through the abandoned food burrows of several species of barkbeetles.

(5) The alpine fir (Abies lasiocarpa), the Sitka spruce (Picea sitch-
ensis), and probably many other trees are injured more or less by bark
maggots that enter wounds and enlarge them or keep them open until
the conditions are such that checks form in the timber,

(6) For preventing losses in timber cut for purposes requiring clear
stuff, select trees growing at altitudes above 1,800 feet and those at
lower elevations which are free from the black indicating spots (old
resin masses) on the bark.

Approved :

JAMES WILSON,
Secretary of Agriculture.

WASHINGTON, D. C., May 24, 1905.

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