The joint worm (Isosoma tritici Fitch.)

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CIRCULAR No. 66, REVISED EDITION. OCT az (eee 18 Issued September 21, 1908.

United States Department of Agriculture,

BUREAU OF ENTOMOLOGY ,

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

THE JOINT-WORM.

(Isosoma tritici Fitch.)

By F. M. WEBSTER,
In Charge of Cereal and Forage Plant Insect Investigations.

Since the first known serious outbreak of the joint-worm (/sosoma
tritict Fitch), which occurred in the wheat fields about Charlottesville
and Gordonsville, Va., during the years 1848 to 1854, this insect has
been reported atirregularintervals and from widely separated localities.
While it is known to occur sparingly over most of the wheat-growing
sections of both the United States and Canada, and probably does
more damage than has generally been attributed to it, its reappear-
ance in the wheat fields of Indiana, Michigan, Ohio, Pennsylvania,

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Fia. 1.—Isosoma tritici: Adult of the joint-worm. Much enlarged (from Howard).

@ West Virginia, Virginia, Maryland, and Kansas in 1904, and in still
greater numbers in 1905, serves to bring it again to notice. In 1904
some fields of wheat in eastern Ohio were so badly damaged that they
were not harvested, and in 1905 a serious outbreak in northeastern
Indiana so discouraged some farmers that they questioned the advisa-
bility of putting in a crop of wheat at all. In southwestern Virginia
the pest was even more injurious in 1905 than it was the previous year.
The pest was also very destructive in western Ohio and eastern Indiana
during the spring of 1908.

52718—Cir. 66—08

Historic, archived document

Do not assume content reflects current
scientific knowledge, policies, or practices.

2

Pe DESCRIPTION OF THE PEST.

The fuily developed insect, somewhat resembling a small, winged
black ant, is clearly shown, enlarged, in figure 1, its natural size being
indicated by a line at the right. The color is black, with joints of legs
and feet yellow. The larva or grub is whitish, with brown jaws, the
length being about the same as that of the adult, and the form much
hke that shown in figure 2, which represents the larva of a nearly

related species.
LIFE HISTORY.

The insect may be found in wheat stems, inits various stages of devel-
opment, throughout the year. It lives through the winter asa larva
or grub in cells formed in the
stems prior to the ripening of
the grain, the adult emerging
therefrom in April or May, ac-
cording to
latitude, or
some time
after the
young grain
has thrown
up stems
and several
joints have
become ex-
posed. The
female, us-
ing her slen-
der, pointed
oviposit or,
places her
egos in the
stems. The Fia.2.—Isosoma grande:

. Larva of the wheat-
exact posl- straw worm; é, anten-

tion assum- na; f, jaw. Line at
: y right indicates natural
ed is shown

length. (After Riley.)
in figure 3,

from a photograph from life
by Mr. G.I. Reeves. The eggs
Fic. 3.—Female Isosoma in act of depositing eggin hatch and the young grubs,

stem. About life size (author’s illustration). forming cells, feed in the
walls of the stem, reaching their maximum growth by the time the
straw becomes fully hardened and ripe. Wintering in the larval
state, they pass a short pupal stage and emerge as adults in the

spring. While there are both males and females among these insects,

[Cir. 66]

@

3

Mr. Phillips of this Bureau has,
during two successive years, found
that unfertilized females will deposit
eggs and that these eggs will hatch
out larve which develop to adult
insects. It is probable, however,
that these adults will be found to be
largely or all males.

EFFECT ON THE STRAW.

The effect on the straw of the work
of the joint-worm is exceedingly vari-
able. Sometimes a distortion occurs
like that illustrated in figure 4; at
other times the straw is bent or
twisted in almost every conceivable
shape; again, there will be no enlarge-
ment of the straw whatever; or there
may be large galls or excrescences, as
it were, bursting out of the base of
the sheath at one side, some of these
abnormal growths having pseudo-
rootlets extending downward from
their lower extremity. Sometimes
the straw will make about normal
erowth and the hardened sections will
be restricted to an inch or there-
abouts just above the lower joints;
and, again, the growth will not exceed
3 or 4 inches, often not heading at
all, or with aborted head and with
the straw galled or hardened to the
base of the head. In some cases
there is no outward indication of at-
tack whatever, the affected part be-
ing wholly inclosed in the sheath, and
when this last isremoved the presence
of the cells is indicated only by a
slight discoloration, and frequently
by a few small, more or less irregu-
lar, elevated ridges.

In thrashing the grain the hard-
ened portions of the straw, as shown
in figure 5, break up into pleces of Fia.4.—One effect of Ufa FO in wheat
from half an inch to an inch or more Peek ee

[Cir. 66]

4

in length, many of which do not go over with the straw and chaff,
but remain with the grain. The presence of these bits of broken straw
in the grain is frequently the first evidence the farmer has seen of the
occurrence of the pest in his fields. Millers and elevator men note
them also, and in sections where the pest has committed serious dep-
redations several bushels of these hardened bits of straw are found
after each day’s cleaning of the grain.

EFFECTS ON THE KERNEL.

The wheat heads from infested stems are foreshortened, and the
kernels thereby necessarily reduced in both size and number, and in
case of severe attack they become shrunken.

NATURAL ENEMIES.

Natural enemies of the joint-worm are quite numerous, and
most of them have the advantage of being double-brooded, whereas
the joint-worm has but one generation
annually. 3

Among the most efficient of these are
two rather common species of insects.
One of these, almost as big as the Isosoma
itself, with dull metallic thorax and yel-
low abdomen and with long ovipositor,
is Ditropinotus aureoviridis Crawford, and
the other, smaller, darker colored, and
slender, also somewhat resembling an
Tsosoma, is FEupelmus allynii French.
The writer reared also another species in
Ohio, Websterellus tritici Ashm., which has
similar habits.

A somewhat similar insect with metal-
lic body and yellow abdomen, Stictonotus
Fic. 5.—Bits of hardened straw re- isosomatis Riley,is very efficient in destroy-

maining with the grain afterthrash- : : = ra
ee ena raat On) ing the larve in the straw. Homoporus

Riley, and beyond a doubt other chalcidoids, are also instrumental in
holding the pest in check. These are all small four-winged flies, and
a number of additional, undescribed forms have been discovered.
The larva of a smail, slender, black and yellow carabid beetle Lepto-
trachelus dorsalis Fab.) crawls up, descends into the stubble, and de-
vours the Isosoma larve, but unfortunately its sense of taste seems to
be too obtuse to allow it to confine itself strictly to Isosoma, and as a
consequence it devours parasites as well as host. A mite, Pedicu-
loides (Hetoropus) ventricosus Newp., is also an enemy, gaining access
to the larvee precisely as does the beetle larva previously mentioned.
[Cir. 66]

(Semiotellus) chalcidiphagus Walsh and @

5
PREVENTIVE MEASURES.

There are no known remedies for the joint-worm, but there are
several preventive measures that are not impracticable and are
reasonably efficient.

In the midst of the outbreak in Virginia, previously mentioned, a
‘‘Joint-worm Convention” was held at Warrenton, in that State, to
devise means for controlling this pest. This body recommended a
better system of farming, the use of guano and other fertilizers to pro-
mote arapid growth and anearly ripening of the grain, and the burning
of the stubble, all of which are as advisable to-day as they were at that
time. The most serious ravages are observed on thin or impoverished
soils, especially along the margins of the fields infested. Anything,
then, that tends to add vigor to the young growing grain will constitute
a preventive measure. Burning the stubble, where this is practicable,
is, of course, most efficacious, but over the larger portion of the terri-
tory ravaged by this pest it is customary to seed with grass after
wheat, and under this condition burning over the stubble field is
impossible. Such fields should be raked over with an ordinary hay
rake, and the loosened stubble removed and burned before the adults
have emerged in the spring. If, however, the grain is cut low at
harvest, and the straw passed through the stables as bedding for
stock during the winter, thus becoming saturated by liquids and more
or less thoroughly composted, the treatment would seem sufficient to
destroy the Isosoma larve so that few, if any, would develop adults
the following spring. In case of bedding for horses, it seems quite
probable that if any larve at all survived the thrashing machine, the
heat from the decomposing manure would develop them prematurely.
However, there has been no experimentation exactly along these
lines, and according to a press bulletin? by Prof. R. H. Pettit, of
the Michigan Agricultural College, serious injuries have followed the
year after application and plowing under of barnyard manure in the
fall before the wheat was sown. In this case the manure would
necessarily be fresh and the bedding of straw of the same season’s
growth, otherwise the adults would have already emerged. This
would be a proposition quite different from that of allowing the stable
manure to accumulate during the winter and applying it in the spring
elsewhere than to the wheat fields, or even of applying it to wheat
fields before plowing, months after the larve surviving the effects of
the stable had developed and escaped. The one might destroy all or
nearly all larve in the straw, and the survivors would emerge about
the stables or in the barnyard; while the other method, simply to take
the straw with the living larve present from an old field, move it

@ Mich. Agr. Col. Exp. Sta., Press Bull. No. 15. The Wheat Joint-Worm.
[Cir. 66]

6

through the stable, cart it out on a new field, and plow it under, is
one that the farmer should evidently be careful to avoid.

Exactly in this connection, an assistant, Mr. Charles N. Ainslie,
while waiting between trains in the city of St. Louis, Mo., found
at the corner of Sixteenth and Locust streets a pile of bricks to be
used in the erection of a building. These bricks werestamped “‘ Mas-
sillon, Ohio,” and were packed in straw which the chief contractor
stated came with the bricks from Ohio. This straw contained larvee
of this species which later on transformed to adults, but the latter
did not emerge from the straw.

Tn the past it has always been thought necessary, as a precautionary
measure, to burn the infested bits of hardened straw that break up
in thrashing the wheat, many
being carried out with the
erain instead of going over in
the straw. Several experi-
ments In rearing adults from
large numbers of these broken
bits of straw (fig. 5), collected
about elevators and thrash-
ing machines, has shown that
almost all of the larve of
both Isosoma and parasites
are killed, probably by the
concussion of the cylinder of
the thrasher. In some cases
we have been able to verify
these experiments by collec-

; e by tions of stubble from fields

Fic. 6.—Wheat straws injured by the joint-worm . ay obeS
(Isosoma tritici), from which the joint-worms have 10 the vicinity of these ele-
been removed by some beneficial animal, perhaps the wators. So far as we have
short-tail shrew (Blarina brevicauda). (Author’s illus- : : 5 “ :
ation) gone into the investigation
everything indicates that the
danger from these broken bits of hardened straw, or even from the straw
itself, is of too little importance to be worth consideration. Prof. R. H.
Pettit, of the Michigan Agricultural College, and Mr. W.J. Phillips, of
this Bureau, in 1906, found in northern Indiana great numbers of
straws affected by the joint-worm, where the enveloping sheath had
been torn away, the galls formed by the larve deftly eaten away, and
the joint-worms missing. Inno case was the entire gall gnawed away,
but just enough of the walls immediately over the larva to make pos-
sible the removal of the latter (fig. 6). While we have not been able to
get definite information as to the identity of this decidedly beneficial

animal, suspicion seems to point to the short-tail shrew (Blarina
[Cir. 66]

(

brevicauda) as the species to which credit should be given, and prob-
ably much of the work is done while the grain is in shock.

Rotation of crops is advantageous, because it necessitates the
migration of adults from one field to another, and if this takes place in
stormy weather or during high winds, many of the migrants will be
killed or blown astray. It is easily seen that where infested straw is
applied to a new field prior to sowing to wheat, this migration of
adults would not be made necessary.

The sowing of early ripening varieties is also beneficial.

Approved:
JAMES WILSON,
Secretary of Agriculture.
Wasuineton, D. C., July 16, 1908.

[Cir. 66]

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