The larger corn stalk-borer (Diatrœa saccharalis Fab.)

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Material Information

Title:
The larger corn stalk-borer (Diatrœa saccharalis Fab.)
Series Title:
United States. Dept. of Agriculture. Bureau of Entomology. Circular ;
Physical Description:
8 p. : ill. ; 23 cm.
Language:
English
Creator:
Ainslie, George G
Publisher:
Government Printing Office
Place of Publication:
Washington, D.C
Publication Date:

Subjects

Subjects / Keywords:
Corn-stalk borer   ( lcsh )
Corn -- Diseases and pests   ( lcsh )
Genre:
federal government publication   ( marcgt )
non-fiction   ( marcgt )

Notes

General Note:
Caption title.
General Note:
"Issued February 7, 1910."
General Note:
"This is practically a revision of Circular no. 16, prepared many years ago by Dr. L.O. Howard."
Statement of Responsibility:
by George G. Ainslie.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 030223264
oclc - 27956460
lccn - agr10000276
System ID:
AA00022905:00001

Full Text

STATE PLANT
BOARD OF
FLA. LIBRARY


CIRCULAR NO. 116. Issued February 7, 1910.
/ United States Department of Agriculture,

BUREAU OF ENTOMOLOGY,
L. 0. HOWARD, Entomologist and Chief of Bureau.


THE LARGER CORN STALK-BORER.a
(Diatrwa sacchtaralis Fab.)
By GEORGE G. AINSLIE,
Associate Professor of Entomology, Clrmson Agricultutral college e of Souith
Carolina.
i
INTRODUCTION.
In many southern cornfields a heavy wind late in the season. b)e-
fore the corn is matured, does great damage by breaking the plants
off at the surface of
the ground, thus t A
ruining them. An t b. r
examination of these
broken stems will. in
most cases, show that .
they have been
greatly weakened by e
the burrows of a
larva or caterpillar. 7
This larva (fig. 1) is
known as "the lar-
ger corn stalk-borer "C ,
(Diatrtea saccawra- FIG. 1.-Thie larger corn stalk-bor.-r bDittrtra saccihaoulix. :
lis). Its work is a, Summer form of larva; b, c, hibernating forms of
largely within the larve: (, third thoracic segment from above; e, (-i ltth
large witin te abdominal segment from above; f, abdominal sc-,-:ment
stem of the plant and from above; g, same from side. a, b, c, Enlarged; di, c, f,
is so concealed that, still more enlarged. (Redrawn from IIoward.)
in most cases, unless weather conditions make it conspicuous, the
presence of the insect passes unnoticed.
a This is practically a revision of Circular No. 10, pireipared many years
ago by Dr. L. 0. Howard. Mr. Ainslie was formerly in the employ of this
Bureau as an agent and expert in cereal and forage insect investigations, and(
this pest was one of the subjects of investigation assigned to him. He after-
wards did some work upon the species for the South Carolina Agricultural
S Experiment Station in cooperation with this Bureau.
21731-No. 116-10
SQ
S33
R 33





2

This insect seems to have been originally an enemy of sugar cane
and to have first transferred its attention to corn in 'the southern
part of this country, where corn and cane are grown over the same
territory. It occurs in many countries where sugar cane is the staple
crop, and has caused great damage in the West Indies, British Guiana,
Australia. and Java. The bulk of the evidence goes to show that it
was first brought into this country with the importation of sugar-
cane cuttings from the West Indies and Central and South America,
where, since early times, it has interfered with the production of this
staple.
In the United States this borer is found almost universally through-
out the South, from Maryland to Louisiana and westward to Kansas.
Among other localities it has been reported to the Bureau of Ento-
mnology from Bennettsville, S. C.. as destroying corn, especially that
planted early in the season. From Waynesboro, Ga., in 1909, reports
were received that in some fields the corn was at least one-third
destroyed" by an insect which later proved to be this species. In
Virginia it has been found recently at Nathalie, where it was studied
by Mr. J. A. Hyslop, of this Bureau, at Allenslevel, at Church Road,
and at Farmville. In late October, 1909, Mr. E. G. Smyth found
that nearly one-half of the cornstalks at Diamond Springs, Va.,
were infested, often as many as three larva? being found in one
stalk, boring from the surface of the ground down to the base of
the root; and while the author has frequently found as many as
a dozen larvN, in a single stalk, there are never more than two or
three pupa' in the same stalk. In each case it had damaged the corn,
and especially that planted early in the season. Detailed investi-
gations of this insect have been conducted by the author during the
last two years, chiefly in South Carolina.
NATURE OF DAMAGE.
Corn is damaged by these caterpillars in two ways. First, in the
early part of the season, while the plants are small, they work in the
"throat of the young corn, and if the tender growing tip within
the protecting leave is once damaged all chances that the plant
will become a normal productive specimen are gone. In nimany sec-
tionis of tlhe South this is commonly known as "butd-worm injury,
an1d thollugh there are several other insects which cause a similar
In utilation of the leaf, a very large proportion of the so-called bud-
v.WJIII (daiI];ige I) bp\e il' iargt to this i isect. The effect of its
work on thle leaves of the youll' corn) plants is similar to that re-
.,ultillng f(roml attacks I tlie co(rii billbiiugs (.p/I /nJ/tior.s splp.) and
'V iVI(denced byI tli miiili a ro-Ws of sinall I liihlr or irregular holes
a('OSS- tlie liaiaes f tle pia it ( lfiL. -).
'The other fr1, It of serious t( i:ain gre (clisrgaeible to tis pest occurs
later in tle season. Tle larva'., lIa'ilg then left the leaves and
[Chr. I 1;]








descended to the lower part of the stalk, tunnel in the pith. (See
fig. 3.) If the larvae are at all numerous in the stalk, their burrows
so weaken the plant that any unusual strain will lay it low and
destroy all chance of its maturing. While frequently ten or more
larvae may live and mature in, one plant, it must be remembered that


FIG. 2.-Work of larger corn stalk-hon r. iu.w nI .-r-- inftilation of leaves of corn liy larva.
Greatly reduciL-d. (Original.)
any infestation, however light, will le-sen in some degree the vitality
of the plant and cause a corresponding loss in the quality and quan-
tity of the harvest.
HABITS OF THE LARV.E.
Immediately upon leaving the egg in spring, the young larva of
the first generation, spinning a silken thread behind it, wanders
down into the throat of the plant as far as the water or dew usually
standing there will allow it to go, and begins to feed on the leaves,
going back and forth through the yet unfolded clusters and soon
riddling the more tender leaves with aimless burrows. If the bur-
row reaches the tender terminal bud where the future joints are
being formed, further growth at that point ceases and the plant be-
comes stunted and misshapen, with no tassel. As the plant continues
to mature, the larva "grows out," as the farmers say. It is more
ICir. 116]






likely that it is the evidences of its work and not the larva itself
that "grow out;" but for whatever reason, the caterpillar soon leaves
the more leafy portion of the plant and attacks the stalk at or near
the ground. Here a hole is cut through the outer wall of the stalk
and the larva burrows upward for a short distance, after which it
seems to run aimlessly through the pith, frequently even leaving the


































FIm. .3.-Thln- Iaror corn stalk-borer Larva in lower part of corn plant preparatory to
hilhernation. Rlduce'd. I Original.)
stalk elttirely and rceiiterir it. at another poiiit. Turning upward,
the caterpillar, when fully grown, bores toward the outside and
cuts a circular hole in the outer wall of the stalk. Then, after
Spin11illg a f-%w loose threads across this opening to keep out un-
de.siraIkl1 visitors, it retreats a short distance, plugs the burrow below
with digested pith, and in the chamber thus created slowly changes
to tlhe next or pupal stage (fig. 4, c).
[Cir. 1161







Seldom is the stalk damaged above the third joint from the ground,
although the larval, when small, are found in the large midribs of
the lower leaves and later in the season, when the food supply is
restricted, even in succulent nubbins farther up. They sometimes
also penetrate the underground part of the stalk in feeding and enter
some of the larger brace roots for a short distance.
The larve of the second generation work in a similar manner, except
that at the time they appear the tassel has been formed; hence the
damage is now confined altogether to the lower stalk. Thus, instead
of arranging to pass the pupal stage in the upper stalk, they pene-
trate to the root to hiber-
nate and there, as larvae, \".
pass the winter in a qui- -- .-...
escent state (fig. 3). ____-" :=_._

SEASONAL HISTORY.
.......................,.=. ....................
^W^'^...3 ,...-:,*,:.*'"'"

During the winter this !
enemy of corn is to be t
found as a robust, creamy- ________
white larva of the second
generation in the lower i
part of the stalk-or of I- '. ._
;.'.\' ... --1-
the stubble, if, as is usui- I!l,, \ .. .
ally the case, the corn '.
has been cut. In this lo- ,,:. 4.--ih, liargr corn stalk-borer: a, Female
cation the larva forms a moth; b, wings of male; c, pupa. All somewhat
small cavity below the sur- vnlrgi'd. (Orit-inal.)
face of the ground, well protected from birds, predaceous insects,
and unfavorable weather conditions. From the time the corn is
mature in the fall until about corn-planting time in the spring this
caterpillar remains inactive. About the time the ground is being
prepared for corn, from March 15 to April 30, depending on the
locality, this larva changes into a reddish-brown pupa or chrysalis
(fig. 4, c). After a further period of ten or more days' inactivity the
adult insect emerges from the pupa case as a pale brownish-yellow
moth (fig. 4, a, b) ,with a spread of wings of about an inch and a quarter.
The moths then mate and the females begin at once to deposit eggs
on the underside of the leaves, the larva- hatching from these eggs
forming the first generation.
The eggs hatch in from seven to ten days and the young larvte
begin their destructive work in the upper leafy portion of the plant,
later descending to the base of the stalk, where they attain full
growth. This period, from egg to full-grown larva, requires from
twenty to thirty days, depending largely on the weather conditions
[Cir. 116]






and the vigor of the plant. The larvae when full grown pupate in
the stalk, usually in the second or third joint from the ground, and
in from seven to ten days the adult moths of the first generation
emerge.
The eggs for the second generation are laid in similar positions
on the lower leaves or on the stem, and the larve, after feeding for
a short time on the leaves, go directly to work in the stalk, completing
their larval growth in the pith of the lower stalk as did the larvae
of the first generation. No damage is done to the upper part of the
1)ldnt by larvae of the second generation.
By the time the larvm- of the second generation are full grown
the corn is rapidly nearing maturity, and, instead of p)upating inI
the stalk, they turn downward, penetrate to the extreme lower tip
of the taproot, and there form a small cavity in which to pass the
wiitcr. At this time the larva? lose the darker markings of the ear-
lier forms, and as overwintering larvae are creamy-yellow in color.
They are plump and active in the fall, but flabby and sluggish after
fli.ting throughout the winter. The only way in which the insect
prices the winter is in the form of this overwintering larva, found
below the ground in the extreme lower tip of the corn roots. Two
generationss n year appear to be the rule. although it is possible that
in the far South and onil sugar cane a partial third generation may
occu~r.
DESCRIPTIONS.
Egg.-The eggs are flat and scalelike, almost circular in outline,
;il] are placed in row- or irregularly, overlapping one another
shiigle fashion. From two to twenty-five eggs are laid in one place
on the underside of a lower leaf or occasionally on the upper side
an d on tlhe stem. Creamy-white when first laid, they gradually
change to a reddih-b)rown, and inll seven to ten dlays a minute. bristly,
reddish caterl)illar cracks tlhe shell and crawls out through a narrow
-lit at one enld. The eggs are about three one-hundredths of an inch
(7.6 ilm.) long and about two-thirds as wide. After hatching, the
white papery sliells are soon washed off the leaves.
Larva.-The larva of thle first generation (fig. 1, a) when full
grown is a robust, dirty-white caterpillar 1 inch in length, thickly
covered with round or irregular dark spots, each of which bears a
sl()rt, dark bristle. When the larva is small these markings are
almost contiguous, giving tlhe whole insect a dark color and a hairy
appe lltirance. Tlie lead and thoracic plate of all the stages are
Ibrownish-yellow. T'lie overwintering larva of the second generation
(fig. 1, b, c) gradually loses the darker markings of the body and
after tihe last molt remains unsp)otte(d and light yellow in color.
x('ep)t for the head and the thoracic plate, which retain the brownish-
yellow of tlhe earlier stages.
[t'r. 1 ii;]






Pupa.-When first formed, the pupa (fig. 4, c) is light honey-
yellow in color, soon changing to a rich mahogany-brown. It is
about seven-eighths of an inch in length and is able to contort itself
violently when disturbed. It lies in the cavity usually with the head
up. On emerging, the moth leaves the brownish shell of the pupa
case, partially withdrawn from the hole.
Adult.-The female moth (fig. 4, a) varies in color from almost
white to smoky yellow. The fore wings, which spread to about 1V
inches, are darker than the hind wings, and bear faint markings.
When at rest the wings are held close to the body, forming an acute
triangle. The egg laying is done for the most part either at night or
in the dusk of evening, the moths flying rapidly from plant, to plant.
The male moth (fig. 4, b) is usually somewhat darker in color than
the female and always smaller.
FOOD PLANTS.
Besides corn and sugar cane. this borer has been reported as feed-
ing on sorghum. Johnson grass, guinea corn, and grama grass. The
injury to the four last-mentioned plants is never severe, but in plan-
ning methods of control they must be considered and an examination
made to determine whether or not they are harboring the pest.
NATURAL CHECKS.
The larger corn stalk-borer has very few natural enemies. A
minute Hymenopterous parasite (Triclioyiai(m iu pretosa Riley) has
in a very few instances been found living in and destroying the eggs.
In one case ten of these minute parasites were reared from two eggs.
The larva of a brown, velvety beetle (Cliauioqfvathls ?i8n)sylC'atyi .'s
DeG.) sometimes enters the holes in the stalks of stubble after the
corn is cut and devours the caterpillar, found therein. This larva
has been found to be of great value in reducing the numbers of the
borers in fields of sugar cane. The termites or white ants (Ternme.s
flavipes Koll.), locally known as "wood lice." have been observed
destroying the larvae in the stubble in the winter, although apparently
only when the presence of the larva interfered with the work of the
ants. In a few cases bodies of the borers have been found in the
stubble killed by a fungus, as yet undetermined, which envelops their
bodies in a white mold. Fungi, however, are too dependent on
weather conditions to be of any practical value in controlling the pest.
PREVENTIVE MEASURES.
Rotation is one of the be-t generall preventive of injury from in-
sects affecting field crops. Experience has shown that where corn
has followed itself upon the s-ame field for two or more years there
has been a much greater lobs from the borer than where an annual
change of crop has been practiced. This is especially noticeable
[Cir. 116]




UNIVERSITY OF FLORIDA
!1111111 N1A1 IIliii NIN111111 IIIII!1
.. :: .....:.
3 1262 09228 3406 ...'.
where stalks or stubble from the previous year have been allowed to 31K
remain undisturbed throughout the winter. The moths, upon emer- I
gence in the spring, finding themselves surrounded by the young
corn. conummence egg laying at once and escape the dangers encountered
in searching for another field of corn. A forced journey in search of
young corn results in many of the females being eaten by birds or
being destroyed because of rain, cold, or failure to find the object of
their quest. A few moths will always succeed in their search, but the
successful proportion will be greatly decreased by persistent crop
rotation.
Another remedy, probably the best for this insect, is the thorough
destruction, some time before the period of emergence of the moths
in the spring, of all the stalks and stubble remaining in the field from
the preceding crop. If all this trash can be disposed of before the
opening of spring, the numbers of the pest must be greatly diminished
if not almost exterminated, for the only form in -which the insect
passes the winter is that of the caterpillar, and the only known loca-
tion is in the lower tip of the corn root, snugly hidden. Some few
may. however, be found to survive in the roots of the larger grasses
mentioned above, and care should be taken in such cases to treat these
in the same way. The method employed in disposing of the stubble
and stalks will depend largely on the conditions in individual cases.
If the stubble is cut low and the land is moderately heavy, a
thorough deep plowing may suffice, an inch or two of well-settled soil
being sufficient to prevent the escape of the adult moths. Bringing
the stubble to the surface where it can dry will kill some of the con-
tained larvw, but this method depends too much on the state of the
weather to be trusted. By far the most effective plan is to remove
the stubble from the field with a rake and burn it.
In the cane field the methods of treatment must be adjusted to
correspond with the methods of handling that crop. The larvae com-
monly spend the winter in the trimmings and tops which have been
discarded at harvest time because of immaturity. This refuse, left
on tlie ground throughout the winter, becomes dry and inflammable
a1d(l. if thoroughly burned before spring, enough larve will be killed
to insure at least temporary relief from the ravages of the borer.
Any method which will insure the complete destruction of the over-
wintering larvte, if persisted in and carried out simultaneously over
1:irt re sections of tihe country, will effectually preclulde serious damage
from the insect.
Approved:
JAM ES XVILSON,
Secretary of A Igriculture.
WASHINGTON, I). C., Deceminber 14, 1909.
[('lr. 116]