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Historic, archived document

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

LE BRAHY,

OF THE

U. S. Department of Agriculture

Classe | Peed seh da

— Book Pan ecraee

TE Se Wee a! ele ee

CIRCULAR No. 86. Issued May 6, 1907.

j, S, Depa ment of Agriculture:
"United States Department of Agriculture,

BUREAU OF. .ENTOMOLOGY,

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

THE CORN LEAF-APHIS AND CORN ROOT-APHIS.

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

The corn leaf-aphis (Aphis mazdis Fitch) and the corn root-aphis

(Aphis macdi-radicis Forbes) are together made the subjects of this
circular because both attack growing corn, because it has yet to be
clearly shown that there is no direct kindred connection between
them, though it is possible that they are distinct species, and because
this question of their identity or relationship presents itself to almost
every observing farmer.
_ The leaf-aphis does the farmer little direct injury. The root-aphis,
on the other hand, sucks the sap from the roots of his corn, thereby
causing the plants to become dwarfed, and in serious cases the leaves
turn brown and die. In an infested field the corn will be ‘‘ spotted,”
as farmers term it—that is, while the plants on certain areas in the
field may make a normal growth and may ear well later on, those
on other areas will make little growth, but tassel out after they have
become a foot or a foot and a half high, producing the almost worth-
less ears known as ‘‘nubbins” or none at all. Thus the damage to
the crop in some fields at times reaches 50 per cent or more, and the
annual loss throughout the corn belt must amount to well on toward
a milliondollars. This root-aphis is really becoming the most serious
of the many insect pests of the cornfield, especially where a strict
system of crop rotation is not carried out.

THE CORN LEAF-APHIS.

The corn leaf-aphis (figs. 1, 2) was described by Dr. Asa Fitch in
1856 from eastern New York, but it is now known to occur from New
England to North Dakota and Texas, as well as on the Pacific coast.
Besides, it was found by the writer in great abundance on sorghum
on the grounds of the Agricultural College of South Australia, at
Roseworthy, February 9, 1889. Professor Lowrie, at that time prin-
cipal of the college, seamed the writer that it sometimes became so
excessively abundant as to render the plants obnoxious as fodder for

30313—No. 86—07

2

stock. The insect is known also from Japan. In our own country,

while not usually a serious pest, it is said.to damage corn, sorghum,~ "

and barley in Texas, while Doctor Forbes has noted a reddish dis-
coloration due, he thinks, to a bacterial effect following its occurrence
on broom corn.

APPEARANCE AND HABITS.

The corn leaf-aphis is bluish green in color. Jt appears on corn
throughout the Middle West early in July—about the time that the
root-aphis begins to decrease in numbers on the roots—sometimes
literally swarming on the leaves, husks, and tassels. Here it gives
birth to its young, and disappears from the plants only as these ripen
and become dry, some individuals even remaining among the husks of
belated ears until freezing weather kills them outright.

Whence these insects come, in July, when the first few winged
females appear on the leaves of the corn, is a mystery, equaled only

Fie. 1.—The corn leaf-aphis (Aphis maidis): Winged female. Much enlarged (original).

by the problem as to the destination of the winged individuals that
leave the same plants in autumn. While on the plants they are
attended by the little brown ant, the same one that cares for the root-
aphis. Thus it will be seen that we have but a fragment of the life
cycle of this insect; for, if it is a distinct species, it must occur else-
where than on corn long before July, and it is equally clear that if
distinct it must migrate in the fall to some plant that will afford food
for the young the following spring, there to deposit its eggs. We
judge this to be the case, as it is known that with most species of
aphides there occurs in fall a generation of winged females that fly
to the spring food-plant, there to produce a generation of both males
and females, the latter laying eggs that do not hatch until spring.
From spring until fall there are no males and no eggs; all young

[Cir. 86]

5)

are born alive, after the manner of mammals, and all are fertile
females. It will therefore be very clear that with no knowledge of
the males and with only this fragment of the life cycle of the females
it is impossible to say whether the leaf-aphis is an above-ground form
of the root-aphis or whether it is distinct from and wholly inde-
pendent of that insect.

FIELD EXPERIMENTS.

In October, 1885, the writer transferred some volunteer plants of
corn from the field of fall wheat, where they were growing, to some
breeding cages. The plants were thickly populated with winged
females of the leaf-aphis, and these were carefully secured with the
plants, both being subjected to the same conditions which would have
influenced them had they remained in the field, except that the ants in
attendance were excluded. On May 8, 1886, corn was planted in these
cages and grew therein till after the 15th of June—when it was thrown
out—without a-single individual of either
root or aerial form of the root-aphis being
on or about the plants.

Dr. 5. A. Forbes, State entomologist of
Illinois, under whose direction most of the
investigations of these insects have been
carried out, in summing up the results of
a long series of carefully conducted experi-
ments of his own, comments as follows:

The foregoing data confirm our ignorance more
than they increase our knowledge, showing, as they ;
dee ail Fatt Fe gat Al Fig. 2.—The corn leaf-aphis (Aphis

® ALES. a ree a kek cated Veneta aS OE Deca e maidis): Winglessfemale. Much
bisexual generation or an alternative food plant of enlarged (original).

Aphis maidis, or to learn how and where it normally

passes the winter. Its willingness to feed on winter wheat and ability to breed
freely on that plant, its indisposition toward grass or the foliage of the apple, and
the natural frequency of successive generations, are the principal other facts evident
from these observations. @

Winged females of the root-aphis occur in summer on the leaves of
corn together with those of the leaf-aphis, but never in such immense
numbers. The two forms of winged females seem to be distinguish-
able, but the sexes have never yet been observed to interbreed—
indeed without males above ground they could nct do so; hence it is
yet too much to say whether there are two distinct species, with the
males of but one yet discovered, or whether these are two forms of a
single species, with as yet undiscovered relationships obscured by
long-continued influences of ants. As it is with the root-aphis that
the farmer has most to do, that species will be chiefly considered here.

a Twenty-third Report, State Entomologist of Hlinois, p. 133, 1906.
[Cir. 86]

4
THE CORN ROOT-APHIS.

Although the corn root-aphis (figs. 3, 4) was not definitely described
until 1891, its presence in the cornfields of Illinois was noticed by
Mr. B. D. Walsh in 1862, near Rock Island, and these two corn
auphides were made the subject of a paper contributed by him to
the Transactions of the Illinois State Agricultural Society.“ Mr.
Walsh, who was afterwards the first State entomologist of Illinois,
stated that his attention was called to the ** lice” on the roots of corn
in this field in the latter part of May, 1862, and about a fortnight later
he visited the field in person. He illustrates a section of corn root
‘Sas I saw it with my own eyes, swarming with these tiny pests.”
Further, he states that from wingless specimens, secured at the time
of his visit, he afterwards reared 15 winged females. From the
fact that the description of the leaf-aphis by Doctor Fitch ** agrees

le aN

Fig. 3.—The corn root-aphis (Aphis maidi-radicis): Winged female. Much eniarged (original).

tolerably well” with that of the species that he found attacking the
roots in June, he suspected that the two were identical. An illustra-
tion of the winged female reared from the roots does not, however,
tend to convince one of the correctness of his opinion, as it best repre-
sents the winged root-aphis and rather sustains the fact that the root-
aphides were present on the roots of corn at that time, in the vicinity
of Rock Island, and that from some of these he succeeded in rearing
winged adults in June. While this is not in the least surprising it is
nevertheless interesting as being a record of the original discovery of
the root-aphis and of the discovery and rearing of the winged female.
The statement made that the root-aphis was attended by little brown
ants is still further evidence of the validity of these observations,
however incorrect Walsh’s conclusions therefrom may have been. As
a matter of fact, up to about that time spring wheat culture had domi-

«Vol. 5, pp. 491-497, 1861-64.

| Cir. 86]

g 5 E

nated over the prairie country east of the Mississippi River and north
of the Ohio River, so that conditions were not favorable for the root-
aphis. But about that time conditions changed and corn culture
became dominant, necessitating the continued cultivation of large areas
to this latter grain for a greater or less number of consecutive years.
Thus this pest was brought into continually increasing prominence,
and Mr. Walsh’s observations were made about the time of what was
probably the beginning of its career of destructiveness.

DESCRIPTION.

For all practical purposes the root-aphis may be sufficiently charac-
terized as follows: The color is bluish-green, slightly whitened by a_
waxy bloom. The body is oval, and on the anterior part of the back
are two short, slender, rather conspicuous cornicles or tubes, either
standing erect or projecting slightiy backward
(fig. 4). The winged female (fig. 3) has a black
head and brownish-black thorax, the abdomen
being pale green, with about three marginal black
spots and numerous small dark specks over the
surface. The antenne are dark, with paler tinge
at articulations, and the legs are mostly black.
The only form of male known is wingless, like
the female found on the roots.

“
THE ROOT-APHIS AND THE LITTLE BROWN ANT.

Before proceeding further it is necessary to :
describe a most important and astonishing do- ae fe 5.
mestic condition involving the brown ant (Las7ws — Wingless female. Much
niger Li., var. americanus Emery) and the other- ‘78° ©"si2))-
wise helpless Aphis maidi-radicis. The presence of ants burrowing
about young corn plants in the field has frequently attracted the
attention of farmers, and damages to the crop are very frequently
attributed to them. The species under consideration is one of our
most abundant and widely distributed ants, occurring in colonies of
from fifty to several hundred in burrows in the fields. While it is of
itself harmless, it is in reality responsible for all of the ravages caused
by the root-aphis, whose life history and habits it appears to have
entirely revolutionized, as will now be explained.

LIFE HISTORY AND HABITS OF THE ROOT-APHIS.

_ The normal life history of aphides in general is as follows: The win-

ter 1s passed in the egg state upon or near the plant upon which the

young must first subsist in spring. From these eggs there hatch young
[Cir. 86]

; 6

aphides that are all females and these in a short time begin to give birth
to living young which are likewise all females. Thus the life cycle
goes on, and though there is usually a radical change of food plant,
there are neither eggs nor males until autumn, when there is a genera-
tion consisting of both males and females, the latter depositing eggs
that winter over. This egg-laying female and the male are the un-
known forms of the leaf-aphis.

Now, taking up the life history of the root-aphis, we find eggs in the
fall, it is true, but only in the burrows of and attended by these ants.
If there are eggs, egg-laying females, or males elsewhere they have
yet to be discovered. The ants care for these eggs. throughout the
winter, shifting them about, according to Forbes, as they do their own
young, to accommodate them to changes of weather and moisture. In
spring, the young, as soon as they hatch from these eggs, are trans-
ferred by the ants to the roots of young foxtail grass, smartweed, and
even ragweed. The young are carried out to pasture, as it were, dur-
ing fair weather, but in bad weather, or on cold nights, they are taken
back to the burrows of the ants. The plants just mentioned are the
ones that push up early in spring in last year’s corn lands, and espe-
cially in fields that have been plowed and allowed to stand untouched
for a week or so. Usually the farmer plows his ground in spring and
pays little attention to this early growth of weeds and grass, as he can
generally dispose of it as soon as he begins to cultivate the corn,
although this is not until the rows of young plants can be followed by
the eye across an ordinary field. As soon, however, as the corn plants
begin to show above ground the ants not only transfer the young
root-aphides from the burrows to the roots of corn, but they will also
remove them from the roots of grass and weeds and recolonize them
on the roots of young corn. Now these young aphides are all females
and within a few days they begin to give birth to young, also all females;
these, too, are cared for by the ants, which piace them on the freshest
and most tender rootlets. This procedure goes on about the roots of
corn throughout the spring and summer. Forbes has found that
under the most favorable artificial conditions there may be as many as
sixteen generations between April 8 and October 10, ten of which may
coexist atthe sametime. Itis hardiy probable, however, that so many
generations can exist under ordinary field conditions; nevertheless it
may be rightly inferred from this that the multiplication of the species
is enormous. These ants not only transfer the root-aphides from
one root to another of the same plant, but will carry them from one
plant to another a considerable distance away. In the spring of 1887
the writer placed a number of flowerpots containing young, growing,
uninfested corn plants between rows of infested hills of corn in the

[Cir. 86]

7

field. The corn in the infested hills was then pulled up, exposing the
roots on which the aphides were clustered. The little brown ants at
once began to carry the aphides to new quarters, and the next day the
latter, some of them full grown, were abundant on the roots of the
corn in the pots, although there were none on them when the pots were
putin place. Ants were observed over a yard away from the plants that
had been uprooted, with root-aphides in their mouths, to all appearances
searching for a suitable place in which to establish their charges on
the roots of corn. Thus it is that from the laying of the eggs in fall
to the last or egg-laying generation of the following year this aphis is
wholly dependent on the little brown ant for its existence in the culti-
vated fields, and the farmer can justly charge up his losses through the
attacks of the root-aphis to the influences of thisant. But the matter
does not terminate here, as will be seen by what follows.

WINGED FEMALES OF THE ROOT-APHIS.

So long as the roots upon which the root-aphides are colonized afford
an abundance of nourishment for them, all will be wingless, but as
soon as the roots become tough and woody or dry out there will be a
generation of both winged and wingless individuals, the former escaping
from the burrows about the roots to fly to other plants, and in all
probability to other fields, where they may be found on the leaves.
The ants usually transfer the wingless individuals to more succulent
roots, but seem to pay little or no attention to the winged individuals,
letting these make their way out and away. But in May, 1887, the
writer was able to watch some of these winged nomadic individuals in
a cornfield to which they had migrated and to note the results of their
wanderings. A field of corn had been planted on May 18. Five days
later there came a heavy rainstorm that flattened the surface of the
ground, which was soon incrusted by the action of wind and sun.
Four days afterwards there were freshly-thrown-up mounds of earth
_ about some of the corn plants, and ants were busily engaged in and about
these and running up and down over the young corn. On examining
these mounds and burrows the writer was surprised to find winged
root-aphides giving birth to young on the roots, attended by ants.
All of these young were very small, at most but a few daysold. Other
winged individuals were found on the leaves and even on the stems of
corn, and when any one of these was placed where the ants could find
it, it was promptly captured by an ant and transported to the roots of
the corn. Observation showed that as soon as the ants running about
over the young corn plants found a winged aphis they made a burrow
about the base of a plant, and soon domiciled the wanderer on the root
under their guardianship. Then when the aphis began to give birth
to young these were promptly removed to another part of the same

[Cir. 86]

8

root or to another root close by, and there watched over by the patient
and industrious ants. The same thing was observed going on about
a young plant of fox-tail grass in this same cornfield.

INFLUENCES LIKELY TO PRODUCE FEMALES.

While the production of winged individuals seems to be brought
about largely by insufficient food supply, Forbes is of the opinion that
the production of egg-laying females is fully as much—if not indeed
much more—influenced by the temperature, a low temperature caus-
ing them to be produced at any time, regardless of generation; and he
himself has secured them from as many as five different generations.
In two cases recorded by him the first young produced developed to
adults that gave birth to their young, whereas the last developed to
adults that laideges. These cases, although seeming rather out of the
ordinary, illustrate the fact that the insect may adapt itself to widely
different autumn conditions; that is to say, an early frost, which pre-
supposes a low temperature, kills the corn but does not annihilate the
insect, for an egg-laying generation is thus precipitated and the ants
promptly secure the eggs. ‘This egg-laying generation is probably
produced in September or October, as these females are found in the
burrows of ants at that time. Possibly it is produced earlier to the
South. Mr. C. N. Ainslie, of this Bureau, one of the writer's assist-
ants, found the egg-laying females quite numerous in such situations
on September 22, at Annapolis Junction, Md. The chief item of
interest to the farmer is the fact that these eges are taken charge of
by the ants and kept through the winter.

THE ANT’S CARE FOR EGGS AND YOUNG OF THE ROOT-APHIS.

There is no indication that the ants hunt the fields for egg-laying”
females; on the contrary, they secure their supply of eggs from females
kept for precisely that purpose in their burrows about the roots of
corn. This affords ample explanation of the increasing abundance of
root-aphides in fields that are cultivated to corn year after year in
succession, and it also points to a preventive measure. The object of
all of this care on the part of the ants is to obtain from the root-aphis
a sweet fluid known as ‘‘honey dew.” Owing to: this peculiar rela-
tion, this and some other aphides are commonly termed ‘‘ ants’ cows.”
Thus the economic importance of this insect and its association with
ants is for practical purposes fully accounted for and an explanation
furnished as to why farmers are misled into believing that it is the
ants that actually destroy the corn. Not only this, but a condition of
affairs is revealed which shows why this young growth of grass and
weeds that springs up soon after the ground is plowed in spring, pre-

[Cir. 86]

g)

paratory to putting out the young crop, and which usually causes the
farmer little concern, is really of vital importance. The farmer rests
secure in the knowledge that he can easily kill this growth of weeds
and grass later. This is true; but he does not do so until his corn has
grown to a size that will permit cultivation, and by this time the ants
have transferred the root-aphis to the corn. The aphides are then no
longer dependent on the roots of the grass and weeds, so that the
destruction of the latter at this time does not seriously affect the
domestic arrangements of the ants and aphides.

NATURAL ENEMIES OF THE ROOT-APHIS.

While the leaf-aphis is attacked by a host of parasites, the root-
aphis does not appear to suffer in the least from inroads of either para-
sitic or predaceous insect enemies. This is, perhaps, owing in part to
the protection offered by the ants. All natural checks must therefore
be meteorological influences, and, as previously shown, these also are
to a marked degree overcome by the watchful care of attendant ants.

PREVENTIVE AND REMEDIAL MEASURES. ,

Preventive measures deal with the pest prior to its becoming estab-
lished on the roots of corn in the fields; remedial measures, with dis-
posing of it afterwards.

CROP ROTATION.

From the fact that in the midst of the corn belt, and where the
root-aphis is known to prove destructive under certain conditions,
almost complete immunity is secured where a system of crop rotation
has been carried out for many years, involving but one corn crop in
the cycle of rotation, it is self-evident that this measure offers the
greatest protection from the ravages of this pest. Indeed, it is only
-where such a system of crop rotation is not practicable that the root-
aphis need be considered in farm practice. To the eastward, where
there is more general rotation of crops, this pest does but little injury.

Unfortunately, local conditions, often extending over large sections
of country, will not permit of crop rotation being generally adopted,
and some other plan more feasible must be put into practice. Two
other methods may be followed. One of these is practicable through-
out the corn-growing section of the country in seasons of not more
‘than normal precipitation during the time intervening between the
first plowing of the ground and the first cultivation of the young corn.
The other is perhaps best adapted to the southern portion of the coun-
try on account of the milder winters.

[Cir. 86]

10

STIRRING THE SOIL AFTER PLOWING AND BEFORE CULTIVATING THE CROP.

The action of the ants in colonizing the young root-aphides on the
roots of young grass and weeds that spring up in the fields almost
immediately after plowing in spring has already been explained.
Indeed, this is the only pasturage for young root-aphides that is avail-
able at that particular period, and if this can be destroyed the pest
can not survive until corn roots are available. If, then, the ground is
frequently stirred from the time it is plowed until the first cultivation
takes place, not only will this pasturage for the pest be destroyed, but
the homes of the ants will be continually broken up and a greater or
less number of their own young, as well as the young root-aphides,
will be killed, while many unhatched eggs of the pest will be destroyed
or lost to the ants. This measure involves additional] labor, it is true,
but in the writer’s experience it has proved effective, and, besides,
every up-to-date farmer knows that the more the soil is stirred, pul-
verized, and compacted prior to the first cultivation, the more thriftily
will his crop grow when it is fairly started and the more grain will it
produce. So, then, the extra labor involved in this practice is not with-
out ample return, aside from the fact that it demoralizes the ants and
destroys the root-aphis. The only sections of the country where this
is not strictly true are some portions of the South, where the planter
must endeavor to curtail the growth of stalk in order to secure larger
and more perfect ears. But here, again, corn is not the major crop,
it is not grown for several consecutive years on the same ground, and
the root-aphis is not so excessively abundant. .

LATE FALL OR WINTER PLOWING.

It is in the southern section of the country that the second prevent-
ive measure, i. e.. late fall or winter plowing, can be best applied.
In the corn belt of the more northern section of the Middle West, not
only is winter plowing, as a rule, utterly impracticable on account of
the more seyere weather, but the fodder, instead of being secured as
in the East and South, is pastured off after the corn has been husked.
To practice late fall plowing, or indeed to fall-plow at all, would mean,
therefore, in this northern section, the sacrifice of this important item
in farm economy. As far north at least as the latitude of Washing-
ton, however, winter plowing is frequently entirely practicable, and
there is little doubt that it will prove entirely effective against the
root-aphis.

During the winter of 1906 Mr. John Bowie, of Annapolis Junction,
Md., winter-plowed the major portion of a 60-acre field in preparation
for corn the following season. The plowed portions occupied each of
two sides of the field and a narrow headland at one end; thus the un-
plowed area was left in the middle of the field and this was plowed in

Cir. 86]

ta
Li

11

the spring. On July 28 the writer went over this field of corn care-
fully and found that over the spring-plowed portion nearly every hill
of corn was infested by the root-aphis. The crop was an almost com-
plete failure. Much of the corn had been killed out previous to the
time of the writer’s visit and the remaining part was dwarfed in growth,
bore few ears, and such as it had were very small and almost worthless.
All over the winter-plowed portion, however, there was every pros-
pect of a heavy yield of both stalk and ears, even to the narrow head-
land previously mentioned. An assistant, Mr. Ainslie, visited the field
in late September and was able, without information from any person,
to locate, to a row, the dividing line between the two plowings. This
was clearly visible on account of the difference in appearance in the
stubble—the corn having by this time been cut and shocked—and also
on account of the number, size, and appearance of the shocks. There
was a difference of fully two-thirds in favor of the winter-plowed por-
tions of this field. As the yield of the winter-plowed portion was ap-
proximately 75 bushels per acre, the spring-plowed would not exceed
25, showing a probable loss of about 50 bushels per acre. Atthe
market price, 75 cents per bushel, the loss would amount to $37.50
per acre, to which must be added the loss in fodder. These figures
show quite conclusively the amount of damage this root-aphis 1s capable
of doing, as well as what can be accomplished in the way of prevention
by thoroughly practical methods.

THE USE OF BARNYARD MANURE.

It seems to bea fact, borne out by field observations, that where
ground has been fertilized with barnyard manure the root-aphis does
not become so destructive. As far back as 1886, on the experiment
farm of Purdue University, at Lafayette, Ind., the writer made some
observations which led to the conclusion that proper fertilizers applied
to the soilare a general preventive of damage. This was clearly proved
by the appearance of the crop on a series of eighteen plats on the uni-
versity farm. These plats were located side by side and numbered 1
to 18. All had produced corn for the previous six crops, those plats
of even numbers not having been fertilized during that time. Plats
1, 7, and 13 had, three and again two years previous, received appli-
cations of gas-lime; plats 3, 9, and 15 had received applications of
superphosphates during the same years, while plats 5, 11, and 17 had
received similar treatment with barnyard manure. The result, up to
July, 1886, was that the corn on all plats except those fertilized by
barnyard manure was small and uneven in growth, while on plats 5,
11, and 17 the plants were fully a third larger, more thrifty, and far less
uneven in height. In fact, these plats could be distinguished from
any of the others at a distance from the field. It was unfortunate

[Cir. 86] :

12

that the carrying on of the experiments forbade any examinations of
the roots in order to estimate the relative number of aphides inhabit-
ing each series of plats.

EXPERIMENTS IN DRIVING THE ANTS FROM THE ROOTS OF CORN IN THE FIELD.

During June, 1886, a number of experiments were made to test the
immediate effect of fertilizers, including salt, upon the aphides, and
also to learn if the antscould be induced thereby to abandon or remove
their favorites to other plants.

The substances used were two commercial fertilizers (Bunner bone
dust and bone guano), barnyard manure, and common salt. A double
experiment was made with each. The first two substances were applied
(1) by scattering a tablespoonful on the surface of the ground about
the plant and sprinkling with water sufficient to wash it at once into
the soil, and (2) by drawing the earth away from the roots, scattering
the same amount of fertilizer about the roots, then replacing the earth,
and sprinkling the surface less thoroughly than with the first. The
barnyard manure was well-rotted and a quantity sufficient to fill a pint
measure was used in the same way. The salt was used in the same
way as the manufactured fertilizers.

The result, a week after, was that the ‘‘lice” were still about the
roots in every case, and, except where salt was used, they were found
in the midst of the substances applied. The salt only drove them from
one portion of the roots to another. Sand dampened with kerosene
was then applied in the same way, but the surface application had no
effect, and that made directly to the roots only drove the aphides from
one part of the roots to another, as did the salt.

TREATING THE SEED BEFORE PLANTING.

During the last two years Doctor Forbes, in Illinois, has been test-
ing a great number of substances with a view to treating the seed
with some repellent that would render it so obnoxious to the ants that
they would not place the aphides on the roots of the young plants.
It has indeed seemed possible to take advantage of the well-known
fastidiousness of these ants and find something that, applied to the
seed, would not injure its vitality, but would give off an odor so dis-
agreeable to the ants that they would shun the vicinity of its applica-
tion. The writer tried something of this sort in 1887—except that in
his experiments substances supposed to be offensive to the ants were
placed in the soil about the roots of the corn—but the results were
not satisfactory. In treating the seed, however, Doctor Forbes seems
to have had very encouraging success and he has permitted the writer
to use here the results of his experiments, which are quoted in brief
as follows:

[Cir. 86]

13

The substance found most effective for the treatment of seed corn was a mixture
of oil of lemon and wood alcohol. To 1 gallon of wood alcohol add 1 pint of oil of
lemon, and sprinkle and thoroughly stir 3 fluid ounces—that is to say, 6 tablespoon-
fuls—of this mixture into each gallon of corn shortly before planting, making sure
that the fluid is equally distributed and that each kernel of corn has its proper
share. A thorough stirring after the application of the mixture is all that is neces-
sary. The odor of this compound, which will last for weeks,in the ground, is
extremely offensive to the cornfield ant, and these insects will not enter corn hills as
long as it continues. As the root lice can not get access to the corn or maintain
themselves there except by the aid of the ants, the hills remain virtually free from
both insects for at least six weeks.

The wood alcohol should not cost more than $1 a gallon nor the oil of lemon more
than $2 a pint, and the above amount of the mixture will be sufficient to treat the
seed for 45 acres, making a cost for materials of less than 10 cents per acre. Care
should be taken to buy these substances from thoroughly reliable druggists, the oil
of lemon especially being subject to adulteration. If the mixture is not entirely
clear when shaken up the materials are impure.

Doctor Forbes has in some cases succeeded by this means in reducing
the number of root aphides 89 per cent and the number of ants 79 per
cent, which is certainly a very creditable showing for this mixture.
The mixture of wood alcohol and oil of lemon is so easily made and the
application so inexpensive and simple that it is to be hoped that farmers
who have suffered from the ravages of this pest will give the prepara-
tion a thorough trial in their fields. While local conditions may pre-
vent the putting into practice of any or all of the other measures of
relief here advised, it is difficult to conceive of a situation that would
prevent a farmer from treating his seed corn before planting, as
recommended.

Approved:

JAMES WILSON,
Secretary of Agriculture.

WasHineton, D. C., April 5, 1907.

[Cir. 86]

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