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SB
818

c576 0. 93, REVISED. Issued June 23, 1909.

si lited States Department of Agriculture,

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

THE SPRING GRAIN-APHIS OR SO-CALLED “GREEN BUG.”
(Toxoptera graminum Rond.)

By Fr M. WEBSTER,

In Charge of Cereal and Forage-Plant Insect Investigations.
The early history in America of the spring grain-aphis (figs. 14),
which has come to be generally known as the “ green bug,” was pub-
lished in Circular No. 85 of this Bureau, and need not be reproduced

Fic. 1.—Spring grain-aphis (Toxoptera graminum): Male. Greatly enlarged. (Original.)

here. Suffice it to say that it is an imported species, long known to be
destructive to growing grain in Europe, but not known in this country
prior to 1882, and not as a destructive insect until 1890. The litera-
ture relating to this, the third and perhaps most destructive outbreak
of the pest, is so misleading that this publication seems necessary in
order to prevent misapprehension among farmers, and to afford them
all possible helpful information in advance of future similar out-

breaks.

DISTRIBUTION IN THE UNITED STATES.

The insect is usually common, and is found from New Mexico,
Colorado, and Montana to the Atlantic coast, approximately cover-
ing the area south of latitude 41°, excepting New York, New Jersey,
and New England, and east of longitude 105°. Within this territory
its area of destructive abundance, as well as the severity of its at-
tack during any year, will be regulated by two factors: First, the

848438—Cir. 93—09—_1
vY

ZOO8TA

2

presence of young growing wheat, oats, barley, or rye; and, second,
weather conditions favoring its rapid increase and unfavorable for
the development of its natural enemies. It will breed freely in the
fields from an altitude of less than 20 feet above sea level on the At-

Fic. 2.—The spring grain-aphis or “green bug” (Towoptera graminum): a, Wingless
female; b, larva; c, pupa. Much enlarged. (From Pergande.)

lantic coast to an elevation of nearly 8,000 feet in New Mexico, and
from eastern Washington, southern Montana, northwestern Minne-

sota, southern Wisconsin, northern Ohio, and southern Pennsylvania
southward to extreme southern South Carolina, southern Texas, and

”

Fic, 5.—The spring grain-aphis or “ green bug” (Towvoptera graminum) : a, Winged mi-
grant; b, antenna of same. a, Much enlarged; b, highly magnified. (From Pergande.)

New Mexico. Yet, with normal weather conditions during the first
four or five months of the year, these facts signify absolutely nothing,
for this insect will not be abundant enough to attract any attention
by its injuries.

(Cir, 93]

3
THE RELATION OF TEMPERATURE TO DESTRUCTIVE OUTBREAKS.

This insect, as with other closely allied species of aphides, repro-
duces in two ways. As cool weather approaches in autumn there
occur in greater or less numbers both males and females, the latter
depositing eggs (see fig. 4), and it is in the egg state only that, under
normal weather conditions as to temperature, the “ green bug ” passes
the winter, and from these eggs it originates in the spring. But from
spring to fall there are neither eggs nor males; all are females, and
these give birth to living young in a series of generations. With the
normal cold of early winter these females gradually disappear and
the winter eggs remain; but if the winter temperature is mild, and
the temperature of the following spring abnormally cold, the summer
method of reproduction continues throughout the winter and during
spring. Indeed, it is not improbable that males and egg-laying fe-
males may be found in spring, especially in the South.

The “ green bug ” will breed freely in
temperatures ranging from above 100°
to below 46° F. As the young mature
in eight days and themselves begin to
give birth to young, it will be seen that
an exceptionally mild winter followed
by an abnormally cold spring offers
the best possible conditions for the

excessive increase of the pest, which :
would ordinarily begin breeding only W
in spring, and from the eggs. Fic. 4.—Spring grain-aphis (Tor
rT: TRNCI ST ACLS E : optera graminum): Egg-laying
With excessive reproduction and the feiale withtaeeGatt boawiercate

destruction or aging of its food plants, enlarged ; at right, egg, still more
this insect develops a corresponding a er me eu ste
abundance of winged migrating females, which are the means of the
spread northward or outward from original centers.

The “ green bug” in normal years—that is, when its breeding be-
gins in spring—is effectively held in check by its natural enemies, and
notably by a minute, black, wasplike insect, Lysiphlebus tritici
Ashm. (see fig. 5) that deposits eggs singly in the “ green bugs,” the
grubs hatching from the eggs feeding internally on the bug and de-
stroying it (see fig. 6). Other natural enemies are the larvee of cer-
tain predaceous flies, and the larvee and adults of lady-beetles. The
little wasplike parasite first mentioned, however, is the one that keeps
the “ green bug” in control in normal years, and in years when the
latter is most abundant finally overcomes it, as was the case in 1907
in Kansas, North Carolina, and other States in the more northern
part of the range of the pest.

[Cir. 93]

+

as with the other beneficial

Unfortunately this parasitic wasp

insects—is active only while the temperature is above 56° F., or at

be

least 10° above that at which the * green bug” breeds freely; and

Fic. 5.—Lysiphlebus tritici, principal parasite of the spring grain-aphis: Adult female
and antenna of male, greatly enlarged. Egg of Lysiphlebus tritici at right, highly mag-
nified. (Original.)

herein is the whole secret of the irregular disastrous outbreaks of the
“ oreen bug” in grain fields. As accounting for the outbreak in the
year 1907, the “green bug” had had a
whole winter and the following late spring
in which to breed and multiply unmolested,
and it accomplished its principal damage,
as in Texas and southern Oklahoma, before
the weather was warm enough for the para-
site to increase sufficiently to overcome it.
As further illustrative of the important
bearing of weather conditions, it is found
that in the case of the three important
outbreaks of this insect, namely, for the
Ligeti ok bc eeies Sa COS 1890, 1901, and 1907, the temperature
"gree bug” containing fOr the first five months of each \oiaiiese
larva of the parasite Ly years, including the latter part of winter
siphlebus tritici. Much en- : ‘ : i
igeed.’. (Onteinal) and spring, was above the normal for the
winter months and below the normal for the
spring months; in other words, warm winters and cold, late springs.
The little parasitic wasp which is so useful in the control of this
pest is native to this country, widely distributed, and every year does
its work with the “ green bug ” and with other aphides. It is always
[Cir. 93]

5

present in grain fields, as shown by its appearance every year, to war

on these pests whenever the weather conditions make its breeding

and multiplication possible, and its rate of breeding is so rapid (there

being a generation about every ten days) that with a week or two of

favorable weather it gains control over its host insects and destroys

them.
FOOD PLANTS.

The spring grain-aphis is essentially a leaf-infesting insect, rarely
being found on the stem. While preferring oats, it will readily attack
wheat, rye, and barley, and may often be found on the underside of
the lower leaves of corn. Corn excepted, its effect on the leaves of
grain, when present in large numbers, is to cause the infested leaves
to change to a red color, which seems to be very characteristic of
Toxoptera and does not follow attacks of other species of aphides
on these grains. The insect has also been found breeding upon a
considerable number of grasses, any one of which may constitute its
alternating food plant upon which it may survive the summer in
different portions of the United States. It has been found breeding
freely upon marsh foxtail (dAlopecurus geniculatus) in Oklahoma
by Mr. W. J. Phillips, and by Mr. C. N. Ainslie in Kansas; on
Agropyron occidentalis, also in Oklahoma, by Mr. Phillips, and by
Mr. E. O. G. Kelly and Prof. C. P. Gillette in Colorado. Slender
wheat-grass (Agropyron tenerum) was found moderately infested
by Mr. Ainslie at Las Vegas, N. Mex. The species was found breed-
ing upon Bromus at Washington, D. C., and also upon Porter’s chess
(Bromus portert) at Las Vegas, N. Mex., and on an undetermined
species of Bromus at Mesilla Park, N. Mex., all by Mr. Ainslie.
The writer observed it very abundantly on orchard grass (Dactylis
glomerata) in Indiana in 1890, and again excessively abundant in a
small isolated meadow of this grass near Midlothian, Va., in April,
1907. This meadow was located in a region not adapted to the grow-
ing of grain, and there was no field of growing wheat or oats within
5 miles. Mr. Kelly found it in Montana, inhabiting marsh spike-
grass (Distichlis spicata) in such abundance as to be damaging this
grass, which in that part of the country is known commonly as
“salt grass.” It was found inhabiting slender wild rye (Llymus
striatus) at Las Vegas, N. Mex., by Mr. Ainshe. Mr. Phillips found
it attacking little barley (Hordeum pusillum) at Beloit, Kans., and
Kingfisher, Okla., while the writer found this to be of frequent
occurrence throughout Kansas. Mr. Kelly observed it abundant
on squirrel-tail grass (Hordeum jubatum) in Montana, while Mr.
Ainslie found it moderately abundant on /Zordeum cespitosum near
Cimarron, N. Mex. Wherever Kentucky blue-grass (Poa pratensis)
grows, the insect will probably be found breeding upon it through-

[Cir. 93]

6

out the entire summer. In fact, this has been actually cbserved to
occur in the city of Washington. Mr. Phillips has observed the
same thing in Indiana, and throughout the northern sections of the
country where the Toxoptera occurs it is more likely to be found on
this plant during summer than upon grain, excepting, perhaps,
during seasons of excessive abundance. Mr. Ainshe also found
it moderately abundant on beard-grass (Polypogon monspeliensis)
about Albuquerque, N. Mex. It has been found breeding on yellow
foxtail or pigeon-grass (lvophorus glaucus) by Mr. Phillips at
Richmond, Ind., and on green stipa (Stipa viridula) at Las Vegas,
N. Mex., by Mr. Ainslie. In the latter case the grass was heavily
infested. As one or more of these grasses will be found to occur
in almost every portion of the United States, it would appear that
the nonoccurrence of Toxoptera in any considerable section of coun-
try can not be due to a lack of uncultivated food plants. Of food
plants other than grasses we have only the one observation made
by Mr. Phillips at Kingfisher, Okla., April 23, 1907, where a species
of ragweed growing up in a badly damaged wheat field was quite
heavily infested with Toxoptera, at the time breeding freely on this
plant.

The outbreak on the grounds of the Department of Agriculture
was notable in some respects, in that the continued close cutting of
the blue grass supplied a continual fresh, tender growth as food for
the “green bug,” thus preventing the development and escape of
winged females; and especially is it notable in view of the total lack
of Lysiphlebus tritici, the most important of the natural enemies of
this aphis. The only natural enemy found in this case feeding upon
the “ green bug” was the diminutive black and yellow lady-beetle
(Hyperaspis undulata Say), not previously known in connection with
this pest.

When this outbreak became known to Mr. E. M. Byrnes, superin-
tendent of Experimental Gardens and Grounds, he at once had the
entire infested block sprayed with a solution of one-half gill of rose-
leaf nicotine to each gallon of weak soapsuds. The application was,
however, ineffective. Four days later a strip through this plat was
thoroughly saturated with a strong solution of barnyard manure,
made by soaking the manure in water. While there was no evidence
that this killed any of the “ green bugs,” after nine days the pest was
notably less on this area than where the application of manure
solution was not made.

A series of experiments was then undertaken under the writer’s
direction by Mr. E. O. G. Kelly, as follows:

Tobacco dust was applied at rates of one-fourth, one-half, and 1
pound to each 100 square feet, but after over a week had elapsed

[Cir. 93]

7

from the date of application no effect was to be observed and no
dead insects were found.

Kerosene emulsion was applied at 8 and 10 per cent strengths.
There was practically no difference in the effect of these two strengths,
and at the end of nine days no “ green bugs” were to be found on the
areas so treated. Also there was no perceivable injury to the grass.

Whale-oil soap solutions, varying in strength from one-fourth of a
pound to 2 pounds of soap to each 5 gallons of water, were applied to
similar areas. In this case the stronger solution injured the grass
shehtly, but not permanently; in the case of the lesser strengths there
was no injury whatever. The effect on the “ green bug” was the
same in every case. They were not only literally exterminated over
the areas treated, but the applications seemed to protect from a rein-
festation. In case of even the weakest solution an examination, five
days after the application was made, revealed the “ green bugs” in
myriads and breeding freely on the untreated space, while but 8
inches away and on the treated area living bugs were scarcely to be
found, though the dead were to be observed almost as abundantly as
were the living on the space untreated. It must be remembered,
however, that these experiments were carried out in grass kept closely
cropped by frequent use of the lawn mower, and the results obtained
in no way reflect upon similar experiments carried out by Messrs.
Ainslie and Phillips in the grain fields of Oklahoma.

INVASION OF 1907.

A better appreciation of the interrelation of the “ green bug” and
its principal parasitic enemy can be conveyed by giving a chrono-
Jogical statement of our investigations of the very disastrous inva-
sion of the “ green bug” during the winter and spring of 1907.

The first rumors of injuries by this pest came to us early in Janu-
ary from east-central Texas, where the “ green bugs” were reported
to Mr. W. D. Hunter, in charge of cotton boll weevil investigations
of this Bureau, as attacking fall oats. During this month in Texas,
east of a line drawn from near Gainesville through Abilene and
San Antonio to Galveston, the temperature was 9° above the normal.
Within this area was a smaller one, the boundaries of which may be
indicated by a line drawn from Texarkana to Fort Worth, Waco,
and Joaquin. Over this latter area the temperature for the same
month was 12° above the normal, and within this area the pest began
its work of destruction.

Also, judging from data received later, the pest began to breed
rapidly in fall-sown oats in southern South Carolina, where the tem-
perature was from 6° to 9° above the normal.

[Cir. 93]

8

During February all over the region west of the Mississippi River
and the Great Lakes the temperature was above the normal, and
in the Carolinas it was only slightly below. During this month
much damage seems to have been done in Texas, and there is every
probability that the pest was breeding freely in the Carolinas, though
it had not yet been reported from the latter States. ;

Up to this time the outbreak in Texas was being investigated by
Mr. E. C. Sanborn, an agent of this Bureau detailed to the Texas
Agricultural Experiment Station. The first report of the insect
outside of Texas was under date of March 6, from Mr. C. H. Drake,
of Summers, Ark., who reported that “a small green bug” had
destroyed the wheat in spots in the fields in his locality. This letter,
received March 11, led to the prompt dispatching of Mr. C. N.
Ainshe for the West, with full instructions to investigate the out-
break thoroughly, to experiment with measures for destroying the
insects in the fields, especially over the spots where they seemed to
be most abundant, and to. determine what could be accomplished in
checking the ravages of the pest by the early introduction of natural
enemies into the infested fields. Arrangements were perfected with
Mr. W. D. Hunter to ship to Arkansas living parasites (Lysiphlebus
tritici), which were then abundant in Texas, and the same train by
which Mr. Ainslie reached Summers brought several boxes of the
parasites. These parasites were promptly placed in the infested
fields and liberated March 18. But Mr. Ainslie found that both the
lady-beetles and the little wasplike parasites (Lysiphlebus tritict)
were already present at Summers and near-by points in greater num-
bers than could possibly have been introduced. The latter were
simply everywhere, running about over the young grain plants and
placing their eggs in the bodies of the “ green bugs.”

Clearly the importation of parasites would be useless under these
conditions, and Mr. Ainshe, hoping to find a more favorable field for
the introduction of parasites or direct experimental work with rem-
edies, proceeded, on March 23, for various points in Oklahoma.

At Chandler and Guthrie, March 23 to 25, the pest was very
abundant, but the conditions at these points were again even less
favorable than in Arkansas for the introduction of parasites. For
example, on one blade containing about 150 of the “green bugs ” Mr.
Ainslie counted 25 that were parasitized. He then proceeded to
Kingfisher (March 26) and here found the parasites apparently less
plentiful than at the other points visited, which were to the eastward.

Arrangements had been made with Mr. Hunter to furnish parasites
from Texas fields when these were called for, and in response to a
telegraphic request he dispatched a quantity of material collected by
his assistants in Texas and in southern Oklahoma. When this was

[Cir, 93]

9

received and the parasites liberated in the infested fields, native para-
sites were already issuing in great numbers. In other words, the
parasite was already beginning unaided its active work of control.
By March 27 the “ green bugs” developed winged adults in great
numbers, and these seemed to drift northward.

Mr. Ainslie was instructed to look for a region to the northward
where the “ green bug” was just starting, and he made his first stop,
March 30, at Wellington, Sumner County, Kans., and found the con-
ditions there such as to offer a favorable field for experimentation
with parasites.

By April 1 the fields about Wellington were generally, though
sparsely, infested with the “ green bug,” represented in many cases
by winged females that had seemingly migrated to these fields and
were giving birth to their young. Lady-beetles were common, but
none of the Lysiphlebus was observed. After a couple of days spent
in the vicinity of Wellington, Mr. Ainslie returned to Kingfisher to
secure parasites for introduction into southern Kansas, but in the
meantime severe weather, accompanied by heavy frosts, had pre-
vailed, and the parasites formerly abundant at Kingfisher had become
exceedingly scarce. By the 5th, however, he began again to find
very many parasitized “ green bugs,” and by the 7th the parasites
themselves began to appear again. A bushel of wheat plants, now
nearly covered with parasitized “ green bugs,” was collected at King-
fisher and taken to Wellington April 9. At this time fully 12 per
cent of the “green bugs” at Wellington were already parasitized,
while on the 12th Mr. Ainslie counted as many as 11 parasitized in-
dividuals on a single blade of wheat.

About the middle of March an appeal came to this Bureau from
the Texas Grain Dealers’ Association, through their secretary, Mr.
H. B. Dorsey, at Fort Worth, to investigate the “ green bug.” In
response to this appeal Mr. W. J. Phillips, of the Bureau staff, was
dispatched to Fort Worth, arriving on the 27th. Several days spent
in examining fields in the vicinity of Fort Worth demonstrated that
the “ green bug” had totally destroyed the grain in that vicinity and
disappeared, and there was no opportunity for experimental work.
He then went, by instruction, to Hobart, Okla., and later relieved
Mr. Ainslie at Kingfisher, and, in response to a telegram from Mr.
Ainslie, sent an amount of parasitized wheat from Kingfisher to
Wellington equal to or larger than the first shipment.

All of the material which Mr. Ainslie took with him from Okla-
homa and that supplied him by Mr. Phillips was placed in a single
wheat field near Wellington. It is safely estimated, from counts of
average wheat blades, that upward of two and one-half millions of
parasites were thus liberated in a single wheat field on April 9, and

84848—Cir. 95—09 2

10

by this time many were already there. This introduction of para-
sites was carried out in order to give a decisive test as to whether it
was possible to aid in protecting fields in this manner along the ad-
vance line of invasion. The weather was still cold, and if the artifi-
cial introduction of parasites would, with the return of warmer
weather, hasten the control of the “ green bug,” the introduction of
such large numbers would clearly demonstrate this fact. And if
such introduction on a large scale proved favorable, it would show
reasonable ground for the more general introduction of parasites in
lesser numbers.

There was a minor introduction of Lysiphlebus started at McPher-
son, Kans., April 18, though this parasite was already found in the
fields in that vicinity at that time.

The weather during the whole of April was generally cold with, as
on May 4, an occasional storm that is known to have killed many of
the parasites, and though there were brief periods of warm weather
during which the parasites would increase rapidly, the Lysiphlebus
did not finally overcome the “ green bug” in southern Kansas until
about the middle of May. .

As will be observed, this experiment was made under weather con-
ditions almost uniformly unfavorable to the parasite and favorable
to the development of the “green bug.” There is no reason for
supposing that the weather would affect the introduced parasites
differently from those already present when the introduction was
made.

Mr. Ainslie remained in the vicinity of Wellington, and more
briefly at McPherson and Sterling, for the purpose of watching
these experiments, and he was, moreover, in direct communication
with Mr. Phillips in northern Oklahoma; and the two were therefore
able to keep under their observation a wide range of country, thus
eliminating the possibility of oversight or misconception on the part
of either that might otherwise have occurred.

It was during this period of generally cold weather in late April
and early May, interspersed by shorter periods of weather favor-
able to the parasites, that the latter increased generally throughout
Kansas and, judging from reports, also in Missouri and Colorado.
It wanted only the more extended warm spell that came soon after
to enable them to get the upper hand and subdue the pest, as they
did throughout the southern Atlantic coast section earlier in the
season.

The field in which the two and a half million Lysiphlebus were
introduced and liberated on April 9 did not, at the time of the over-
coming of the pest in this and the adjacent country in May, indicate
any benefit whatever above other fields, near or remote, where no |

[Cir, 93]

11

artificial introductions had been made. The result of the minor
experiment at McPherson was, as reported by Mr. Knaus, no more
favorable.

During the last two weeks of April a great many small lots of
parasites were distributed over the southern and central counties of
Kansas by Mr. S. J. Hunter, of the Kansas State University. The
artificial sending out of these parasites by Mr. Hunter and the test
of distributing an enormous quantity in a single field, described
above, were legitimate experiments, but the evidence showed very
conclusively that they resulted in no benefit whatever. In other
words, as noted above, the parasites were already infesting 12 per
cent of the “ green bugs” at Wellington, Kans., April 9, when the
artificial introduction was made, and 50 to 75 per cent at King-
fisher, Okla., at the same date, and they were only waiting for
weather conditions to make it possible for them to do their work.
Just as soon as the favorable weather arrived the parasites bred enor-
mously and quickly overcame the “ green bug.” In no case was there
a field of the hundreds examined in southern Kansas where the para-
sites natively present did not outnumber by many thousands or hun-
dreds of thousands any number that could have been introduced
artificially, at a time when weather conditions had become such that
the liberations could have had any benefit. As shown by the careful
investigations of the agents of this Bureau in the field, and independ-
ently of Prof. E. A. Popenoe, entomologist of the Kansas State
Agricultural College, and his assistants, the parasites were equally
abundant in all fields in May, when weather conditions became favor-
able, irrespective of whether distributions had been made or not.

The weather, therefore, is the important influence. As demon-
strated by the experience of this and other years, these parasites,
always present in limited numbers, will overcome the aphis unaided
as soon as weather conditions permit, and no artificial introduction.
great or small, appears to hasten or increase their efficiency.

The writer left Washington for Kansas May 13 to take personal
charge of the field work in relation to the “ green bug ” and to make
a thorough survey of actual field conditions. The “ green bug” at
this time (May 15) had become abundant in oats as far north as
Manhattan, Kans.; but wherever present there were numbers of para-
sites also already in evidence. Indeed, Mr. Phillips found this
to be true at Kearney, Nebr., which point he visited about a week
later. In no instance was a field observed, either in the vicinity of
Manhattan or, during the next week or ten days, anywhere in Kan-
sas, where the parasite was not present wherever the “ green bug ”
occurred.

[Cir. 93]

12

A further experiment, this time tried for the purpose of testing the
possibility of hastening the work of the parasite during favorable
weather by large introductions, was carried out as follows: The sub-
jects of the experiment were two fields of oats, each containing 4
acres. In one of these it was determined to introduce enormous
numbers of parasites artificially, keeping records of this field for
comparison with the other field in which no introductions were made,

Fic. 7.—Stalk of wheat, the leaves covered with dead ‘“ green bugs” killed by the parasite
Lysiphlebus tritici. About natural size. (Original.)

thus determining the measure of benefit, if any, which resulted from

the artificial introduction. Mr. Ainslie was instructed by wire to ship

from Wellington, Kans., 6 bushels of the wheat plants that had been

destroyed by the * green bug” and which, in some cases, were literally

covered with the parasitized bodies of the pest, upward of 500 having

been found on a single plant. (See fig. 7.) Before taking up the ex-
[Cir. 93]

13

periment, however, it was desirable to know just what the conditions
were under which it was begun. As stated above, one of these oat
fields was used for the experiment of introducing parasites, while the
other was kept as a check. The fields were so widely separated that
the introductions could not have spread from one field to the other.
Six areas of a square yard each, selected for the examinations in dif-
ferent parts of each field, were gone over by Mr. Phillips and two of
Professor Popenoe’s assistants. Examinations of both of these fields,
made on May 17 and 18, showed that the field in which the parasites
sent from Wellington by Mr. Ainshe were to be liberated contained
approximately fifty millions of the unparasitized “ green bugs ” and
approximately one and three-quarter millions that were undoubtedly
parasitized ; in other words, approximately 3.5 per cent of the * green
bugs ” were at that time parasitized. In the check field the parasites
were even more abundant, about 7.8 per cent being there found, by
similar counts, to be parasitized.

On May 18 parasites from 12 packages, each containing about half
a bushel of wheat plants, were liberated in one of these fields. Now,
a count similar to that made before the parasites were introduced
was made on May 23, and this showed that the percentage of para-
sitism in the field in which the experiment was carried out had in-
creased only to 5.4 per cent, while in the field in which no parasites
had been liberated it was 19.3 per cent. On May 27 a similar count
was made, when the percentage of parasitism in the field where the
introduction was made was 27.1 per cent, while in the check field it
was 32.5 per cent. Clearly, under weather conditions favorable for
their development, an introduction of these parasites to the extent of
millions, carried out under field conditions, did not indicate enough
efficiency to afford any encouragement for the use of this measure in
the protection of the grain fields of the farmer in case of future
attack.

With all the artificial introductions of this parasite that were made
in the grain fields of Kansas and adjacent States and Territories,
there is no probability that a single bushel of grain was saved thereby
or that the United States harvested one bushel more of grain than
it would have harvested had no introductions of parasites been made
or attempted. In substantiation of this statement it is interesting
to note the history of the “green bug” during 1907 throughout
North and South Carolina, upward of a thousand miles from where
any introduction of parasites had been attempted, excepting two
that the writer himself conducted. A considerable amount of ma-
terial was sent from Winston Salem, N. C., on April 20, to a point
a few miles west of Richmond, Va., where it was introduced into a
small meadow of orchard grass, with no grain field within 5 miles.

[Cir. 93]

14

But even here the effect was uncertain, as the writer had found the
parasite present in this locality before the introduction was made.
in the other case a larger consignment was sent from the same local-
ity in North Carolina to Sumter, S. C., to be placed in a field of oats
that the writer visited in company with the owner on the 16th of
April, when parasites were found in considerable numbers. In this
case the owner of the field, writing under date of June 18 and report-
ing on the outcome of the experiment, said:

I am sorry that the information to be derived from our experiments with the
parasites is so indefinite. It just happened that other conditions probably over-
came the aphis before the parasites had time to multiply sufficiently to get in
their work. About the time that your box was received weather conditions
changed somewhat from cool to warmer weather and the bugs seemed to dis-
appear very rapidly. From the day the bugs disappeared, the oats, the only
grain grown, began to improve, and while they will not make a full crop by any
means, they are much better than we anticipated when you were here.

This is, as the writer personally observed, also the history of the
disappearance of the pest in western North Carolina, where both fall
wheat and fall oats are grown and where no parasites were intro-
duced, but where they were literally swarming on April 20.

From all of this it would seem that throughout the greater areas
over which this insect becomes injurious it has so far been impos-
sible to assist the work in any way. We have apparently been wholly
unable to aid the parasites in getting the upper hand. They accom-
plished their work earlier in the Carolinas than in the West, but
reference to the records of the Weather Bureau will show that the
weather conditions as regards temperature were precisely such as to
bring this about. d

The only possibility of accomphshing anything by the artificial
use of natural enemies of the “ green bug” seems to be in Texas and
South Carolina, where the pest gets its start earhest, making its ap-
pearance in the fields in spots of greater or less area in the fall or
early winter. If these incipient outbreaks can be stamped out by
farm methods, as indicated further on, or by the encouragement of
parasites, or if they can be so weakened as to prevent the “ green bug ”
from developing in such enormous numbers, it will serve to protect
the grain crops not only of these two States, but of all those to the
northward over which the pest ravages in seasons favorable for its
development. The Texas Agricultural Experiment Station is con-
templating an experiment whereby they hope, by the artificial intro-
duction at the proper time of a large number of the natural enemies
of the “ green bug ” into these spots of early infestation, to forestall
a future outbreak. If this can be accomplished it will prove of great
benefit to the farmers. Whatever the outcome may be, the experi-
ment seems worth trying.

[Cir. 93]

15
DEVELOPMENT AND INFLUENCE OF LYSIPHLEBUS TRITICI.

Although there are several natural enemies of the “ green bug,”
including one recently described by Dr. L. O. Howard as A phelinus
nigritus, yet all of them seem to be of little importance as compared
with the one minute parasitic species, Lysiphlebus tritici. It is this
species, or what we are at present terming as such, that normally
holds Toxoptera in check in this country, and so long as its develop-
ment and activity are not obstructed by adverse meteorological condi-
tions it will probably continue to control it. Indeed, so important is
this insect and so powerful is its influence that in a short space of
from ten days to two weeks it can overcome a most serious outbreak of
Toxoptera, and thus save from destruction vast areas of growing
grain. The species winters over in the field in the body of its host.
In many cases these parasites, having been prevented from emerging
the previous fall by the advent of cold weather, hibernate as nearly
developed or fully developed adults, ready to emerge when the tem-
perature rises to about 56° F. and remains there for a suflicient
length of time. This is clearly shown by the fact that Mr. E. O. G.
Kelly found hibernating adults at Leavenworth, Kans., on November
13. In one lot of 50 dead, parasitized Toxoptera that had been
washed or rubbed from the leaves of the young grain and taken from
the mud about the wheat plants on February 28, after the winter was
practically over, Mr. Kelly found 17 containing full-grown larvee of
the parasite, 12 containing pupex of a light color, and 21 containing
dark-colored pup, the latter evidently ready to develop promptly
with the advent of warm weather. Mr. Kelly, on the same date, also
secured a large number of Toxoptera in various stages of development
that were hibernating in wheat fields near Leavenworth, Kans. The
weather had been such as to preclude the possibility that these had
been recently parasitized. Yet some of them soon began to show the
yellowish color characteristic of Toxoptera parasitized by Lysiphle-
bus, and adults were afterwards reared from them. This shows con-
clusively that the Lysiphlebus parasites hibernate in advanced stages
of development in the bodies of their host, which they have killed the
previous autumn, and also as larve in those passing the winter from
half to fully grown.

The female Lysiphlebus is even more prolific than the female
Toxoptera. Mr. Phillips has found females which had upward of
400 eggs in their ovaries, and Mr. Kelly has reared in some cases
206 individuals from a single mother Lysiphlebus. The eggs are
lemon-shaped.and white. When excessively abundant this parasite
will thrust its ovipositor into old and young aphides: of both sexes,
including the sexual female even though previously parasitized; and
Mr. Phillips has observed that it will even oviposit in the dead bodies

[Cir 93]

16

of those that have been killed by fungous attack. When its numbers
are not so great it shows more discrimination and seems to prefer
half-grown individuals for oviposition.

This species of Lysiphlebus is parthenogenetic, as was first ob-
served by Mr. Phillips at Richmond, Ind., and afterwards more fully
elucidated by Messrs. E. O. G. Kelly and T. D. Urbahns at Welling-
ton, Kans. The experimental breedings by Mr. Phillips in 1907
indicated that the offspring of virgin female Lysiphlebus were nearly
always exclusively males. In a series of upward of 80 breeding
experiments carried on indoors, in 1908, by Kelly and Urbahns, only
48 gave results of any kind. In only four of these were females pro-
duced, the others giving exclusively males. In the 4 exceptional cases
the females remained virgin, and all finally gave birth to males alone,
2 with the first generation, 1 with the second, and 1 with the third.
The mode of procedure was as follows:

Starting with a mated female, the females from among her off-
spring were isolated, even before emergence. On their appearance
these were given Toxoptera reared under cover to preclude parasit-
ism; the few females from among the second generation were again
isolated in the same manner, the females in all cases being kept un-
mated. It was thus found possible to breed a limited number of
females parthenogenetically to and including the third generation.
Beyond this all offspring were males, this seemingly being the limit.
Just why such a large percentage of these experiments should have
proved abortive is not clear. The conditions under which they were
carried out were of course unnatural but much more protected from
the adverse elements of the open field.

The egg of the Lysiphlebus normally develops to the emerging
adult in about ten days, during the first six of which the host insect
remains alive, and at the end of which it commences to take on a
yellowish hue, the larva of the parasite showing clearly through the
skin of the abdomen.

The celerity with which an invasion of Toxoptera is overcome by
Lysiphlebus is frequently a matter of wonder, as it hardly seems
possible that this host alone could be the source of the swarms of
parasites tlfat make their appearance after a few warm days have
clapsed in the midst of an unseasonably cool spring preceded by a
winter abnormally mild.

In order to determine the origin of these myriads of parasites
Messrs. Kelly and Urbahns began a long series of experiments at
Wellington, Kans., to determine whether there might not be a mul-
tiplicity of host species from which great numbers of Lysiphlebus
would emanate to fall upon and destroy Toxoptera whenever it be-
comes excessively abundant. The entire failure to introduce these

[Cir. 93]

aad —

IY

parasites in advance of an invasion of this character from the
South, as was the case in Kansas in May, 1907, has indicated that
such introductions were not possible and that to attempt it was veri-
tably “ carrying coals to Newcastle.”

Female individuals of Lysiphlebus from the cabbage aphis (Aphis
brassicae L.) taken in the field were first allowed to parasitize Toxop-
tera and from the latter the adults were obtained. This experiment
was several times repeated. Females of Lysiphlebus reared under
cover from the corn root-aphis (Aphis maidi-radicis Forbes) were in
two cases allowed to parasitize Toxoptera and adults obtained. Fe-
males of Lysiphlebus were taken from Ap/is setariw in the field and
the issuing parasites in two cases allowed to parasitize Toxoptera and
adults secured. This experiment also was repeated several times.
Female individuals of Lysiphlebus were taken from the corn leaf-
aphis (Aphis maidis Fitch) in the field and the adult parasites per-
mitted to parasitize Toxoptera, from which finally the adults emerged.
This experiment was repeated several times. female specimens of
Lysiphlebus were taken from the cotton or melon aphis (Ap/ds
gossypii Glov.) from
New Mexico and given
Toxoptera as a host, the
adult parasites develop-
ing successfully there-
from. Female specimens
of Lysiphlebus were
taken from Aphis se-
tarie in the field and
ee Re crainaphle, Much enlarged, (OrfEViak)
host, their offspring
transferred to A. maidi-radicis, and the next generation transferred
back to Toxoptera. Female individuals of Lysiphlebus were taken
from A. setariw in the field and allowed to parasitize Toxoptera, their
offspring transferred to A. setariw, the next generation to Toxoptera,
and the following generation to A. brassicw, from which adults were
secured.

In many cases these breedings were reversed. The only cases of
failure were in attempting to transfer Lysiphlebus issuing from
Toxoptera to Chaitophorus and in transferring Lysiphlebus issuing
from Toxoptera to Iacrosiphum rudbehiew. These experiments were
reversed with the same results.

The female goes about, if in grain fields, among the plants, and
when she finds an aphis she quickly throws her abdomen underneath
her body and between her legs and with a springlike motion thrusts
her ovipositor into the body of the aphis (fig. 8), leaving therein a

[Cir. 93]

18

tiny egg. This egg hatches into a larva in a few days, and the usual
position in the body of the “ green bug” of the larva up to the time
it becomes full-grown is shown in fig. 6, page +. Up to this time it
has fed within the body of the “ green bug” without reaching any
of the vital parts, but preventing to a greater or less degree the
giving of birth to young. This is an important fact, for, as the
parasite seems to prefer partly grown young, it begins to check the
increase of the pest before the death of the “ green bug ” takes place.
Mr. Phillips has found that females parasitized at this period of their
development do not reproduce for more than a very few days. After
about six days the larva of the parasite reaches full growth and becomes
more active, working its way about within the still living body of its
host, which now dies a seemingly terrible
death. The motions of the parasitic larva
within cause the skin of the “ green bug”
to become rotund in shape, as shown in fig.
9; the skin also becomes darker and
hardens. Within four days (the life eycle
in warm weather occupying about ten days)
the adult Lysiphlebus emerges through a
round hole in the dried skin of the “ green
bug,” as shown also in fig. 9. In fields
that have been destroyed the leaves become
almost covered by their brown bodies, as
shown in fig. 7. As stated, many of the
LSE ‘ oreen bugs ” are stung by the Lysiphlebus
| Neleraataie el while quite young, and if these develop to

CELELLELELLELL winged adults, as they do at times in

Fic. 9—Dead “green bugs,” myriads and drift away to distant fields,
Ne ey a re they carry the parasite with them in their
Iebus tritici emerges. The bodies. One of these parasitized winged
top fe shovs te i sll females is shown in fig. 10
the bottom figure shows the The very act of migration of the “ green
ec Sea Enlarged. bug,” therefore, brings the parasite, and

| there is no need of artificial introduction, for
if the center from which the “ green bug ” is migrating has the para-
sites, as it always does, the latter are of necessity carried by their
hosts, and, furthermore, the adult parasites fly with the latter with
favoring winds.

During strong winds the Lysiphlebus does not use its wings, but
crawls about over the plants and probably does not become scattered
by gales. But in warm, comparatively still weather the writer has
observed both winged * green bugs ” and parasites crawling about on
the windows of railway coaches many miles away from seriously
infested fields of grain.

[Cir, 93]

19
EXPERIMENTS IN DESTROYING “ GREEN BUGS” OVER SMALL AREAS.

On leaving Washington both Mr. Ainslie and Mr. Phillips were
instructed to place themselves in the position of a farmer whose grain
fields were beginning to show the presence of the “ green bug” by
small deadening spots, and to leave nothing undone or untried that
would seem to afford relief and save the crop.

Mr. Ainslie instituted some experiments in the use of a brush drag
at Summers, Ark., and Mr. Phillips carried out similar experiments
at Hobart, Okla., but in neither case was the measure sufliciently
effective to warrant its recommendation. Experiments in rolling
infested fields with heavy farm rollers were conducted by both of
these agents, but it was invariably found that this measure was only
effective on smooth lands. When the seeding is done with a grain
drill, as most of it is, the plants grow up in the bottoms of shght
furrows, and the roller comes
in contact with the ridges only,
leaving the young plants and
their inhabitants almost wholly
untouched. This measure, also,
is therefore of little practical
value.

Mr. Ainslie tried dusting with
lime and also with sulphur, but
both substances were ineffective.

Both Mr. Ainshe and Mr. Phil-
lips carried out a series of care- Fic. 10.—Winged female of the “green
ful experiments in spraying with Hi ar eemteae ern anes
kerosene emulsion and with Ry re.
whale-oil soapsuds. From these experiments it was found possible
to destroy 50 per cent or more of the “ green bugs” at an expense of
about $4 per acre. This treatment, of course, is intended for use only
where, as seems to be more usual to the southward, the outbreaks of
the pest originate in spots in the fields.

Mr. Ainslie also tried covering some of these spots with straw and
burning it, thus destroying, of course, both grain and “ green bugs.”
This, too, gave encouraging results, and probably would prove effect-
ive if applied earlier in the season, when the pest first begins to
appear and the infested spots are small.

At Hooker, Okla., Mr. Phillips tried the efficiency of plowing these
spots under, and as the field in which he was working was isolated
and the “ green bugs” did not make their way in from without, he
was able to show conclusively that such outbreaks, under certain
conditions, may be stopped.

[Cir. 93]

20

In summing up these field experiments, then, it is found that these
spots may be treated successfully either by plowing under and har-
rowing and rolling the surface of the ground, by spreading straw
over them and burning, or by treating with a 10 per cent solution of
kerosene emulsion. Except in the southernmost regions infested by
this pest, however, the greatest difficulty does not arise from these
isolated colonies, which seem to extend outward day after day, but
from the fact that, after their food supply has become either largely
destroyed or the grain too old and tough for them to feed upon,
immense swarms of winged adults are produced, and these drift,
in general, northward with the advance of the season and infest the
grain fields of entire sections of the country much earlier and more
completely than would be possible from the scanty stock natively
present. This habit is also seen in the behavior of the pest in its
original home in Europe. It may therefore prove that the country
north of the Red River may be more or less protected if the pest can
be early overcome in northern Texas.

AGRICULTURAL METHODS OF CONTROL.

The fact that the “ green bug” in the South originates in spots in
the grain fields has been alluded to, and also that from these fields
come the vast swarms of winged females that develop and drift over
the country, dispersing themselves in uninfested fields. Early sown
fields or fields overgrown with volunteer grain seem especially to
invite early attack in the more southern localities. Where these im-
mense swarms settle down in a section of country, even the best fields
of grain may succumb to their attacks. But usually, outside of an
extremely limited area, there is a noticeable difference in intensity of
attack as between different fields. In Oklahoma and northward, fields
that have been late sown or that were pastured during the winter
suffered worst and were the first to be destroyed. It has been fre-
quently noticed that a field of grain may be totally destroyed, while
an adjoining field, though seriously injured, will frequently produce
a partial crop. An investigation of the history of these fields has
invariably shown that the result in the latter case is due to fertile soil,
proper cultivation, and seeding at the proper time. It seems to have
been almost universally true, outside of the lmited area of total
destruction, that the best farmed fields have suffered the least. This
does not apply alone to wheat, as the writer observed a field of oats
near Hutchinson, Kans., that gave promise of a fair yield, where
almost the entire crop would otherwise have been destroyed. The
owner of this field, who had been obliged to plow up other fields

where the cultural methods had been the same, expressed his opinion
[Cir. 93]

21

that the reason the one field escaped the attack of the “ green bug ” to
such an extent was that it had been for many years in alfalfa, only
one crop, and that corn, having been taken from it since alfalfa had
been turned under. He stated that the “ green bug ” was at one time
as abundant in this field as in the ones which he had been obliged to
plow under, but that in the one case the plants had withstood the
attack better and were in better condition when the “ green bugs ”
were overcome by the parasites, and thus able to start growth anew
and yield to the owner a fair percentage of a crop.

In extreme western [Kansas a field of 10 acres of oats lying adjacent
to an irrigating ditch, but which had not been irrigated, showed very
forcibly the effect of irrigation: Along this irrigation ditch was a
ragged border of vigorously growing oats from 10 to 30 or 40 feet in
width where the “ green bug” had seemingly done no injury. Be-
yond this, where the moisture from the irrigating ditch had not
penetrated, the loss was total. In another case in the same locality
a part of the wheat in an unirrigated field came up in the fall and the
rest not until spring; the former was uninjured by “ green bugs,”
while the latter was killed. While late sowing in Texas will prob-
ably lessen attack in the fall, it is doubtful if this can be recom-
mended north of the Red River. November-sown wheat was cer-
tainly less affected than others in North Carolina.

THE PRESENT ‘“ GREEN BUG” SITUATION IN THE SOUTHERN STATES,
mAY 1, 1909.

The situation over the country with reference to a future invasion
of this pest, though not alarming, is sufficiently serious to render a
word of warning exceedingly appropriate. In widely separated
localities from Western North Carolina to eastern New Mexico the
insect has become sufficiently abundant during March and April to
work considerable injury locally. This shows that the pest has re-
covered from the severe reverse given it by its natural enemies in
1907, and that a repetition of the mild winter of 1908-9 and the
present cold, backward spring will be almost certain to precipitate a
more or less disastrous invasion. Of course no one knows what the
winter of 1909-10 and the spring of 1910 will be, but it stands the
grain growers in hand throughout the country south of Virginia,
Kentucky, Missouri, and Kansas to destroy, as far as possible, all
volunteer grain coming up in the fields during the coming autumn;
and where fall oats are sown, as is generally the case throughout this
country, the sowing should be delayed as late as possible. These two
measures have a tendency to prevent the pest from becoming so thor-
oughly established in the grain fields during the autumn months, and

[Cir. 93]

22
are the only measures that can be taken that will have a tendency to
ward off an impending invasion.

We have found that where serious damage has been done to fields
of grain in late winter and spring such fields had become seriously
infested during the preceding autumn. The carrying out of these
measures in the southern portion of the country has a tendency to
protect the grain fields farther north, for we have had additional
illustration of the fact that winged individuals are, during the spring
months, being almost continuously carried northward by the wind.

It is somewhat a question as to whether the spring-sown oats far-
ther north would suffer to a less degree if there were no invasion
in the South in fields of fall-sown grain, both of oats and wheat.
While it is not possible for an insect to make its way or be carried
by the wind from Texas to northern Kansas, Missouri, southern Ili-

nois, Indiana, and Ohio, nevertheless continuous breedings to the
southward certainly do influence the numbers over this last-mentioned
territory.

If the farmers of the country, instead of being carried away by
the highly colored newspaper reports of the effect of the introduc-
tion of a few parasites in their fields, will seek to evade the pest by
the destruction of volunteer grain in the fall and late sowing in the
extreme South and turn their attention to better farm methods, in-
cluding not only cultural methods but by all means rotation of crops,
watching for and stamping out the pest when it first appears in the
South in the fall and winter, they will in all probability suffer far
less from destruction of their crops when the next invasion of this
pest occurs.

Approved:

JAMES WILSON,
Secretary of Agriculture.

WasuineoTon, D. C., April 27, 1909.
[Cir 93]

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