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ENT io. 103. Issued June 20, 1908.

nited States Department of Agriculture,

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

THE HARLEQUIN CABBAGE BUG.

(Murgantia histrionica Habn.)

By F. H. CHITTENDEN,

Entomologist in Charge of Breeding Haperiments.
INTRODUCTORY.

A moderate-sized red and black plant-bug, variously known as
* calico back,” “ fire bug,” and “ terrapin bug,” as well as harlequin

Fic. 1.—Harlequin cabbage bug (Murgantia histrionica) : a, Adult; b, egg mass; ¢, first

DD
stage of nymph; d, second stage; e, third stage; f, fourth stage; g, fifth stage. All
enlarged (original).

‘abbage bug, is the most destructive insect enemy of cabbage and

related crops in the southern part of the United States. At one time

it was a serious pest northward to New Jersey and westward to Ohio
42055—Cir. 1083—08

2
and, indeed, threatened to invade New York and New England. In
recent years, however, its progress in the northern States has been
checked by atmospheric conditions.

This plant-bug accomplishes its work of destruction by sucking the
sap from leaves and veins of cabbage and other crucifers, the af-
fected plants wilting, withering, and dying as if they had been swept
by fire, whence the name “ fire bug.” It is a pest which, if permitted
to propagate unmolested in seasons which favor its increase, is certain
to destroy a portion if not all of the fields which it infests. <A half
dozen mature insects are capable of destroying a small plant in one
or two days. Some years ago, when this species was abundant in’
the vicinity of the District of Columbia, the writer saw many large
fields in Maryland and Virginia from which not a single good cab-
bage could be picked, and observed similar injury to horse-radish
and some other crucifers.

The harlequin bug has been compared to the boll weevil as a pest
in the South and to the San Jose scale as a scourge in New Jersey.
Certainly it is to the cabbage grower what the other two insects are
to the cotton planter and fruit raiser respectively. If growers gen-
erally, however, will undertake the methods of control, as advised
in this circular, there is no reason why it should be longer destructive.

DESCRIPTIVE.

The name harlequin cabbage bug scarcely requires explanation to
any one familar with the appearance of the insect. Its gay red and
black ornamentation is suggestive of the dress of the stage harlequin.
In the figure of the adult (fig. 1, a) the dark portions illustrated are
either black or dark metallic blue and the light portions are bright
yellow in freshly transformed bugs and red in fully hardened in-
dividuals.

The eggs (fig. 1, 6) are beautiful objects and remarkable for the
fact that they closely imitate in miniature white barrels bound with
black hoops and with black spots set in the proper place for bung-
holes.

The younger stages, or nymphs, of this species bear considerable re-
semblance to the mature form, differing, however, in the lack of
wings and in having only four joints to the antennz, whereas the adult
has five. There are five stages in all, illustrated at c, d, e, f, and g.
Tn the third and fourth nymphal stages the body is hemispherical and
the resemblance to a turtle or terrapin is striking.

DISTRIBUTION..

The harlequin cabbage bug is a native of Mexico and Central

America—where it obviously originated—and perhaps also of the

semitropical regions in Texas, Arizona, and New Mexico. ‘It was first
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5)

recorded in injurious numbers in Texas, in Washington County, in
1864," and since then has traveled gradually northward, although not
with uniform rapidity. Normally the species is probably tropical and
has been diffused through two additional life zones, the Lower and
Upper Austral. In the latter zone, however, it has not become per-
manently established much farther north than about the lower or
warmer half. The region about Norfolk, Va., “the gateway of the
South,” is probably the northern limit of actual establishment in the
Kast.

A year or two following its discovery as a pest this species had in-
vaded Louisiana, and by 1867 was recorded from North Carolina. Its
spread was most noticeable along the Atlantic seaboard and up the
Mississippi River valley. In 1870 it had appeared in Missouri and
Tennessee, and by 1876 had reached Delaware. In Maryland and Vir-
ginia, however, it did not attract attention until 1880. It was first
recorded as injurious in New Jersey, at Woodbury, in 1892,’ and in
1894 it was seen at Jamaica and “* New Lots Road,” New York.¢

Westward we have office records of its occurrence in Colorado in
1882, at Pueblo and Denver, but it has never been an important pest
in that region, and it was not until 1890 that it was recorded in
Indiana and not till 1891 in Ohio. In the latter State it progressed
steadily northward until it was checked by the same atmospheric
conditions which prevailed in the Eastern States and which will be
mentioned presently. In the Pacific region the species is well estab-
lished in southern California, but there seems to be no published
record of the time of its first appearance in that State. We received
specimens from San Diego, Cal., as early as 1878. The insect is also
recorded from Nevada.

The dispersion of this species in the Middle States has been traced
by Mr. F. M. Webster,’ and from what has just been stated and what
has been placed on record by Messrs. Webster and Howard it is very
evident that it has become diffused largely by what Doctor Howard
terms “ commercial jumps,” as in the case of insects like the aspara-
gus beetle. This is a matter quite simple of accomplishment, as fertile
egg masses can be carried long distances on the insect’s food plants—
for example, on the outer leaves of cabbages—by railroads and by
boat. It will be noted that after the establishment of the pest in
Delaware it did not attract attention farther north until twenty
years later; also, that other introductions were made in different
directions quite independently of each other.

’ @ Recorded by Gideon Lincecum, Practical Entomologist, Vol. I, p. 110, Aug. 21,
1S66.
- bVintner, 9th Rept. New York State Ent. f. 1892 (1893), pp. 815-817, 441.
¢ Sirrine, Bul. 83, New York Agl. Exp. Sta. (Geneva), Dec., 1894, p,. 683.
4Proc. Ent. Soc. Wash., Vol. III, pp. 288-290, 1896.
[Cir. 103]

a

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To recapitulate: This species has obviously become diffused from a
central point of dispersal, Mexico, chiefly in the following three direc-
tions: (1) From Texas eastward through the Gulf States and north-
ward along the Atlantic seaboard to Long Island; (2) from Texas
northward through the Mississippi Valley and thence through the
Ohio River region into Ohio; (8) from Mexico into the neighboring
States and Territories, and from Lower California into southern Cali-
fornia and Nevada.

The northward migration of the harlequin bug, although not with-
out interruption, was apparently quite steady until recent years.
Beginning with the year 1897, at which time the insect had reached
its maximum as a pest in Maryland, Virginia, Delaware, and adjoin-
ing States, climatic conditions adverse to its existence developed.
These consisted of sudden changes of temperature, such as cold snaps
followed by warm spells and the reverse during the winter. As a
result this bug, with several other forms of southern origin, was killed
while hibernating and practically disappeared in the North until, at
the date of writing (1908), it is scarcely, if ever, reported as in-
jurious from the District of Columbia northward. These conditions
were particularly noticeable in the winter of 1898-99.° Small scat-
tering colonies are, however, occasionally found in this region, chiefly
on wild plants, late in the fall.

LIFE HISTORY.

in the warm and equable climate of the South where this species
is at home it is more or less active throughout the year. Farther
northward, however, after the first severe frosts of December it goes
into hibernation in tufts of grass or under rubbish at the bases of
‘abbage stalks or in any convenient place. This takes place chiefly
in the adult stage, although some nymphs of the last stages remain
afield as late as November and December. Doubtless the nymphs
succumb in time to cold, and hence fail to survive the winter.” The
first warm days of February or March, in the Gulf region, or of
April, farther north, see the bugs appear abroad and beginning to
feed. At first wild mustard and other cruciferous weeds are attacked
and soon the insects are ready to reproduce their kind. On these wild
plants the eggs are deposited, on end, generally in two more or less

4 See Bul. 22, n. s., Div. Ent., U. S. Dept. Agric., pp. 54, 55.

®’A number of adults and nymphs in the last two stages obtained from Lam-
bert’s Point, Va., October 21, 1907, were placed in a rearing cage with growing
cabbage plants, grass, and similar rubbish to provide means of hibernation, Tor
over a month or until some time in December the insects continued feeding, but
when examined during the first week of March it was found that all had suc-
cumbed to the severe cold weather of February.

[Cir, 103]

4)

parallel rows cemented together in groups of about a dozen, as shown
in figure 1. They are normally placed on the under side of the leaves
and hatch, in warm weather, in three or four days after deposition
and in five to eight days in the cooler weather of early spring. The
young bugs or nymphs pass through their five stages of metamor-
phosis with considerable rapidity. It has been stated that the life
cycle could be completed in warm weather in about two weeks, but
this is obviously an exaggeration, as it requires four or five weeks for
the completion of the cycle in related insects.

The life periods of this species were unknown until worked out
by Mr. H. O. Marsh, of this office. Specimens (from Texas) were
under observation from the first week of March until the first week
of May. They were under somewhat unnatural conditions, being
confined in our office room, which was maintained during this period
at an average temperature of from 68° to 70° F. The first or egg
stage covered 11 days. The time from the hatching of the eggs until
the first molt gave the first larval instar or nymph period 7 days;
the second instar required 13 days; the third, 8 days; the fourth, 14
days, while the fifth or pupal instar covered 17 days—a total of 70
days, or 10 weeks, in all, which will be not far from the maximum
active period of this species. The minimum will probably fall into
much lower figures, probably half of this time, or at most not more
than 42 days in extremely hot midsummer weather.

When cabbage and similar plants come up the insects migrate to
them. It has been surmised that owing to the rapid development of
the cabbage bug in the South there is a possibility of as many as seven
or eight generations each year, while in the North three or more occur.
The first supposition is doubtless overdrawn, as we know of no simi-
lar insect producing so many generations annually. This is a prob-
lem for future study. It seems probable that four or five generations
would be a more natural limit in the South and two, or possibly
three, in the North.

FOOD PLANTS.

In the autumn after the cabbage crop has been made and in early
winter, even as far north as Washington, the bugs are still afield,
seeming loath-to seek shelter for the cold months. At this time they
cluster on cabbage stalks and sprouts and the leaves of turnip and like
plants, and when the supply of crucifers has become exhausted they
will attack almost any form of succulent vegetation which is most
available and palatable.

On one farm the writer observed a field of 10,000 cabbage plants
completely ruined, which at the time of his visit, the first week in
October, had been deserted by the bugs. An adjoining field of pota-

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6

toes was then attacked, afterwards one of eggplant, and numerous
bugs in various stages were observed sucking the juices of these
plants. Unripe fruit of eggplant was especially relished, and ripe
pods of okra and beans were also attacked.

The list of useful plants which this species has been found to
damage includes all forms of crucifers or cole crops—cabbage and
related plants, kale, collards and cauliflower, turnips, radish, horse-
‘adish, mustard, rape, and the hke—and when these crops have been
killed out truck crops of nearly all kinds are attacked, of which egg-
plant, asparagus, potatoes, tomatoes, okra, beans, and beets are most
affected. Damage is sometimes done to ornamental plants such as
roses, sunflowers, and chrysanthemums in flower gardens, and Mr.
J. M. Rankin, while an agent of this Bureau at Chico, Cal., in Octo-
ber, 1905, reported that this species, after entirely destroying a half-
acre plat of cabbage, attacked the other plants in the vicinity, includ-
ing nursery plants of citrus, loquat, cherry and plum, squash, egg-
plant, “and in fact everything green.” The fruit of grapes and
Jate corn has also been attacked. The bugs are very partial to rag-
weed (Ambrosia), pigweed (Amarantus), wild lettuce (Lactuca
canadensis), and lambsquarter (Chenopodium), congregating on all
parts of these weeds but appearing to prefer the stems.

The wild food plants on which the species actually breeds include
wild mustard and cresses of different kinds, shepherd’s purse, pepper-
grass, bitter-cress, rock-cress, and practically all other plants of the
mustard family (Cruciferze) as well as some of the closely related
‘caper family (Capparidacee).

NATURAL ENEMIES.

The comparative freedom from the attack of natural enemies
which the harlequin cabbage bug enjoys is remarkable, and is due to
two causes: First, to the warning type of its coloration—black and red
or yellow; and, second, to its distasteful odor and flavor. This latter
has been tested frequently. In the writer’s experience birds that
would attack most common insects would, when offered one of these
bugs, either peck at it or look at it askance, or if by chance they ate
a bug they did not repeat the dose.

Nevertheless the insect has one effective natural enemy, a minute
parasite, Zrissolcus murgantie Ashm., which develops in the egg.
Prof. H. A. Morgan when in Louisiana discovered that out of over
a thousand eggs under observation in 1902 nearly all were killed
by this useful little creature. The eggs are also attacked by QOoen-
cyrtus johnsoni How. and have been parasitized artificially by Z'rés-
soleus podisi Ashm.

[Cir, 103]

(if

This species is also preyed upon by another bug, Arius cristatus
L., the wheel bug, which the writer has frequently seen attacking the
young harlequins.

The influence of natural elements, particularly cold winters, has
already been mentioned as a means of decimating this pest. It is well
to add, however, that the writer had this species under close obser-
vation in 1899, and that as a result of sudden cold snaps, 85 per cent
of the bugs in fields near Washington in that year had been killed by
January 15, 1900.

METHODS OF CONTROL.

The experience of years has shown that in order to obtain the best
results in the treatment of the harlequin cabbage bug preventives are
necessary, as there is great difficulty in obtaining insecticides which
are effective and which do not at the same time injure or kill the
plants. These preventives are: (1) Clean cultural methods, espe-
cially in the fall; (2) the use of trap crops of mustard or other plants
in the spring, and (3) hand methods. With strict observance of clean
farming few of the insects will survive the following spring and the
adoption of trap crops leaves fewer still to be destroyed by mechanical
measures. In some cases all three methods should be adopted, for if
they are neglected the grower will find it a most vexatious matter to
control the pest in the midst of the growing season.

Clean cultural methods.——Of prime importance are clean cultural
methods. The value of clean methods of farming has been recognized
by nearly everyone who has had experience with this insect. The
practice of leaving stalks of cabbage and other cruciferous plants in
the field late in the autumn and in the early winter, or of permitting
rank weeds to grow up, or, in fact, allowing any sort of débris to accu-
mulate, serves as a means of protracting the life of this insect, as all
such material either affords it food late in the season or quarters for
protection against the elements during winter. It is even inad-
visable to plant crucifers in the vicinity of outhouses and barns, as
the bugs are apt to enter these latter for passing the winter.

Throughout the year wild plants of the mustard family, on which
the insect chiefly breeds, should be carefully kept down not only in
the fields but in the immediate neighborhood. <A list of such plants is
given on page 6.

Trap crops.—Some plants, such as cabbage, turnip, or kale, may be
planted late, to be left at intervals throughout infested fields. These
trap plants attract the insects in the fall, and here the latter may be
killed with pure kerosene, or by mechanical methods. Where it is con-
venient to leave piles of rubbish until the insects are attracted to
them this may be done, and the entire material, insects and all, should
then be burned.

[Cir. 103]

8

The best remedy, however, and one that should be put into opera-
tion by every cabbage grower who is troubled by this pest, consists in
planting an early crop, which may be either mustard, rape, or kale,
as a lure for the first-appearing insects. Radish and turnip serve a
similar purpose. In the Gulf States the overwintered adults appear
in February and March, and in the District of Columbia and vicinity
in the latter part of April. For some reason they appear to prefer
the plants that have been enumerated, and wild mustard and other
crucifers, for the first deposition of their eggs. On these crops and
on weeds the insects can be killed with kerosene or by the hand torch
or may be collected in nets, or they may be destroyed by burning the
entire trap crop when this is of no special value. Numerous reports
have been received at the Department of Agriculture, and others have
been recorded, of the value of trap crops as a means of controlling
this pest. Some of these are worth repeating.

The first test of the trap-crop remedy was made by Lincecum
(1. ec.) in Texas, in 1866. Noticing that the bugs were numerous on
mustard and radish in April, he handpicked them and thus protected
his cabbage crop. The practical utility of this method, however, does
not appear to have been recognized until considerably later. In
1891, Mr. H. E. Weed, when entomologist of the Mississippi Agri-
cultural Experiment Station, sowed a row of mustard through the
center of a l-acre field of cabbage. In April this mustard attracted
the bugs in large numbers and on it they were killed with undiluted
kerosene, with the result that throughout that season the field re-
mained free from the pest, whereas the previous year the crop was
almost entirely destroyed.’

Hand methods.—\f determined efforts are made to stamp out the
first generation fewer insects will remain to be dealt with and very

4A correspondent, Mr. J. H. Hevey, Ingomar, Miss., tested the trap-crop
remedy, and wrote that when the bugs made their appearance on a bed of mus-
tard he destroyed them by “ bugging,” i. e., by shaking them inte pans of water
on which a thin film of kerosene was floating. When the mustard was removed
to make room for another crop a few cabbage plants became infested, but the
bugs were killed as above, and finally, after the middle of July, none was left.

One of the largest growers of cabbage in Delaware reported (Sanderson,
Bul. 26, n.s., Bur. Ent., U. S. Dept. Agric., p. 67, 1900) that at one time it was
impossible to raise cabbage on account of this pest, but for several years he
had used kale as a trap crop, and as a result of this procedure and careful
handpicking of the few bugs that strayed to the cabbage, he had been troubled
very little, while his neighbors’ cabbage had frequently been ruined.

In April of one year in Maryland half an acre of kale became freely infested
on one side by harlequin bugs. The insects had all congregated on this side.
Under the writer’s direction this portion was burned, straw being used to
facilitate ignition. Two weeks later not a single bug could be found in a walk
about this patch, and the cabbage which was growing in several plats in the
vicinity was free from injury.

[Cir. 103]

9

few will fly from other quarters for the continuation of the species.
Thus injury may be greatly curtailed if not absolutely prevented for
an entire season. The large size and bright colors of the insect render
it easy of detection and its sluggish nature assists in its easy capture.
Mr. H. Walter McWilliams, Griffin, Ga., reports that by offering
a bounty to school children for the destruction of this pest he suc-
ceeded, in March and April, 1902, in destroying the first generation in
that vicinity, and estimated that this experiment saved him $100 on
his cabbage crop alone, not counting the benefit to the children.

As instance of the ease with which this insect may be hand-picked,
a grower at Denton, Tex., gathered, in February of one year, 47,000
bugs. In case hand-picking has not been thoroughly done and some
bugs have escaped this process and succeeded in depositing their eggs,
the masses, which may be easily recognized by comparison with fig-’
ure 1, 6, should be carefully gathered and crushed.

Kerosene emulsion, according to the testimony of many who have
experimented with it, is not effective against the adults and only par-
tially effective when sprayed on the younger nymphs. Quite recently
Prof. A. F. Conradi* has found that a 10-per-cent kerosene emulsion
is effective in killing the nymphs, as is also whale-oil soap, at the rate
of 2 pounds to 4 gallons of water. If the insects are sprayed just
after they have molted these insecticides almost invariably kill them.
It is obvious that further experimentation is desirable along this line.

‘ Other remedies.—A few words should be said of other remedies and
may be prefaced with the remark that since the harlequin cabbage
bug feeds exclusively by suction and does not chew its food, the ar-
senicals, hellebore, and such remedies as are useful against cabbage
worms are absolutely valueless against the present species. Pyre-
thrum is not effective and is, moreover, too costly. Hot water applied
at a temperature of about 130° F. to the infested cabbage plants should
be tested. It is not applicable, however, to large fields on account of
the difficulty of maintaining the temperature at a given point, but
may be found useful in kitchen gardens.

The value of hand torches for insecticidal purposes is extremely
limited. The plumbers’ torch is used considerably in Texas as a
means of killing this insect, but growers are apt to expect too much
of this method, and to apply it to too many kinds of insects, to the
ultimate detriment of their crops.

It is possible that some of the natural enemies of this species,
especially southern egg parasites, might be utilized in its control; 1. e.,
by shipping parasitized eggs from localities where they are abundant
to northern regions in which they do not occur.

4 Bul. 89, Texas Agr. Exp. Sta., pp. 9-11, 1907.

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10

SUMMARY.

The general acccount which has been given of this insect in preced-
ing pages has been brought together at this time because of the practi-
‘al certainty that in the natural course of events this bug will before
long endeavor to reinvade territory north of its present range (in
1908), and may again become a pest for a number of years, until
climatic conditions adverse to its development or increase check its
northward spread.

In conclusion, it should be repeated that the systematic destruction
of the insects by means of the trap-crop method described, together
with a system of clean cultural practice throughout the entire season
and especially in the late fall, will leave little else to be done save the
gathering by hand of such insects as escape these measures or which
may fly from infested to uninfested fields.

To prevent the pest from advancing farther northward than its
present limits, careful watch should be kept for the first appearance
of the insect, and remedies should be prompt and thorough. The im-
portance of killing off the first or hibernated brood of bugs and their
progeny can not be too strongly emphasized.

Approved:

JAMES WILSON,

Secretary of Agriculture.

Wasuineton, D. C., May 4, 1908.

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WAKA

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