The leopard moth. (Zeuzera pyrina Fab.)

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CIRCULAR No. 109. i Issued July 6, 1909.

United States Department of chica tre

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

THE LEOPARD MOTH.

(Zeuzera pyrina Fab.)4@

By L. O. Howarp and F. H. CurrrenDeEn.
INTRODUCTORY.

Deciduous trees of many kinds, grown for shade and for ornament
in northern New Jersey and eastern New York, are subject to severe
injury by the larval stage of the European leopard moth (Zeuzera
pyrina Fab.). Among the shade trees, elms and maples suffer the
greatest damage, but as this species is a very general feeder it attacks
practically all descriptions of trees and shrubs with the exception of the
evergreens. In the region mentioned this species is, everything con-
sidered, the most serious menace to the growth of shade trees, since,
unlike the majority of lepidopterous insects, the larve of the leopard
moth do not feed upon the foliage, but bore into the branches of the
plants which they infest and feed upon the living wood. The larvee
usually begin operations in twigs and small branches and with their
larger growth bore and tunnel into the larger branches and trunks.
This work has the effect of girdling, the injured portions being blown
down by heavy wind storms, while in the case of severe attack the
growth of the tree is checked, frequently causing its death. Attack is
not confined solely to shade and ornamental plants, but orchards are
often injured.

DESCRIPTIVE.

Injury by this species is accomplished solely by the larva, which is
a fleshy, grublike caterpillar, pale yellowish in color, frequently with
a pinkish tinge. The head, thorax, and anal plates are brownish-
black and the surface of the body is very sparsely hairy but covered

aFamily Cosside. Synonyms: Zeuzera esculi L., Z. decipiens Kby., ete
87868—Cir. 109—09

2

with large and prominent tubercles arranged as shown in the
illustration (fig. 1, c). When fully mature the larva attains a total
length of about 2 inches. A lateral view of the larva in its burrow
is shown in figure 1 at ¢. |
This species derives its name from the spotted appearance of the
moth, illustrated at figure 1, a, 6. There is great diversity in the
size of the two sexes, the female (a), which is a heavy-bodied moth
and a very feeble flyer, being much the larger. It will be noticed that
the smaller male (6) has a more slender body, which permits a more
ready flight, and is also distinguished from the female by the pos-

fit

ont tte 110k

Fic. 1.—The leopard moth (Zeuzera pyrina): a, Adult female; 6, adult male; c, larva; d,empty pupal
case. Enlarged. (Original.)

session of broad bipectinate or feathery antenne. ‘The wings are
semitransparent and white, thickly dotted with blackish spots
which are more or less distinctly tinged, giving them a dark blue or
greenish cast. The thorax is marked with six large black spots and
one small one, the latter being located in the center. The female has
a wing expanse of upwards of one and a half inches, while that of the
male is much less.
An empty pupa-case in its cell in the wood is shown in the illustra-
tion at d.
[Cir. 109]

5)

ORIGINAL HOME AND DISTRIBUTION.

The leopard moth, like so many other dangerous pests, is a European
species which has been introduced into the United States in com-
paratively recent years. Its old world distribution is credited as
central and southern Europe, southern Sweden, southwestern Africa,
Algeria, and northern Morocco, and the western portion of Asia Minor.
_ This species was introduced into the United States some time
prior to 1879, in which year, on the authority of Mr. Jacob Doll, a
living moth was captured in a spider’s web at Hoboken, N. J.* In
1884 Dr. E. B. Southwick, then entomologist of the public parks of
New York City, recognized the destructive work of this species in
Central Park. In 1887 it was seen at Newark, N. J., but was not
actually recorded as occurring in this country until the following
year. In 1890 the junior author observed the moths at electric lights
at Orange, N. J.

Fortunately the spread of this insect, particularly in the immediate
vicinity of New York City, has been very slow, a fact which may be
attributed to several causes, (1) the slowness of the flight of the
female, (2) the dominance of sparrows in large cities, causing our
native birds, such as woodpeckers, to be driven to the country, where
they destroy the moths, and (3) the bowl-shaped electric-light globes,
hollow at the top and closed at the bottom, which were formerly in
general use in our large cities. The males are strongly attracted to
brilliant lights and many were captured and perished in these globes
in earlier years. Other cities in New Jersey where this species has
been troublesome are Elizabeth, Irvington, Montclair, Arlington,
Asbury Park, Ocean Grove, and New Brunswick. Mr. H. M. Russell
of this Bureau collected specimens at Bridgeport, Conn., in 1901.
The species is now an inhabitant also of Staten Island and has spread
on Long Island well beyond the confines of greater New York. South-
ward it was reported a pest, in 1901, at Ocean Grove, N. J., and by
1905 it was recorded by Felt as occurring at Kensico, N. Y., 25 miles
north of New York City. By 1907 it was captured at New Haven,
Conn., by Prof. H. W. Foote. It is now stated to be injurious in the
vicinity of Boston, Mass.

FOOD PLANTS.

In its original home the leopard moth is recorded as living on a
considerable number of common trees, including elm, lime or linden,
ash, beech, birch, walnut, oak, chestnut, poplar, alder, and, rarely,
horse-chestnut. Among orchard trees it is reported to do injury to
pear, apple, and plum. In the United States it attacks all of these

a2 Entomological News, March, 1904, p. 110.. b Insect Life, Vol. VII, p. 138.
[Cir. 109]

-

trees and many others, the list including such important shade trees
as have been mentioned, as also practically all of the maples, elms,
and oaks, mountain ash, tulip tree (Liriodendron tuliprfera), aspen,
the willows, and such shrubs as privet, lilac, and honeysuckle. <A
list of trees which this species has been actually observed to attack
was compiled in 1894 by Doctor Southwick and includes 77, observed
in the public parks of New York City alone. A total list of 83 trees
and shrubs was made at that time.?

It will be seen by the list of food plants already presented that
the number could be almost indefinitely extended, particularly in
reservations like Central Park, New York City, and Prospect Park,
in Brooklyn, where special effort has been made to bring together a
great variety of trees and shrubs. The in-
sect is, in fact, nearly omnivorous, attack-
ing, as previously stated, practically ali
forms of woody plants which are of suitable
size for its purpose, with the exception of
conifers.

HABITS AND LIFE HISTORY.

aly
eae

In Germany the moths are stated to
make their appearance during July and
August, while in this country they appear
as early as May and continue issuing until
late in September.

The gravid female, being particularly
heavy, is unable to fly very far or very
high. She deposits her oval, salmon-col-
ored eggs in a large mass or group, when
not in confinement, and as many as 300

eggs have been counted in a single mass.
Fic. 2.—Section of wood showing bur- Smtue :
dow ond girdling ettect produced ‘by This is, however, probably not the maxi-
larva of leopard moth. Reduced. yum number, since an estimate of as many
Sue Hote as 1,000 has been made. The eggs are in-
troduced by the rather hard ovipositor into the soft tissue of young
erowth where the bark is smooth, or are inserted into crevices in the
rough bark of older trees.

The larve soon hatch—in about ten days, according to Mr. J.
V. D. Walker—and penetrate the wood, frequently entering the
nearest crotch but boring in at other points, and burrow tunnels into
the heart or pith of twigs and the heartwood of the larger branches
or trunks. When a larva has grown too large for the branch in which
it is feeding it crawls out and migrates to a larger one. In a single

ite a iw enn Tew

yan

aSee list on page 529, Rep. Ent. N.. J. Agr. Exp. Sta. for 1894. This article, by
Dr. J. B. Smith, covers pages 517-533 and presents a very complete account of the insect.
[Cir. 109]

D

tree 6 inches in diameter Southwick observed as many as six larve,
any one of which would have been able to destroy the tree if not re-
moved. Mr. A. Hufnal wrote that in maple trees which this species
was infesting at Ocean Grove, N. J., there was an average of from
six to eight borers to a tree and that he had found from ten to fifteen,
and in one instance as high as thirty-four, in a single tree. By the
time the larve within have attained full growth infested limbs of a
certain size are likely to break off, especially during or after a severe
storm, for the full-grown larva in many cases girdies the branch.
The manner of girdling is shown at the top of the section of wood
illustrated in figure 2. In 1893, after every storm in Central Park
great quantities of limbs were seen, some entirely broken off and
others still hanging to the trees.

The larva, when fully mature, transforms to pupa within the
burrow, the change beginning to occur during the second May after
the hatching of the eggs, the larva thus requiring nearly two years
to complete its growth. The pupa, by means of a snarp protuber-
ance on its head, is enabled to force its way partly out of the burrow,
after which the skin splits open and the moth emerges. The empty
pupal skin remains for some time projecting from the orifice.

The presence of this borer in a branch is manifested by little
accumulations of chips, matted excrement, or frass, which indicate
the entrance to the burrows. After a time these orifices are closed
from within by a silken web, which is doubtless to protect the con-
tained insect from its natural enemies. Smaller twigs wilt and
break off and often it is only when the severed twigs or branches
have been brought down in numbers by high winds that the work
of the insect is. first recognized. Where the larger larve have
worked just under the bark this splits open the next season, leaving
an ugly scar as a reminder of its pernicious operations.

NATURAL CHECKS.

No specific natural enemies of the leopard moth appear to have
been recorded in this country, although in Europe E. A. Fitch has
reared an indeterminate chalcidid of the subfamily Encyrtine.¢

In the explanation of the cause of the slow spread of the moth
from cities and large towns to the country, allusion has been made
to the fact that native birds probably assist in holding this insect
in check in the suburbs. Actual observations on this head appear
to be wanting, but there are the best of reasons for believing that
birds, like the woodpeckers, which naturally look over the bark
and collect all kinds of borers, prey on this species, while it is believed

2 Entom. Mo. Mag., Vol. XVIII, p. 116. Perhaps Copidosoma truncatellum Dalm.,
mentioned by Dalla Torre (not Mayr), Catalogus Hymenopterorum, p. 246.
(Cir. 109]

6

that sparrows sometimes destroy the eggs or young larve in such
places. Smith has expressed the belief that when the insect suc-
ceeds in getting away from the outskirts of cities its enemies Increase
in number, many insectivorous birds aiding in holding it down.

During the day the moths must be fed upon by birds and later
by bats and night-flying birds. The habit of the larve of desert-
ing one twig and migrating to a larger one undoubtedly leaves them
exposed to the same natural enemies, as this has been observed to
happen in the daytime as well as after nightfall. It follows that the
protection of native birds, especially the woodpeckers and related
species, will greatly assist in restraining the undue increase of this
borer.

METHODS OF CONTROL.

The protected and concealed manner of life of this species, as
shown by the life history, which will apply in the main to other
borers also, renders it very difficult of treatment by means of insect-
icides or other direct measures. The most efficacious remedial meas-
ure consists in cutting off and destroying affected branches and
in the injection of bisulphid of carbon into the holes or burrows
where the larve are at work.

Pruning and cutting back.—Twigs or branches which, by their
wilting or by the frass which accumulates at the entrance to their
burrows, indicate the presence of this borer, should be carefully
searched out, the smaller ones pruned away and the larger ones
cut back, the amputated portions being promptly burned. After
windstorms, the affected branches which have fallen to the ground.
and those which remain attached to the tree should be collected and
burned. Wherever trees show that they are past recovery it is best
to take them out and promptly destroy them. The word promptly
is used advisedly, for this insect, as has been shown previously, fre-
quently migrates from one twig or branch to another.

Bisulphid of carbon.—in the case of young and rare trees and
others which show only a few larval burrows in the bark, bisulphid
of carbon is the best remedy and one which has been in general use
against the present species in the public parks of New YorkCity. It
is Injected into the openings of the burrows, and the openings are
afterwards closed with various substances. For this injection a
mechanic’s long-spouted oil can of small size may be used on large
trees, but against a related species the writers have made very good
use of a small glass syringe, such as may be purchased at any drug
store for ten cents. These glass syringes are most serviceable, be-
cause the exact amount of bisulphid may be seen when drawn into
the syringe and because the reagent does not injure the thread pack-

(Cir. 109]

a

7

ing.* Metal syringes may also be used, but it is more difficult to
measure the exact amount and the bisulphid acts on the leather
packing. Rubber syringes can not be used because of rapid corrosion.
About a teaspoonful of the liquid bisulphid is sufficient for each
burrow.

For stopping the holes after injecting the liquid, putty and moist
clay, advised by some, have not been found so serviceable as grafting
wax. Coal tar may be substituted for the latter, or the holes may be
closed by inserting a wooden plug and breaking or sawing it off level
with the trunk. In any case the stopper should be tight, to exclude
water from rains, which might tend to produce decomposition of the
surrounding wood or invite other insects, like black ants and second-
ary borers, of which there are many species, and injurious fungi.

Carbon bisulphid should be handled with the usual precautions
against fire, which means that the operator should not smoke while
at work. Although a deadly poison, it will not injure ordinary
trees when applied as described.

Killing with wires.—It is possible to reach and destroy some larve
by forcing a copper or other pliable wire into the channels. This is a
well-known borer remedy. It is impossible, however, by this means
to kill the insects in all cases, owing to the length or crookedness of
the burrows. Bisulphid of carbon should then be used.

Electric lughts—To what extent electric lights are serviceable as an
agency in the destruction of the moths of this borer has not been
definitely determined. Col. Nicholas Pike and Dr. J. B. Smith,
however, have advised placing shallow pans around electric-light
poles in and around parks to attract the moths. The pans are par-
tially filled with water and a few drops of kerosene are poured into
them. The moths flying against the globes drop into the pans and
are promptly killed when they come into contact with the oil. In
this way many males can be destroyed.

Inspection.—In large parks the destruction wrought by this borer
annually is an important item, and it will be found a source of profit
to establish a system of inspection consisting in the employment of
parkkeepers and boys, and others who may be engaged at lower

a During the last years of the nineteenth century a long row of beautiful red oaks
bordering the street between the grounds of the Department of Agriculture and those
of the Smithsonian Institution were badly infested by the related carpenter worm
(Prionoxystus robinie Forst.). .Nearly every tree was infested and frequently two or
three burrows showed near the tops of the trunks. Bisulphid of carbon was applied,
as described above, and the holes closed with grafting wax. A year later no insects
could be found at work, but wherever this remedy had been applied a small scar
remained. Two years later these had entirely disappeared and the trees looked as if
they had never been infested.

(Cir. 109]

8

wages, to keep a constant lookout for evidences of borer attack on
valuable trees. On this head Southwick has reported that in 1893
he spent two months in fighting this insect alone in the city parks of
New York, collecting wagon loads of limbs and branches and destroy-
ing the larve or pupe.

Maintaining trees in thrifty condition.—If valuable trees are to be
protected, the insect should not be allowed to breed in useless growth.
The borers in such trees should be destroyed or the trees promptly
felled and burned. Care should be exercised in transplanting new
trees, and fertilizers should be used in order that the trees may be
always thrifty, the better to withstand attack. This means protect-
ing them from the attack of aphides, scales, and defoliators, such as
tussock moths and the fall webworm, and keeping them free from
disease.

Finally, in the control of this species promptness and thoroughness
can not be too strongly emphasized. The bisulphid of carbon
remedy should always be used where applicable, and the inspection
system advised should be instituted in all public parks and on city
streets infested by this pest. Individual owners of valuable trees
should become acquainted with the pernicious nature of this borer,
and united action should be secured with neighbors who also suffer
from the ravages of the pest.

Notr.—After this publication was in type we received information that trees in
the college yard of Harvard University, Cambridge, Mass., are being severely injured,
the large elms being the most seriously attacked.

Approved:
JAMES WILSON,
Secretary of Agriculture.
WasuineTon, D. C., May 27, 1909.

[ Cir. 109]

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