UNIVERSITY OF

AGRICULTUPJ

WON CIRCULATING

CHECK FOR UNBOUND
CIRCULATING COPY

OF

UHWERSITY OF

UNIVERSITY OF ILLINOIS

Agricultural Experiment Station

BULLETIN NO. 151

BY STEPHEN A. FORBES
STATE ENTOMOLOGIST

URBANA, ILLINOIS, OCTOBER, 1911"

CONTENTS OF BULLETIN NO. 151

PAGE.

The Catalpa Sphinx (Ceratomia catalpa Bdv.) 464

The Fall Web-worm (Hyphantria textor Harr.) 466

The Yellow Poplar-Caterpillar (Apatela populi Riley) 468

The Walnut Caterpillar (Datana integerrima G. & R.) 470

The White-marked Tussock-moth (Hemerocampa leucostigma S. &A.) 472

The Brown-tail and Gypsy Moths (Euproctis chrysorrhcea L., and

Porthetria dispar L. ) 476

The Forest Tent Caterpillar (Malacosoma disstria Hbn.) 483

The Common Canker-worm (Paleacrita vernata Peck) 485

The Lilac Borer (Podosesia syringa Harr.) 489

Two Poplar Borers (Memythrus tricinctus Harr. and M. dollii Neum.) 493

A Viburnum Borer (Sesia pictipes G. & R.) 496

The Maple Borer (Sesia acerni Clem.) 497

The Ninebark Borer (Sesia scitula Harr.) 499

The Bag- worm (Thyridopteryx ephemera -formis Harr.) 500

The Poplar and Willow Borer (Cryptorhynchus lapathi Linn.) 502

The Dogwood Twig-girdler (Oberea tripunctata Swederus) 506

The Locust Borer (Cyllene robinia Forst.) 510

The Oak Twig-pruner (Elaphidion villosum Fabr.) 512

The Bronze Birch-borer (Agrilus anxius Gory) 515

The Scurfy Scale (Chionaspis furfur a Fitch) 517

The Oyster-shell Scale (Lepidosaphes ulmi Linn.) 519

The San Jose Scale (Aspidiotus perniciosus Comst.) 520

Putnam's Scale (Aspidiotus ancyhts Putnam) 523

The Walnut or Willow Scale (Aspidiotus juglans-regia Comst.) 523

The Cottony Maple Scale (Pulvinaria vitis Linn.) 524

SOME IMPORTANT INSECTS OF ILLINOIS
SHADE TREES AND SHRUBS

BY STEPHEN A. FORBES, STATE ENTOMOLOGIST

The protection of the shade trees and ornamental shrubs of
Illinois against insects has been for several years a problem of rap-
idly increasing importance. Many of our most desirable trees
and shrubs are liable to slow destruction by obscure insect
pests understood little if at all by those immediately con-
cerned. Trees which have grown for years, becoming more at-
tractive, more valuable, and more highly valued year by year, begin
to weaken and decay, the owner does not know why. This is often
due to borers or to scale insects, the presence of which has not been
detected or suspected, but whose injuries might have been prevented
if the facts had been known in time. More sudden losses are fre-
quently caused by overwhelming attacks of leaf-eating insects
which, altho conspicuous, are not dealt with because proper measures
of procedure are not known. Observations and experiments upon
this subject have been for several years a prominent part of the work
of the office. Beginning in 1898, repeated careful examinations
have been made of the trees and shrubs of the parks and boule-
vards of Chicago, and this work has been extended from time to
time to other cities and towns thruout the state. With the estab-
lishment of a field assistant in Chicago in 1907, the subject received
more continuous attention at the hands, first, of Mr. H. E. Hodg-
kiss and, later, of Mr. John J. Davis, the latter of whom espe-
cially has made many studies of the life histories of species previ-
ously but little known, and has added a mass of details to our
knowledge of the subject in all its parts.

The general subject is still under investigation, and will be in
due time reported upon in a much fuller and more elaborate article,
but the present brief preliminary paper has been prepared in the
hope that it may be found of immediate practical use to municipal
authorities in control of parks, boulevards, and streets, to town im-
provement societies, and to owners of lawns and other private
premises the appearance of which they are striving to improve by
the use of trees and shrubs.

464 BULLETIN No. 151 ^ [October,

THE CATALPA SPHINX
(Ceratomia catalpce Bdv.)

One of the most destructive of the few insects to which the
catalpa tree is subject is a large showy caterpillar known as the
catalpa sphinx (Fig. i). It is a southern insect, and has not been
found in this state north of Clay and Richland counties, altho it has

F g. l. Catalpa Sphinx (Ceratomia catalpa?.): a, egg mass; b, newly hatched
larvae; c. d, larvae one-third grown and one joint showing its dorsal pattern;
«t /, ff, h, i, mature larvae, variously marked, and single joints showing dorsal
patterns; j, pupa; k, moth; I, egg, enlarged; others all slightly less than
natural size. (Ohio Experiment Station.)

191 1] IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 465

extended up the Atlantic coast as far as New Jersey. It is likely
to appear suddenly in large numbers upon single trees, stripping
them completely.

The full-grown caterpillar (Fig. i, e, f, h) is rather strongly
marked, with a broad velvety black stripe on the back and sulphur-
yellow sides spotted with black, while the under side of the body is
pale green. It is unusually variable in color, however, there being
both light and dark forms. It is from two and a fourth to three
inches long, and has a hornlike appendage projecting from the
hinder end of the back. The young caterpillars (Fig. I, c) are
pale yellow and spotted with black. There are probably but two
generations in Illinois. The caterpillars leave the trees and go
into the ground to pupate (Fig. 2).

Fig. 2. Catalpa Sphinx, Ceratomia
catalpce, pupa in cell in earth.

The parent insect is a large heavy-bodied moth (Fig. i, fc) with
strong, narrow, brownish-gray wings, with obscure lines and spots
of black. The eggs (Fig. i, a) are laid in masses on the leaves,
sometimes as many as a thousand in a bunch, and the young, on
hatching, feed at first in companies — a fact which makes it easy to
destroy them if their presence is detected early, by picking off or
spraying the infested leaves. A general spraying of a tree with
arsenate of lead or Paris green will destroy the caterpillars at any
time. Professor H. Carman, of Kentucky, says that the nearly
grown worms can be shaken or jarred down from most catalpa
trees and readily destroyed by hand.

466

BULLETIN No. 151
THE FALL, WEB-WORM

[October,

(Hyphantria textor Harris)

The fall web-worm is the only common Illinois insect which
makes a large conspicuous web in late summer and in fall, inclos-
ing a considerable number of the leaves and twigs of a branch, together

Fig. 3. Pall Web-worms, Hyphantria textor, and their web, on apple-tree.
(New Hampshire Experiment Station.)

/9//1 IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

467

with a colony of caterpillars which feed under its protection (Fig.
3). It is un fortunately often called in Illinois the tent caterpillar,
but the latter name is properly applied only to a caterpillar, not
often seen in this state, which makes a small compact web in the
forks of a branch in spring, which it uses only for protection while
not eating.

The web-worm is an almost universal feeder and has been
found on about a hundred and twenty species of fruit, shade, and
ornamental trees, upon the leaves of which it feeds. It is one of
the most annoying pests of the tree grower, its numerous large
webs, enclosing brown, skeletonized leaves, making the tree very
unsightly, and the injury done, as it spreads from branch to branch,
often being considerable. While the caterpillars are growing they
do not wander from their common web, but enlarge this to cover
fresh leaves as fast as those within it are devoured. When they
have nearly completed their growth, however, they scatter far and
wide, running briskly about when disturbed, and feeding on almost

Fig. 4. Fall Web-worm. Hyphantria textor: a, b,
larvas, light and dark varieties; c, pupa; d, moth,
spotted variety. All slightly enlarged. (New Hamp-
shire Experiment Station.)

468 BULLETIN No. 151 [October,

every green thing they find. At this time they become, when very
abundant, an extremely destructive and annoying pest.

They are about an inch long when full grown, varying from pale
yellow or grayish to a dark bluish-black hue. (Fig. 4, a, &.) The
body is covered with long straight hairs grouped in tufts rising
from small black or orange-yellow tubercles, of which there are a
number on each segment. When mature, the caterpillars go to the
ground, into which they burrow a short distance, or they creep
under shelter above ground, where they form slight cocoons of
silken web interwoven with the hairs from their bodies. Within
these they change to dark brown pupae (Fig. 4, c), and in this con-
dition they pass the winter. The moths emerge in spring and
lay their eggs in broad patches of several hundred each, on
the under side of the leaves near the end of a branch, late in
May and early in June. The adult insect is usually pure white,
but is sometimes white spotted with black. There are either one
or two broods of this species, according to the latitude, two in
southern and central Illinois and probably but one in the northern
part of the state.

The simplest and most effective method of controlling these
insects is to destroy their webs, and the caterpillars within them,
either by cutting off the twigs which bear them and crushing or
burning them immediately, or by burning the webs on the tree.
A bundle of rags or a few corn-cobs, or even a porous brick, wired
to the end of a pole long enough to reach the nest and saturated
with kerosene, makes a good torch for the purpose. Care must
be taken, however, not to injure the tree, and to destroy the scat-
tering worms which may drop from the nest without being killed.
Where the infestation is too general to make this method con-
venient, or where the webs are so high in the trees that they can
not be readily reached, a spray of arsenate of lead will eventually
kill the web-worms as they extend their webs over the poisoned
foliage. Paris green may be used instead, but the lead arsenate
is to be preferred because, being much more adhesive, it lasts longer
on the tree. This method is most effective when the caterpillars
are young, since they are then extending their webs rapidly and are
likely to be more promptly poisoned than when they are virtually
full grown.

THE YELLOW POPLAR- CATERPILLAR
(Apatela populi Riley)

The prominence of the Carolina poplar as a city tree, especially
in situations where it is difficult to find any other which can en-
dure the conditions prevailing, makes it the duty of the Entomolo-
gist to discuss the insect enemies of even this rather inferior va-
riety.

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 469

Among those which have recently been found most injurious
to* the poplar is a large and rather handsome, light yellow or pale
green, very hairy caterpillar (Fig. 5), most easily known by five
long pencil-like tufts of black hairs rising one behind the other on
the middle line of the back, the first on the fourth segment of the
body and the fifth on the last. This caterpillar was particularly in-
jurious to poplars and considerably so to willows in Chicago in
1909. It has been noticed by us also in Peoria, Danville, and East
St. Louis. It feeds on the leaves in midsummer and again in fall,
there being two generations in a year. It sometimes completely

Fig. 5. The Yellow Poplar-Caterpillar, Apatela popuii,
natural size.

strips a tree, rendering it unsightly and putting it in poor condition
to withstand unfavorable conditions or to resist the attacks of
more destructive insects.

The caterpillar when full grown is about an inch and a half long,
the skin yellowish-green, and the long, soft, drooping hairs yellow.
The pencil-like tufts referred to rise from the fourth, sixth, sev-
enth, and eleventh segments, those on the seventh and eighth being
the smallest. The head is shining black and there are black spots
on the top of segments one and two. The young are almost white,
and the black tufts of hairs are shorter, but still conspicuous. The
caterpillar is of a sluggish habit, and when at rest it commonly lies
curled up, with the ends of the body together. When full grown
it spins a loose, pale yellow cocoon of silk interwoven with its
own hairs. This is generally placed in a crevice of the bark, under
the edge of a fence board, or in some similar sheltered place. The
winter is passed in this chrysalis stage, from which a large, pale
gray moth emerges the following- May.

The caterpillars are most easily destroyed when young, for they
do not at first scatter from the branch upon which they were born.

470 BULLETIN No. 151 [October,

Later they can readily be collected singly by hand from trees of
small size, or they may be poisoned, like most of the leaf feeders,
by spraying with arsenicals when they are active on the tree.

THE WALNUT CATERPILLAR
(D at ana integerrima G. & R.)

The most annoying insect enemy of the walnut is a blackish,
somewhat striped, hairy caterpillar (Fig. 6), an inch and a half
long when full grown, which eats the leaves during the latter part
of the summer, often largely denuding the tree. It makes itself
particularly offensive on lawns by dropping quantities of refuse
from the tree and by crawling over walks and buildings when it
comes down to go into the ground.

This caterpillar is readily distinguished by its loose coat of
soft whitish hairs, and particularly by its habit of raising both ends
of the body when at rest and throwing itself into this position and
jerking sidewise when disturbed. It often attracts attention by col-
lecting in masses upon the larger branches or the trunk of the tree
preliminary to molting, piling up in this way two or three layers
deep. When full grown it comes down the trunk to the ground,
wanders about to a short distance and enters the earth an inch or
two, changing there to a reddish-brown or blackish-brown chrysalis
(Fig. 6, B). In this stage it winters, emerging the following sum-
mer, mainly in June and July, in the form of a buff-brown moth
(Fig. 6, A) with darker bands across the fore wings. The females
lay their eggs in clusters varying from seventy-five to a hundred,
according to some observers, and from five hundred to twelve
hundred, according to others, and the young hatching from these
feed in dense clusters, completely devouring every leaf as they go.
When all the leaves on one twig or branch are destroyed, they mi-
grate to another, sometimes in a distant part of the tree. They
lose their gregarious habit as they mature, and by the time they are
full grown they scatter here and there over the greater part of
the tree. There is but a single generation in a year.

Altho they are most frequently seen on the walnut, they are
common on butternuts and hickories, and are a pest to the grower
of the pecan. They have likewise been found on beech, oak, willow,
honey-locust, apple, and thorn. Trees in the forest are not likely
to suffer, but those on streets and lawns are sometimes so completely
stripped by September that they stand almost as naked as in mid-
winter, only the green nuts remaining on the branches.

This account of their habits is sufficient to suggest various avail-
able methods of destroying them. On trees small enough to be
reached they can be readily killed while young by clipping off the

797 1] IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

471

infested twigs on which the caterpillars are grouped in colonies.
They are particularly exposed to attack as they assemble in masses
for their later molts, when a light spray of kerosene will readily
kill them. They are also susceptible to arsenical poisons sprayed

F/g. 6. Walnut Caterpillar, Datana integerrima: A, moth; B, pupae. Natural size.
(Kentucky Experiment Station.)

472 , BULLETIN No. 151 [October,

upon the leaves, but these must be used in unusual strength. We
have found three pounds of arsenate of lead to fifty gallons of wa-
ter sufficient to kill the full-grown caterpillars. On one occasion
a tree nearly fifty feet high was effectively sprayed by the aid of a
twenty-eight-foot ladder and a twelve-foot extension rod with a
nozzle on the end, about twenty- five gallons of the spray being nec-
essary for a thoro treatment. If these various measures have
been neglected and the caterpillars have left the tree, they may still
be disposed of in the pupa stage by digging up and working over
the ground under the branches and for a little distance outside, to
a depth of three or four inches.

THE WHITE-MARKED TUSSOCK-MOTH
(Hemerocampa leucostigma S. & A.)

The most destructive leaf -eater infesting shade trees in the
larger cities of Illinois and especially in Chicago is the caterpillar of
the white-marked tussock-moth. It often completely defoliates large
trees, those most seriously injured being the elm, the soft maple,
the linden, the birch, and the horse-chestnut. (Fig. 7.) Almost
every kind of tree, excepting conifers, is subject to its attack, and
it sometimes becomes decidedly injurious in orchards. In Chi-
cago it has been noted as injurious to apple, box-elder, hard maple,
Norway maple, poplar, willow, oak, ash, locust, hickory, catalpa,
and sycamore, and to several shrubs, including dogwood, button-
bush, Viburnum, and bladdernut (Ptelea). In September and
October, 1910, it was found in every one of eighteen towns visited
by Mr. John J. Davis, present in small numbers in seven of them,
common in nine, and in destructive numbers in two.

This is a well-marked insect, very easily recognized, especially
the caterpillar and the egg mass — the two conditions against which
measures of destruction must be taken. The hairy caterpillar (Fig.
8), bright yellow in general color and striped with black, and about
an inch and a half long when full grown, is a really beautiful object.
It may be known by its coral-red head, by two plumelike tufts of
long black hairs projecting upward and forward from the back near
the head, by a single similar tuft at the hind end of the body, and
especially by four thick, short, brushlike clusters of cream-colored
hairs arranged, one behind the other, in front of the center of the
back. In this condition it may be found upon infested trees in
June, July, and August.

There are two generations of the caterpillar in a year in north-
ern Illinois, possibly three farther south. The egg masses (Fig. 9)
from which the caterpillars hatch may be found in fall, winter, and
early spring. They form, when first deposited, frothy, oval, snowy

/9//] IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 473

Fig. 7. Linden tree in a park in Chicago, defoliated by larvae
of White-marked Tussock-moth (Hemerocampa leucostigma). The
few leaves on the tree have all appeared since the defoliation.

white patches about an inch in length, on the tree trunks, in the
crotches of the larger branches, or in other more or less sheltered
places, such as the edges of weather-boards and the under sides of
the eaves of porches. Conspicuous objects at first, their color, under
exposure to the sooty air of Illinois towns, is soon deadened to a
dirty gray. The caterpillar begins to hatch from the over-wintering
egg masses about the middle of June in Chicago (June 18 in 1909)
and gets its growth in about a month. Feeding at first on the under
side of the leaf, which it skeletonizes by eating off the soft tissue,
it later eats inward from the edge of the leaf, devouring everything
except the principal veins.

474

BULLETIN No. 151

[October,

The young caterpillars drop down, hanging by silken threads,
when the tree is jarred, and sometimes spin down without being dis-
turbed, when they may be blown to a considerable distance by the

Fig. 8. White-marked Tussock-moth, Hemerocampa
leucostigma, larva. Natural size.

wind. When nearly full grown, they are great travelers, going
from tree to tree and even moving in large numbers from a de-
foliated tree to others near by. When full grown, the caterpillar

Fig. 9.

White-marked Tussock-moth, Hemerocampa leucostigma, cocoons
and egg masses on tree trunk in a park in Chicago.

i9i i] IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 475

spins, on the tree, a delicate grayish cocoon of silken web mixed with
its own long hairs. It changes to a pupa within a few hours after
the cocoon is finished and continues in this condition from ten days
to two weeks.

The adults are moths, the females (Fig. 10) of which differ
very widely from the males (Fig. n) in the fact that they are
almost absolutely wingless. The males have good wings and at

Pig. 11. White-marked
Tussock-moth, Hemero-
campa leucostigma, male.
Natural size.
Fig. 10. White-marked Tussock-
moth, Hemerocampa leucostigma,
female and egg masses. Natural
size. (Connecticut Experiment
Station.)

least the average power of flight. They are of an ashy gray color,
with dark wavy bands across the fore wings, a small black
spot on the outer edge near the tip, a blackish stripe be-
yond this, and a minute white crescent near the hind angle.
The wings, when expanded, measure about one and a fourth
inches across. The female has little of the appearance of a
moth, her wings being reduced to the merest rudiments. Her
thick, oblong-oval body is of a light gray color, with rather
long legs, and is distended with eggs. When she comes out
she lays her egg mass on the cocoon from which she emerged — a fact
which makes it plain that the species can spread only by way of the
wandering caterpillars, or by the transportation of egg masses on
young trees. The eggs of the last generation are ordinarily pro-
duced in September and the winter is passed in this condition.

Many insect parasites infest the pupa and do much towards hold-
ing the species in check. They are not usually abundant enough,
however, to control it completely. In the fall of 1907, for example,
one of my assistants reported that 75 percent of the cocoons of
the tussock-moth in the Chicago parks were parasitized, but the
caterpillars were nevertheless very numerous and destructive the

476 BULLETIN No. 151 [October,

following year. Birds eat them, but not freely enough in the larger
cities to reduce their numbers materially.

Three measures of destruction are applicable to this pest and
sufficient for its control. These are the destruction of the egg
masses in winter, banding trunks of uninfested trees in spring, and
spraying infested trees in summer. The trunks and larger branches
of trees, as well as all objects surrounding those infested the season
before, should be carefully examined in winter and spring for egg
masses, and all these within reach should be scraped or cut away
and burned or otherwise destroyed. Those beyond convenient reach
may be killed in place by touching each egg mass with a sponge or
brush attached to the end of a long pole and dipped in crude creosote.

As the insect spreads from tree to tree only in the caterpillar
stage, an uninfested tree may usually be protected completely by
banding the trunk in such a way that the caterpillars from adjacent
trees can not climb beyond the band. Sometimes, however, the
branches of trees intermingle or touch in such a way that the cater-
pillars may go from one tree to the other without coming down
to the ground. These bands should be applied to the tree soon
after the caterpillars begin to appear in spring, and they should
be renewed from time to time as they are made useless by exposure
to the weather.

Either one of two kinds of bands may be used. The trunk
may be surrounded, at a convenient height, by a belt nine inches
wide of what is known as tree tanglefoot, applied with a brush;
or bands of cotton batting about four inches wide may be tied
closely about the tree by a string passed around the middle of the
band, the upper half of which should then be turned down over it.

Where the preceding measures have been neglected and trees
are being defoliated, the injury may be stopped by spraying with
Paris green or arsenate of lead. This, however, is a difficult and
somewhat expensive operation with large trees, and may be ren-
dered unnecessary by destroying the egg masses and banding the
trees as above described.

THE BROWN-TAIL AND GYPSY MOTHS
(Euproctis chrysorrhcea Linn, and Porthetria dispar Linn.)

These two frightful insect pests, altho present in America,
the first for about forty years and the second for nearly half as
long, have neither of them become established in Illinois, or indeed
made any permanent appearance outside of New England. It will
probably be long before the gypsy moth becomes an inhabitant of
this state, its powers of migration being limited to the larva. The
female, altho well provided with wings, has a very heavy body,
and does not fly. The brown-tail moth, on the other hand, is a

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

477

strong, swift flier, and is virtually certain to occupy the whole
country in due time, and it is further particularly likely to be in-
troduced into the state direct from its European habitat on nursery
stock imported from France. It winters in the caterpillar stage
partly grown, hundreds of young collecting in single colonies on the
trees, where they hibernate in closely webbed nests (Fig. 12). Hun-
dreds of these nests containing living young were sent, in 1909, in-

Fig. 12. Brown-tail Moth, Euproctis chrysorrfuza, winter nests. Natural
size. (Connecticut Experiment Station.)

to Illinois from France, and only the most active and fortunate in-
spection work prevented their escape in this state that winter. Worse
than this, however, infested cases of nursery stock originating in
France were reshipped into Illinois from other states where the
force of inspectors was not sufficient to deal with the shipments
arriving, and danger from these sources will continue year after
year unless other states strengthen their inspection systems. Fur-
thermore, since stock received in Iowa was shipped to this state
that winter bearing living brown-tail caterpillars, it is extremely
likely that the part retained in Iowa was similarly infested and
that the brown-tail has thus obtained a lodgment there and possibly
in other states adjacent to Illinois. If this is the case it will pres-
ently spread to our state also, especially as -the moth flies long dis-
tances before the prevailing winds. It is important, for these rea-

478

BULLETIN No. 151

[October,

sons, that our people should be fully informed and carefully in-
structed in advance in order that the first of these insects to appear
may be detected and destroyed without delay.

The brown-tail moth is a caterpillar (Fig. 13) in the destruc-
tive stage, and, of course, goes thru the four stages of egg, larva,
pupa, and adult. It is easily distinguished in the last of these stages

Fig. 14. Brown-tail Moth, Eu-
proctis chrysorrhcea. Slightly en-
larged. (Massachusetts Experi-
ment Station.)

Fig. 13. Brown- tail
Moth, Euproctis chrys-
orrficsa, larva. Natural
size. (Massachusetts
Experiment Station.)

from any American insect by the character to which it owes its
name of "brown-tail," namely, a thick brushlike tuft of orange-
brown hairs at the tip of the abdomen, especially in the female
(Fig. 14). Otherwise both sexes are pure white thruout, except
that occasionally there may be a few black spots on the fore wing of
the male. They measure about an inch and a quarter from tip to
tip of the expanded wings. Any pure white moth of approximate-
ly this size with an orange-brown tuft of hairs at the tip of. the
abdomen may be at once set down as the brown-tail; and any one
seeing it in Illinois will render a notable public service by reporting
the fact promptly to the State Entomologist, at Urbana, 111.

The winter nests of these caterpillars are also easily identi-
fied, since no native Illinois species hibernates on either tree or
shrub in colonies of living caterpillars inclosed in a web. Any
such cluster of young caterpillars so protected by a common web
may consequently be set down at once as the brown-tail and should,
of course, be promptly destroyed and the facts reported to the
Entomologist. Nurserymen importing European seedling stock can

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 479

not guard too carefully against the accidental importation of this
insect pest, as it is widespread in Europe, breeding abundantly on
hedges, trees, and various shrubs, and making its way into the
nursery from infested surroundings.

The brown-tail feeds upon practically all deciduous trees and
many shrubs and even upon herbs. Thousands of fruit trees in
the vicinity of Boston have been killed by it, and damage to maples
and elms in wooded regions has caused the forest to appear brown
in June, an injury which, if repeated for three or four years, has
killed many trees. As the caterpillars pass the winter about a quar-
ter grown, they begin to devour the leaves of trees as soon as these
put out in spring, and even eat the buds and blossoms before the
leaves have spread. Old trees may thus lose all their buds, or, if
not, the foliage itself may be devoured at a later date.

The caterpillar reaches its full size in New England during the
last half of June, and the moths emerging, fly about and lay their
eggs some twenty days later. The small round eggs are laid in
brownish masses (Fig. 15) on the under side of leaves, each mass

Fig. 15. Brown-tail moth, Euproctis chrys-
orrfCxa, egg masses on leaves. Natural size.
(Connecticut Experiment Station.)

two-thirds of an inch long by a fourth of an inch wide, and con-
taining about three hundred eggs. The full-grown caterpillar is
about two inches long, reddish-brown, with an interrupted
white stripe on each side and two red dots on the back near
the hind end. It is also blotched with orange and is cov-
ered with tubercles bearing long barbed hairs, those on the
back and sides with short brown hairs additional, which give
them, when magnified, a velvetlike look. The young hiber-
nating larvae are blackish, with reddish-black hairs and black
heads. The pupa is formed among the leaves on the infested tree
or shrub, most frequently at the tips of the branches, where sev-
eral caterpillars may spin a loose web together, each forming, how-

480 BUTXETIN No. 151 [October,

ever, its own cocoon within the web. When the insect becomes
abundant, cocoons may be found under fences and at the edge
of clapboards on houses, and in many similar places.

One of the most disturbing peculiarities of a brown-tail in-
festation is the fact that the long barbed hairs already mentioned
are covered with a poisonous excretion, and that they readily pierce
the skin, causing an irritating rash which occasionally results in
serious illness. "Indeed," says Dr. Howard, "it is not necessary
for the caterpillar itself to come in contact with the skin; at cer-
tain times of the year it seems as though the hairs were actually
floating about in the air. At the time of the caterpillar's change
of skin, and particularly at the time of the spinning of the cocoon
and the final change, certain of these hairs appear to become loos-
ened in such a way that they are carried by the wind." Others
report that these poisoned hairs may collect on clothing hanging on
the line, to the intense annoyance of those who wear it.

The readiest and most obvious means of controlling the brown-
tail moth, and certainly the easiest one, is the collection and destruc-
tion of the winter nests after the leaves have fallen. After April
the only practical remedy is spraying the trees with an arsenical
mixture. The young caterpillars are readily enough destroyed with
arsenate of lead, but the older ones become resistant to poison
sprays, and as much as five pounds of the arsenate to a barrel of
water has been found necessary to kill the full-grown caterpillar.

When this insect appears within our borders it will be most
destructive in parks and towns and forest plantations, since these
are not regularly sprayed and will require a special treatment to
protect them. It will also aid the San Jose scale in putting out
of business the neglectful or indifferent orchardist, but the business
fruit grower, who values his property and takes care of it as well
as he can, will have much less to fear from this insect, since his
ordinary spraying operations will be practically certain to destroy
it as it enters his orchard. The fact, however, that the full-grown
caterpillar requires a heavier insecticide treatment than does the
codling-moth and the canker-worm, for which most of our spray-
ing is done, may make it necessary to go over the orchard in winter
to remove and destroy the hibernating colonies.

The gypsy moth may be more briefly considered, altho it
is even a more destructive pest than the brown-tail, especially for
the reason that it eats the leaves of evergreens — trees which are
often killed by a single defoliation. It is conveyed to distances in
the caterpillar stage only by accident. Passing wagons, automo-
biles, trolley cars, or even railroad trains, may carry the cater-
pillars to uninfested districts, but in this way its spread is slow,
especially as all possible measures are being taken in infested dis-
tricts of New England to keep the roadsides free from the pest,

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 481

and thus to reduce to a minimum the possibility of an extensive
spread.

The caterpillar of the gypsy moth (Fig. 16) is a voracious feed-
er, eating the leaves of nearly every kind of tree or shrub, and de-
vouring sometimes also grasses and field and garden crops. The
very fact that it spreads but slowly makes it locally all the more

Fig. 16. Gypsy Moth, Porthetria dupar, larvae. Natural size.
(Connecticut Experiment Station.)

injurious, since it accumulates in enormous numbers upon infested
localities. Forests, orchards, gardens, parks, and street shrubs and
trees may be stripped of every leaf between the first of May and
the middle of July.

The insect winters in the egg stage, the eggs being plastered
in conspicuous masses (Fig. 17) on the trunks of trees and on va-
rious other objects. They may readily be destroyed by touching
them with a mixture of creosote oil, 50 percent, carbolic acid, 20
percent, turpentine, 20 percent, and coal-tar, 10 percent, in sufficient
quantity to soak the mass. The caterpillar may also be killed on the
trees with arsenical poisons, but these must be applied in unusual
quantities, since the gypsy moth is not readily poisoned in the cater-
pillar stage. Five pounds of arsenate of lead to fifty gallons of
water will kill the young, but even this can not be depended upon
for the full-grown caterpillars. These are about three inches long,
of a sooty or dark gray color. Along the back is a double row

482 BULLETIN No. 151 [October,

of blue spots, followed by a double row of red spots, and the back
is marked with yellow. The cocoon is formed among the leaves
like that of the brown-tail and the moths appear from the middle
of July to the middle of August. The male is bluish-yellow, ex-
panding about an inch and a half, and the female (Fig. 17) is

Pig. 17. Gypsy Moth, Porthetria dispar; female moths, laying eggs on bark. Natural size.
(Connecticut Experiment Station.)

nearly white, somewhat spotted and barred with black. Its wing
expanse is about two and a fourth inches. The female is very slug-
gish and so heavy that she can not fly; but the male is an active
flier.

The oval egg masses, about one and a half inches long by
three-fourths that in width, are laid in summer on the trunks of
trees, on fences, on the sides of houses, and in various other places
Large holes in old trees are often found filled with them. The
caterpillars feed principally at night, especially after they reach
some size, and they seek to hide during the day, often coming down
upon the larger limbs and trunk of the infested tree in search of
hiding places. This habit has led to the use of bands of burlap
tied around the trunks of trees, under which the caterpillars may
rest during the day and where they can be easily destroyed by hand.

The probabilities of widespread destruction to forest, park, and
orchard properties by these insects are greatly reduced by the truly

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

483

tremendous and unexampled work being done by the United States
Department of Agriculture and the state of Massachusetts in bring-
ing from Europe the native parasites of these insects. This work
is making successful progress, and it is all the more hopeful because
the parasites of both these species seem to keep them substantially
in check in the Old World, where they rarely become seriously
destructive.

THE FOREST TENT CATERPILLAR
(Malacosoma disstria Hbn.)

There occasionally appears in the forest region of southern
Illinois an overwhelming eruption of caterpillars which denude
large areas of woodlands, especially the oaks and the maples, and
the black and sweet gum trees, and thence invade orchards, parks,
and town premises, carrying the same destruction to fruit and shade
trees generally. This is one of the species which moves in masses
such as actually to delay the passage of railroad trains, piling up

Fig. 18. Baltimore Oriole attacking nest of Forest Tent Cater-
pillar, Malacosoma disstria. (New Hampshire Experiment Station.)

484

BULLETIN No. 151

[October,

on the rails several inches deep. It is known to entomologists as
the forest tent caterpillar, but in the South it is commonly called
"the caterpillar" simply. The name of "tent caterpillar" is, in fact,
inappropriate for it, since it spins but little and never makes a tent.
It is closely allied, however, to the common tent-caterpillar of
eastern orchards and has received its common name because of this
resemblance.

When full grown (Fig. 19) it is about two inches long and a
quarter of an inch thick. It is of a brownish general color, and is
conspicuously marked with a series of whitish or cream-colored
spots down the middle of the back. On the upper part of each side

Fig. 19. Forest Tent Caterpillar, Malacosoma
disstria, larva. Natural size.

is a Bather broad blue line edged above and below with a
yellowish-brown line. When disturbed it drops from the branch
and hangs suspended in mid-air by means of a fine thread
spun from the mouth. In moving about on the tree these cater-
pillars follow each other in single file. They feed mostly in the
tops of the trees, often eating out the central part of the base of a
leaf, allowing the remainder to fall to the ground. When preparing
to molt, they mass together on the limbs and may continue thus for
a day or two. They often form similar masses in stormy weather
and in general when at rest. The eggs (Fig. 20) are laid in a
thick hard band around a twig and covered with an impervious
varnish. From these the young hatch in early spring, sometimes
before the appearance of the leaves on which they depend for food.

Fip. 20. Forest Tent Caterpillar,
Malacosoma disstria: e, egg ring re-
cently laid; g, hatched egg ring.
Slightly enlarged. (Cornell Ex-
periment Station.)

Fig. 21. Forest Tent Cater-
pillar, Malacosoma disstria:
m, male; /, female. Natural
size. (Cornell Experiment
Station.)

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 485

They are capable, however, of fasting for a considerable time with-
out injury, and they may even survive the destruction of the leaves
by late frosts. They scatter for pupation late in May or early in
June, spinning cocoons which they fasten among clusters of
leaves or exposed on fences and in other similar situations. There
is but a single generation in a year. The parent moths (Fig.
21 ) measure about an inch and a quarter across the expanded
wings. The general color is brownish-yellow and the fore wings
are marked by two straight dark brown lines which cross them
obliquely, parallel with each other and the hinder edge.

Trees may be protected by spraying with arsenical poisons
shortly after the young caterpillars begin to appear, or by clipping
off in winter the twigs bearing the conspicuous belts of eggs and de-
stroying these by burning. Even overwhelming hordes may be ar-
rested by surrounding the tree trunk with a band of cotton batting
about four inches wide, tied around the middle with a string, the
upper part being then turned downward over the string. Or, the
trunk may be surrounded with a band of printers' ink applied as
described in the article concerning the common canker-worm
(P- 488).

THE .COMMON CANKER-WORM,, OR SPRING CANKER-WORM
(Paleacrita vernata Peck)

The common canker-worm is best known as a pest of the apple
orchard, but it is sometimes even more destructive to elms (Fig. 22)
than to apple-trees. It feeds also on cherry, at first eating small
holes thru the leaves, but when larger devouring the whole leaf ex-
cept the midrib and some of the coarser veins. Modern methods
of orchard management require a regular and frequent spraying
with arsenical poisons as a protection of fruit against the codling-
moth, and this has the incidental effect — often unnoticed by the
orchardist — of speedily killing off any colony of canker-worms
which may have chanced to make a start in the orchard. Hence
it is only neglected orchards, or those not in bearing either because
too young or by reason of a crop failure for the year, which are
liable to serious canker-worm injury.

With the elm, however, the case is different. The canker-worm
lives on this tree as willingly and successfully as on the apple. Elms
are rarely sprayed in Illinois, and if the canker-worm once comes
to infest them there is no natural end to the injury except the death
of the tree, unless, indeed, the parasites of the insect and other
natural checks on its increase may happily suppress it before that
event.

486

BULLETIN No. 151

[October,

The spraying of large elms is, of course, a difficult and expen-
sive operation, and canker-worms are less susceptible to arsenical
poisons than many other insects. There is, however, a much cheaper
and more convenient method of protecting the elm, by which ad-
vantage is taken of two features in the economy of the insect.
When the caterpillars are full grown they leave the tree to pupate
in the earth, and the female moth emerging, being wholly without
wings, can only reach the tree to lay her eggs by climbing up the

1

Fig. 28. Injury" to elms at Calamus Lake, Niantic, Illinois,
by common Canker-worm (Paleacrila vetnata).

trunk. If this is encircled at the proper time by a sticky band im-
passable by her or by young canker-worms just hatched from the
egg, the tree is virtually secure against canker-worm injury except
as worms may reach it from neglected trees with which its own
branches interlace.

Altho the female canker-worm (Fig. 23, b) is wingless, the
male (Fig. 23, a) has two pairs of rather large, thin, ashy or
brownish-gray wings, the first pair with a broken whitish band near
the outer edge and three interrupted brownish lines between that
and the body. There is also a short oblique black mark near the
tip of the wing, and a black line at its edge at the base of a fringe
of hairs. The eggs (Fig. 24, &) are about .03 of an inch long, oval
in outline, and of a pearly luster at first, changing to yellowish-
green with a golden, greenish, or purplish iridescence. They are

/9//] IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

487

laid in irregular masses, often as many as a hundred together, and
usually .hidden in crevices of the bark of trees.

The female comes out of the ground to lay her eggs from
February to April, the date varying with the latitude and the sea-
son. The young caterpillars appear about the time that the apple-
tree unfolds its leaves, commonly, in this state, in April or early
May, and they usually get their growth in about a month from the
time when they issue from the eggs. They then go into the ground
to a depth of two to five inches, each one in a small cell, where
they change to the chrysalis, remaining there until the following

Fig. 23. Common Canker-worm, Paleacrita
vernata: a, adult male; 6, female; c, portion
of female antenna; d, joint of abdomen, en-
larged; e, ovipositor.

Fig. 24. Common Canker-
worm, Paleacrita vernata: a,
larva; b, cluster of eggs, nat-
ural size, with one enlarged: c,
side view of one of the seg-
ments, d, back view of same,
both enlarged.

winter or early spring, when the change to the adult insect takes
place. There is thus but a single generation produced each year.
The canker-worm is widely distributed thruout the country and
may occur in destructive numbers in any part of Illinois. Its feeble
power of locomotion prevents its rapid spread in any locality, but
by concentration of its injuries it is the more destructive where it
does occur.

In its injurious or caterpillar stage (Fig. 24, a) it is readily
recognized. It has a long and slender form and the habit of a
"looper" or measuring worm. When not eating it usually adheres
only by its hinder prolegs, extending the body from this point of
support at an angle of about 45 degrees. As it is colored much like
the bark of a tree, it then has the appearance of a stubbed twig. It
also has the habit of spinning down from the tree at the end of a
thread, particularly if the branch is jarred or shaken. Both the just-
mentioned habits are doubtless advantageous to it ; the first by con-
cealing it to some degree from the observation of birds and the
second by putting it beyond their reach. The full-grown canker-
worm is about nine-tenths of an inch in length and may vary from
greenish-yellow or gray to dusky or even dark brown, with paler
stripes along the sides. A close examination will show also two
light lines running close together along the middle of the back.

488 BULLETIN No. 151 (October,

The young are usually olive-green. The wingless female, with its
small gray body from a quarter to two-fifths of an inch in length
and its rather long legs, gives more the impression of a spider than
that of a moth. The chrysalis is pale grayish-brown, with a dark
green tinge on the wing sheaths, and measures about a third of an
inch in length.

This insect has not recently been abundant in Chicago, but its
capacities for injury are well illustrated in a recent attack on elms
at Big Rock, Kane county. Some ten years ago it was generally
prevalent thruout the south-central part of the state, both in
towns and in forests, to which it had apparently escaped from neg-
lected orchards, although in some cases orchards were invaded in
turn from adjacent forests. A most threatening attack was made
on the magnificent old elms of Jacksonville, but a vigorous cam-
paign, first of spraying and later of the application of adhesive
bands, presently brought the outbreak under control.*

A cheap and available band for the trunk of a tree is made by
laying around the trunk first a strip of unglazed cotton batting
two or three inches wide and over this a four- to six-inch strip- of
tarred paper tied around the middle with ordinary wrapping twine.
Upon this paper belt should be spread a layer a quarter of an inch
thick of cheap printers' ink with which a small amount of car wheel
oil has been mixed, just enough to make it easy to spread. If the
tarred belt becomes slightly hardened by exposure so as to permit
an insect to cross, it may be made sticky again by brushing it with
a little of the same kind of oil. The cotton batting beneath the
paper is necessary to keep the young canker-worms or the female
moths from crawling up behind the paper where the roughness of
the bark would give them passageway. These bands should be
placed on the tree as early as the middle of February or the first
of March, the time varying according to the latitude, and they may
be safely removed by the middle of June. The cost of the bands
will approximate ten cents a tree.

If the canker-worms have already ascended the tree, it is some-
times necessary to spray the leaves with an arsenical poison, which
may be either arsenate of lead or Paris green, the latter at the rate
of one pound of the poison and one pound of lime to seventy-five
gallons of water. If the arsenate of lead is used, three pounds of
it dissolved in fifty gallons of water will kill even the full-grown
caterpillars.

*The Canker-worm on Shade and Forest Trees. By S. A. Forbes. Twen-
ty-second Report State Ent. 111., page 139.

191 1] IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 489

THE LILAC BORER
(Podosesia syringes Harris)

Among the borers whose instincts lead the female to choose,
for the deposit of her eggs, scars or injured places on the bark of
trees and shrubs, with the effect greatly to increase the injury and

Fig. 25. Trunk of ash in one of the parks in Chicago, showing injury
by the Lilac Borer, Podosesia syringce.

to prevent its healing, is a species commonly known as the lilac
borer (Podosesia syringes}, because it was first noticed to infest
lilacs. It is much more important, however, by reason of its in-
juries to various species of true ashes,* and to the mountain ash,

*It has been found injurious to the lilac (Syringa sp.), to the mountain
ash (Sorbus americana), and to the white, green, and English ashes (Frax-
inus americana, lanceolata, and excelsior).

490

BULLETIN No. 151

[October,

Fig. 36. Trunk of ash, in one of the parks in Chicago, showing injury
by the Lilac Borer, Podosesia syringce.

on the trunks and branches of which it produces large, rough, scar-
like outgrowths from knots, roughened places, or wounds, by un-
dermining the bark and boring into the wood. (See figures 25 and
26.)

The eggs are laid in summer in masses on rough, scarred, or
knotty places. They hatch in about six days and the young borers
eat thru the bark into the outer layers of the sapwood, where
they mine irregularly about, penetrating the harder wood and go-
ing to the center of small branches. (Fig. 27.) In fall, when they
are nearly or quite full grown, they make a hibernating cell by
plugging up the burrow both before and behind with frass, and
there they pass the winter as larvae. They do practically no bur-

1911} IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

491

rowing in spring, but pupate in April or the first part of May. As
a preparation for pupation, they burrow outward and cut their
way thru the bark, leaving only a thin outer film to close the pupal
cavity. By means of short teeth with which each segment of the
abdomen is armed, the pupa, when mature, works its way out of

Fig. 28. Lilac Borer, Podo-
sesia syringce, larva. About
5 times natural size.

Fig. 27. Lilac Borer, Pod-
osefia syringoR. Burrows
in ash made by larvae.
Slightly reduced.

its gallery until it projects some three-quarters of an inch. The
winged insects, altho moths, closely resemble wasps in movement,
color, and form. They make their appearance from the latter part
of April to the middle of June in central and northern Illinois.

The borer or larva (Fig. 28) is very variable in length. It is
white, yellowish anteriorly, the head of a bright mahogany color,
becoming very dark at the mandibles, which are stout, broad, and
provided with five teeth. The segments of the body are distinctly

492 BULLETIN No. 151 [October,

marked, somewhat flattened, the first segment reddish and leathery
above, the last with a broad yellowish patch.

The moth (Fig. 29) has a black head, a deep brown thorax
more or less marked with bright chestnut-red, and a black abdomen
sometimes marked with chestnut, but sometimes with a small yel-
low spot on each side of the fourth segment, or with the segments
banded with yellow. The femora are black, the anterior pair of
the tibiae orange, the middle and hind tibiae black with orange bands.

Fig. 29. Lilac Borer, Podosesia syringes, adult.
Slightly enlarged.

The tarsi are yellow, the hind pair with a black band above. The
fore wings are deep brown, with a violaceous luster and usually
with a rusty red dash on the outer part. At the base is a transpar-
ent streak. The hind wings are transparent and yellowish, the
veins, discal marks, and margins deep brown, sometimes tinged
with red.

The spread of the wings is from an inch to nearly an inch and
a half, the females being considerably larger than the males.

This insect is very abundant and destructive, especially to the
green ash in Chicago parks, and has been bred by us also from the
white ash at Kankakee. Its injury is very noticeable and character-
istic, especially on the trunks of small trees. Sometimes the smaller
branches break off at the point of injury, but this does not usually
happen until after the moth has escaped. George D. Hulst says,
writing of these insects in New York: "In this section they are
very destructive to both lilac and English ash. Large shrubs of
lilac are now very rarely seen, and the English ash is being rapidly
exterminated. In the latter I have seen the wood completely rid-
dled with the holes made by the larvae and the entire tree dead."

To check the multiplication of the species and the spread of the
injury it will be sufficient to cut away and burn infested branches

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 493

and trees in winter. It may also be practicable to protect trees espe-
cially exposed by painting rough, knotty, and injured places on the
bark with a poison mixture commonly used by orchardists to prevent
infestation by ordinary borers. A number of substances are avail-
able for this purpose, the simplest of which, perhaps, is a mixture
of soft soap and soda, with the addition of Paris green. The fol-
lowing is a convenient formula : To a saturated solution of wash-
ing soda add soft soap sufficient to make a thick paint, and to each
ten gallons of this wash add a pint of crude carbolic acid and half a
pound of Paris green. This may be painted thickly upon scarred,
roughened, or knotty surfaces in April and early May and renewed
as necessary until August.

Two POPLAR BORERS

(Memythrus tricinctus Harris)

(M. dollii Neum.)

Two boring caterpillars, similar in appearance, but differing in
the larval or boring stage mainly in size, infest poplars in this state
to an injurious degree. They are most destructive to young nursery
trees, particularly to the balm of Gilead (Populus candicans}, but
the Carolina poplar (P. deltoides}, Figure 30, is. also sometimes
badly infested. They are generally present thruout Chicago, often
infesting trees which are likewise injured by a boring larva, Cryp-
torhynchus lapathi, discussed on p. 502. They have also been found
by us in park and street trees in several Illinois cities and towns
from Centralia northward. In the case observed by us in Chicago,
the eggs of one of these species, which one we do not know, were
deposited July 22, mostly in a crevice of the bark or in the neigh-
borhood of a bud, and young larvae were first seen July 26, altho
some of these had apparently hatched at least a week before. The
borers winter in the larval stage in the wood, pupate in spring, and
come out as winged moths in June and July — at various dates from
June 18 to July 26, if we may judge by results obtained in our in-
sectary. From a willow in Cook county a specimen of M. tricinctus
was bred which emerged July 2.

The boring larvae are whitish caterpillars, with brown or yellow-
ish heads and a smooth neck shield. The two species are most easily
distinguished by the markings of the head and by the number of
hooks on the abdominal legs. In M. tricinctus the head is yellowish
and mottled with large patches of brown, while the abdominal feet
have from eighteen to twenty-two hooks in a row. In M. dollii

494

BULLETIN No. 151

[October

(Fig. 32) the head is brown with large darker patches on the sides,
and a black band or blotch between the antennae. The abdominal
feet have ten to fifteen hooks in each row. Both these species are

•T

Fig. 30. Small poplar infested with sesiid borers (Memythrus).

distinguished from some other borers of their family by the fact
that the first segment of the thorax bears two oblique dark marks,
approaching each other behind.

/<?//] IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

496

The winged insects are readily distinguished by a comparison of
the wings and abdomens. In tricinctus (Fig. 35) the fore wings
are violaceous-black, the hind wings are transparent, and the ab-
domen is black with three or four yellow bands. In dollii (Fig.
36) the fore wings are brown, the hind wings are brown and

Fig. 31. Poplar Borer,
Memyttirus tricinctus or
dol it, egg. Greatly en-
larged.

Fig. 32. Poplar Borer, Mem^thrus dollii, larva.
About 3 t mes natural size.

opaque, except at the base, and the abdomen is brown, sometimes
with one or more yellow bands.

In our work with these borers it was not at first known that two
species were concerned, and the larvae were not distinguished in our
notes. It was only when the adults appeared that the specific dis-
tinctions were established.

Fig.33. Poplar Borer,
Memyihrus tricinctus or
M. dollii, pupa. About
3 times natural size.

Fig. 34. Poplar Borer,
Memylhrus tricinctus or M.
dollii, anal end of pupa.
Greatly enlarged.

496

BULLETIN No. 151

[October,

Fig. 35. Poplar Borer, Memythrus tricinctus,
adult female. About twice natural size.

A third species, allied to the two above mentioned, but more
commonly found infesting ninebark (Opulaster opulifolius), has
been once bred by us from poplar at Chicago.

Fig. 36. Poplar Borer, Memythrus dollii, adult. About
twice natural size.

A VIBURNUM BORER
(Sesia pic tip es G. & R.)

A boring caterpillar, somewhat larger than that described from
ninebark and dogwood, but otherwise extremely similar, has been
found doing considerable damage to viburnum shrubs in all the
parks of Chicago, and, in one case, to wild black cherry at Riverside.
It burrows beneath the bark, frequently killing the branches. It
spends the winter in the larval stage, and has emerged in our breed-
ing cages during the latter part of June, from the twentieth to the
twenty- fourth. Elsewhere it is reported to emerge during June and
July. The species is known also from plum, cherry, beach-plum,
peach, Juneberry, and chestnut, and has been bred from the black-
knot of the plum.

The placing of the eggs has not been noticed by us. but another
observer, Dr. Bailey, found a cluster of them, ninety-two in number,

/pi/] IMPORTANT INSECTS OF ILLINOIS SHADE TREKS AND SHRUBS 497

on the under surface of loosened bark a few inches from the root of
a badly infested plum-tree.

The removal and destruction of infested branches at the proper
time of the year, that is, during the winter and spring, is the only
measure practicable for the control of this pest.

The winged insect has a blue-black head, thorax, and abdomen,
the thorax with a narrow pale line each side, and the abdomen with
a narrow pale yellow ring on the second and fourth segments, en-
circling the body completely on the latter. The fore wings are
transparent, with very narrow blue-black margins, and a narrow,
straight, discal mark. The inner margin is sometimes scaled with
pale yellow. The hind wings are transparent, with a very narrow
outer margin and no discal mark. The spread of the wings is from
15 — 26 mm., the smaller specimens being males.

•*£,

THE MAPLE BORER
(Sesia acerni Clem.)

The worst of the borers of the maples, both hard and soft, very
common and destructive to soft maples in Chicago, and common
also in towns thruout the state, is a white or nearly white caterpillar
(Fig. 37, a) about half an inch long when full grown, with a yel-
low head and a neck shield of a paler tint. It is especially injurious
to young trees, but usually originates in some surface injury which
attracts the parent moth in search of a place of deposit for her eggs.

Fig. 37. Maple Borer, Sesia acerni: a, a,
larvae; b, b, b, cocoons; c, adult; d, pupal
skin left in mouth of burrow.

498 BULLETIN No. 151 [October,

It burrows mainly just beneath the bark, where it can be found and
destroyed in fall or early spring. It comes to maturity in May or
June, eats its way nearly thru the bark, and pupates the.re. We
collected the adult in considerable numbers, at electric lights, in Ur-
bana, from May 18 to June 3, 1887. When ready for its transfor-
mation the pupa wriggles partly out of its burrow, and the adult
insect escaping leaves the empty pupa-case still sticking in the open-
ing, which is about an eighth of an inch across. (Fig. 37, d.~)

The adult is a handsome wasplike moth (Fig. 37, c; Fig. 38)
with thin transparent wings, a slender yellow body banded and
trimmed with red, and a brushlike tuft of hairs at the tip of the

Fig. 38. Maple Borer, Sesia acerni, adult. About 3 times
natural size.

abdomen. The eggs are laid chiefly in rough or injured places, al-
most wholly in the trunk of the tree, and not in its branches. The
effect of the injury is to kill the bark undermined, and to enlarge
surface wounds and prevent their healing, converting them into
permanent, rough, and very unsightly scars. Sometimes the tree
is killed by a girdling of the trunk.

To prevent attack by these borers the tree should be protected
from injury, and such wounds as it receives should be painted over
or covered with grafting wax. Dr. Felt, State Entomologist of
New York, says that "the deposition of eggs could probably be pre-
vented to considerable extent by treating the trunks of trees about
the middle of May with a wash prepared as follows : Thin one
gallon of soft soap with an equal amount of hot water and stir in
one pint of crude carbolic acid (one-half pint, refined), let it set
over night and then add eight gallons of soft water. Apply thor-
oughly to the trunk, especially about all crevices and wounds, from
the ground to about six or eight feet high, and renew if necessary
before the middle of June." As the borers work near the surface,
they can be easily dug out and destroyed in fall.

191 1] IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 499

THE NINEBARK BORER
(Sesia scititla Harris)

Dogwood and ninebark shrubs (Cornus sp. and Opulaster opuli-
folins) in the Chicago parks are generally infested, and often seri-
ously injured, by a boring 01 girdling caterpillar (Fig. 39) which
works just beneath the bark, mainly at the junction of the branches

Fig. 39. Ninebark Borer, Sesia scitula larva.
About 3 times natural size.

or in the neighborhood of an old dormant bud. The burrows of the
borer sometimes extend lengthwise of the branch, and sometimes
girdle it near its origin. In 1908 nearly every shrub of the ninebark
in Washington Park was infested, and many of the branches were
killed by this larva. The species also infests the chestnut, and has
been bred from galls on twigs of the oak.

The creamy white larva, half an inch long in September, passes
the winter in its burrows, and emerges, according to our observa-
tions, in late June or in July. The head is brown, darkening almost
to black towards the mandibles. The prothorax is slightly brownish,
with two oblique brown markings on its posterior half. The re

Fig. 40. Nitrebark Borer. Se»ia scitttla. adult female.
About 3 times natural size.

maining segments are creamy white, except the last, which is pale
reddish-brown.

The winged insect (Fig. 40) is deep blue-black on the thorax
and abdomen, the former with a yellow line and a yellow patch on
each side, and the latter with a yellow line at its base and, in the

500

BULLETIN No. 151

[October,

male, a narrow yellow ring on the second and fourth segments,
broadening below on the fourth to cover the whole surface. In the
female the fourth segment is yellow both above and below. The
head and antennae are black, the femora blue-black, and the tibiae
yellow. The fore wings are transparent, except the borders and
the discal mark, which are blue-black. The outer margin is marked
with yellow rays. The hind wings are transparent, with very nar-
row blue-black margins. The spread of the wings is from 18 — 22
mm.

This insect can evidently best be destroyed by cutting out and
burning infested branches in winter or early spring.

THE BAG-WORM
(Thyridopteryx ephemeraformis Harris)

One sometimes sees hanging from the branches of trees, in late
summer or in fall or winter, especially in the southern part of the
state, rough excrescences, about two inches long, shaped somewhat
like a spindle full of yarn, soft to the touch, and more or less covered
with pieces of dead leaves which seem to be woven into their web-
like substance (Fig. 41, /). In summer it may be further noticed

Fig. 41. Bagworm. Thyridopteryx (phemertfformis: a, larva; b
and c, pupa, side and back views: d, aault; e, case containing the
eggs; /, larva in case; g, eggs. Natural size..

that these spindle-shaped sacks can creep along the twig, and that
there projects from the end nearest the twig the head and front part
of a caterpillar, the remainder of which is enclosed in the protect-
ing bag. In winter this is hung to the tree by a rather tough liga-
ment composed of material like spider-web. An examination of
these peculiar bodies at that season will show either that they are

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

501

virtually empty, or that they contain a mass of soft yellow eggs.
(Fig. 41, <?.) '

The insect known as the bag-worm, to which these constructions
are due, is in several respects one of the most curious in Illinois.
Altho the parent form is a moth, the female is wingless and naked
(Fig. 41, c), looking more like a grub than a moth, and the wings
of the male, instead of being covered with scales, are smooth and
transparent, somewhat like those of a wasp. (Fig. 41, d.} The
caterpillar infests a considerable variety of both fruit and shade
trees, including among the latter evergreens (especially red cedar
and arbor-vitae, Fig. 42) and several kinds of deciduous trees.

Fig. 42. Bag-worm, Thyridopteryx ephemerceformis, cases hanging- on arbor-vitae twig.;
(Ohio Experiment Station.)

It does its injury by eating the leaves of trees, and its numbers are
often such that they may take virtually every leaf off a tree of
considerable size.

The eggs, contained during the winter in the bag-like cases on.
the trees, hatch the following May or June, and the young caterpil-
lars begin at once to spin for themselves small conical cases (Fig.
41, g) to which they fasten pieces of leaves from the tree upon
which they are feeding. As they grow these cases are enlarged
until they take the form and dimensions already described. The
caterpillars (Fig. 41, a) travel but slowly, and seldom leave the
tree upon which they were hatched until they are about full grown,

502 BULLETIN No. 151 [October,

when they are likely to spin down and wander about. They change
to the chrysalis (Fig. 41, fr) within the bags, which they fasten to
the twigs of the trees as a preliminary, but the grublike female
moth, destitute of wings and with only minute and useless legs,
deposits her eggs within her native sack, works her way out of it,
drops to the ground exhausted, and dies. The winged males (Fig.
41, d*) appear in September and October, and soon thereafter the
eggs are laid.

The bag-worm is a southern insect in its general range, and is
rarely seen in northern Illinois. It' increases in importance south-
ward, and in southern Illinois is often a troublesome pest. In a
general trip to eighteen towns, well distributed thruout the state,
Mr. J. J. Davis, in 1910, found the bag- worm in four out of six
southern Illinois towns visited, but in no others.

The simplest method of destroying these insects is to collect the
bags during the winter and burn them — a thing easily done with the
aid of pruning shears if they can not be reached by hand. If this
measure is neglected, infested trees may be cleared by spraying them
with arsenical poisons soon after the hatching of the eggs — the latter
part of June or early July. A pound of arsenate of lead to forty
gallons of water is a safe and effective poison.

THE POPLAR AND WILLOW BORER
(Crypt or hynchus lapathi Linn.)

The weeping willow, the Carolina poplar, the balm of Gilead, and
the red birch are ornamental trees of sufficient popularity to make
the existence of any insect pest destructive to them a matter of gen-
eral interest. The Carolina poplar especially has had an enormous
distribution of late years in Illinois towns, largely because of the
ease and certainty with which it may be raised, and the rapidity with
which it grows in our soils.

The advent into this country nearly thirty years ago of a
European snout-beetle well known in the Old World as a destroyer
of alders, poplars, and willows, and occasionally injurious to birches
also, has seriously endangered our American plantations of these
trees. Detected first in New York in 1882, and found on Staten
Island in 1886, it appeared in considerable numbers near Buffalo by
1896, and the following year was reported as abundant in Boston,
Mass., and very destructive there to willows and poplars of all kinds,
and to the red birch. By 1901 it had reached northeastern Ohio; in
1903 it was found in two Wisconsin nurseries; and in 1904 it was re-
ported from North Dakota in poplars lately brought into that state
from New York. In Illinois it was first seen by us in 1908 in Caro-
lina poplars at Chicago ; but once detected there it was soon found
to be generally distributed and very destructive to both poplars and
willows in all parts of the city. (Fig. 43.) It has not yet occurred,

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

503

to our observation, elsewhere in Illinois. Wherever it appears it
multiplies locally, but makes a slow spread, a fact apparently due to
the sluggishness of the parent beetle, which, although provided with
wings, makes extremely little, if any, use of them. In consequence

Fig. 43. Small poplar tree In Chicago showing dying of upper
branches resulting from attacks of the Poplar and Willow Borer,
Cryptorhynchus lapat/ii.

of this fact, an infested grove may be nearly destroyed before an-
other, near at hand, becomes even infested. It extends its range
most readily along watercourses by means of the willows and cot-
tonwoods with which our streams are likely to be fringed. Its
spread to distant points seem to have been mainly, if not altogther,
by way of the nursery trade, especially that in poplars and willows
of various kinds. These facts make it particularly important that

504 BULLETIN No. 151 [October,

the signs of its presence should be generally known, in order that
it may be promptly recognized and suppressed upon its appearance
in any new locality.

Injury by this borer may be suspected when the general health
of a tree is evidently affected, where there are dead patches of the
bark, irregularly cracked open (Fig. 44, 45), or where openings in

Fig. 44. Injury by Poplar and Willow Borer,
Cryptorhynchus lapathi.

the bark give exit to a soft excrement like moist sawdust mixed
with fine splinters. The burrows beneath the bark, made chiefly in
the cambium layer, are irregular in direction, sometimes girdling a
small tree, and show nothing of the symmetrical pattern made by
many borers which undermine the bark. Those of the older larvae
dip into the wood, usually reaching the center of the branch unless
this is large. These deeper burrows finally become filled with
powdered wood and splinters, except a chamber at the farther end
in which the larva pupates. In the active boring stage these in-
sects are soft, yellowish, fleshy, cylindrical, footless grubs (Fig.
46) with a pale-brown head and darker mouth-parts. They are
half an inch long when they reach full size, which is about the last
of June for those most advanced. At this time, however, young
larvae may be found under the bark down to a fifth of an inch in
length.

The adult beetles (Fig. 47) begin to appear in July, and con-
tinue abroad at least until October. They are well marked and
easily distinguished insects, a little more than a quarter of an inch

i9ii] IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS SOS.

long, thick-bodied, with a roughened and punctured surface, and a
stout curved beak projecting downward from the head. The gen-
eral color is dark sooty brown, more or less specked and spotted

Fig. 46. Poplar and Willow Borer, Crypto-
rhynchus lapathi, larva. About 4 times natural

size.

Fig. 45. Injury by Poplar and Wil-
low Borer, Cryptorhynchus lapathi.

with gray, and there is a very conspicuous large patch of light gray
on the hinder end of the wing-covers, contrasting strongly with the
adjacent colors. The sides of the prothorax are gray, and there is
a pair of rather definite oblique gray marks just behind the front
outer angle of each wing-cover. The beetle is slow and lumbering
in its movements, and when disturbed drops to the ground like a
curculio, without attempting to fly. It feeds upon the cambium
layer of the younger branches, which it reaches by puncturing the
bark with its snout. It lays its eggs in the older bark, mainly of
branches from two to four years old. This the female does by
first eating downward into the bark by means of the jaws at the
tip of her snout, taking half an hour or more to hollow out a cav-
ity in which the egg is concealed. She then turns end for end, and
leaves an egg in the chamber thus made, and presently moves away
to repeat the process at another point.

The young hatch mainly in August and September, penetrate at
once to the cambium layer, and hibernate there while most of them
are still very small. The following spring they continue to work in
the cambium until nearly ready for pupation, when they enter older
wood.

506 BULLETIN No. 151 [October,

The dependence of the beetle for food upon the bark of the tree
which it infests has suggested the use of poisons for its destruction,
and some tests made at the New York Agricultural Experiment
Station show that the ordinary arsenical poisons applied as a spray
will destroy it. Arsenate of lead is the best of these for the pur-
pose, because of its adhesive quality. Trees to be protected should
be thoroly sprayed at intervals of about a fortnight, beginning

Fig. 47. Poplar and Willow Borer,
Cryp'Oi hynchus lapathi, adult. Length,
about one-fourth men.

with the middle of July and continuing thru August. Moder-
ately infested trees may be saved by cutting out the grubs and cov-
ering the wound with tar. Badly infested trees should be taken out
and burned, either during the winter or before July I of the follow-
ing season. Nursery trees infested by this insect should be un-
hesitatingly destroyed, since they are far worse than worthless, and
are the principal means of conveying the species to places not pre-
viously infested by it.

THE DOGWOOD TWIG-GIRDLER
(Oberea tripunctata Swederus)

Among the insects whose nice and elaborate instincts connected
with the placing of their eggs are the wonder of entomologists, we
must class the twig-girdlers, for their careful preliminary opera-
tions are such as to suggest a knowledge of vegetable physiology
and a prevision of the possible difficulties in the way of the de-
velopment of their young certainly quite beyond the powers of
insect intelligence, and an unsolved puzzle if regarded as a product

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

507

of natural selection. The twig-girdler of the dogwood is an ex-
ample.

This is a small, cylindrical beetle (Fig. 48), about half an inch
long and less than an eighth of an inch in diameter, which prepares
a chosen twig for the reception of the egg by first cutting a groove
around it a few inches from its tip in such a way that the twig

Fig 48. Dogwood Twig-gird-
ler, Oberea tripunctata, adult.
About 5 times natural size.

Fig. 49. Cornus twig
g i r d 1 e d by Dogwood
Twig-girdler, Oberta tri-
punctata, and part en-
larged, showing egg in
position.

presently breaks off at this point, and afterwards making a second
girdle, not so deep as the firsthand from two to four inches farther
back. (Fig. 49.) It then makes two parallel cuts, about half an
inch long, lengthwise thru the bark between the two girdling in-
cisions, and at the proximal end of these makes a short transverse
slit in a way to form an angular flap, beneath which it pushes its
egg. The effect of all this surgery must be to stop the growth of
that part of the branch operated on, and to check the flow of sap
to the section in which the egg is laid.

508

BULLETIN No. 151

[October,

These operations are distributed, in northern Illinois, over the
month between the middle of June and the middle of July. The
eggs hatch within a week or ten days, and the young larvae pene-
trate the twig, burrowing downwards towards its point of attach-
ment, and making holes to the surface at intervals thru which to
discharge their excrement. After a time the larva cuts off, from
within, the part of the twig thru which it has made its way, and
plugs the open end of the burrow with coarse bits of frass. It oc-
casionally repeats this plugging, pursuing its way until winter
overtakes it, and pupating within its burrow from the middle to the
latter part of the following May, first, however, commonly cutting
off the branch obliquely and plugging the cavity a little beyond its
pupal cell. (Fig. 50, 51.) The adult emerges during the latter

Fig. 50. Dogwood Twig
girdler, Oberea tripunc
fata, larva. About 4
times natural size.

Fig. 51. Cornus twig
with burrow of Dog-
wood Twig-girdler, Obe-
rea tripunclata: a, end
obliquely cut off by
larva; 6, /, plugs of
trass; c, openings made
by larva and plugged
up later; d, cocoon of
icnneumoned parasite;
e, remains of parasitized
Oberea larva.

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

509

half of June, eats its way thru this terminal twig, and feeds dur-
ing its short life on the leaves of the infested tree, making oval
holes thru the leaves along the course of the veins. (Fig. 53.)

The presence of this borer is commonly first betrayed by a with-
ering of the leaves at the tip of the girdled shoots. It is a rather
common pest in the Chicago parks, where it has often been abun-
dant enough on the red-osier dogwood (Cornus sanguined} to be
decidedly injurious. Like the other small twig-girdlers, this species
can best be destroyed by cutting off and destroying the affected

Fig. 52. Dogwood Twig-
girdler, Oberea tripunctata,
pupa. About zys times
natural size.

Fig. 53. Cornus leaf injured by
feeding of adult Dogwood Twig-
girdler, Oberea tripunctata.

branches at a time when they are certain to contain the borer; that
is to say, in this case, in any month except June and July.

The various species of this genus have been so imperfectly dis-
tinguished that a specific description of this will not be attempted
here; but the reader is referred to the illustrations for its general
characters. Its larva is much subject to destruction by parasites;
and a characteristic parasitic species has been repeatedly bred by
us from infested twigs.

510

BULLETIN No. 151

[October,

THE LOCUST BORER
(Cyllene robinice Forst.)

A great obstacle to the growth of the common black locust as
a timber tree in Illinois has been the work of a borer which in-
fests this tree only, multiplying year after year in a locust grove
until it destroys every tree. It was a common practice in the early
settlement of the northern part of the state for the farmers to plant
a grove of locusts, with a view especially to a supply of fence-posts.
These groves were, however, all destroyed by this borer during the
middle part of the nineteenth century, and the planting of this
tree was universally abandoned at that time. Of course, with the
disappearance of the tree the borer likewise disappeared, and the
growing of the locust is now again possible if due precautions be
taken against its destruction by this insect. Fortunately, the recent
work of Dr. A. D. Hopkins, in charge of forest insect investigations
for the United States Department of Agriculture, has made it per-
fectly feasible to grow locusts with little or no loss from this cause,
and the following account is mainly taken from his publications on
this subject.

The first evidence of attack by this borer in spring is a fine
brownish dust and an oozing of sap from the bark. Later, gumlike
exudations appear on the injured spots, and quantities of yellowish

Fig. 54. Locust Borer. Cyller,e robinice; pupa: a, front view
b, back view. Enlarged as indicated. (D. S. Dept. of Agri
culture.)

/9//] IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

511

dust lodge in the forks of the tree or branches, and in the loose bark
on the trunk and around its base. Badly infested trees show a
dwarfed, faded, or sickly foliage about the middle of May, and
many of the leaf buds fail to open. The author of this injury is
a whitish, thick-bodied, distinctly segmented, seemingly footless
grub, nearly an inch long when full grown, with small head, and only
a pair of minute feet on the next segment behind. It hatches from
eggs laid in crevices of the bark from August to October. The
young borers are still very small when the winter overtakes them,
and they hibernate in small cavities made by them in the outer bark
of the trunk and branches. They commence operations when the sap
of the tree begins to flow the following spring, and presently pene-
trate the wood, burrowing actively about until July or August, in
central Illinois, when they begin to change to the pupa (Fig. 54),
to emerge about a month later in the beetle stage (Fig. 55).

Fig. 55. Locust Borer, Cyllene robinice: a, male; b. female. Enlarged as
indicated. (U. S. Dept. of Agriculture.)

The adult is a very showy, elongate, brown beetle, five-eighths to
three-fourths of an inch in length, conspicuously marked with three
straight bands of bright yellow across the thorax and five broken or
irregular bands of the same color across the wing-covers. There is
also a bright yellow patch on the upper side of the tip of the ab-
domen. The beetles are to be found in September, and occasionally
in early October, on locust-trees, and on various species of golden-
rod, upon the flowers of which they feed. Now and then a speci-

512 BULLETIN No. 151 [October,

men may survive the winter and be taken abroad in April, or even
in May.

From the foregoing statements it is evident that the time of cut-
ting trees, whether to thin the grove or for commercial use, is an
important item in the control of this beetle. All such cutting should
be done between October i and April i, care being taken that all
trees showing the presence of the borer are selected for removal.
The bark should then be taken off, and the brush and rubbish should
be burned. Simply to kill the larvae and borers in badly infested
and damaged trees, these should be cut and destroyed in May and
June, when their condition can be readily detected; but the work
should be completed by the time the flowers have all fallen from
the trees, as otherwise the borers may mature and escape. Where
the beetles are abundant on the goldenrod, they may be attracted and
killed, according to Dr. A. D. Hopkins, by smearing molasses
poisoned with arsenic upon the trees, due account being taken of
the fact that honey-bees are liable to destruction by this poison, and
that it should not be used where these are kept. Unsuccessful ex-
periments were made by one of my assistants, Mr. W. P. Flint, in
1910, with a mixture of sugar and vinegar, and another of sugar
and alcohol. Altho attractive to a variety of other insects, the
beetles of the locust-borer paid no attention to them. Tanglefoot,
on the other hand, placed on the trees September 16, when the
beetles were freely running about mating and laying their eggs,
disabled the beetles and put a stop to their operations.

Highly useful directions for the management of locust plan-
tations in a way to prevent injury by borers, are contained in Bulle-
tin 58 of the Bureau of Entomology of the U. S. Department of
Agriculture, printed in 1910.

THE OAK TWIG-PRUNER
(Elaphidion villosum Fabr.)

Among the more striking and curious kinds of insect injury to
trees are those which take the form of amputation of twigs and
small branches during the growing season — an injury which seems
purposeless and excessive until one sees just how it benefits the
author of it.

The oak twig-pruner (Fig. 56) is one of the best known Ameri-
can insects with this habit of injury, affecting, as it does, a large
variety of trees and shrubs, and injuring most frequently some of
the commonest and most useful species. It is best known, perhaps,
for its work on oaks, hickories, and maples, altho it has been re-
ported to attack also apple, peach, pear, plum, quince, locust, redbud,
sumach, Osage orange, fir, grape, and climbing bittersweet. In Illi-
nois we have bred it from oaks, hickories, persimmon, and peach,

191 1] IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 513

and have found it thruout the state. In parts of Michigan, peach-
trees have sometimes been nearly destroyed by it, and an equally se-
rious injury has been done by it in New York to pears. In Illinois
we once found it at Effingham cutting off young apples-trees from

Fig. 56. Oak Twig-pruner, Elaphidion villosum, larva.
About 5 times natural size.

one to two feet above the groun^ ; and Dr. F. W. Coding reported
it, in 1884, as doing great damage to hickory and elm at Ancona, in
Livingston county. In Pennsylvania, oak forests have been so in-
fested by it that carloads of the twigs might have been collected
from under the trees ; and in Connecticut, hickories have been so
thoroly pruned that a barrel of twigs and branches have fallen
from a single tree.

The injury done by this insect is not, however, so severe as it
looks. It may affect considerably the appearance of young trees,
by deforming their top; but large trees are generally little harmed
by the pruning they receive, and the littering of lawns with ampu-
tated twigs is at most an annoyance merely. The girdled twigs and
branches may vary in length from a few inches to several feet, but
Dr. Fitch mentions one that was ten feet long and over an inch
thick. Commonly, however, they are a quarter of an inch or less
in diameter, and vary from two to six inches in length. Occasion-
ally a single one will contain two larvae, the burrows then running
down each side of the twig. Fallen limbs, if not disposed of, may
serve, as Chittenden has said, as breeding places for various kinds
of injurious borers, which may come out from them to attack and
injure living trees.

The method of the primer's work is such that a fallen twig is
seen to have been hollowed out centrally — a large part of its interior
often being eaten away — and plugged with sawdust, and its larger
end has been gnawed off from within, having a cut surface as smooth
as if made by a chisel.

The adult twig-pruner is a rather slender, dark brown beetle
(Fig. 57) from a half to three-quarters of an inch in length,
sparsely covered with coarse white or yellowish hairs which show
a tendency to collect in irregular clumps or spots. The edge of the
tip of each wing-cover is concave between two stout sharp spines
or teeth", of which the outer is usually the larger. The female lays

514

BULLETIN No. 151

[October,

her eggs in the smaller twigs of living trees, most commonly in
July. The young larva first eats out the wood under the bark in
the direction of the grain, packing its burrow behind it with its
castings, and working towards the base of the twig. Later it cuts
holes in the bark thru which these castings are rejected, and
then follows the center of the twig, making a channel more or less
oval in cross-section, corresponding to its own shape. When it has
reached its growth it begins to gnaw, from within, a circular groove,
deepening this until the twig or branch is so weakened at this

Pig. 57. Oak Twig-pruner, Elaphidion mllosum,
adult. About 5 times natural size.

point that the wind readily breaks it off, usually carrying the insect
with it. Occasionally, however, the larva is left in its burrow on
the tree and finishes its transformations there. The value of
this operation to the pruner would seem to be a preparation for
the exit of the beetle, which originates within the burrow, but
which has not jaws of a sufficient strength to enable it to gnaw
its way out thru the wood inclosing it. This explanation, given
by Chittenden, seems at least to be the most reasonable among
several that have been proposed to account for this curious habit.
After the twig has been cut off the larva within it plugs up the
severed end, changes to the pupa, and later to the beetle, coming out
as an adult the following summer.

191 1] IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 515

Published accounts disagree as to the length of the life cycle of
this species. It seems to be a single year under the most favorable
conditions, but capable of being lengthened to two or even three
years, particularly if the branch dies before the larva is full grown.

As nearly all the borers pass the winter in the fallen twigs, it
easily follows that their injuries may be readily arrested by gather-
ing these up and burning them in winter or in spring. This effec-
tive measure is so simple and so easily applied that no other seems
necessary.

THE BRONZE BIRCH-BORER
(Agrilus anxius Gory)

This insect is a deadly pest of the birches, especially of the beau-
tiful and popular white birch, which it is quite capable of extermin-
ating locally if its presence is not early detected and if prompt meas-
ures are not then taken for its destruction. As an infested tree is not
likely to last more than two or three years, the necessity of energetic
measures is obvious. Unfortunately, this insect does not usually
make conspicuous local marks of the injury it is doing, and the
earliest sign of its presence is often the death of one or more
branches in the top of the tree. If a birch is seen to be dying at the
top it should at once be examined for evidences of the presence of
this borer, since in some cases this condition may be due to drought
or other general causes. If the bronze borer be the cause, the fact
may be ascertained by lifting the bark from dead branches which
are not yet dry, or from the more unhealthy looking spots on the
living parts of the tree. If the insect be present, its tortuous or
zigzag burrows will be noticed, and further search will disclose the
borer itself in one or more of its stages of larva, pupa, or adult.
Sometimes, indeed, its presence is shown by a ridged appearance of
the bark, the ridges running crosswise of the branches or in a more
or less spiral direction. Peculiar rusty or reddish spots may also be
seen on the larger branches or on the trunk where the bark has been
undermined by the interlacing burrows of the borer. Often branches
weakened by the borers and by consequent decay of the wood, break
at the point of injury, either hanging down or falling from the
tree. This appearance is rather characteristic of the work of the
borers, and may serve to distinguish an infested tree from a "stag
head," due to drouth.

In its destructive stage this insect is a small, flattened, footless,
creamy white grub about three-fourths of an inch long when full
grown, with dark mouth-parts and a small head which is partly
drawn back into the broad, flat, pale brownish, first segment of the
body. At the opposite end is a pair of minute forceps-like spines,
brown and hornlike, with two teeth on the inner edge of each. In
this larval condition the borer may be found in its burrows beneath

516

BULLETIN No. 151

[October,

the bark at any time during fall, winter, and early spring. If the
tree has been long infested, the bark is usually perforated by small
roughly semicircular holes about twice the diameter of the head of
an ordinary pin. (Fig. 58.) These holes are made by the beetles
when they come out in May and June for their brief life in the
open air.

The beetle (Fig. 59) is a hard, small, bronze-green or violet in-
sect, varying somewhat in size, but approximately half an inch long
or a little less. It is shining but minutely punctured under a glass,

Fig. 58. Exit holes of the Bronze Birch-borer, Agrilus
anxius, in the bark. Natural size. (Cornell Experiment
Station.)

- Fig. 59. Bronze Birch-borer, Agrilu
anxius, adult. About 5 times natura
size.

with the sides nearly parallel, tapering conspicuously behind to a
blunt tip, notched where the rounded ends of the wing-covers come
together.

Altho most notorious for its injury to the white birch, es-
pecially the cut-leaved variety, it infests all the birches. It is the
most destructive enemy of these trees in the Chicago parks, thru
which it is generally distributed. It is especially dangerous because
there is no means of destroying it which does not involve also the
destruction of the infested tree. It is a saddening conclusion which
is forced upon the owner of a beautiful birch infested by this borer,
that the tree is doomed, and that the only means of saving other
trees in its neighborhood is to cut it close to the ground in winter or
spring, as early as the first of May, and to burn it, trunk and
branches, before the beetles can emerge to lay their eggs elsewhere.

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 517

The larvae hatch in June, and possibly also in July, from eggs
laid in crevices in the rougher places of the bark. They bore
thru the bark at once and begin to mine in the sapwood, some-
times dipping inward to the older wood or even penetrating to the
center of a small branch. The irregular mine is always packed with
the castings of the grub, and increases in diameter, of course, as
the latter grows, measuring at the largest about an eighth of an inch
across. Here the borer lives in the larval state until the latter part
of the following April or early May, when it begins to transform
within its burrow to the pupa stage, and within another month to
the beetle. This escapes from the tree from the middle to the last
of June in northern Illinois, by gnawing through the bark, flies
abroad to feed on the leaves of trees, and soon pairs and lays its
eggs. Curiously, it seems to feed but little on the birch, preferring
the leaves of poplar, willow, and elm to those of its native tree.
There is, indeed, some evidence that it infests the willow, producing
gall-like swellings on the twigs, but the identity of the species to
which this injury is referred is not positively settled.

Trees of large size are often killed by this borer within three or
four years after they first become infested, and' few live more than
two or three years after the top branches begin to die. The neces-
sity of prompt action is thus manifest, and as the time of the escape
of the beetles varies with latitude and the weather of the year, it is
best to take time by the forelock and to destroy the infested tree
as early at least as April i. Then one may be sure that nothing can
have escaped from it to extend the injury.

This insect is not now known to range beyond Virginia to the
south or Illinois to the west, but it very likely occurs wherever
birches are grown. We have lately found it (1910) outside Chi-
cago, in Elgin, Rock Island, Moline, and Bloomington, abundant
enough in all these places to be decidedly injurious to the birches.
It has been quite fully discussed by Professor M. V. Slingerland in
Bulletin 234 of the Cornell University Agricultural Experiment
Station, published in January, 1906, and briefer accounts may be
found in the report of Dr. E. P. Felt, State Entomologist of New
York, in "Insects Affecting Park and Woodland Trees" (page
284), published in 1905 ; in an article by F. H. Chittenden published
in 1898 in Bulletin 18, new series, of the Division of Entomology,
U. S. Department of Agriculture; and in a paper on "A Disease
of the White Birch," by John Larsen, printed by the Michigan
Academy of Science in its third report (1902).

THE SCURFY SCALE
(Chionaspis furfur a Fitch)

The so-called scurfy scale is the commonest of all scale insects
thruout the state on shade and orchard trees. The female scale

518 BULLETIN No. 151 [October,

(Fig. 60, a, c) is about a tenth of an inch in length, irregularly
oval, with a yellowish point at one end, and but very slightly con-
vex. It is nearly white when fresh, but becomes gray or sooty
with exposure. The scale of the male insect (Fig. 60, b, d) is

Fig. 60. Scurfy Scale, Chionaspig furfura:
a, b. female and male scales, natural size; c,
d, same, enlarged.

narrow, with sub-parallel sides, and is marked by three longitudinal
ridges. The species may be readily recognized in winter by the
fact that under each female scale will be found a small mass of
minute, purplish eggs. The young appear to the naked eye as
active, snowy whitish or reddish specks. These insects are often
so abundant on an infested tree as to give a scurfy appearance to
the trunk and limbs.

This scale insect is a general feeder, but is especially common
on rosaceous plants. It also heavily infests the elm, which seems the
most susceptible to its injuries of any of our ordinary shade trees.
The red-twigged dogwood is often incrusted by it, and the moun-
tain ash, hawthorn, pear, and currant are sometimes attacked. The
scurfy scale winters in the egg, and hatches, with us, during the
latter half of May — earlier or later according to the season and the
part of the state. In central and southern Illinois eggs are laid
for a second generation, the date of which, however, has not been
accurately determined. Altho this can not be classed among the
more destructive scale insects, it is nevertheless injurious where es-
pecially abundant, checking the growth and diminishing the vitality
of the infested tree or shrub in a way to make it less presentable and
more susceptible to the attacks of other insects and of disease.

Two insecticide sprays are fairly effective against this insect;
one a winter spray of lime and sulphur, prepared and administered
as described in detail under the article concerning the San Jose
scale, and the other a summer spray of kerosene emulsion, a formula

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

519

for the preparation of which is given tinder the cottony maple scale.
The lime-sulphur mixture should be applied as late in the winter as
practicable, best just before the opening of the leaves in spring. The
kerosene emulsion must be applied immediately after the hatching
process is virtually complete, a point which can only be determined
accurately by careful observation. If the young are allowed to live
too long they become covered and protected, after fixing themselves,
by a waxy scale which the emulsion will not penetrate. It should be
applied in a strength to contain ten percent of kerosene. Dr.
James Fletcher, Dominion Entomologist, Canada, recommended
spraying infested trees with a whitewash made by slaking a pound
of lime to the gallon of water, one such application to be made in
fall as soon as the leaves have. fallen, and a second immediately after
the first has dried. This is said to loosen the hibernating scales,
which subsequently fall from the tree with the dried whitewash.

THE OYSTER-SHELL SCALE
(Lepidosaphes ulnii Linn.)

The oyster-shell scale is among the more conspicuous and easily
recognized of the smaller scale insects of our trees and shrubs, the

Fig. 61. Oyster-shell Scale, Lepidosaphes ulmi: a. female scale,
under side, showing insect and its eggs within; b, same, from
above; c, same, natural size; d, e, male scale, enlarged and
natural size.

520 BULLETIN No. 151 [October,

common name suggesting its most conspicuous character. It has,
indeed, the convex, elongate, and more or less bent and irregular
form of an oyster shell. The female scales (Fig. 61, a, b, c} are
about an eighth of an inch long, the male scales (Fig. 61, d, e)
smaller, with a little hinge or flap behind, thru which the winged
males escape when mature. The scale is usually brown to dark
brown in color, tho occasionally bleached to gray by exposure
to the winter weather. The eggs of the species hatch in Illinois
shortly after the time the apple blossoms fall. Each female scale
has during the winter from fifty to a hundred and twenty-five pale
yellowish eggs beneath it, from which the young emerge during
the latter part of May or the first of June. A second generation
occurs in central and southern Illinois early in July. The young
are able, at first, to crawl about somewhat actively, and it is
principally by this means that the species is distributed, altho it
may be conveyed to distant points upon infested nursery stock.
The scale insect is both larger and more injurious than the scurf}
scale, and infests also a larger variety of trees and shrubs. Elm,
poplar, willow, horse-chestnut, lilac, red-twigged dogwood, and
currant are among those most frequently and seriously injured.

The treatment for this scale is identical with that described in
the article for the scurfy scale, just preceding.

THE SAN JOSE SCALE
(Aspidiotus perniciostis Comst.)

This notorious and destructive pes.t is much less injurious to
ornamental vegetation than to fruit trees and shrubs, but is never-
theless decidedly harmful to several of the former, particularly to
those belonging to the family of roses. It is also very injurious to
the mountain ash, but the Japanese quince (Pyrus japonica) is the
common shrub most likely to betray its presence.

It is a circular, grayish or yellowish, scale insect about one-
sixteenth of an inch in diameter, but slightly convex, and marked
by a central nipple and one or two surrounding circular ridges. It
is an inconspicuous object, but is recognizable by the appearance
which it gives to a badly infested bark (Fig. 62), which it covers
with dark gray patches of a continuous grayish crust, which exudes,
when crushed with the finger-nail, an oily, yellowish substance due
to the pressure on the living insects under the scales. The bark of
a tree but sparsely infested may be seen, on close examination, to
be irregularly specked with small circular granules which give it an
unhealthy look. The surface immediately beneath the living scales
often shows a reddish discoloration; and on the leaves and green
twigs are more conspicuous red blotches which surround the scales.

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 521

The largest scales are about the size of the head of an ordinary
pin, and the smallest ones are mere specks on the twig.

This insect passes the winter partly grown, reaches its full size
in spring, and begins to bring forth its living young about the first
of June, in average years, in the central part of Illinois. These may
be seen as minute yellow specks wandering over the surface in search
of a suitable place to establish themselves. This period of active
life is often limited to a few hours, and at most to one or two days.
Three or four generations are bred in a single season.

Fig. 62. San Jose Scale, Aspidiotus
perniciows. Natural size. (Connec-
ticut Experiment Station.)

It has been found commonly infesting and often injuring more
than seventy trees and shrubs, and occasionally nearly as many
more. The commoner kinds coming under the former list are some
of the dogwoods, the hawthorns (Cratcegus}, the quinces, the pop-
lars, the cherries and pears, currants and gooseberries, roses, willows,
mountain ash, snowberry, lilac, basswood, Osage orange, and the
elms. Those less seriously infested are the maples, horse-chestnut,
Virginia creeper, the birches, chestnut, catalpa, hackberry, the flow-
ering and other dogwoods, the persimmon, Forsythia, white ash,

522 BULLETIN No. 151 [October,

honey-locust, Althea, pecan, black walnut, mountain laurel, honey-
suckle, mulberry, white spruce, sour cherry, sumach, smoke-bush,
locust, raspberry and the blackberry, elder, sassafras, various species
of Spiraa, arbor-vitae, Viburnum, and grape. Popular species not in-
fested by it are Ailanthus or tree of heaven, papaw, spice-bush, bar-
berry, trumpet-vine, the hornbeams, cedar, bittersweet, buttonbush,
Judas-tree, fringe-tree, pepperbush, leatherwood, gingko, Kentucky
coffee-tree, witch-hazel, English ivy, hickories except the pecan,
hydrangeas, yellow jasmine, butternut, juniper, larches, sweet gum,
tulip-tree, matrimony-vine, wax myrtle, black gum, syringa, pine,
sycamore, the oaks, the rhododendrons, bald cypress, trumpet-
creeper, blueberry, hemlock, Wistaria, and prickly ash. The last
list is especially important in Illinois, thruout which the San Jose
scale is certain ultimately to become generally distributed, because
it includes a large and varied list of ornamentals from which selec-
•tions may be made without the risk of loss or injury by this most
destructive pest.

The San Jose scale is conveyed to distant points mainly by
the trade in nursery stock, and otherwise it spreads only by means
of the minute crawling young. Its means of dispersal are so slight
that it tends to concentrate upon any tree infested until the latter
becomes completely covered by it, a fact which, taken together with
its numerous generations, its rapid rate of multiplication, and its
freedom from parasites capable of overcoming it, make it the dan-
gerous enemy which it has become.

The San Jose scale can be destroyed by the winter use of one of
the lime and sulphur mixtures, which may either be purchased ready-
made in condition for use by dilution only, or may be brought into
solution by boiling the raw materials together according to the fol-
lowing directions.

Materials : 15 pounds of lime, 15 pounds of sulphur, and 50 gallons of
fairly soft water. For 50 gallons of the spray, heat 12 gallons of water in a
4O-gallon iron kettle, mixing, in the meantime, in a separate vessel, 15 pounds
of sulphur with enough water to form a thin paste. Add this sulphur to the
water in the kettle and bring the mixture to a temperature just below boiling.
Then add 15 pounds of best lump lime, keeping cold water at hand to use as
the mixture threatens to boil over. After the lime is fully slaked, boil for
40 minutes, with almost constant stirring. Then strain into a 5O-gallon spray-
tank and fill with water, which had better be warm, although cold water will
do. To prepare 100 gallons of the spray at a time, heat 20 gallons of water
in the 40-gallon kettle, add 30 pounds of sulphur — previously reduced to a thin
paste with water — and to this put 30 pounds of lime. Boil as before, and
dilute to 100 gallons.

If a supply of steam is available for cooking the mixture, this will be
found a much more convenient source of heat. The cooking is then done in
barrels or other vessels, from which the fluid is strained into the spray-tank.
The disturbance caused by the introduction of steam makes stirring unneces-
sary. When cooked with steam the mixture does not ordinarily become so
dark as when boiled over a fire, but the insecticide effect is nevertheless the

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 523

PUTNAM'S SCALE
(Aspidiotus -ancylus Putnam)

This is a circular or oval, dark gray or black, scale insect, about
one-twelfth of an inch in diameter, with a brick-red point at one side
of the center. It closely resembles the San Jose scale in general
appearance, but does not present the conspicuous ring and nipple
structure of the latter, altho the young have usually a nipple and
a rather indefinite ring.

It passes the winter but partly grown, but differs from the San
Jose scale in the fact that it reproduces by means of eggs laid in
late spring or early summer. There is but one generation in a
season.

It has been found on elm, willow, oak, hemlock, mountain ash,
Ilex, white birch, Primus, ash, beech, hackberry, linden, maple,
Osage orange, and water-locust. It is rarely injurious enough to
require special attention.

THE WALNUT OR WILLOW SCALE
(Aspidiotus juglans-regice Comst.)

This species, altho common on a number of shrubs and shade
trees, is of little importance except on the willow, to which it is a
veritable pest. It is easily distinguished from other scales of the San
Jose relationship by its relatively large size, its diameter being 3
mm., or an eighth of an inch. The female scale (Fig. 63, a, e,} is

Fig. 63. Walnut Scale, Asp'diotusjuglans-regia: a, b female and male scales,
enlarged; c, male pupa; d, e, male and female scales, natural size.

circular, flat, with a prominent pink or reddish point at one side
of the center. The male scale (Fig. 63, b, d) is elongated, with a
corresponding point near one end. The female passes the winter
as an adult, and lays her eggs in early spring.

Treatment the same as that for the scurfy scale.

524 BULLETIN No. 151 [October,

THE COTTONY MAPLE SCALE
(Pulznnaria vitis Linn.)

The cottony maple scale (Fig. 64) is one of the best known
scale insects because it heavily infests several very common shade
trees, and because the cottony masses beneath the body of the adult
female in early summer make it a very conspicuous object. These
large white masses are a deposit of waxy threads within which are
the minute, oval, pale yellowish eggs.

The history of this insect in Illinois since 1867 exhibits suc-
cessive periods of abundance and of scarcity, each averaging about
four or five years for the state as a whole. That is, thruout
some considerable part of the state, and often over most of it,
the maple scale has been injuriously abundant once in eight or ten
years, and its period of abundance has lasted, as a rule, about half
this time. In any given locality, however, it has usually been in-
jurious for a much shorter time, often for not more than one or two
years. The cessation of its injuries and its virtual disappearance
from the trees infested by it have seemingly been due almost wholly
to the agency of its insect enemies.

The soft maple (Acer saccharinum) is the tree most generally
and heavily infested by this insect. The hard maples, on the other
hand, are infested but slightly if at all. The box-elder is also greatly
subject to injury, and next to this, perhaps, the linden or basswood.
Among the other trees and woody plants often more or less injured,
are the elm, honey-locust, black locust, black walnut, sumac, willow,
poplar, beech, hawthorn, bittersweet, grape-vine, and Virginia creep-
er. We have found mature egg-laying females on the horse-chest-
nut, honeysuckle, dogwood, trumpet-creeper, mulberry, snowberry,
smoke-tree, Spiraa, false syringa (Philadelphus}, and Wistaria.
Oak, ash, and catalpa are not infested in northern Illinois, but injury
to oaks is reported from Georgia. The pear is said to be most liable
to injury among the fruit trees, and apple, plum, and peach are
sometimes infested. Serious damage to fruit trees is, however, very
unlikely. The migrating young, which are often washed from trees
by rain, or blown off in considerable numbers, may maintain them-
selves for a time on a great variety of woody and herbaceous plants,
those on the latter, of course, perishing with the advent of frosts.

In early summer this scale, when very abundant, coats the under
side of heavily infested limbs with a thick layer of cotton-like waxy
masses, each projecting from beneath a brown cap or scale — the
flat body of the mature female. This "cotton" is secreted and the
eggs are deposited within it in late May or early June in the latitude
of central Illinois, but usually one or two weeks later in the Chicago
district.

Something over 3,000 eggs are usually laid by each female, the
number ranging, in our counts, from 2,856 to 3,863, with an average

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS 525

Fig. 64. A Soft maple twig badly infested with adults of the Cottony Maple Scale,
Puivinaria vitis. About natural size.

526

BULLETIN No. 151

[October,

of 3,410. In central Illinois the eggs ordinarily hatch in June, and
in the northeastern part of the state in early July, of later if the
weather of the time is unfavorable. Virtually all are hatched, as
a rule, by the end of July.

When first hatched the six-legged young (Fig. 65, a, e, /) move
slowly about as creeping yellowish specks about twice as long as
wide. They soon settle upon the leaves, mostly upon the under side

Fig. 65. Cottony Maple Scale, Pulvinaria vitis, immature stages: a, newly
hatched young, under side; b. c. young female, top and side views; d,
young mdle; «,/, young on leaf and leat stem. Natural size shown in a.

along the veins, but a considerable percentage also on the upper
surface. Soon after settling down, a thin waxy layer forms on the
back, and in about three weeks the insect has virtually doubled in
size. As they increase in size the male and female scales become
distinguishable (Fig. 65, b, c, d) by the fact that the former are
comparatively narrow and more convex. From these the winged
males (Fig. 66, a, b, c} emerge to fertilize the stationary females
in August and September, perishing soon thereafter. In autumn
the young females migrate from the leaves, which are about to fall,
to the twigs, upon wrhich they pass the winter and, indeed, the re-
mainder of their lives. In spring the female scale (Fig. 67) is ellip-
tical, convex on the back, with a low, rounded, median ridge. It is
pale greenish or whitish yellow, marked with black or dark brown.
When full grown, about the middle of May, it is 4 to 6 mm. long
and 3 to 4.5 mm. wide. Its body is at first closely applied to the sur-
face of the twig, but with the development of the eggs beneath it the
abdomen is gradually raised from the bark to an angle of forty-five
degrees or more.

It is usually difficult to say whether trees infested by this insect
should receive special treatment, or whether they may be safely left

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

527

to the natural course of events. The cottony maple scale is ex-
tremely subject to parasites and attacks of other insect enemies,
particularly to the black hemispherical ladybugs and their larvae, the
latter of which feed upon the egg masses in spring and summer.
With an extraordinary abundance of the scale insects themselves

Fig. 66. Male of Cottony Maple Scale, Pulvinaria vitis: a, adult;
b, c. antenna and leg enlarged; d, e, second stage of pupa and its
cast skin; /, g, true pupa and its cast skin. All greatly enlarged.

these insect enemies improve the opportunity for unusual multiplica-
tion in a way to produce a greater number than can possibly be
maintained permanently by the scale insects. A check is thus put
upon the increase of the latter which, within a few months, may re-
duce them to insignificance. The consequence is an irregular peri-

Fig. 67. Cottony Maple Scale, Pulvinaria vitis.
Adult female in spring, just before the forma-
tion of the cottony egg sac. Enlarged.

odicity in the numbers of the cottony maple scale such that two years
of injurious abundance rarely succeed each other in the same place.
Nevertheless, where trees are evidently suffering from the scale at-
tack it is always prudent, and often necessary, to take artificial
measures of protection.

528 BULLETIN No. 151 [October,

As the newly hatched young are especially susceptible to the
petroleum insecticides, which act by contact, a definite knowledge of
the hatching period has an important practical value. In central
Illinois this period extends approximately from June 15 to July 20.
In and about Chicago it commonly begins about two weeks later, and
continues for a period of three weeks, this retardation being appar-
ently due to the higher latitude and to the neighborhood of Lake
Michigan. The period varies, in short, as to its beginning time, with
the advancement of the season, and once begun, the rapidity of the
hatching will depend, other things being equal, on the warmth of the
weather. It is also influenced locally by the amount of foliage on
the trees, the eggs hatching later and more slowly in a dense tree-
top than in one more open to the sun.

The only insecticides available against these insects are those
which kill by contact, and of these the kerosene mixtures have thus
far been found the most useful. Even these can be applied only to
the young scales shortly after they hatch from the egg, no insecti-
cide treatment being available for the destruction of the large and
conspicuous females upon the twigs in May and June. The common
kerosene emulsion, made by thoroly and intimately mixing kero-
sene with one-third of its volume of a strong soapsuds, is a satis-
factory spray when diluted to contain ten percent of kerosene for
summer use, and sixteen to eighteen percent is used in winter. As
a summer spray this emulsion must be used twice in succession, once
when about half the eggs are hatched and again about ten days there-
after. A single treatment in winter is about the equivalent in prac-
tical effect of two such summer sprays. Large trees in a sandy soil,
and especially those in more or less unthrifty condition, should be
guarded against possible injury to the roots from the dripping of the
kerosene spray, or from that part of it which may run down the
trunk and so reach the earth. For this purpose it would be well to
cover the ground before spraying with a thin layer of straw, packed
closely around the base of the trunk, and later to gather this up and
carry it away.

The cost of materials for large trees will average approximately
fifteen cents a gallon for the summer spray, and about twice as much
for the winter strength.

Kerosene emulsion is made as follows : Dissolve one pound
of common soap, or half a pound of whale-oil soap, in one gallon of
water by boiling, remove from the fire, and add two gallons of kero-
sene. Then with a spray pump force the mixture back into itself for
about five minutes, or until it presents the appearance of a thick
cream and no longer separates on standing. This is the undiluted
emulsion. For a mixture containing ten percent of kerosene, add
seventeen gallons of water to the three gallons thus prepared. For

IMPORTANT INSECTS OF ILLINOIS SHADE TREES AND SHRUBS

529

an eighteen-percent kerosene emulsion, add eight gallons of water
to the stock emulsion. Soft water is to be preferred.

The following tables will show the effects of kerosene sprays
as applied by us in 1905 and 1906.

SUMMER SPRAY

Treatment

Insecticide

Part of
hatching
period

No. of
trees

Leaves
ex-
amined

Scales
ex-
amined

Percent
killed
by spray

10 percent kerosene

Beginning1

i

48 78^

10 percent kerosene . ...

Middle

1

50

19,425

64

10 percent kerosene

End

3

150

281,271

68

10 percent kerosene

Middle
and end

1

100

57,179

82

WINTER SPRAY

When sprayed

Percent
of
kerosene

Date of

counting

Scales
counted

Percent
killed

December 26 to January 5
(once)

19

Feb. 1

12,703

86

January 11 to 13 (once)

20

Feb. 1-2

23,061

91

January 11 to 13 and March 30
(twice)

19-24

June 10

48,395

91

m

UNIVERSITY OF ILLINOIS-URBANA

711 CD