THE * WILT DISEASE,’ OR “FLACHERIE,”

OF

tre GyYRoy MOTH.

BY

WILLIAM REIFF,
BUSSEY INSTITUTION OF HARVARD UNIVERSITY.

UNDER THE DIRECTION OF

F. W. RANE, STATE FORESTER.

BOSTON :
WRIGHT & POTTER PRINTING COMPANY, STATE PRINTERS,
18 POST OFFICE SQUARE.
1911.

APPROVED BY
THe State BOARD OF PUBLICATION.

CONTENTS.

PAGE
Introductory, . : : , . : : ; : : ; 5
I. Caterpillar Diseases in General, i ; : 3 i
Common Diarrhcea; Bead Disease; Muscardine; Pébrine;
Flacherie.
II. Résumé of Some Experiments with Flacherie in 1909, . ¢ CD
III. Flacherie Experiments in 1910, : , : ; : a SAA:
A. General, . ! 14
Acknowledgments; General Points of tne Work: ane
trol Experiment.
B. The Single Experiments, . : 20
Concord, North Carver, Boxford, West t Bedford, Haver-
hill, Marshfield, Kingston, Brockton, Beverly, Co-
hasset, Hingham, Byfield.
IV. Summary, ‘ : ‘ ; s ; ; : , 3) BB
V. Final Conclusions, 55

INTRODUCTORY.

Anything that offers promise of being effective in our war-
fare against the gypsy moth is hailed with delight by our
Massachusetts people.

It is with pleasure that the State Forester is able to offer
this publication, setting forth the work with the “ wilt disease,”
or ‘‘ Flacherie,” of the gypsy moth, which has been carried on
during the past two years by Mr. William Reiff, under the
supervision of Prof. W. M. Wheeler of the Bussey Institution
of Harvard University. Professor Wheeler’s co-operative in-
terest in the moth-suppression work in the State is highly appre-
ciated by the State Forester, and the results shown in this
bulletin will prove, we are sure, of great interest generally.

This bulletin is a companion, in a way, to that issued on
parasites, in that it is another method of attacking our foe.
We desire to have as many strings as possible to our bow in
fighting this pest. That this ‘“ wilt disease” is a most hopeful
remedy there is little question. We anticipate carrying on
even more extensive work with it the coming season.

Upon reading this bulletin it will be readily apparent that
any one can easily assist in furthering this work at little, if
any, expense; and it is to be hoped that many will not only
acquaint themselves with the methods employed, but experi-
ment on their own initiative. If the State Forester can assist
you in any way do not hesitate to call upon him.

ACKNOWLEDGMENTS.

The experimental work and writing up of the data in this
bulletin was done by Mr. William Reiff of the Entomological
Laboratory of the Bussey Institution of Harvard University.

The State Forester decided that the work undertaken by
Mr. William Reiff during the season of 1909 was well worthy

6

cf being continued upon a much larger scale, and co-operative
plans were happily agreed upon with Dr. Wheeler, with the
results as outlined in this bulletin.

Besides Professor Wheeler and Myr. Reiff, there are the field
agents and local superintendents of the regular moth staff,
who made it possible to get results. To these we are also under
obligations for their loyal support and co-operation,

K. W. RANE;
State Forester.
Boston, Mass., March 21, 1911.

THE “WILT DISEASE,” OR “FLACHERIE,” OF
THE GYPSY MOTH.’

I. Caterpillar Diseases in General.

The production of diseases is one of nature’s methods of
quickly checking the overproduction of living things. Animals,
including man, and plants all have their own specific infec-
tious diseases, which usually appear whenever a species be-
comes so numerous that it menaces the prosperity of the
coming generations. In the animal kingdom the possibility
of overproduction is especially apt to occur in insects, since
they form by far the largest portion of the world’s fauna,
and have a high rate of reproductivity. Insects, small though
they are individually, form in their totality an immense mass
of living matter. Of this mass we can get only a slight con-
ception, even when we consider that insects are everywhere
present, not only as a few scattered individuals, but in such
enormous numbers that they constitute, as it were, a world in
themselves. We may say without hesitation that among all the
conditions which arise from and are caused by animals, there
is none more widely distributed, more many-sided and which
interferes more deeply with life on our planet than that which
is brought about by insects. As Graber says: —

Man may unwisely neglect these creatures — as he does many things;
but their power for evil crushes him the more; indeed, it may destroy
him if he persists in his neglect.

Now, such a power may be checked by nature by one of the
most efficient means which she possesses, —the infectious
diseases.

Owing to the profound influence which insects exert upon us
and our culture, attention has been drawn to their diseases.
A close study has been made of some of these; especially of

1 Contributions of the Entomological Laboratory of the Bussey Institution, Harvard Uni-
versity, No. 36.

8

those known to occur in the silkworm (Bombyx mort) and in
the “nun” moth (Psilura monacha), which latter destroys the
forests of Central Europe.

The first scientific knowledge tinal we have of caterpillar
diseases we owe to the valuable investigations of the French
scientist Pasteur. Since his time many other investigators have
been engaged in this study, among them the Germans Standfuss
and Emil Fischer, the Italians Verson and Bolle, and the
Americans Snow and Forbes. By their experiments and in-
vestigations we are now able to recognize the character of the.
more common caterpillar diseases.

We may mention some of those diseases with which the
lepidopterist will come in contact in the course of a few years.

A very frequent disease of caterpillars is the common
diarrhea, which is produced in most cases by too juicy or too
wet food. This is shown by the unusually wet excrement, the
fluid part of which is green. If the disease is of longer stand-
ing, the excrement does not cling together, but is voided as a
pulpy mass, in which the single vegetable particles swim around
undigested. This disease in itself is not dangerous, since it
is not infectious, but it may prepare the way for the attack of
other infectious diseases, which will be mentioned further on.

In another disease, which has no popular name as yet, and
which I shall call bead disease, the excrement masses hang
from the body like a string of beads. This intestinal disease
is probably due to unhealthy food, but the specific cause has
not been determined. Apparently this disease, too, is not
infectious.

Of much greater importance is the disease known as muscar-
dine. This is really a collective name for a series of fungous
diseases, which convert the infected caterpillar in a short time
into a stiff, swollen mass, with the skin invested with a grayish-
white coating. Very hairy caterpillars are especially suscep-
tible to museardine, but in extremely wet years even smooth
caterpillars suffer from fungous diseases. It is easy to deter-
mine whether muscardine is present in a given locality because
the diseased caterpillars crawl toward the exposed tops of grass
blades, poles or stems, and remain there after death, thus be-

a

coming visible for a considerable distance. On a trip which I
made in June, 1910, to Raymond, N. H., I saw thousands of
brown-tail moth caterpillars dead from muscardine, and com-
monly hanging in this characteristic manner. Since these
fungous diseases are extremely infectious, and propagate with
incredible swiftness, and since healthy caterpillars are much
inclined to gnaw at dead ones, the artificial production and
propagation of muscardine has been hopefully considered dur-
ing the last few years as a means of destroying the brown-tail
moth.

There are two fungi, especially, which are responsible for
the death of most caterpillars; these are Botrytis bassiana Bals
and Hntomophthora aulicae Reichhardt. Experiments with
fungous diseases of the brown-tail moth are being conducted by
Mr. A. T. Speare, under the direction of Dr. R. Thaxter of
Harvard University.*

The pebrine or pebrina, which has become so notorious
through the great damage it has caused to the silk industry,
is the caterpillar disease which has been studied so far most
thoroughly. Caterpillars with this disease always have a
wet anus, and if they are hairy, the hairs on this region of
the body stick together. Smooth caterpillars also change their
color considerably ; for instance, green caterpillars turn yellow-
ish, and are often mottled with dark, irregular spots; gayly
colored caterpillars lose their brilliancy. This disease does
not kill in a few hours or days, but the infected caterpillars
languish slowly, lose their appetite, and become transparent
and ill-nourished. They then shrink more and more, till
finally at death only the flabby dry skin remains. Pébrine
appears preponderatingly in wet years, and its cause seems to
be lack of nourishment. The specific cause, however, the dis-
position, has not yet been absolutely determined. The carriers
of the disease are known under the name Corpuscoli di Cornalia,
and have been described by Lebert? as the fungus Panhisto-
phyton ovatum (Micrococcus ovatus). Here it might be of
interest to cite from a review in “ Deutsche Entomologische

1 ‘Seventh Annual Report of the State Forester of Massachusetts, ’’ 1910, pp. 98-101.
2 “Berliner Entomologische Zeitschrift,’’ 1858, p. 170.

10

National Bibliothek,’ No. 3, Jahrg. II., 1911, where it is
stated that the botanist Naegeli described the carrier of the
pébrine, as early as 1857, as Nosema bombycis. This review,
moreover, mentions the fact that W. Stempell (38. Jahresber.
Zool. Sekt. Westf., Prov. Ver. f. Wiss. u. Kunst, 1909-10, p. 37)
has made artificial infection experiments with this parasite,
and found that it develops with extreme rapidity and great
virulence, not only in caterpillars of the silkworm, but also
in caterpillars of several local species of the same family. Thus
Stempell reached the conclusion that this susceptibility of the
individuals towards the pébrine parasite might be used prac-
tically in combating injurious caterpillars. He further men-
tions that his researches on this and other Microsporidia are of
biological interest, since it would seem that there must be
organisms so minute that they cannot be seen, even with our
most modern optical instruments. In several infectious diseases
the carriers of the disease have not yet been optically demon-
strated, and it may be that these carriers are such small
organisms. These little oval shining bodies are now no longer
regarded as plant organisms, but as belonging to the Psoro-
spermu, a group of Protozoa. Pébrine is extremely in-
fectious, and is carried over, as Pasteur has proved, from gen-
eration to generation in the eggs, with increasing destructive-
ness.

We come now to the last and probably most important of
all the common caterpillar diseases, the disease called Flacherie,
Flaccidenza or caterpillar cholera, and in America known also
under the name “ wilt disease.” This disease is characterized
as follows: a caterpillar suffering from it soon stops eating,
becomes weak and lazy, and usually crawls up on some object,
as the trunk of a tree, a fence, a wall, or other vertical surface,
where it remains without motion. In a few hours there drops
from its mouth and anus a dirty, blackish, foul-smelling liquid ;
the caterpillar becomes more and more flaccid, one leg after the
cther looses its support, and finally the creature, reduced to a
black skin, hangs dead, still holding on with one or two of its
false feet or with the anal claspers. The slightest touch now
suffices to break the skin, and a thin, dark, offensive-smelling

At

liquid flows out. Flacherie kills the older more quickly than
the younger caterpillars. Young caterpillars, indeed, often
live several days before they are killed by the disease. It is
not positively known what organisms produce Flacherie. The
bodies of caterpillars which have died of this disease show ex-
tremely small bacilli, innumerable schizomycetes, and, more
particularly, many small strings of micrococci; but which of
these micro-organisms, 1f any, is the real carrier of the disease
is still unknown to specialists." To the investigations of Dr.
E. Fischer, in Ziirich, Switzerland, we owe considerable infor-
mation regarding the primary causes leading to Flacherie, and
the manner in which the disposition to this disease may be in-
duced. He has pointed out that a decrease in the nutritive value
of the food of the caterpillars, which induces a disturbance in
their metabolism, is the first condition leading to the contraction
of the disease. As a result of these disturbances the organisms
responsible for the disease immediately find conditions suitable
for their growth. One of the main causes of the disease is
therefore to be sought in the predisposition of the caterpillars,
while the specific infection of Flacherie is to be regarded as
coming more or less secondarily; in other words, without this
predisposition infection cannot take place, and the predisposi-
tion can be brought about artificially by insufficient nourish-
ment.” Flacherie seems to be influenced by climate and weather
conditions less than any other caterpillar disease. We meet
with it both in the old and the new world, in wet, in dry and in
normal weather. As a result of its comparatively great abund-
ance and its extremely easy infection, Flacherie has become the
“guardian angel” of the Central European forests. When the
“nun” (Psilura monacha) makes its appearance in some places
in Europe in vast numbers, man with his wit and the powerful
means at his command is quite unable to stop the destruction,
but Flacherie always comes to his assistance. Although this
disease has been much studied, it has not yet been positively

1 Very recently C. Sasaki, in Tokyo, Japan, found that there were also polyhedral corpuscules
present in caterpillars which were sick from Flacherie (‘‘ Deutsche Entomologische National-
Bibliothek,”’ Jahrgang II., 1911, No. 1, Referat). Since polyhedric corpuscules, however, are
found chiefly in caterpillars which have been infected by the pébrine, a close relationship of these
two diseases is highly probable.

2 See Fischer’s detailed accounts in the ‘‘ Biologisches Centralblatt,’? Band XXVI., No. 13-16.
Leipzig, 1906.

12

established whether it is hereditary or not. There is at present
no argument that can be brought against the heredity of the
disease, while there are some important facts which indicate its
heredity. These will be considered later.

II. Resume of Some Experiments with Flacherie in 1909.

Fischer called attention, in his excellent paper, already men-
tioned, to the manner in which Flacherie can be artificially
developed. He says that the disposition to the disease is
secured by giving the caterpillars food which has been placed
in water and renewed only every three or four days. This
treatment apparently causes an injury to the leaf protoplasm,
due to the presence of too much water, and there is a con-
comitant increase in the acidity of the leaves.' If, now, a cater-
pillar eats such leaves, the alkalinity of its digestive fluid,
which is very strong in healthy individuals, decreases, and in
this manner the first susceptibility to the disease is given.
Before the visible outbreak of Flacherie, Fischer could recog-
nize as an early symptom a characteristic sweet odor in the
breeding cages, which could be compared best to that of some-
what withered lilac blossoms. Whenever this odor was notice-
able Flacherie soon made its appearance, and as it progressed
the odor increased proportionately. Fischer recommends the
artificial production of Flacherie among the caterpillars of the
“nun” (‘die Nonne” of the Germans) by intentionally giv-
ing the larvee this kind of food as soon as an abundance of the
pest is noted in any particular locality.

Bearing in mind the close relationship existing between the
“nun” and the gypsy moth, I attempted during the summer
of 1909 to put Fischer’s conclusions regarding the artificial
production of the wilt to a practical test. These experiments
were published in detail in the entomological journal ‘‘ Psyche,”
Vol. XVI., No. 5, October, 1909. There appeared also a Ger-
man translation of the paper in the “ Societas Entomologica,”
Jahrgang XXIV., pp. 178-181, Ziirich, Switzerland. The
main facts in these experiments are here noted. Up to 70
per cent. of the caterpillars were killed by artificially produced

™ 1 See the experiments which Sasaki performed on mulberry trees in Japan, “ Zeitschrift fiir
Pflanzenkrankheiten,’’ XII. Band, Jahrgang 1902, 4. Heft, pp. 203-226; 5. Heft, pp. 258-278.

13

Flacherie, while all caterpillars which were kept apart for con-
trol remained healthy. From these results I was therefore
led to believe that the artificially produced Flacherie might be
utilized as a valuable aid in the destruction of gypsy moth
caterpillars. If the disease appears in nature during normal
weather conditions, the caterpillars are in most cases almost
full grown when attacked; but the farther the weather condi-
tions of the year differ from the normal, the earlier in their
life will the disease affect them. The fact that I succeeded in
rendering the caterpillars susceptible to the wilt before the
third molt suggested that this may be of importance in the
practical use of the disease, since by artificially inducing
Flacherie, relief might be had weeks sooner than happens in
nature.

Better to understand the conclusions drawn from the last
experiment, which was performed on trees on which a consid-
erable number of gypsy moth caterpillars occurred naturally,
the following account is given: A group of oak and another of
willow trees were infested with about 5,000 caterpillars each.
Shortly before their fourth molt, upon each of these two groups
of trees 100 sick and 50 dead caterpillars were destributed.
The disease spread with amazing rapidity, and even on the
following day many freshly killed caterpillars could be counted.
By the time of pupation about 4,000 caterpillars on each group
of trees had succumbed to the disease. Two conditions which
did not enter into my previous experiments united to cause this
unusual result. In the first place, the two groups of trees had
been badly infested and injured by gypsy moth caterpillars
the previous season, as was evidenced by the unhealthiness of
the leaves during the summer of 1909, and the caterpillars had
probably become predisposed to the disease on account of the
resulting decrease in the value of their food. As a second
very important factor may be mentioned the dry weather,
which by its desiccating effect upon the leaves served to render
the food for the caterpillars still less nutritious. Hence, from
the beginning there was a decreased vitality in the tissues, and
digestion was early disturbed. In short, the caterpillars were
already very susceptible to the disease at the time I introduced it

14

among them, and conditions were therefore most suitable for the
spread of the wilt. Always in the places that have been injured
by gypsy moth caterpillars in previous years, there is a pre-
disposition on the part of caterpillars of the following year
toward Flacherie. The heavy defoliation checks the normal
metabolism of the attacked vegetation, which causes a weak
and sickly development of the shoots, and these therefore do
not furnish the caterpillars sufficiently wholesome nourishment.
It should be remembered that these facts, in the long run,
mean a self-protection of the vegetation. If at this time dead
and sick material is introduced among the caterpillars in such
a locality, the organisms of the disease will act readily upon
the individuals present. Infection will take place even in
eases where a locality is badly infested by the caterpillars for
the first time, because one can always find a large number of
weak and therefore susceptible specimens. Then, as the disease
progresses, it acquires such virulence that even the previously
healthy specimens become infected.

In the article mentioned I called attention to other ways in
which the caterpillars advance the infection among themselves,
that is, during the resting period, during the feeding time,
ete., and how easily the disease may be carried over by the
caterpillar to its pupal stage. The great probability of an
economic value in Flacherie for destroying the gypsy moth was
suggested, but it was thought that the experiments of only a
single year had better not be taken as a comprehensive method
for the practical use of the wilt, and that further experiments
should be undertaken on a larger scale to substantiate the
obtained results.

III. Flacherie Experiments in 1910.

A. GENERAL.

In the spring of 1910 the author was requested, by the State
Forester of Massachusetts, to make similar experiments on a
large scale in different parts of the State.t These experiments
were undertaken with the help and kind encouragement of
Prof. W. M. Wheeler. I would also express my indebtedness

1 Cf.; “Sixth Annual Report of the State Forester of Massachusetts,’’ 1909, p. 86.

15

to all those from whom I have received advice and actual
assistance. My thanks are also due to State Forester Frank
W. Rane and Assistant Forester L. H. Worthley for much
help; and to their division agents, Norman Souther of Bridge-
water, and Francis C. Worthen of Georgetown, and to Mr.
H. P. Richardson, local moth superintendent of Concord, for
their support in the field work. Last but not least, I owe,
through correspondence, several valuable hints to Dr. E. Fischer,
Ziirich, Switzerland, who, through his investigations on insect
diseases, is to be regarded the proper instigator of these ex-
periments.

In the beginning of the work each of the division agents was
asked by letter to suggest convenient localities in which to con-
duct the experiments. Three of the division agents stated
that they had no suitable places in their districts. In the
remaining divisions 29 places were chosen, but at the end of
my investigations unfortunately 13 of these could not be used,
since some of the local moth superintendents had not followed
instructions, and other places had been sprayed with arsenate
of lead. Isolated forest districts, varying from small areas
to several acres, were chosen for the experiments. The isola-
tion was for the purpose of making easier a control of the
place, since in such a locality an eventual increase or decrease
of the caterpillar mass by migration was less probable. The
local superintendents of the different places were instructed not
to use any artificial means for destroying caterpillars in the
selected woods. I was, however, obliged to use some localities
in which, during the preceding winter, some of the egg clusters
had been killed by creosote. According to the size of the
various places, the local superintendents were requested to col-
lect a corresponding mass of gypsy moth caterpillars shortly
before their second molt. These amounted to from 50 to 100
individuals per acre. Where many egg clusters were present
but few caterpillars had to be collected, and vice versa. Hence,
the number of caterpillars to be collected was decided in ad-
vance for each locality. The reason for this is that an in-
fection spreads more easily and rapidly in a heavily infested
district than in places less damaged by caterpillars. In a

16

badly infested forest of 10 acres or more the average number
of caterpillars to be collected was placed at less than 50 speci-
mens per acre, since the disease spreads best in such localities.

The local superintendents had been instructed to feed the
collected caterpillars daily with oak leaves, or with apple leaves
where oak leaves could not be secured. These leaves were
not to be removed from the twigs, and were to be placed in
water for at least four days before feeding. A special em-
phasis was laid on not giving as food leaves of trees which had
been sprayed with arsenate of lead. As breeding cages com-
mon wooden boxes were used, to which the entry of air was
provided for by means of gauze coverings. Further, the local
superintendents, who were not familiar with the wilt, were
taught the character of this disease and its manner of appear-
ance, and were instructed to communicate with me at once on
the first appearance of Flacherie in their breeding cages. The
local superintendents were asked to attend to this part of the
work, since at that time it was not convenient to rear several
thousand gypsy moth caterpillars in one place, and also in
order that their interest might be awakened in the experiments.

As soon as the wilt was determined to be present in a brood
the whole material was transplanted upon the previously chosen
places, with the help of the respective superintendents. This
was done as follows: a piece of clean cloth, burlap, for instance,
about 2 feet long by 1 foot wide, was hung in dense foliage
between the limbs of a tree, or from one tree to another close
by (Fig. 1). In this hammock-like bag were placed, besides
the dead and still living caterpillars of the brood, also all food
remaining in the breeding cage, since such remains might also
be supposed to contain organisms of the disease. No means
were used to prevent the escape of the sick but still crawling
caterpillars, in order that they might disseminate the organ-
isms." Where possible, the bag with the material was hung
about 6 feet or still higher from the ground, in order that the
wind might aid in the spread of the disease. In planting
the diseased material the direction of the prevailing wind of the

1 That this is the case is proved by some experiments which I shall consider particularly later,
where only sick caterpillars were transplanted, but no dead caterpillars.

17

season was taken into consideration. For instance, in locali-
ties which had prevailing east winds the infected material
was exposed near the eastern border of the forest, but still
inside of it, so that the wind, before reaching the larger part
of the wood, was forced to strike first the center of the diseased
area. It may be mentioned that in some cases, where no con-
venient cloth was at hand, the breeding cages themselves with
the material, after the removal of the cover, were hung between
limbs. No difference was observed in the results. The in-
fected material was planted in most of the localities at a time
when most of the caterpillars in the field were undergoing the

Fig. 1.— Method of hanging hammock in tree.

third molt. The respective ages of the caterpillars will be
mentioned under each experiment.*

It was important to select places which gave the best guaran-
tee for the health of the growing caterpillars; hence, special
attention is called to the fact that in the experimental localities
no disease is known to have occurred among the caterpillars
of previous years.

1 T had always planned to plant the disease as soon as it made its appearance in one or the other
of the broods. This was, however, frustrated on several occasions by various circumstances.
For instance, some local superintendents did not notice the Flacherie till after the disease had
prevailed for several days. It was, further, not always possible for me to depart immediately
upon receiving a communication concerning the outbreak of the disease. It was also almost
impossible for one man to transplant the infected material to all the chosen places during the
short time in which the gypsy moth caterpillars were in the third or beginning of the fourth stage.
This is the reason why in some localities the disease was planted later, although the caterpillars
were already beyond the third molt.

18

After the eggs were laid in the autumn of 1910 all localities
were carefully inspected, and the number of the fresh clusters
was determined as nearly as possible. For examination of the
single eggs, five clusters, when possible, were collected from each
locality. Five clusters from a place in the western part of
Concord, Mass., served for control. These eggs must be con-
sidered as normal because they come from a place in which
positively no disease whatever has occurred. In collecting
clusters for examination the first five found were taken; and
were not taken at random.

Every single egg of all these clusters was examined micro-
‘scopically. This, it is true, required very much time, but it
was nevertheless indispensable. The eggs were separated into
three kinds: first, those that showed no signs of development of
the embryo (empty or unfertilized eggs); second, those in
which the more or less developed embryo had been killed before
its complete development; and finally, those which showed a
perfectly developed embryo (normal and supposedly living
eggs). In every case in which the egg could not be absolutely
assigned to the second series it was counted with the third
series.*

In the details of all the work everything which seemed to
suggest the economic value of the wilt has been purposely re-
garded from the most unfavorable standpoint, for the purpose
of meeting any objections. When estimating the egg clusters
from the selected localities there was always present either the
division agent or the local superintendent, and at that time
written notes were made of these estimates before the intro-
duction of the disease. In the spring we made the lowest
possible estimate on the number of clusters present, while
with the second estimate in the autumn, after the disease had
produced its effect, the fresh clusters were estimated as liberally
as possible.

The average which resulted from the examination of the
single clusters must not be taken as absolutely fixed, since the
small number of the clusters examined admits of a variation

1 The eggs of the control clusters could all be distributed with exactitude into the respective
series.

19

from the mean in both directions. The main purpose of the
experiments, however, was not to make mathematically exact
calculations, but to find out in what manner and to what degree
the gypsy moth may be infected by the wilt. or these pur-
poses the calculations made should be sufficient, and the figures
given will not be far from the real average.

As to the control experiment, the average of eggs in a normal
cluster was found to be 437. I am not aware that the eggs of
a large series of normal clusters have ever been counted in order
to establish an accurate average. In published reports the aver-
age of eggs in a normal cluster is stated as “ 400 to 500.”

Control Hxpervment, Concord, Mass.

Five clusters were taken in the western part of this locality,
where there certainly did not occur any disease among the gypsy
moth caterpillars. These clusters, therefore, must be regarded
as normal. The microscopic examination of the eggs of these
clusters gave the following results: —

Cluster 1.

Unfertilized eggs
a2") = .73 per cent., or about 1 per cent.

Eggs with dead embryos, _ 3
Eggs apparently alive, . . 543 =99.27 per cent., or about 99 per cent.
otal : she ans . 47 eggs.
Cluster 2.

Unfertilized eggs,

SS heoasds Dalia .47 per cent., or about .5 per cent.

Eggs apparently alive, . . 424 =99.53 per cent., or about 99.5 per cent.
Total, bee a ts ao epg:
Cluster 3.

Unfertilized eggs
= sae = 1.74 per cent., or about 2 per cent.

Eggs with dead embryos, 4
Eggs apparently alive, . . 3095 =98.26 per cent., or about 98 per cent.
Total, : ; ' . 402 eggs.
Cluster 4.

Unfertilized eggs,
Eggs with dead embryos, .. 3
Eggs apparently alive, . . 424 =99.07 per cent., or about 99 per cent.

= .93 per cent., or about 1 per cent.

Total, : : : . 428 eggs.

20

Cluster 6.
Unfertilized eggs, , lL
Figve withidend embryos) Pe is .79 per cent., or about 1 per cent.
Eggs apparently alive, . . 3877 =99.21 per cent., or about 99 per cent.
Total, , ‘ ‘ . 380 eggs.

The average of these 5 clusters is as follows: —

Dead eggs, ; : : : 4 = .92 per cent., or about 1 per cent.
Eggs apparently alive, . . 433 =99.08 per cent., or about 99 per cent.
Total, : : ; . 487 eggs.

The results of this control experiment are used in estimating
the departure from the normal of the egg masses in all the
other experiments.

B. Tue Srinetr EXprerIMeEnNts.

Concord, Mass.

Division Agent, CoHas. W. Minot; Local Superintendent, Henry P.
RICHARDSON.

As a suitable place for my experiments, I located, on May 20, 1910,
an isolated forest of about 244 acres, belonging to the estate of Mr.
William Brewster. This place is situated in the eastern part of Con-
cord, about half a mile west of the West Bedford railroad station.
The forest consists mainly of oaks about twenty years old and of a
group of pines about fifty years old, all mixed with brush; and along
the border, especially on the northern pari, are birches about ten years
old.

According to the local superintendent and to the owner, Mr. Brewster,
the gypsy moth caterpillars were quite numerous during the summer
of 1909. Both are certain that there was no disease among the ecater-
pillars. We estimated this place to contain about 10,000 clusters of
eges in May, 1910.

On June 6 I received notice from the local superintendent that the
wilt had appeared among the caterpillars which he had collected and
fed according to instructions. Two days later I went to Concord, and
found that some 10 caterpillars were already dead and the others were
apparently very sick, as they remained motionless even when irritated.
The superintendent had begun to feed the caterpillars on May 26, and
had noticed the first dead specimen on June 5. Accordingly, he had
succeeded in developing the wilt artificially in the course of eleven days.

21

With the assistance of the local superintendent the whole breeding
material was immediately exposed in the western part of the selected
forest. The distance from the ground to the material, which was hung
between the limbs of a tree, was about 15 feet. The largest number of
gypsy moth caterpillars in this locality were at this time in the third
molt, or about to pass into this molt. The wilt soon spread over
the whole forest, as was seen during occasional visits to the place
by Mr. Richardson, Mr. Brewster and myself. On Sept. 7, 1910, the
fresh ege clusters were estimated by the local superintendent and
myself to amount to about 5,000. Often 4 or 5 of these clusters to-
gether would not make more than 1 normal ¢luster; the actual number
of eggs was thus much less than would have been present in the same
number of normal clusters.

The examination of 5 clusters which had been collected Sept. 7,
1910, on Brewster’s estate showed the following counts: —

Cluster 1.

Unfertilized ;
cre Daeg = 9.66 per cent., or about 9.5 per cent.

Eggs with dead embryos, . 11
Eggs apparently alive, . . 131 =90.34 per cent., or about 90.5 per cent.
Total, ; : ‘ . 145 eggs.
Cluster 2.
Unfertilized eggs, 2
Gilgen with dead embryos, >. 9 =7.43 per cent., or about 7.5 per cent.
Eggs apparently alive, . . 137 =92.57 per cent., or about 92.5 per cent.
Total, : q 5 . 148 eggs.
Cluster 3.
Unfertilized eggs, . : reds
Higgs with dead embryos... 49 =48.06 per cent., or about 48 per cent.
Eggs apparently alive, . . 67 =651.94 per cent., or about 52 per cent.
Total, ‘ ; : . 129 eggs.
Cluster 4.
Uniertilized eggs, . . . 1 "
Eat whdeed eee a 8.64 per cent., or about_8.5 per cent.
Eggs apparently alive, . . 74 =91.36 per cent., or about 91.5 per cent.

Total, 3 4 é . 81 eggs.

Cluster 6.

Unfertilized eggs,

a) 96. t 6.5 per cent.
Eges with dead embryos, . 5 6.76 per cent., or about 6.5 per cen

Eggs apparently alive, . . 69 =93.24 per cent., or about 93.5 per cent.
Total, ; : : . 74 eggs.

Averaging these 5 clusters we have: —

Dead eggs, F f : . 20 =17.24 per cent., or about 17 per cent.
Eggs apparently alive, . . 96 =82.76 per cent., or about 83 per cent.
Total, : ; : . 116 eggs.

A normal egg cluster contains on an average 433 eggs (p. 20) which
are apparently alive. Since the infested locality averages only 96 eggs
which are apparently alive per cluster, 44 clusters are necessary to
equal the size of a normal cluster. The number of the fresh clusters,
estimated at 5,000, thus has to be reduced to about 1,100 clusters to
compare with the 10,000 clusters present in the spring of 1910. The
number of apparently vital eggs, therefore, is decreased to about 11
per cent. through the action of Flacherie.

The local superintendent informed me that the disease had also spread
into the neighboring forest districts. By an extended walk through
about 5 acres of these woods I learned that the wilt had operated in
the same manner as in the first locality. He is of the opinion that
the number of clusters in this 5 acres has been decreased to about
15 per cent. Adjoining these woods there are about 15 acres of forest,
in which the local superintendent found that all egg clusters which
had been laid in the summer of 1909, and which had been deposited
1 foot or more above the ground, had failed to produce caterpillars,
that is, the eggs had remained unhatched; but the caterpillars had all
emerged from those eggs in clusters placed less than 1 foot above the
ground. I found that these statements corresponded very closely with
the facts. Here and there I noticed a shght exception by occasionally
finding either a high-placed cluster from which a few caterpillars had
emerged, or I detected close to the ground a cluster from which only
a portion of the caterpillars had emerged. These exceptions, however,
were insignificant, for they represented in each case hardly more than
10 eggs. J am unable, so far, to find any explanation for this peculiar
occurrence. At first I thought that an egg parasite might have exerted
its helpful power, but the examination of eggs from several clusters
which had remained unhatched showed that almost all eggs contained
a fully developed dead embryo, and no signs of a parasite could be
found. The moisture of the soil cannot be made responsible, for bor-

23

dering this forest there is another with exactly the same soil, the same
kind of trees and of the same age as the other place, and although
these forests are separated only by a very broad road, in the latter wood
the caterpillars of almost all egg clusters of 1909 had emerged from
clusters that had been placed at any height on the trunks of the trees.
There were exceptional cases of clusters, sometimes on the upper, some-
times on the lower part of the trees, from which all caterpillars had not
emerged, but there was no evidence of the peculiar condition that
characterized the clusters in the place first mentioned. Whether any
caterpillar disease has any effect in this occurrence, I cannot now say.
The solution of this question may come in the future from careful ob-
servations at this particular locality.’ .

An extensive forest in the southwestern part of Coneord was visited,
in which, according to the information of the local superintendent, the
wilt had broken out naturally. The peculiar conditions which we found
here require a detailed description of the locality and of the manner
in which the disease operated. The largest part of the forest, about
20 acres, is situated upon the ridge of a hill. On the east and west
the hill slopes to wet meadows. On the north and south the hill gently
passes over into level country, and it is bordered here by broad roads.
The principal trees on the ridge of the hill are high pines about sixty
to eighty years of age; brush is almost absent. The slopes are covered
in large part with young oaks, which are much mixed with brush of
different kinds. Now, while the forest of the whole ridge, including
the northern and southern slopes, suffered considerably from injuries
by gypsy moth caterpillars during the summer of 1910, the eastern and
western slopes were exempt from this damage. Soon after the cater-
pillars had passed the third molt Flacherie made its appearance among
those feeding on the pines upon the ridge of the hill. The disease
developed here so rapidly that probably all caterpillars were killed, for
we were unable, even by careful search in these 20 acres, on Sept. 7,
1910, to find a single fresh cluster. The statement, therefore, seems
justified that all caterpillars, at least all the females (100 per cent.),
were here killed by the wilt. This very high number, however, was
restricted to the forest upon the ridge of the hill. On the first trees
of the northern and southern slopes fresh egg clusters were found, and
the number of these increased as we went toward the plain. But the
inspection of such dead caterpillars as were observed showed that the
wilt had also operated in the woods of these slopes. The local super-
intendent looked here for Flacherie, but it did not appear till the eater-
pillars were in their last stage. The reason for this behavior of the
wilt might be that the ridge of the hill, with its high trees, was much
exposed to the effect of the wind, and after Flacherie had once devel-
oped it could be spread very rapidly along the ridge. On the northern

1 Similar observations, where eggs have not hatched, were made elsewhere by different per-
sons connected with the moth work, but no definite observations, as at Concord, were reported.

24

and southern slopes, however, the wind could not strike so hard, and
the spreading of Flacherie toward the plain, therefore, took place com-
paratively slowly. Upon the eastern and western slopes, on account
of the lack of caterpillars, the conditions necessary for developing the
wilt were not present.

A map of the place, sketched by Mr. Richardson (Fig. 2), which may
aid in understanding the deseription, is given herewith.

Fig. 2.— Experiment, Concord, Mass. A. Summit of hill, now cleared. B.
Northern slope, infested. C. Southern slope, infested. D. Eastern slope,
not eaten. E. Western slope, not eaten. EF. Meadows.

Five clusters were examined for comparison from the localities in
which Flacherie developed naturally. These were collected on a walk
through the forest district at the southern end of the hill, and from
different trees taken at random. The result was: —

Cluster 1.

Unfertilized eggs,

4
Eggs with dead embryos, 16 \ = 12.59 per cent., or about 12.5 per cent.

Eggs apparently alive, . 139 =87.41 per cent., or about 87.5 per cent.
Total, 5 Uverale : “159 eggs.
Cluster 2.
oem: nel ; = 5.30 per cent., or about 5 per cent.
Eggs apparently alive, . . 1438 =94.70 per cent., or about 95 per cent.

Total, i ‘ P . 151 eggs.

20

Cluster 8.

fertilized
merulized eges, = 2.14 per cent., or about 2 per cent.

Eggs with dead embryos, _ 4
Eggs apparently alive, . . 229 =97.86 per cent., or about 98 per cent.
Total, : : : . 234 eggs.
Cluster 4.

fertilized eggs,
Baterwed cae = 3.17 per cent., or about 3 per cent.

Eggs with dead embryos, 3
Eggs apparently alive, . . 122 =96.83 per cent., or about 97 per cent.
Total, : ‘ 5 . 126 eggs.
Cluster 5.
Wnfertalized eges, . . . , 6) _
Beeaahdetiembryon (932°) > 12.93 per cent., or about 13 per cent.
Eggs apparently alive, . . 256 =87.07 per cent., or about 87 per cent.
Total, ee OP Au 204) epas,

Averaging these 5 clusters we get this result: —

Dead eggs, .. - « Is = 7.77 per cent., or about 7.5 per cent.
Eggs apparently alive, . . 178 =92.23 per cent., or about 92.5 per cent.
Total, - : , . 198 eggs.

We notice also that the egg clusters from this place, where the wilt
developed naturally, are considerably less than the normal size, about
21% clusters being equal to 1 normal cluster. This, and the fact that
only 7.5 per cent. of the eggs would fail to hatch, while in the experi-
ment 17 per cent. were dead, is probably due to the fact that upon
this southern slope Flacherie appeared late and spread but slowly.

North Carver, Mass.

Division Agent, Joun A. Fartny; Local Superintendent, HurBERT F. AtTwoop.
This locality was visited on May 9, 1910, with the inspector of the
southern districts of the State of Massachusetts, Mr. Norman Souther
of Bridgewater, to find suitable places for the intended experiments.
The gypsy moth does not occur here in such enormous numbers as in
the northern parts of the State, but I wished to have some experiments
at places where the gypsy moth has but recently gained a foothold.
An isolated wood of about 2 acres, situated somewhat southwest from
Makepeace’s cranberry bog, was found to be a suitable place. It con-
sists of pines about forty years old and of oaks about twenty to twenty-
five years of age, with considerable brush.

26

The gypsy moth was discovered here for the first time during the
winter of 1909-10, by finding egg clusters. Several of these clusters,
unfortunately, had been already killed with creosote before my first
visit, but there were present, according to Mr. Souther’s and my esti-
mation, about 25 clusters. Whether there was any disease among the
caterpillars of the previous year could not be ascertained, but it is
highly improbable, considering the youth of the colony and the large
size of the clusters.

On June 14, 1910, the local superintendent sent me word that
wilt had made its appearance among the eaterpillars which he had
collected and fed according to instructions. I therefore went to North
Carver on June 16, and found that in Mr. Atwood’s colony about
3 per cent. of the caterpillars had already died of Flacherie. Most
of those still living were very sick. He therefore had developed the
wilt artificially after a feeding of about fourteen days.

This same day, with the assistance of the local superintendent, a
part of the breeding material was exposed on the western side of the
selected place. The bag containing the material was fastened about
8 feet from the ground, between young oak trees. Most of the cater-
pillars of this locality had just passed the third molt.

On Oct. 7, 1910, an extended search was made by the local super-
intendent and myself, but only 4 fresh clusters could be found. The
microscopic examination of these 4 clusters resulted as follows: —

Cluster 1.
Unfertilized eggs,
Eggs with dead embryos, .
Eggs apparently alive, . . 405 =93.97 per cent., or about 94 per cent.

Total, : ; ; . 4831 eggs.

5
oh tes 6.03 per cent., or about 6 per cent.

Cluster 2.

Unfertilized eggs, . : : Sek 5.38 :

Eggs with dead embryos, . 18{~ ™ per cent., or about 5.5 per cent.

Eggs apparently alive, . . 3/5 =94.62 per cent., or about 94.5 per cent.
Total, : : : . 396 eggs.

Cluster 8.

Unfertilized eggs, . . - 2\_ ya b
Tee dkn Me Cm ed g ( = 4.65 per cent., or about 4.5 per cent.

Eggs apparently alive, . . 205 =95.35 per cent., or about 95.5 per cent.

Total, : : : . 215 eggs.

2 *

Cluster 4.
Unfertilized eggs, Bly
eee dead embryos, ig f= 13.38 per cent., or about 13.5 per cent.
Eggs apparently alive, . . 1386 =86.62 per cent., or about 86.5 per cent
Total, 4 ; B . 157 eggs.

Averaging these 4 clusters we get: —

Dead eggs, Sak ae . . 20 = 6.67 per cent., or about 6.5 per cent.
Eggs apparently alive, . . 280 =93.33 per cent., or about 93.5 per cent.
Total, : : : . 300 eggs.

Since, as we have seen, a normal cluster contains on the average
433 eggs with apparently living embryos, the living eggs of these 4
clusters, after the wilt did its work, amount to about 64.5 per cent.
The ege clusters which were present in the spring of 1910 were esti-
mated at about 25, while only 4 fresh clusters were found in the
autumn of 1910. The total number of all apparently living eggs was
decreased in tliis locality to about 13 per cent., as compared with the
number present in the spring of 1910.

Another place for experiments, very similar to the last one, was
selected in North Carver. This is a forest district of 3 acres, and is
situated east of the cemetery on Wenham Street. The timber and
brush here are the same as in the other locality, and the egg clusters
of the gypsy moth were also first discovered here during the winter
of 1909-10. Unfortunately, several clusters were killed with creosote
before my first visit. The clusters still present were estimated by Mr.
Souther and myself at about 600. On account of the young age of the
eolony and the considerable size of the clusters probably no disease
had appeared among the caterpillars of the preceding year.

The remaining part of the wilt material was planted among the ecater-
pillars of this locality on the same day and in the same manner as in
the first colony. Here, also, most of the caterpillars at this time had
just undergone the third molt.

The estimate of the fresh clusters, which was made by the local super-
intendent and myself Oct. 7, 1910, was about 400, from which the first
5 found were used for microscopical examinations. The result is as
follows : —

Cluster 1.

Unfertilized eggs, 4
Eggs with dead embryos,
Eggs apparently alive, . . 280 =95.89 per cent., or about 96 per cent.

i> = 4.11 per cent., or about 4 per cent.

Total, : , ; . 292 eggs.

Cluster 2.
Cee ca ee . =17.17 per cent., or about 17 per cent.
Eggs apparently alive, . . 193 =82.83 per cent., or about 83 per cent.
Total, : : : : 933 eggs.
Cluster 3.
aA Le ae 3 = 7.38 per cent., or about 7 per cent.
Eggs apparently alive, . . 113 =92.62 per cent., or about 93 per cent.
Total, a gd! pee p22 epost
Cluster 4.

Unfertilized eggs,

1
Hegel with dead/embryos! 14 = 4.89 per cent., or about 5 per cent.

Eggs apparently alive, . . 292 =95.11 per cent., or about 95 per cent.
Total, : : : . 307 eggs.
Cluster 5.
es ee g ( = 2-95 per cent., or about 3 per cent.
Eggs apparently alive, . . 862 =97.05 per cent., or about 97 per cent.
Total, : : : : 373 eggs.

Averaging these 5 clusters we get: —

Dead eggs, : : ‘ . 17 = 6.42 per cent., or about 6.5 per cent.
Eggs apparently alive, . . 248 =93.58 per cent., or about 93.5 per cent.
Total, : ! : . 265 eggs.

Since this place, after infection with Flacherie, contains on the
average only 248 eggs with apparently living embryos per cluster,
almost 2 clusters of this locality are necessary to equal a normal
cluster. The number of the fresh clusters, estimated at about 400, thus
has to be reduced to about 250. The number of apparently living eggs
in this locality therefore decreased, after the wilt had operated, to
about 42 per cent.’

1 This forest was cut down by the owner in the beginning of the winter of 1910-11, and all egg
clusters which the forest contained were collected by the local superintendent; 444 clusters were
found. Our estimate of the clusters in the autumn, which was 400, therefore was nearly correct.
The number of apparently living eggs which remained after Flacherie did its work has to be in-
creased 3 per cent., that is to say, to 45 per cent.

29

Boxford, Mass.

Division Agent, FRANctis C. WorTHEN; Assistant Local Superintendent, HARRY
L. Come.

Two places were selected in the West Boxford district for the in-
tended experiments. The locality which we shall consider first is situ-
ated opposite the almshouse, near the Almshouse Road, and is only
about a quarter of an acre in size. This small isolated wood is com-
posed of oaks almost fifty to sixty years of age, and there is no brush.
The gypsy moth eaterpillars were numerous here in the summer of
1909. No disease had been noticed among them, according to Mr.
Worthen and Mr. Cole, nor have any artificial means of destroying the
gypsy moth been undertaken here. Mr. Worthen and I estimated the
number of egg clusters at the time of my first visit, on May 6, 1910,
at about 200.

Mr. Cole was intrusted with raising the eaterpillars for the Boxford
experiments. Having received no notice of the wilt making its appear-
ance in the brood, on the 14th of June, 1910, I went to Boxford to
inspect the material. It was found that Mr. Cole had reared the
eaterpillars in a very cold cellar, where they were eating but little
and were retarded considerably in their development. He was in-
structed to place the caterpillars immediately in a warmer place in the
open air. On June 19, 1910, a letter from him announced that
Flacherie had broken out in his brood. On June 21 I went to Boxford
to confirm his statement. About 5 per cent. of the caterpillars of this
brood had already died of Flacherie, and most of the individuals still
living showed all the signs of the disease.

One part of this brood was exposed, with the assistance of Mr. Cole,
on the same day in the western part of the selected locality. The bag
containing the material was fastened between twigs of oak trees, about
6 feet from the ground. Most of the caterpillars of this locality were
at this time about ready for the fourth molt.

The fresh clusters at this place were estimated, on Aug. 26, 1910,
by the division agent and myself, to be about 60. The first 5 clusters
which were found were collected and examined. The examination re-
sulted as follows: —

Cluster 1.
Wniertilized eggs; =
Eggs with dead embryos, . 6
Eggs apparently alive, . 7 EG

ll

4.92 per cent., or about 5 per cent.

95.08 per cent., or about 95 per cent.

Total, Seabed ae wt Lod epee:

30

Cluster 2.

Unfertilized eggs, d il
eeyotinckelenteeg, . 12) > 10.16 per cent., or about 10 per cent.

Eggs apparently alive, . . 115 =89.84 per cent., or about 90 per cent.
Total, ; : : . 128 eggs.
Cluster 3.

“i
Unt criized eens, = 7.14 per cent., or about 7 per cent.

Eggs with dead embryos, _. a
Eggs apparently alive, . . 91 =92.86 per cent., or about 93 per cent.
Total, : : : . 98 eggs.
Cluster 4.
Unfertilized eggs, . 3 : Sl
Basin Geral ula UE = 28.24 per cent., or about 28 per cent.
Eggs apparently alive, . . 61 =71.76 per cent., or about 72 per cent.
Total, ; : : . 85 eggs.
Cluster 6.

fertilized
Ualcrlzed e&es) = 2.96 per cent., or about 3 per cent.

Eggs with dead embryos, _. 5
Eggs apparently alive, . . 164 =97.04 per cent., or about 97 per cent.
Total, F : ; . 169 eggs.

The average of these 5 clusters gives the following result: —

Dead eggs, : : : . 11 = 9.17 per cent., or about 9 per cent.
Eggs apparently alive, . . 109 =90.83 per cent., or about 91 per cent.
Total, : ; ; . 120 eggs.

Since this place, weakened by the wilt, contained only 109 eggs with
apparently living embryos to the cluster, almost 4 clusters were neces-
sary to equal the size of a normal cluster. The number of fresh egg
clusters, which were estimated at 60, thus must be reduced to about
20 clusters. The number of apparently living eggs was therefore de-
creased, as the result of Flacherie, to about 10 per cent. ;

The second place which was selected in West Boxford for experi-
ments with the disease consists of an isolated wood of about half an
acre. Most of the trees are oaks about thirty years of age, mixed
with underbrush. This locality is situated on Highland Street, between
two apple orchards. In the summer of 1909 the gypsy moth eater-
pillars were relatively more numerous than at the first place. No dis-

ol

ease was noticed among them by Messrs. Worthen and Cole, but it is
nevertheless possible that the wilt might have made its appearance.
No artificial means for destroying the gypsy moth had been undertaken
here. The number of egg clusters present at the time of my first visit
in the spring of 1910 was estimated by Mr. Worthen and myself at
about 550.

Flacherie, which had been developed artificially by Mr. Cole, was
planted in this locality June 21, 1910, in the same manner as in the
place first described. The caterpillars were about ready for the fourth
molt, as in the first experiment. With the assistance of the division
agent the fresh clusters at this locality were estimated on Aug. 26,
1910, to be about 80. The microscopical examination of the first 5
clusters found shows: —

Cluster 1.

fertilized
Ubterpiized exes, = 6.67 per cent., or about 6.5 per cent.

Eggs with dead embryos, . 10
Eggs apparently alive, . . 154 =983.33 per cent., or about 93.5 per cent.
Total, : 5 ; . 165 eggs.
Cluster 2.
Unfertilized eggs, . ‘ , 1
Bipeatwitl dead’ evibryos,) Bila 6.25 per cent., or about 6 per cent.
Eggs apparently alive, . . 90 =983.75 per cent., or about 94 per cent.
Total, : : ; . 96 eggs.
Cluster 3.

Unfertilized
pete ee = 7.09 per cent., or about 7 per cent.

Eggs with dead embryos, . 7
Eggs apparently alive, . . 118 =92.91 per cent., or about 93 per cent.
Total, : : , . 127 eggs.
Cluster 4.
Unfertilized eggs, . ’ ; 3
Bee th devdicnibryose 12 on 9.68 per cent., or about 9.5 per cent.
Eggs apparently alive, . . 140 =90.32 per cent., or about 90.5 per cent.
Total, : 5 : . 155 eggs.
Cluster 5.

This cluster proved to be entirely without eggs, and it consisted only of a
mass of wool of about 1 square centimeter in size. The female moth, which
deposited this cluster, seems to have been absolutely sterile. It started
mechanically, it is true, to lay eggs, but of course it could deposit nothing
except the hairs from its abdomen.

32

The average of these clusters gives the following result: —

Dead eggs, y L : ; 8 = 7.34 per cent., or about 7 per cent.
Eggs apparently alive, . . 101 =92.66 per cent., or about 93 per cent.
Total, : : . 109 eggs.

Since this locality, which had been infected with the wilt, showed
only 101 eggs with apparently living embryos on the average per
cluster, about 4 clusters would be equal to a normal one. The fresh
ege’ clusters, which were estimated at about 80, thus have to be re-
duced to about 20. The number of apparently living eggs in this
infested locality has thus decreased to about 4 per cent.

A third locality in which the wilt appeared naturally was somewhat
closely inspected. A small isolated wood of about 3,000 square feet
is situated on Main Street, about 500 yards south of Wood’s Corner.
The trees consist of oaks a hundred years or more of age, and the
place is free from underbrush. The gypsy moth caterpillars were very
numerous here in the summer of 1909, but no definite statement can _
be made as to whether or not there was disease among them. If the
disease was present, it was doing little harm, as otherwise dead cater-
pillars in large numbers would have been noticed, without doubt, by
the division agent or the local superintendent. Mr. Worthen estimated
the number of clusters present in the spring of 1910 at about 400. No
artificial means for destroying the gypsy moth were undertaken. Meas-
ured in a straight line this place is at least 1 mile from the nearest
of the two localities previously mentioned. Flacherie was noticed here
at a time when most caterpillars were in the fourth molt. Here, too,
the disease worked considerably among the caterpillars. It was hard
to find even 50 clusters when Mr. Worthen and I estimated the freshly
Jaid ones, on Aug. 26, 1910. For comparison the first 5 clusters found
were collected and examined. They gave the following results: —

Cluster 1.
Unfertilized eggs,

Meee mrith dead emibr os; 8 f =11.27 per cent., or about 11 per cent.

Eggs apparently alive, . . 63 =88.73 per cent., or about 89 per cent.
Total, : 3 : . 71 eggs.
Cluster 2.

Unfertilized eggs,
Eggs with dead embryos,
Eggs apparently alive, . . 96 =89.72 per cent., or about 90 per cent.

1
10 = 10.28 per cent., or about 10 per cent.

Total, : é ; . 107 eggs.

33

Cluster 3.
Be ey iiss : = 6.94 per cent., or about 7 per cent.
Eggs apparently alive, . . 1384 =93.06 per cent., or about 93 per cent.
Total, , : : : “144 eggs.
Cluster 4.

Unfertilized eggs,

Enea ittidendlcrbryost Pais 4.26 per cent., or about 4 per cent.

Eggs apparently alive, . . 90 =95.74 per cent., or about 96 per cent.
Total, é , F : a, eggs.
Cluster 5.
Te fe = 8.59 per cent., or about 8.5 per cent.
Eggs apparently alive, . . 149 =91.41 per cent., or about 91.5 per cent.
Total, : : : : “163 eggs.

The average of these 5 clusters gives the following result : —

Dead eggs, : : : ; 9 = 7.08 per cent., or about 7 per cent.
Eggs apparently alive, . . 106 =92.92 per cent., or about 93 per cent.
Total, : F . 115 eggs.

Thus in this locality, also, in which the wilt appeared naturally, the
ege clusters were far below the normal size. Examination showed that
about 4 of these clusters would be necessary to equal a normal one
in size. The estimated sum of 50 clusters, therefore, must be reduced
to about 14. Hence, the apparently living eggs which remained amount
to about 4 per cent.

Finally, a forest of about 30 acres was inspected. This is situated
at an angle of 45°, and half a mile distant from the two first localities.
Tn this forest, which consists mainly of large pines and oaks, the gypsy
moth caterpillars had been present in considerable numbers during
the summer of 1909, and were still more numerous during the
first part of the summer of 1910. The owners of this place intended,
according to the division agent, to cut down the forest, thus preventing
a total stripping and decrease of the value of the wood. A powerful
ally came to the support of the owners during the latter part of the
summer of 1910, in the guise of Flacherie, which cleared up the cater-
pillars in a manner that left nothing to be desired. It cannot be deter-
mined whether the disease appeared naturally or was spread to this

34

forest from the two localities in which the experiments were performed.
However this may be, the wilt had acted at any rate in such a virulent
manner that in all these 30 acres of forest not a single fresh egg cluster
could be found, notwithstanding the most painstaking search on the
part of Mr. Worthen and myself.

Mr. Worthen also undertook, on his own behalf, the breeding of sev-
eral hundred caterpillars, feeding them according to my instructions.
The disease could be noticed in this brood as early as June 14, 1910.
Most of these caterpillars had just passed the third molt. Three days
later he exposed all the material among the caterpillars of a forest near
his home. Soon he observed the “ dying off” of the caterpillars which
were there present. The number of the dead ones grew astonishingly,
but the final result cannot be stated, since, unfortunately, the trees
were later sprayed with arsenate of lead.

West Bedford, Mass.

The division agent and the local superintendent in this locality were
not requested to perform the experiments. My friend, Mr. L. W.
Swett, the well-known specialist in Geometride, asked me in the spring
of 1910 to undertake an experiment with the wilt upon his estate on
Davis Street, northeast. of the railroad station, in West Bedford. We
inspected the place for this purpose on May 29, and the locality ap-.
peared to be a very suitable one for the work. It consists of two iso-
lated strips of wood, which meet at a right angle. One strip comprises
oaks about fifty years of age, mixed with some brush; while the other
consists of dense birch brush about six years old. The whole locality
comprises about three-quarters of an acre. The gypsy moth was first
discovered here in 1908, and the place since that time has been under
continuous observation by Mr. Swett. He assured me that there were
positively no signs of a disease among the caterpillars. During the
summer of 1909 the caterpillars were quite numerous. Part of the egg
clusters, which were laid in the autumn of 1909, were killed with
creosote, but there were still present, according to Mr. Swett’s and my
estimation at the time of my first visit, about 400 clusters on the oaks
and about 100 clusters on the birches.

The caterpillars for this experiment were raised by the author at
Forest Hills. They began to die from Flacherie after a continuous
feeding of fourteen days, and just as they had passed the third molt.
This material was planted, June 22, 1910, in the birch brush, and the
bag was fastened about 6 feet from the ground. Most of the eater-
pillars of this locality were at that time half way between the third
and fourth molt. The place was visited again on July 18, 1910, to
determine the progress of the disease. Mr. Swett and I found that
the caterpillars were dying in considerable numbers, and the percentage
of dead individuals was greatest on the shortest brush, and decreased

30

gradually the higher the vegetation grew. For instance, all the cater-
pillars which had been feeding on the small willow brushes were already
dead. This brush, hardly 3 feet high, occurs here and there in front
of the two rows of woods. The dead caterpillars were readily seen,
as they were hanging all over the brush. Many of the caterpillars on
the birches were dying, but a considerable number of living individuals
was still present. In the colony of the high oaks, however, the wilt had

Fig. 3.— Experiment, West Bedford, Mass. A. Dense birches. XX. Exposure of
disease. B. Oaks and underwood. C. Field. D. Marshy meadow with a few
scattered willows.

not spread so much, although dead individuals were found in consider-
able numbers.

On Sept. 23, 1910, the freshly laid egg clusters were estimated. We
made the interesting discovery that there existed no fresh clusters in
the row overgrown with birch. Thus, all the caterpillars, at least the
females, had been killed by Flacherie. To be certain of this fact the
crevices of the bordering stone wall were carefully examined, since
the gypsy moth female selects with preference such hidden places for
oviposition. But no fresh clusters could be found here. The other row
with the high oaks, however, proved to have a relatively large number

36

of fresh clusters, which were estimated at about 150. Mr. Swett later
made an examination and confirmed these facts. There is no sufficient
explanation so far for the peculiar behavior of the wilt in this locality.
Apparently the wind here played a special role. The difference in the
vegetation may also have had some influence. Does the eating of birch
foliage hasten the production of the disposition to Flacherie among
the caterpillars?

The accompanying map will complete the description of the West
Bedford locality (Fig. 3).

The microscopic examination of the 5 first egg clusters, found on
the oaks, gave the following result : —

Cluster 1.
ere E = 2.69 per cent., or about 2.5 per cent.
Eggs apparently alive, . . 181 =97.31 per cent., or about 97.5 per cent.
Total, i ; : : “186 eggs.
Cluster 2.

Unfertilized eggs,

elie 2.67 t bout 2.5
Eggs with dead embryos, 7 [ = 4.0¢ per cent., or about 2.5 per cent.

Eggs apparently alive, . 328 =97.33 per cent., or about 97.5 per cent.
Total, : : : ; 337 eggs.
Cluster 3.
Pea ee ; ; = 3.25 per cent., or about 3 per cent.
Eggs apparently alive, . . 149 =96.75 per cent., or about 97 per cent.
Total, : : , : “154 eggs.
Cluster 4.
a os ere = 20.65 per cent., or about 20.5 per cent.
Eggs apparently alive, . . 269 =79.35 per cent., or about 79.5 per cent.
Total, ee : ; "339 eggs.
Cluster 4.

Unfertilized eggs, :
Eggs with dead embryos, _.. 9
Eggs apparently alive, . . 303 =96.81 per cent., or about 97 per cent.

= 3.19 per cent., or about 3 per cent.

Total, : ; : . 313 eggs.

37

The average of these 5 clusters gives the following result ; —

Dead eggs, : . 2 . 20 = 7.52 per cent., or about 7.5 per cent.
Eggs apparently alive, . . 246 =92.48 per cent., or about 92.5 per cent.
Total, : é : . 266 eggs.

Since this locality, in which the wilt has worked, contained only
246 eggs with apparently living embryos in average per cluster, nearly
2 clusters were necessary to equal a single normal cluster. The num-
ber of fresh clusters, which were estimated at about 150, must therefore
be reduced to about 90. The number of apparently living eggs of that
part of this locality which bears the oaks was therefore decreased to
about 22.5 per cent. after the wilt had worked, while, as already men-
tioned, the part with the birches contained probably no living eggs.

Haverhill, Mass.

Division Agent, H. F. Armstrone; Local Superintendent, G. F. Moore.

With the assistance of the local superintendent a place was selected
for the experiment in East Parish, Haverhill; it is situated west of
East Broadway and northeast of Millway Pond, and on the Old Coun-
try Road. This locality represents almost 50 acres of isolated forest,
in which oaks about thirty years old, mixed with underbrush, prevail.
Only about 12 acres of this forest are infested with the gypsy moth.
The caterpillars were numerous here during the summer of 1909, but no
disease was present, according to the local superintendent. On May
18, 1910, our joint estimation gave 1,000 clusters per acre, i.e., alto-
gether about 12,000 clusters. No artificial means of destroying the
gypsy moth had been undertaken.

Mr. Moore, owing to lack of time, could not raise caterpillars for
the experiment, and he had no reliabie man to whom he could entrust
the work. Upon the recommendation of Mr. Fitzgerald, the field in-
spector of the northern divisions, the brother of the local superin-
tendent of Methuen, Mass., Mr. Wagland, was intrusted with the raising
of the caterpillars. As no communication was received from Mr. Walter
Wagland by June 21, 1910, that his caterpillars showed signs of
Flacherie, I went on this day to Methuen, to convince myself of the
condition of the insects. The local superintendent, A. H. Wagland,
Mr. Walter Wagland’s brother, was with me, and we found that all
the caterpillars were sick and that several had already died. The reason
why ! had received no word from Mr. Walter Wagland was that he
did not recognize the disease. The planting of the material in the se-
lected piace in Haverhill was accomplished the next day. All the
material was exposed in a pasteboard box in the western part of the
forest, about 6 feet from the ground and between limbs of oak trees.

38

Most of the caterpillars of this locality were at this time about half
way betweeu the third and fourth molts.

The place was visited again Aug. 30, 1910, with the local superin-
tendent of Haverhill, to see how the wilt had operated, and how many
fresh egg clusters were present. First it was noticed that the infested
portion of the forest was not uniformly infected with Flacherie. While
the periphery of the infested area (about 8 to 9 acres) showed a very
considerable decrease of the egg clusters in comparison with those of
the spring of 1910, the real center of the colony, which covered 3 to
4 acres, had been more resistant to the disease, although here also
the number of the fresh clusters had decreased considerably in com-
.parison with the clusters of the previous year. Altogether the num-
ber of fresh clusters of the whole colony was estimated by us to be
about 3,500. The 5 clusters which served for examination proved to
be as follows: —

Cluster 1.
Hae ie poera e = 28.57 per cent., or about 28.5 per cent.
Eggs apparently alive, . . 90 =71.48 per cent., or about 71.5 per cent.
Total, : : : . 126 eggs.
Cluster 2.

Unfertilized
Pe ee = 3.31 per cent., or about 3 per cent.

Eggs with dead embryos, _.. 5
Eggs apparently alive, . . 146 =96.69 per cent., or about 97 per cent.
Total, . : f . 151 eggs.

Cluster 8.

Unfertilized eggs,
a es = 5.63 per cent., or about 5.5 per cent.

Eggs with dead embryos, . 13
Eggs apparently alive, . . 285 =94.37 per cent., or about 94.5 per cent.
Total, ‘ P ; . 9802 eggs.
Cluster 4.

nd

Unfertilized eggs, 7
Onn 12.36 per cent., or about 12 per cent.

Eggs with dead embryos,

Eggs apparently alive, . . 227 =87.64 per cent., or about 88 per cent.
Total, . ; : . 259 eggs.
Cluster 6.

Unfertilized eggs, : -
Eggs with dead embryos, 6
Eggs apparently alive, . . 802 =98.05 per cent., or about 98 per cent.

Total, : : ; . 3808 eggs.

= 1.95 per cent., or about 2 per cent.

/

39

The average of these 5 clusters gives the following result: —

Deadeggs, . . . . 19 = 8.80 per cent., or about 8 per cent.
Eggs apparently alive, . 5210 91.70 per cent., or about 92 per cent.

Total, : : : . 229 eggs.

Since a normal cluster contains, on the average, 433 eggs with ap-
parently living embryos, and this locality in which Flacherie had pre-
vailed contained only 210 eggs with apparently living embryos on the
average per cluster, 2 clusters were necessary to equal a normal one.
The number of fresh clusters, which were estimated to be about 3,500,
must therefore be reduced to about 1,750. The number of apparently
living eggs had decreased in this locality, after the wilt had operated,
to about 14.5 per cent.

Marshfield, Mass.

Division Agent, JoHn A. Farry; Local Superintendent, P. R. LiveRMorRE.

I did not visit this locality, but the experiment was undertaken by
the local superintendent with the assistance of Mr. Joseph Shermann
of Marshfield, who raised the caterpillars according to my instructions.
On visiting Marshfield on June 24, 1910, it was found that Mr. Sher-
mann’s caterpillars, most of which were ready to undergo the fourth
molt, were sick with Flacherie. He was instructed to expose the ma-
terial, with the assistance of the local superintendent, in a forest in-
fested with the gypsy moth. This was done on June 26, 1910, in a
forest of 10 acres. On Oct. 25, 1910, the local superintendent sent,
upon my request, a number of fresh egg clusters from the locality
where the disease had been planted, and he remarked that the number
of egg clusters were considerably decreased in comparison with those
present in the spring of 1910. Unfortunately, further detailed com-
“munications regarding this locality were not received. - The first 5
clusters, which were taken from the top of the shipment, were exam-
ined microscopically. The result was as follows: —

Cluster 1.
Unfertilized eggs, . 5 f me
Hee Penidendiembryoss i 10 f= 4.26 per cent., or about 4 per cent.
Eggs apparently alive, . . 247 =95.74 per cent., or about 96 per cent.

Total, : : . . 258 eggs.

Cluster 2.
Unfertilized eggs, : 8 lio
Eee meaembruos es (o 13.47 per cent., or about 13.5 per cent.
Eggs apparently alive, . . 469 =86.53 per cent., or about 86.5 per cent.

Total, : ; F . 542 eggs.

40

Cluster 3,

Unfertilized eggs,

: 2
IDE Gat al GAL 41 =10.59 per cent., or about 10.5 per cent.

Eggs apparently alive, . . 3863 =89.41 per cent., or about 89.5 per cent.
Total, : ; 3 . 406 eggs.
Cluster 4.

Unfertilized eggs,

il
Tee ealh Gleal sans 14 = 5.28 per cent., or about 5 per cent.

Eggs apparently alive, . 269 =94.72 per cent., or about 95 per cent.
Total, # Vi : . 284 eggs.
Cluster 6.
Sauer eg hime . | = 6.64 per cent., or about 6.5 per cent.
Eggs apparently alive, . . 181 =93.36 per cent., or about 93.5 per cent.
Total, ; ; : : “194 eggs.

The average of these 5 clusters gives the following result: —

Dead eggs, . : : . 381 = 9.20 per cent., or about 9 per cent.
Eggs apparently alive, . . 3806 =90.80 per cent., or about 91 per cent.
Total, 5 , : . 337 eggs.

After the wilt had operated in this locality the size of the egg clusters
was not up to the average size of the normal cluster, and the percentage
of dead eggs was very high.

Kingston, Mass.

Division Agent, Joun A. Faruny; Local Superintendent, C. C. Faunce.

With the help of the field inspector, Mr. Norman Souther of Bridge-
water, two places were selected for the intended experiments. The lo-
eality which we will first consider is an isolated part of the so-called
“Rocky Nook,” and is situated about 1 mile east of the Kingston-
Plymouth car jine. This place is about a quarter of an acre in size
and mainly overgrown with oaks about twenty-five years of age. The
gypsy moths were discovered here in the autumn of 1909 by finding egg
clusters. The youth of the colony made it seem improbable that there
was any disease among the caterpillars of 1909, and, moreover, the
ege clusters had a considerable size. Several of the clusters found
had been killed with creosote, but there were still left about 60 clusters,
according to Mr. Souther’s and my estimate.

41

The local superintendent was intrusted by Mr. Souther with the
breeding of caterpillars. On June 24, 1910, I found the wilt in this
brood. The same day, with the assistance of the local superintendent,
one part of the material was exposed in the locality mentioned. This
brood was thoroughly sick, but the “dying off” of the caterpillars had
not begun. The bag containing the material was fastened between
twigs about 7 feet from the ground. The caterpillars in this locality
were at this time half way between the third and fourth molt.’

On Oct. 25, 1910, the fresh egg clusters of this locality were esti-
mated by the local superintendent and myself. We found that the
place contained almost the same numbers of clusters as in the spring
of 1910, with the difference, however, that many clusters had the hairy
covering only in part. Several clusters completely lacked this covering.
Tt seems that the disease spread very slowly, and that it did not kill
many caterpillars but had merely given them a mild form of the dis-
ease, which manifested itself later in the manner mentioned, when the
females laid their eggs. The 5 clusters which were first found were ex-
amined, like those of other localities. The examination gave the fol-
lowing interesting results : —

Cluster 1.

fertilized
crullized ees) = 3.97 per cent., or about 4 per cent.

Eggs with dead embryos, . 138
Eggs apparently alive, . . 3863 +=96.03 per cent., or about 96 per cent.
Total, 4 : : . 9378 eggs.
Cluster 2.
Unfertilized eggs, . . . Onl
Meeaeiiiidendicmbryosn i.) . 02 =18.85 per cent., or about 19 per cent.
Eggs apparently alive, . . 422 =81.15 per cent., or about 81 per cent.
Total, ! Mtn hiss OSU ens,
Cluster 3.
Unfertilized eggs, 2
Eggs with dead embryos, . 58 > 13.48 per cent., or about 13.5 per cent.
Eggs apparently alive, . . 3885 =86.52 per cent., or about 86.5 per cent.
Total, mh Nes : . 445 eggs.
Cluster 4.

Unfertilized eggs,
Eggs with dead embryos,
Eggs apparently alive, . . 467 =79.02 per cent., or about 79 per cent.

1
123 = 20.98 per cent., or about 21 per cent.

Total, 2 é : . 591 eggs.

1 This experiment was intentionally undertaken with sick caterpillars only, and no dead ones,
in order to see what effect the exposure of only sick individuals might have upon the healthy
caterpillars in the field,

42

Cluster 65.
Unfertilized eggs,
Eggs with dead embryos,
Eggs apparently alive, . . 381 =983.94 per cent., or about 94 per cent.

Total, F . ; . 0 eggs.

5 = 6.06 per cent., or about 6 per cent.

The average of these 5 clusters gives the following result : —

Dead eggs, : : : . 60 = 15.23 per cent., or about 15 per cent.
Eggs apparently alive, . . 3834 = 84.77 per cent., or about 85 per cent.
Total, : : : . 394 eggs.

Since this place, in which Flacherie had operated, contained on the
average only 334 eggs with apparently living embryos per cluster, the
size of these clusters was about one-quarter less than normal. The fresh
clusters, which were estimated to be about 60, i.e., the same number
which was found in the spring, thus must be reduced to about 45. The
number of apparently living eggs of this locality therefore was de-
creased, after the wilt had worked, to about 77 per cent.

This experiment also shows that the exposure of sick instead of dead
caterpillars contributes to the spread of the wilt. As in such eases,
however, the disease spreads slowly, the caterpillars, it is true, will not
be killed in large numbers, but they will be infected more or less
lightly. The result is that a high percentage of the eggs deposited
by the females will fail to hatch.

The second place which was selected in Kingston for an experiment
is situated on the eastern side of Jones River, opposite the poor farm.
This is an isolated wood of about one-eighth of an acre in size, which
eoutains several large oaks and underbrush. The gypsy moth was dis-
covered here also by the finding of egg clusters first in the autumn of
1969. It cannot be stated whether disease was present among the eater-
pillars of the summer of 1909, but this seems improbable, owing to the
youth of the colony. Several of the clusters were killed with creosote,
but there were still left, according to Mr. Souther’s estimate, about
50 elusters.

The planting of the sick material was accomplished on the same
day and in the same manner as in the first locality. Estimating the
fresh clusters on Oct. 25, 1910, unfortunately I found that most of
these fresh clusters (about 25) had been already killed with creosote
by the men working under the local superintendent. Even with the
assistance of the local superintendent, only 2 untouched egg clusters
could be found. Only 1 of these could be collected, since the second
was out of reach. Although, therefore, we are unable to draw any

43

complete and final conclusions in regard to the work of the wilt in
this locality, nevertheless the result of the examination of the single
cluster which could be secured may be given: —

Unfertilized eggs,
Eggs with dead embryos,
Eggs apparently alive, . . 306 =96.48 per cent., or about 96.5 per cent.

Total, : : ; . 369 eggs.

1
12 = 3.52 per cent., or about 3.5 per cent.

All we can say concerning this locality is that through the operation
of Flacherie, which was introduced by sick material only, the number
of fresh clusters seems to have been reduced in comparison with that of
the previous year.

Brockton, Mass.

Division Agent, L. W. Hopexins; Local Superintendent, E. Mouran.

The place which, with the assistance of the inspector, Mr. Norman
Souther of Bridgewater, was selected for an experiment, is situated
near Oak Street, northwest of Brockton Center and east of the Dutch-
land Farm. The place, of about half an acre, consists of a growth
of oaks about forty to fifty years of age; no brush is present. The
caterpillars of the gypsy moth were abundant here in the summer of
1909, but no disease was noticed among them. Several of the clusters
were killed with creosote during the winter of 1909-10. The clusters
which were left were estimated by Mr. Souther and myself to be
about 40.

The raising of caterpillars for the intended experiment Mr. Souther
intrusted to Mr. Rudolph Marshall, 218 Battle Street, Brockton. On
June 24, 1910, the brood was inspected. Several caterpillars had
already died from the wilt and the others were found to be sick. This
same day the whole material was exposed in the selected place. The
bag was fastened between oak limbs, about 8 feet from the ground.
Most of the caterpillars of this locality were at this time about half
way between the third and fourth molt.

This place was visited again on Oct. 7, 1910, with Mr. Souther, to
determine the number of fresh clusters. But in spite of the most strenu-
ous search there were found but 4 clusters; these were collected for
examination. They resulted as follows: —

Cluster 1.

Unfertilized eggs,
Eggs with dead embryos,
Eggs apparently alive, . . 889 =97.01 per cent., or about 97 per cent.

2
10 = 2.99 per cent., or about 3 per cent.

Total, : é . 401 eggs.

44

Cluster 2.
Unfertilized eggs, . : sea 3c ios
Dee ais cislowpas, | | 22 =11.71 per cent., or about 11.5 per cent.
Eggs apparently alive, . . 264 =88.29 per cent., or about 88.5 per cent.
Total, ; 4 : . 299 eggs.
Cluster 3.
Unfertilized eggs, . : : ola hae
Epa tdcanierieryas) nl ae = 5.47 per cent., or about 5.5 per cent.
Eggs apparently alive, . . 294 =94.53 per cent., or about 94.5 per cent.
Total, : ; ; . dll eggs.
Cluster 4.
Unfertilized eggs, . : 2
eeeryithidesdicniniyo: ame ale = 4.81 per cent., or about 5 per cent.
Eggs apparently alive, . . 3896 =95.19 per cent., or about 95 per cent.

Total, : , : . 416 eggs.
The average of these 4 clusters gives the following result : —

Dead eggs, : : . 21 = 5.88 per cent., or about 6 per cent.
Eggs apparently alive, . . 336 94.12 per cent., or about 94 per cent.

Total, . : 2 . 38057 eggs.

Since this place, in which the wilt had operated, contained only
336 eggs with apparently living embryos on the average per cluster, the
size of these clusters was about one-fourth less than normal. The num-
ber of the fresh clusters, which were found to be 4, must thus be re-
duced to 3. The number of apparently living eggs of this locality
therefore was decreased, after Flacherie had worked, to about 7.5 per
cent.

Beverly, Mass.

Division Agent, Saunt Puruiips; Assistant, W. F. Hotmes.

With the help of the assistant of the division agent two places were
selected for the experiments. The place which we will first consider
is situated near Hart Street, north of Greenwood Avenue, Beverly
Farms. It is an isolated wood of about 1 acre, mainly overgrown with
maple about fifty to sixty years of age, and yellow birch, and has dense
underbrush. The gypsy moth eaterpillars were very numerous here
during the summer of 1909, but no disease was noticed among them.
A small percentage of egg clusters was killed with creosote during the

45

winter of 1909-10. A joint estimate of the egg clusters in this locality
made with the assistant of the division agent in the spring of 1910 re-
sulted in finding about 500 clusters.

The rearing of caterpillars was undertaken by Mr. Phillips’s as-
sistant. On June 20, 1910, he noticed the first dead individuals in
the brood. Three days after the receipt of this communication I went
to Beverly to inspect the material. Many of the caterpillars had
already died from the wilt. This same day (June 25), with the help
of the assistant, one part of the material was exposed in the western
portion of the locality mentioned. The bag containing the material
was fastened about 6 feet from the ground, between limbs with dense
foliage. Most of the caterpillars of this locality had at this time just
passed the third molt.

After the wilt had operated all through the summer among the eater-
pillars of this locality, the place was visited again on Sept. 13, 1910,
together with Mr. Phillips’s assistant. We estimated the number of
fresh clusters present to be about 250. The decrease in the size of
the clusters compared with’ those of the previous year was very strik-
ing. The examination of the first 5 clusters which were found gave
the following result : —

Cluster 1.

Unfertilized eggs,

5
Hees with dead embryos, 12 =13.60 per cent., or about 13.5 per cent.

Eggs apparently alive, . . 108 =86.40 per cent., or about 86.5 per cent.
Total, Y 5 bet (te . 125 eggs.
Cluster 2.

Unfertilized
gS ge eee = 5.92 per cent., or about 6 per cent.

Eggs with dead embryos, . 8
Eggs apparently alive, . . 159 =94.08 per cent., or about 94 per cent.
Total, : ; ; . 169 eggs.
Cluster 3.
Unfertilized eggs, ere k
fee ieadicmibues y Fed 7.37 per cent., or about 7 per cent.
Eggs apparently alive, . . 88 =92.63 per cent., or about 93 per cent.
Total, : f : . 95 eggs.
Cluster 4.

Unfertilized eggs,
Eggs with dead embryos, . i
Eggs apparently alive, . . 131 =94.24 per cent., or about 94.5 per cent.

Total, : : : . 1389 eggs.

= 5.76 per cent., or about 5.5 per cent.

46

Cluster 6.
Unfertilized eggs,
Eggs with dead embryos,
Eggs apparently alive, . . 68 =98.55 per cent., or about 93.5 per cent.

Total, : 2 ; . 62 eggs.

A = 6.45 per cent., or about 6.5 per cent.

The average of these 5 clusters gives the following result : —

Dead eggs, : i 5 9 = 7.63 per cent., or about 7.5 per cent.
Eggs apparently live: : . 109 =92.37 per cent., or about 92.5 per cent.
Total, 2 : : . 118 eggs.

Since a normal cluster contains on the average 433 eggs with appar-
ently living embryos, and this place, in which Flacherie had operated,
contained only 109 eggs with apparently living embryos on the average
per cluster, about 4 clusters were necessary to equal the size of a
normal one. The number of fresh clusters, which were estimated to
be about 250, thus must be reduced to about 65. The number of ap-
parently living eggs of this locality therefore was decreased, after the
wilt had worked, to about 15 per cent.

For the second experiment. a small isolated group of oaks, about
eighty years of age, was selected. This place is situated near the
railroad station, Beverly Farms, between the railroad track and the
ocean. The caterpillars of the gypsy moth have always appeared here
only in small numbers, and there were hardly more than one dozen
clusters in the spring of 1910, according to our estimate. It must
be mentioned, especially, that this locality is always exposed to very
strong winds.

Flacherie, artificially developed by the assistant of the division agent,
was planted among the caterpillars at this place on June 25, 1910, in
the same manner as in the first locality. Considering the heavy breeze
the material was placed in a wooden box, which was then fastened
between linibs; thus the wind was not able to carry off the whole

material. Most of the caterpillars of this place were about ready
at this time to undergo the third molt.

On Sept. 13, 1910, this locality was visited again. The wilt had
done very Goutideraile damage to the caterpillars. Although the place
was carefully searched with Mr. Holmes’s assistance, we could find but
2 fresh clusters. One of these is especially remarkable, as it lacks com-
pletely the protecting covering. The microscopic examination of both
clusters gave the following results: —

47

Cluster 1.
Unfertilized eggs, . : : 3
Beer Midesdtembryosel. 8 = 9.17 per cent., or about 9 per cent.
Eggs apparently alive, . . 109 =90.83 per cent., or about 91 per cent.
Total, : ; : . 120 eggs.
Cluster 2.+
Unfertilized eggs, . i B. igts:
Eggs with dead embryos, . 116 = 87.50 per cent., or about 87.5 per cent.
Eggs apparently alive, . . 22 =12.50 per cent., or about 12.5 per cent.
Total, : : ; . 176 eggs.

The average of these 2 clusters gives the following : —

Dead eggs, : : ; . 83 =655.70 per cent., or about 55.5 per cent.
Eggs apparently alive, . . 66 =44.30 per cent., or about 44.5 per cent.
Total, : : : . 149 eggs.

Since this place, in which Flacherie had operated, contained only
66 eggs with apparently living embryos on the average per cluster,
the size of these clusters was about five-sixths less than normal. The
number of fresh ciusters, which were found to be 2, thus equal together
only one-third of a normal one. ‘The number of apparently living
egus of this locality therefore had decreased, after the wilt had worked,
to about 3 per cent.

Cohasset, Mass.

Division Agent, F. A. Bates; Local Superintendent, J. E. GRassIE.

An island, known as Barron’s Island, which is situated southeast of
Cohasset in the headpart of Bailey’s Creek, was selected for the ex-
periment. This island has an area of about 10 acres, and is densely
overgrown, mostly with oaks about twenty-five years of age and with
underbrush. ‘The gypsy moth was quite numerous here in 1909, but
there was no disease among the caterpillars, according to Mr. Grassie’s
statement. Our joint estimate of the clusters which were present in
the spring of 1910 was about 2,000. No artificial means of destroying
the gypsy moth had been undertaken here.

Mr. Grassie, who was intrusted with the breeding of the caterpillars,
noticed the wilt in this brood after a feeding of about sixteen days.
On June 27, 1910, the caterpillars were inspected, and there were found

1 Without the protecting cover.

48

about 70 per cent. individuals already dead from the disease." The
same day all the material was exposed, with the assistance of Mr. Gras-
sie, in the western part of the selected place, and about 6 feet from
the ground. Most of the caterpillars of this locality were at this
time about ready to undergo the fourth molt.

On Sept. 26, 1910, the island was visited again, in company of the
local superintendent, to determine in what manner the wilt had op-
erated among the caterpillars. An especially considerable reduction
of the number of the fresh egg clusters, compared with those of the
previous year, had not ocenrred. According to our estimate there were
about 1,500 fresh clusters. The size of each of these clusters, com-
pared with the clusters found in the spring of 1910, was diminished
in such a degree, however, that the clusters were often no larger than
a bean. The eggs also were often only covered in part with hair. This,
as well as the comparatively small mortality and the smallness of the
fresh clusters, may be perhaps a consequence of the late planting of
the disease. It is true that a number of caterpillars were killed, but
most of them only grew slightly sick, the disease again expressing it-
self at the time of oviposition. The fresh clusters of this locality were
also of an abnormally light yellowish color, which was noticed nowhere
else.

The examination of the first 5 clusters found gave the following re-
sult : —

Cluster 1.
Pee a ee : = 6.36 per cent., or about 6 per cent.
Eggs apparently alive, . . 162 =93.64 per cent., or about 94 per cent.
Total, : : : : “173 eggs.
Cluster 2.
Baeetarca eee 15 = 23.68 per cent., or about 23.5 per cent.

Eggs apparently alive, . . 658 =76.32 per cent., or about 76.5 per cent.
Total, : : : . 76 eggs.
Cluster 8.

Unfertilized
Baer ee = 12.28 per cent., or about 12 per cent.

Eggs with dead embryos, _.. 6
Eggs apparently alive, . . 50 =87.72 per cent., or about 88 per cent.
Total, z A ; . 57 eggs.

1 It should be mentioned that Mr. Grassie sent a telephone communication on June 12, 1910,
that the wilt had made its appearance among his caterpillars, but by a mistake I did not receive
this notice until June 23.

49

Cluster 4.
Se ot vi fy =18.31 per cent., or about 18 per cent.
Eggs apparently alive, . : 116 =81.69 per cent., or about 82 per cent.
Total, ‘ : : . 142 eggs.
Cluster 5.

Unfertilized eggs,
Eggs with dead embryos,
Eggs apparently alive, . . 115 =60.85 per cent., or about 61 per cent.

Total, ‘ ; , . 189 eggs.

pt =39.15 per cent., or about 39 per cent.

The average of these 5 clusters gives the following result: —

Deadeggs, . . . . 27 =+=21.26 per cent., or about 21 per cent.
Eggs apparently alive, . . 100 =78.74 per cent., or about 79 per cent.
Total, ; : : . 127 eggs.

Since this place, in which Flacherie had worked, contained only 100
egos with apparently living embryos on the average per cluster, more
than 4 clusters were necessary to equal a normal cluster. Thus the
number of fresh clusters must be reduced to about 370. The number
of apparently living-eggs of this locality therefore had decreased, after
the wilt had operated, to about 18 per cent.

Hingham, Mass.

Division Agent, F. A. Barres; Local Superintendent, A. W. Youna.

For the experiment an island of about 1 acre was selected, very
densely overgrown with low wood. This island is situated east of
Water Street and south of the railroad track in the so-called Millpond.
The wood consists mainly of oaks and birches of five to six years of
age, and of underbrush. The gypsy moth was quite numerous here
in the summer of 1909, but there was no disease among the caterpillars,
according to the statements of the division agent and the local super-
intendent. Several of the clusters were killed with creosote during the
winter of 1909-10. The number of the clusters which still remained
was estimated by Mr. Young and myself to be about 100.

The breeding of a series of caterpillars was accomplished exactly
according to my instructions by the local superintendent, but unfor-
tunately he omitted to send word when the wilt made its appearance,
since he had understood that he was to notify me only after all the
caterpillars of the brood had died. To convince myself about the con-

50

dition of the brood, I inspected the caterpillars July 1, 1910, and found
that about 60 per cent. of them had succumbed to Flacherie. The first
dead caterpillars were noticed by Mr. Young about fifteen days before.
On the same day the whole of the material was exposed, with Mr.
Young’s assistance, in the southwestern part of the island, about 5 feet
from the ground. Most of the caterpillars of this locality had at this
time just undergone the fourth molt.

On Sept. 26, 1910, this island was visited, again in company with the
local superintendent. We could see that the wilt had done very con-
siderable damage to the caterpillars, for there were only a few scattered
clusters. According to our estimate there were hardly 15 fresh clusters
present; these, moreover, were much smaller in size than those of the
previous year. It was also noticed that the clusters were often only
partly covered with hair. All these conditions may well be attributed
to Flacherie. The almost full-grown caterpillars had contracted the
disease, and the females which then emerged from pupe produced by
these caterpillars were unable to oviposit like healthy moths.

The examination of the first 5 clusters found gave the following re-
sult: —

Cluster 1.
Unfertilized eggs, :
Figes with dead embryos, -: “10 f= 9.56 per cent., or about 9.5 per cent.
Eggs apparently alive, . . 123 =90.44 per cent., or about 90.5 per cent.
Total, j : ‘ . 186 eggs.
Cluster 2.
Unfertilized eggs, . : : Shik e
Eggs with dead embryos, . 12 = 8.82 per cent., or about 9 per cent.
Eggs apparently alive, . . 155 =91.18 per cent., or about 91 per cent.
Total, . 3 ‘ . 170 eggs.
Cluster 3.
Unfertilized eggs, . 5 5 1
Bue ine deadiemires a rae 4.73 per cent., or about 4.5 per cent.
Eggs apparently alive, . . 161 =95.27 per cent., or about 95.5 per cent.
Total, : : ; . 169 eggs.
Cluster 4.
Unfertilized eggs, . . . 2
Hgas with dead embryos, |. 5 =10.77 per cent., or about 10.5 per cent.
Eggs apparently alive, . . 58 =89.23 per cent., or about 89.5 per cent.

Total, f 5 : . 665 eggs.

o1

Cluster 6.
Unfertilized eggs, ,
Eeidend embryos 1 0 Glee 9.22 per cent., or about 9 per cent.
Eggs apparently alive, . . 128 =90.78 per cent., or about 91 per cent.
Total, : : : . 141 eggs.

The average of these 5 clusters gives the following result : —

Dead eggs, ; : . . 11 = 8.09 per cent., or about 8 per cent.
Eggs apparently alive, . . 125 =91.91 per cent., or about 92 per cent.
Total, f : 3 . 186 eggs.

Since this place, in which Flacherie had operated, contained only 125
eggs with apparently living embryos on the average per cluster, almost
4 clusters were necessary to equal a normal one. The number of the fresh
clusters thus must be reduced to about 5. The number of apparently
living eggs of this locality therefore had decreased, after the wilt had
worked, to about 5 per cent.

Byfield, Mass.

On June 30, 1910, a letter was received from Mr. James O. Hale
of Byfield, in which he stated that he had heard of my Flacherie ex-
periments of 1909, and asked for aid in diminishing the gypsy moth
caterpillars by using Flacherie. I therefore visited the locality on
July 5, 1910, and took with me sick and dead caterpillars which had
been raised at Forest Hills. The forest in question is about 4 to 5
acres in size, and consists mainly of oaks of different ages and some
underbrush. It is situated on the border between Rowley and Newbury.
It is not isolated, but connected with woods which belong to other
persons. At the time of my arrival most of the caterpillars had already
undergone the fifth molt, so that it seemed questionable whether the
disease would be able to show much success this year. The infected
material was exposed in the southwestern part of the forest, about
7 feet from the ground. It proved to be impossible to secure a correct
estimate of the caterpillars which were present; all that could be stated
was that the caterpillars were quite plentiful.

This locality was visited again with Mr. Hale on Sept. 16, 1910, to
determine the results. Mr. Hale gave his opinion that there was, at
the least, no increase in the number of egg clusters compared with that
of the previous year, although there was no visible decrease in the
number of the fresh clusters. However, these fresh clusters were con-
siderably smaller than those of the preceding year.

The first 5 clusters collected gave the following counts: —

52

Cluster 1.
Unfertilized eggs,
Eggs with dead embryos, .
Eggs apparently alive, . . 88 =91.67 per cent., or about 92 per cent.

: \ = 8.33 per cent., or about 8 per cent.

Total, : : : . 96 eggs.

Cluster 2.

Unfertilized eggs, . : ; | a
Deny atin Glass @alnsacy, YI ie 3.76 per cent., or about 3.5 per cent.
Eggs apparently alive, . . 128 =96.24 per cent., or about 96.5 per cent.
Total, A ; : . 133 eggs.
Cluster 3.

fertilized
Unierulizedieaes, = 2.75 per cent., or about 2.5 per cent.

Eggs with dead embryos, . 5
Eggs apparently alive, . . 212 =97.25 per cent., or about 97.5 per cent.
Total, : ; : . 218 eggs.
Cluster 4.
Unfertilized eggs, . : : Ze
Be even dendicmbprrcatane 4 = 4.72 per cent., or about 4.5 per cent.
Eggs apparently alive, . . 121 =95.28 per cent., or about 95.5 per cent.
Total, ‘ ; : . 127 eggs.

Cluster 5.
Unfertilized eggs,
Eggs with dead embryos, .
Eggs apparently alive, . ~ AS

Total, ; ; ; . 161 eggs.

; = 5.59 per cent., or about 5.5 per cent.
2 =94.41 per cent., or about 94.5 per cent.

The average of these 5 clusters gives the following result : —

Dead eggs, : A : , 7 = 4.76 per cent., or about 4.5 per cent.
Eggs apparently alive, . . 140 =95.24 per cent., or about 95.5 per cent.
Total, : ‘ ; . 147 eggs.

We notice that the clusters of this locality in which the wilt had
operated are far smaller than normal ones, since about 3 clusters are
necessary to equal the size of a normal one. The percentage of dead
eggs, however, does not attain that of other localities.

D3

IV. Summary.
The artificially developed Flacherie was planted, after the
“dying off” of the breeding material had begun, among the
caterpillars of the gypsy moth in the following localities, the de-

Fig. 4.— Diagram showing percentage of living eggs in healthy colonies.

tails in regard to these experiments being given in the preceding
pages. The number of apparently lving eggs was reduced to
the following percentages : —

Per Cent.
Concord, Mass. (Brewster’s estate), . . Oe oc!
Carver, Mass. (southwest of Makepeace’s oumieses beet: : 5 Oe
Carver, Mass. (on Wenham Street), . : 5 , : : E a1 145
Boxford, Mass. (near the almshouse), a et eee ; Bh oN ae LO
Boxford, Mass. (on Highland Street), , : : 4
West Bedford, Mass. (Swett’s estate), 0 per cent. + 2914 per recat. = 11%

Haverhill, Mass. (west of East Broadway), . ; : ; . 14%

o4

Per Cent.

7%
15

Brockton, Mass. (on Oak Street),
Beverly, Mass. (on Hart Street),

3
18

Beverly, Mass. (beside railroad track),
Cohasset, Mass. (Barron’s Island),

5

Hingham, Mass. (island in the millpond),

Taking the average of these results, we see that the total
number of apparently living eggs has been decreased by intro-

duction of the artificially developed Flacherie to about 14 per

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a}5)

V. Final Conclusions.

The foregoing experiments prove conclusively that Flacherie
has an injurious influence upon the prosperity of the gypsy
moth caterpillars, this influence varying according to the man-
ner and time of the appearance of the disease. There was
no difference noticed in the progress of the wilt which broke
out naturally and that of the artificially developed Flacherie.
The latter, however, is probably the more important factor,
for with its help we may be able to introduce the disease among
caterpillars of localities in which the wilt, perhaps, would not
make its appearance naturally. The infection of a place with
sick material only seems to be, as regards the “‘ dying off” of
the caterpillars, less favorable for the spread of Flacherie than
with material which already contains a number of dead indi-
viduals. In selecting the localities in which the disease is to
be introduced, it is unimportant whether the caterpillars of the
gypsy moth are present in large or small numbers. It is true
the wilt will get a stronger foothold and attain a greater viru- ~
lence the larger the number of caterpillars. In places, how-
ever, which are not badly infested, the disease will also spread
to the healthy caterpillars, as was shown by several of the
experiments. According to the observations, we are almost
inclined to believe that the direction of the wind plays an
important rdle in spreading the disease. This opinion is
strengthened especially by the observations made in Concord
and West Bedford.

Wherever the naturally as well as the artificially developed
Flacherie occurs the female caterpillars will always succumb
to it more readily than the male. This may perhaps be due to
the fact that they require a longer time to mature than the
male caterpillars. If, at the flying period of the moth, we visit
such a diseased locality, — one in which during the summer
the caterpillars were quite plentiful, — we find ourselves sur-
rounded by male moths, which to the superficial observer
would indicate that the wilt had caused no considerable diminu-
tion. As soon, however, as we begin to search for adult females,
we discover that they are present in a decided minority, and

56

that they are by no means in the same large proportion to the
male moths as in localities where the disease has not occurred
among the caterpillars. The effective result, then, will be shown
at the time of oviposition, in the decrease of the number and
size of the fresh clusters, compared with those of the previous
year. To be sure, this will not always be the case; for instance,
in localities in which Flacherie appears very late. However.
places infected early enough, always show as a result a diminu-
tion in the number of the fresh clusters, sometimes to 100 per
cent. The reduced average size of the clusters also has a close
connection with the wilt. Heretofore it has often, but errone-
ously, been supposed that small clusters were deposited by
small female moths, which suffered during their caterpillar
stages from lack of food. Certainly such cases are not rare,
but the origin of small clusters is capable of yet another ex-
planation. For instance, in localities in which there are few
gypsy moth caterpillars, and where there is no lack of food, but
where the wilt has worked, egg clusters are found which are no
larger than a pea or a bean. Such clusters contain from 4 to 12
eggs, with embryos which are usually incompletely or not at all
developed. In such localities it may often be recognized, from
the volume of the abdomen, even of the freshly emerged female
moths, which were little below the normal size, that the body
contained only a small number of eggs. Also, in several cases
the interior of the body was examined, and then it was found
that the cause of the small circumference of the body was that
the ovary was small. Females which had already oviposited and
died were examined to see whether they contained more eggs in
their bodies. Eggs were always found in females that had laid
egg clusters which were only partly, or not at all, covered with
hair. But there were sometimes found undeposited eggs in fe-
males which had completely covered the cluster with their ab-
dominal hairs. All this must be taken in connection with the
wilt, for female moths from healthy colonies deposit all the eggs
they contain, as long as they are not interrupted at the time of
ego laying, and it does not matter whether the individuals are
large or small.

The most important point to be noticed is the fact that the

o7

clusters which are found in localities in which Flacherie oper-
ates among the caterpillars contain, on the average, a compara-
tively high percentage of dead eggs. Hence, Flacherie has a
direct effect even upon the next generation. If, however, the
number and the quality of the eggs in the female adult are
affected by the wilt, is it not then possible that the disease goes
directly over to the eggs? Certainly we have no direct proof
of this at the present time, but we do know that Flacherie can
be carried over from the caterpillar to the pupa, and from the
pupa to the adult, and we have seen that the eggs in the ovary
of females which come from infected colonies are influenced
by the disease in regard to their number and vitality. In spite
of the many investigations which have been made by celebrated
bacteriologists in both the old and the new world, the carriers
of the disease have not yet been determined. This shows what
a difficult problem science has before it to solve. Although
several scientists accept neither the heredity of the disease,
nor believe that it can be carried over to the next generation,
there are others (Pasteur, Fischer) who believe in its trans-
missibility. Perhaps the disease is carried over to the follow-
ing generation through the adult female only, in a similar
manner to the pébrine. Perhaps, moreover, the name Flacherie
covers several diseases, which, it is true, make their appearance
in the same manner in the infected individuals, but neverthe-
less are specifically distinct. One of these diseases may be
restricted, indeed, to caterpillar and pupa only, while the other
disease is carried over to the adult, and might possibly be in-
herited through the female organism by the descendants. It
may be possible to throw some light on these complicated ques-
tions by breeding experiments, but only the investigations of the
bacteriologist and pathologist can secure the final proof. It
would be of the highest importance for the economic value of
Flacherie if the inheritance of the disease could be definitely
proved. If the wilt proves to be the direct cause for the “ dying
off” of many embryos of eggs from infected localities, death
would be caused by the organisms of the disease themselves,
and probably not be a result of the weak constitution of the
female moth. The still living embryos of the same cluster will

58

then contain, without doubt, at least partially, the carriers of
the disease, which, according to their number and to the con-
stitution of the embryo, will kill, early or late, the larva after
it has hatched. Thus Flacherie will be carried again through
the whole ontogeny of the descendants of those individuals
which were originally infected by the disease. In this case the
wilt would be hereditary, and it would have by far the greatest
possible economic value and benefit. If, however, the “ dying
off ”’ of several of the embryos is only a consequence of the
weak condition of the female adult, which perhaps was slightly
infected during the caterpillar stage, then of course the guaranty
for the wilt is not yet given for the next generation. Among
the hatching caterpillars there will always be a considerable
percentage of weak individuals which thus possess from the
beginning the necessary predisposition to the disease. If, then,
the climatic conditions develop favorably for the disease, these
weak caterpillars will be attacked first by the wilt, but as it
increases in virulence it will attack the stronger and healthier
individuals. If the climatic conditions are less favorable for
the natural appearance of Flacherie, we hope the introduction
of the artificially developed Flacherie in the respective localities
will transmit the disease to the weak caterpillars. Then the
disease will operate as though it had appeared naturally.

The existence of the wilt does not depend upon climatic
conditions as soon as the disease is once established. It is true
weather conditions will often be of great advantage in spreading
the disease, but not likely to be of considerable harm. Hence,
Flacherie, even if its nonheredity should be proved, is a factor
of great importance to economic entomology. It will be advis-
able to work with the wilt against the gypsy moth in large
wooded areas of all kinds, and it has the great advantage of
cheapness, while the spraying with arsenate of lead or with
other poisons is expensive. A very good scheme would be to
furnish as many trees as possible with rings of tanglefoot in
heavily infested forest districts, and not to kill the caterpillars
after they are gathered together under the rings, but to assist
in this manner the more rapid spread of the wilt, since the sick
and weak individuals thus have a greater possibility of coming

59

in contact with healthy caterpillars. The effect of this method
was observed in one case during the summer of 1910. In com-
pany with the division agent, Mr. Worthen, I came in touch
with a locality in Boxford where gypsy moth caterpillars were
gathered together in considerable numbers under tanglefoot
rings. It had been decided to kill the caterpillars with burning
oil, but I dissuaded the men from doing this by giving as my
opinion that the wilt would ‘make its appearance in all prob-
ability in a few days. This assumption was right, for there
was seen, after three days, the first signs of the disease, which
then spread so quickly that in a few more days the caterpillars
had succumbed.

Perhaps it might be worth while to work with the wilt in
different ways from those in the experiments described. There
is, for instance, the recapitulation of the experiments of 1909 on
a large scale. Caterpillars which had been killed by Flacherie
were mixed with water in different ways, and the mixture was
then either sprayed upon trees or was painted as rings around
the trunks. One or the other of these methods may prove to be
valuable, but the expense will be quite high, while the use of the
simple exposure method incurs but small expense. There might
be mentioned still another point; Dr. E. Fischer of Ztrich,
the discoverer of the predisposition of caterpillars towards
Flacherie, wrote me some time ago the following directions for
developing Flacherie artificially in the field: cut some of the
larger roots of a tree that is infested with a sufficient number
of caterpillars, water frequently the ground around the cut
surfaces and put into the trunk as much water as possible
through a hole bored at an angle of about 45° to the base of
the tree. By these means the same unhealthy food is produced
on the tree as is otherwise obtained by the placing of twigs in
water. It is certain that the wilt can be developed artificially
in the manner just described, but such an experiment needs
constant attention, and trees thus treated are, of course, de-
stroyed.

I doubt whether the gypsy moth will ever become extinct in
America, but the wilt will probably produce, first, a consider-
able reduction of the mass, and then it is to be hoped that the

60

insect parasites and other natural enemies will contribute in
diminishing the pest to a minimum. I am quite convinced that
we can apply the wilt in a systematic manner to the benefit of
our forests, and that in so doing we shall come considerably
nearer to a solution of the problem of destroying the gypsy
inoth. In wooded areas mainly much more attention should be
given in future to the wilt as an aid in combating the insect,
while for street trees, garden trees, etc., which are more easily
managed, the eggs and caterpillars of the gypsy moth may be
removed according to established methods. The wilt should
eventually reduce the pest to a condition in which it can be easily
kept in check, and prevent serious outbreaks and damage.

PLATE I. —Egg clusters from a healthy colony.

PLATE II.—Egg clusters from a colony where disease was
introduced.

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BRARY OC UNGER

WAU

@ 001 424 727 Oe