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ENTOMOLOGY
LIBRARY

PARASITIC AND I'KKDACEUl*

INSECTS

IN

APPLIED ENTOMOLOGY

C. V. RILEY, Ph. D.

[ READ AT THE FIFTH ANNUAL MEETING OF THE ASSOCIATION OF

ECONOMIC ENTOMOLOGISTS, MADISON, WIS., AUGUST 15, 1893,

AND REPRINTED FROM 1XHEGT LIFK, VOL. VI, NO. .'.

AVASIIINdTOX:

GOVERNMENT 1» II IN TING OFFICE.

1893.

PARASITIC AND PREDACEOUS

INSECTS

IN

APPLIED ENTOMOLOGY

BY

C. V. KILEY, Ph. D,

\\

[READ AT THE FIFTH ANNUAL MEETING OF THE ASSOCIATION OF

ECONOMIC ENTOMOLOGISTS, MADISON, WIS., AUGUST 15, 1893,

AND REPRINTED FROM INSECT LIFE, VOL. VI, NO. 2.

WASHINGTON:

GOVERNMENT PRINTING OFFICE.

1893.

ENTOMOLOG/f
LIBRARY

[Reprinted from tin- Proceedings of the 5th Annual Meeting of the Association of
Economic Entomologists, held in Madison, Wis., August 15, 1893, and published
in Insect Life, Vol. vi, No. 2.]

PARASITIC AND PREDACEOUS INSECTS IN APPLIED ENTOMOLOGY.

By C. V. RILEY. Washington, D. C.

The importance to man, and especially to the agriculturist, of the
parasitic and predaceous insect enemies of such species as injure veg-
etation, has been recognized by almost all writers on economic ento-
mology. Indeed, it is a question whether the earlier writers did not
attach too much importance to them ; because, while in the abstract
they are all essential to keep the plant-feeding species in proper check,
and without them these last would unquestionably be far more difficult
to manage, yet in the long run our worst insect enemies are not mate-
rially affected by them, and the cases where we can artificially encourage
the multiplication of the beneficial species are relatively few. While
fully appreciating the importance of the subject, therefore, it is my pur-
pose in this paper to point out the dangers and disadvantages result-
ing from false and exaggerated notions upon it.

There are but two methods by which these insect friends of the
farmer can be effectually utilized or encouraged, as, for the most part,
they perform their work unseen and unheeded by him, and are practi-
cally beyond his control. These methods consist in the intelligent pro-
tection of those species which already exist in a given locality, and in
the introduction of desirable species which do not already exist there.

The first method offers comparatively few opportunities where the
husbandman can accomplish much to his advantage. That a knowledge
of the characteristics of these natural enemies may, in some instances,
be easily given to him, and will, in such instances, prove of material
value, will hardly be denied. The oft-quoted experience which Dr.
Asa Fitch recorded, of the man who complained that his rosebushes
were more seriously affected with aphides than those of his neighbors,
notwithstanding he conscientiously cleaned off all the old parent bugs
(he having mistaken the beneficial ladybirds for the parent aphides)
may be mentioned in this connection. Other cases will recur to you
and I will mention one rather striking experience related by my assist-
ant, Mr. L." O. Howard. The Army Worm (Leucania unipuncta) was
overrunning a large and valuable field of timothy and threatened the
destruction of the adjoining fields. The insect was as yet, however,
circumscribed, and susceptible of remedial treatment. The owner of
the field, observing the buzzing swarms of the Ked-tailed Tachina-fiy,
assumed that the fly was the parent of the worms, and as the former

274382

131

was an active, wrngeVl mature, capable of extended flight, lie con-
cluded that remedial work was useless, since the flies could, and doubt-
less -would, deposit their eggs over the entire surrounding country.
As a consequence the worms were allowed to travel to the adjoining
fields and the injury thus increased through ignorance of the fact that
the Tachina flies were the most important of the parasitic enemies of
the worm. For many years well-informed gardejiers in parts of Europe
have practiced collecting ladybirds and some of the ground beetles to
liberate upon plants infested by plant-lice or by cutworms. The char-
acteristics of these two families, Coccinellidae and' Carabidse, should be
taught in our schools, as a definite knowledge of certain species, which
is readily acquired, may often be turned to account in a limited way by
the cultivator.

In a few cases like this there is no reason why the farmer should not
be taught with advantage to discriminate between his friends and his
foes, and to encourage the multiplication of the former; but for the
most part the nicer discriminations as to the beneficial species, some
of the most important of which are microscopically small, must be left
to the trained entomologist. Few of the men practically engaged in
agriculture and horticulture can follow the more or less technical
characterizations of these beneficial species, and where the discrimi-
nating knowledge is possessed it can, as just intimated, only excep-
tionally be turned to practical account. Thus our literature on this
subject in the past has been of interest from the entomological rather
than from the agricultural point of view, as most writers on economic
entomology have contented themselves with describing and illustrating
such beneficial species.

In other cases much good may be done without any special knowl-
edge of the beneficial forms, but as a result of a knowledge of the
special facts which enables the farmer to materially encourage the mul-
tiplication of parasitic species while destroying the plant- feeding host.

The Rascal Leaf-crumpler (Mineola indiginella Z.), a common insect
which disfigures and does much damage to our apple and other fruit
trees and which hibernates in cases attached to twigs, is a case in
point. Many years ago I urged the importance of preserving the sev-
eral parasites known to prey upon it, in the following language:*

The orchardist has but to bear in mind that it (the leaf-crumpler) is single-
brooded and that it passes the winter in its case, and he will understand that by
collecting and destroying these cases in the dead of the year when the tree is bare,
he effectually puts a stop to its increase. * * * Whether collected in winter or
pulled off the trees in spring or summer, these cases should always be thrown into
some small vessel and deposited in the center of a meadow or field away from any
fruit trees. Here the worms will wander about a few yards and soon die from
exhaustion and want of food, while such of the parasites, hereafter mentioned, as
are developed or in the pupa state will mature and eventually fly off. In this
manner, as did Spartacus of old, we swell the ranks of our friends while defeating
our foes.

*Fourth Report, Insects of Missouri, 1871, p. 40.

132

The practical value of this suggestion was subsequently fully dem-
onstrated, and especially by the late D. B. Wier. who, at a meeting of
the Illinois Horticultural Society, as secretary of a committee appointed
by said society to consider the best means of securing cooperation in
the warfare against the fruit-growers' insect enemies, announced that
this policy had been followed with happy results.

A similar course was urged by me in the case of our common Bag-
worm (Thyridopteryx ephemercvformis). This species, as we know, is
also subject to parasites, and the bags or cases which are collected in
winter, instead of being burned, should be allowed to remain until the
middle of the next summer in some vessel well separated from trees and
shrubs, in order that the young worms, when they hatch in spring from
the eggs contain d in the female bag, may perish, while the parasites
develop and escape. Prof. J. H. Comstock has suggested in a similar
way the placing of the hand-collected chrysalides of the imported Cab-
bage Worm (Pieris rupee) in boxes covered with wire netting, in order
to admit of the ready escape of the little (Jhalcid parasite (Pteromalus
puparum) and at the same time retain such of the butterflies as may
issue — a practice which had, I believe, been successfully employed in
Europe. Other similar cases of this mode of encouragement will occur
to you, but, as already stated, with comparatively few exceptions, such
as those indicated, the multiplication of our parasitic and predaceous
species on the line of the first method is practically beyond our control.

It is quite different in the second method of dealing with beneficial
insects, for here man has an opportunity of doing some very effective
work, and it is only within comparatively recent years that the impor-
tance of this particular phase of the subject has been fully realized. The
Rev. C. J. S. Bethune, of Canada, was probably the first entomologist
to suggest, in one of the earlier volumes of the Canadian Farmer, the
importation of the European parasites of the Wheat Midge (Diplosis
t t-it id) into America, on the supposition that this cosmopolitan species
might thus be kept in check on this continent to the same extent that
it was in Europe. So far as I am aware, the attempt was never
actually made, and though some subsequent correspondence was
entered into between Fitch and Curtis, and later between Walsh and
some of his English friends, nothing tangible resulted. The matter
was, in fact, never seriously studied with this purpose in view.

The importance of this phase of the subject was early forced upon my
attention, as it was upon that of others, and is frequently referred to in
my earlier writings. Thus, in 1869-'70, in studying the parasites of the
Plum Curculio, it became evident that they were of such a nature that
they could easily be transported from one locality to another, and I
distributed from Kirkwood, Mo., Siyalphus curculionis Fitch and Pori-
zon conotraeheli Kiley to several correspondents in other parts of the
State. 1 also urged a similar course with regard to some of the para-
sites of the Coccidie, which it happens may be easily transported from

133

one place to another in their undeveloped or adolescent stages.* Le
Baron, in his studies of the Oyster-shell Bark-Louse of the Apple and one
of its parasites (Aplielinus mytilaspidis), transported scale-covered twigs
during winter from Geneva, 111., to Galena, 111., with beneficial results.
The experiment was conducted on a small scale, but the parasites
issued and became domiciled in t*heir new locality, thus proving the
practicability of his scheme. In neither my own experiments nor in Le
Baron's, however, was sufficiently thorough examination made to prove
that the parasites did not already exist in the localities in which they
were colonized.

Planchon and myself introduced Tyroglyphus phylloxerce from America
into France in 1873,t and it became fully established, as subsequent
correspondence and observation showed. In 1874 efforts were made
to send over from England to New Zealand certain Aphid parasites to
check the alarming increase of those plant pests there, and while I have
no records at hand to show with what success, the later successful intro-
duction of bumblebees to the latter country to fertilize the red clover
is well-known history. In his report upon the parasites of Coecida3 in
the Annual Keport of the Department of Agriculture for 1880, Mr.
Howard gave the subject some theoretical attention and elaborated
upon the ease with which Coccid parasites could be transported from
one part of the country to another during winter. He suggested the
experiment of transporting Dilophogaster calif ornica from the Pacific
coast to certain of the Southeastern States, where it might be expected to
prey upon certain large species of Lecanium. In 1883, after previous
futile attempts by myself and Mr. Otto Lugger, and with the assistance
of G. C. Bignell, esq., of Plymouth, England, the living cocoons of
Microgaster glomeratus, a common European parasite of Pieris rapce,
were successfully imported by the Department and the colonization of
the species was established, not only in the District of Columbia, but
in Iowa, Nebraska, and Missouri, as specimens were simultaneously
sent to the agents of the Division in those States.f It has become
so widely distributed since then as to lead to the inference that
it must have been previously introduced at some other points, though
the spread of an introduced species, even when introduced at a single
point, is often so rapid that it surprises us, especially of a species
that is winged, as evidenced by the spread of the Horn Fly (Hcemato-
Ma serrata) over the whole eastern United States in about four years.
Later, in 1891, with the aid of Mr. Fred. Enock, of London, a success-
ful effort was made to introduce into this country from England an
important Chalcid parasite of the Hessian Fly, Entedon epigonus Walker
(Semiotellus nigripes Lind.). The details of this experiment will be

*Tliird Rep., Ins. Mo., 1870, p. 29; Fifth Rep., do., 1873, p. 90.

t Sixth Report, Ins. Mo., 1874, p. 55.

t Report of the Etomologist in Rep. U. S. Dept. Agric. for 1884, p. 323.

134

found in my published writings, especially in my report as U. S. Ento-
mologist for 1891, and it is only necessary to state at this time that
parasitized paparia of the Hessian Fly were received in large numbers
and distributed to various points, and placed in the care of competent
observers in Illinois, Indiana, Michigan, and Canada. The results so
far have not been marked, and but one positive report as to the accli-
mation of the parasite has been received, viz, from Prof. S. A. Forbes,
of Champaign, 111. I am of the opinion, however, that the lack of
evidence from other points is due almost entirely to lack of proper exam-
ination, and I have every hope that the species will before long be found
to have obtained a secure foothold at all of the several points of intro-
duction. It is a very difficult matter to ascertain the existence of a
parasite of this minute size, except when it occurs in great numbers.
It requires an eye trained not only to the examination of these minute
creatures, but one familiar with the allied imported species and native
species. The reason for attempting the introduction of this particular
species was simply that in England it was found to be far more abun-
dant and far more beneficial than any of our native species have so far
proved.

The present year I have become interested in the matter of the
importation of a predaceous Noctuid (Erastria scitula) which preys upon
the Black Scale (Lecanium olece) in south Europe and helps materially
to keep it in check. With the help of Prof. H. Kouzaud, of Montpel-
lier, France, who has studied the habits of this insect with extreme
care, I hope to establish it in southern California, where the climatic
conditions are sufficiently close to those of south Europe, and where
the Black Scale does great damage to olive orchards and to oleander
trees, and also affects less seriously the Orange and Lemon. The Black
Scale has already an important enemy in California in the shape of the
Dilophogaster above mentioned, but the latter is only two-brooded, and
the scale insect, multiplying more rapidly, outstrips it in the race for
maturity. The Erastria, on the contrary, passes through five or six gen-
erations in the course of a summer, and, as it is purely predaceous, it
will, I believe, prove a most useful auxiliary against the Black Scale,
especially if brought over without its parasites.

So far I have spoken only of the insects which have been imported
into this country, but some effort has also been made in the opposite
direction. Thus we have endeavored (and with some success) to return
the service done us by sending to Australia and New Zealand some of
our predatory Coleoptera, some of the Pacific coast parasites of the
Codling Moth, and a species of the interesting genus Eaphidia, which
also preys upon the Codling Moth.

In 1887 and 1888 the now well-known importation of Vedalia cardi-
nalis from Australia and New Zealand to California, to prey upon
leery a purchasi, was successfully carried out. The history of this
striking example of the beneficial results that may, in exceptional

135

cases, flow from intelligent effort in this direction, is now sufficiently
well known to American economic entomologists; but anticipating that
we shall have foreign delegates among us, and that our proceedings
will be published more widely than usual, it will, perhaps, be wise to
give the salient historical facts in the case, even at the risk of some
repetition of what has been already published. In doing this the
indulgence of the society is craved for the prominence of my own part
in the work, rendered necessary by the disposition in some quarters to
distort the facts.

The Fluted Scale, otherwise known as the White or Cottony-cushion
Scale (Icerya purchasi Maskell), is one of the largest species of its
family (Coccida3), and up to 1888 had done immense injury to the orange
groves and to many other trees and shrubs of Southern California.
From Australia, its original home, it had been imported into Xew
Zealand, South Africa, and California, the evidence pointing to its
introduction into California about 1868, and, probably, upon Acacia
latijolia.

In my annual report as U. S. Entomologist for 1886 will be found a
full characterization of the species in all its stages; but the three
characteristics which most concern the practical man, and which make
it one of the most difficult species to contend with, are its ability to sur-
vive for long periods without food, to thrive upon a great variety of
plants, and to move about throughout most of its life.

The injuries of this insect, notwithstanding the efforts to check it,
kept on increasing, and some ten years ago I felt that the work of this
particular species and of others which seriously affected the fruit-
growing interests of Southern California justified the establishment of
agencies there. Up to this time no special entomological effort had been
made by the Government on behalf of the fruit-growers of the Pacific
coast. Through agents stationed, the one at Los Angeles, the other
at Alameda, a course of elaborate experiments was undertaken as to
the best means of treating the insects affecting the Orange there, and
more particularly this Fluted or Cottony-cushion Scale. During the
progress of these investigations, however, the fact impressed itself
upon my mind that we had here an excellent opportunity of calling to
our aid its own natural enemies, for while there were some doubts as
to the origin of Icerya, the question was finally settled to my own sat-
isfaction that it was of Australian origin, and that in its native home
it was not a serious pest, but was kept subdued by natural checks.
These facts were not positively ascertained without a good deal of
correspondence and investigation, involving, in fact, a trip to France,
as has been set forth in my published writings upon the subject.

In my report as U. S. Entomologist for 1886, in an address before

the State Board of Horticulture at Riverside, California, in 1887;

in a paper before the Philosophical Society of Washington in the

winter of 1888, and elsewhere, I urged, with all the force at my com-

9052— No. 2 6

13f>

raand, the advisability of endeavoring to introduce the natural enemies
which were known to keep it in check in Australia. Certain indige-
nous species had been discovered preying upon it in California, and I
expressed the belief that, as they increased, the fruit-growers would
get more and more relief from the Icerya; but I also urged that there
was much more chance of success from those which keep it in check in
its native home, and which were not imported with it to the countries
of its introduction. The case was exceptional, and the attempt thus
urged gave every promise of a rich reward. Efforts were made to
introduce some of these natural enemies through correspondence,
especially with the late F. S. Crawford, of Adelaide, with what ulti-
mate results the subsequent success of Vedalia forever rendered
uncertain.

The Hon. H. H. Markham, present Governor of California, was at
that time a Representative in Congress, and through him chiefly, but
also through others, I urged upon Congress the desirability of sending
some one to Australia to make a thorough study of the subject with a
view of introducing those natural enemies. Again, in the winter of
18S7-?88 appeals were made to Congress, not only of a personal nature,
but through memorials from various societies in California, for an appro-
priation to send one or two men to Australia to collect and increase
these natural enemies. Congress, however, failed to make any specific
appropriation, and also failed to remove the restriction in the appro-
priation to the Division of Entomology which limited traveling expenses
to the United States and prevented independent action of the Depart-
ment of Agriculture. It happened, however, that about this time an
appropriation was made and a commission created to represent the United
States at the Melbourne Exposition, and, with the appreciative aid and
sympathy of the Hon. Norman J. Colman, Commissioner of Agriculture,
I took active steps to gain the cooperation of the Secretary of State in
my pet scheme, and by an arrangement with the Department of State,
accepted by the commissioner to said Exposition, Hon. Frank McCoppin,
the Department of Agriculture was finally enabled to send to Australia
two agents of the Division of Entomology, one of them to be under my
instructions, and the expenses of both, within the sum of $2,000, to be
paid out of the appropriation for the aforesaid Exposition.

It was thus that Mr. Albert Koebele, in the fall of 1888, was sent to
Australia for this special purpose. The history of Mr. Koebele's efforts
has been detailed from time to time in Government publications and in
the press, especially that of California. It suffices to state that a num-
ber of living enemies, both parasitic and predaceous, were successfully
imported, but that one of them, Vedalia cardinalis, proved so effective
as to throw the others entirely into the shade and render their services
really unnecessary. It has, so far, not been known to prey upon any
other insect, and it breeds with surprising rapidity, occupying less than
thirty days from the laying of the eggs until the adults again appear.

137

These facts account for its exceptionally rapid work, for in point of fact,
within a year and a half of its first introduction, it had practically
cleared off the Fluted Scale throughout the infested region. The expres-
sions of two well-known people may be quoted here to illustrate the gen-
eral verdict. Prof. W. A. Henry, Director of the Wisconsin Agricul-
ture Experiment Station, who visited California in 1889, reported that
the work of Vedalia was u the finest illustration possible of the value
of the Department to give the people aid in time of distress. And the
distress was very great indeed." Mr. William F. Channing, of Pasa-
dena, son of the eminent Unitarian divine, wrote two years later:

We owe to the Agricultural Department the rescue of our orange culture by the
importation of the Australian ladybird, Vedalia cardlnalis.

The white scales were incrusting our orange trees with a hideous leprosy. They
spread with wonderful rapidity and would have made citrus growth on the whole
North American continent impossible within a few years. It took the Vedalia,
where introduced, only a few weeks absolutely to clean out the white scale. The
deliverance was more like a miracle than anything I have ever seen. In the spring
of 1889 I had abandoned my young Washington navel orange trees as irrecoverable.
Those same trees bore from two to three boxes of oranges apiece at the end of the
season (or winter and spring of 1890). The consequence of the deliverance is that
many hundreds of thousands of orange trees (navels almost exclusively) have been
set out in southern California this last spring.

In other words, the victory over the scale was complete and will prac-
tically remain so. The history of the introduction of this pest, its
spread for upwards of twenty years, and the discouragement which
resulted, the numerous experiments which were made to overcome the
insect, and its final reduction to unimportant numbers by means of an
apparently insignificant little beetle imported for the purpose from
Australia will always remain one of the most interesting stories in the
records of practical entomology.

The Vedalia has since been successfully colonized at the Cape of
Good Hope and in Egypt, and has produced the same results in each
case. In Egypt the Vedalia was introduced to prey upon an allied
species of leery a ( I. cegyptiacum, Douglas). We hope soon to be able to
send the same insect to India, where it has recently transpired that
Icerya cegyptiacum occurs, while recent information received from Phra
Suriya, royal commissioner of Siam at Chicago, would indicate that its
introduction into Siam for the same or a closely allied insect will be
desirable in the near future.

In fact, the success of the experiment was so striking and so impor-
tant, and resulted in the saving to California of an industry of so great
a money value, that it has given rise, not only in the popular mind but
in the minds of a certain class of entomologists also, to the idea that
remedial work against injurious insects should be concentrated upon
this one line of action, and that our best hope for their destruction
lies with the parasitic and predaceous species, not to mention fungus and
bacterial diseases. From an extreme of comparative incredulity the

138

farmer and fruit-grower have gone, perhaps, to the other extreme of
too great faith. The case of leery a and Vedalia, as I have frequently
pointed out, was exceptional and one which can not easily be repeated*

One of the humorous phases of the Vedalia experiment is, that the
wide newspaper circulation of the facts — not always most accurately
set forth — has brought me communications from all parts of the world
asking for supplies of the renowned little Ladybird for use against
injurious insects of every kind and description, the inquiries being
made, of course, under a misapprehension of the facts.

While this California experience thus affords one of the most striking
illustrations of what may be accomplished under exceptional circum-
stances by the second method of utilizing beneficial insects, we can
hardly expect to succeed in accomplishing much good in this direction
without a full knowledge of all the ascertainable facts in the case and
a due appreciation of the profounder laws of nature, and particularly of
the interrelations of organisms. Year in and year out, with the condi-
tions of life unchanged by man's actions, the relations between the
plant-feeder and the predaceous and parasitic species of its own class
remain substantially the same, whatever the fluctuations between them
for any given year. This is a necessary result in the economy of
nature ; for the ascendancy of one or the other of the opposing forces
involves a corresponding fluctuation on the decreasing side, and there
is a necessary relation between the plant-feeder and its enemies, which,
normally, must be to the slight advantage of the former and only
exceptionally to the great advantage of the latter.

This law is recognized by all close students of nature, and has often
been illustrated and insisted upon by entomologists in particular, as
the most graphic exemplifications of it occur in insect life, in which
fecundity is such that the balance is regained with marvelous rapidity,
even after approximate annihilation of any particular species. But it
is doubtful whether another equally logical deduction from the prev-
alence of this law has been sufficiently recognized by us, and this is,
that our artificial insecticide methods have little or no effect upon the
multiplication of an injurious species, except for the particular occa-
sion which calls them forth, and that occasions often arise when it were
wiser to refrain from the use of such insectides and to leave the field
to the parasitic and predaceous forms.

It is generally when a particular injurious insect has reached the
zenith of its increase and has accomplished its greatest harm that the
farmer is led to bestir himself to suppress it, and yet it is equally true
that it is just at this time that nature is about to relieve him in strik-
ing the balance by checks which are violent and effective in proportion
to the exceptional increase of and consequent exceptional injury done
by the injurious species. Now the insecticide method of routing this
last, under such circumstances, too often involves, also, the destruc-
tion of the parasitic and predaceous species, and does more harm than

139

good. This is particularly true of those of our Coccidae and Aphi.
didae and those of our Lepidopterous larva} which have numerous natu-
ral enemies of their own class; and it not only emphasizes the impor-
tance of preventive measures, which we are all agreed to urge for other-
cogent reasons, and which do not to the same extent destroy the para-
sites, but it affords another explanation of the reason why the fight with
insecticides must be kept up year after year, and has little cumulative
value.

But the problem of the wise encouragement and employment of the
natural enemies of injurious insects in their own class is yet more com-
plicated. The general laws governing the interaction of organisms are
such that we can only in very exceptional cases derive benefit by
interference with them. The indigenous enemies of an indigenous phy-
tophagous species will, cceteris paribus, be better qualified to keep it
in check than some newly introduced competitor from a foreign coun-
try, and the peculiar circumstances must decide in each case the
advisability of the introduction. The multiplication of the foreigner
will too often involve the decrease of some indigene. If a certain phy-
tophage is generally disastrous in one section and innocuous in another
by virtue of some particular enemy it will be safe to transfer and
encourage such enemy, and this is particularly true when the phy-
tophage is a foreigner and has been brought over without the enemy
which subdues it in its native home. Icerya had some enemies in Cali-
fornia, presumably American, but they were not equal to the task
of subduing it. Yedalia, in the Icerya's native home, Australia, was
equal to the task and maintained the same superiority over all others
when brought to America. The genus was new to the country and
the species had exceptionally advantageous attributes. But there is
very little to be hoped from the miscellaneous introduction of preda-
ceous or parasitic insects for the suppression of a phytophage which
they do not suppress in their native home or in the country from which
they are brought.

The results of the introduction by Mr. A. D. Hopkins of Clermformi-
carius to contend with the Scolytids which were ruining the West Vir-
ginia pines were doubtful, for the reason that indigenous species of the
genus were already at work in America. Yet the experiment was safe
and desirable, because the European Olerus is more active and more
seemingly effective than our indigenes. The Gypsy Moth was evidently
introduced into Massachusetts without its European natural enemies,
and as in some parts of Europe it is often locally checked by such natural
enemies, a great number of which are known, a proper study of them
and the introduction of the most effective could result in no possible
harm and might be productive of lasting good. Such a course was
advised by me at a conference upon the subject held in the rooms of
the State Board of Agriculture, Boston, March 4, 1891,* and in corre

INSECT LIFE, in, p. 369, ff.

140 i1; \ Y

spondence with the Secretary of the Board I,i nHtli-T <>f
should we expect the predaceous or parasitic forms to subdue their
hosts more effectually in America than they do in Europe, except in so
far as they were relieved, in the introduction into America, of whatever
enemies they possessed in their native home.

There are two other laws which it is worth while to consider in this
connection. One is, that while a plant-feeder's natural enemies are < pt
to cause its excessive abundance to be followed by a corresponding
decrease, yet this alternation of excessive abundance and excessive
scarcity will often be produced irrespective of such natural checks. An
injurious insect which has been on the destructive march for a period
•of years will often come to a sudden halt, and a period of relative, and
sometimes complete, immunity from injury will follow. This may result
from climatic conditions, but more often it is a consequence of disease,
debility, and want of proper nutrition, which are necessary corollaries
of undue multiplication. Frequently, therefore, it may be inaccurate
and misleading to attribute the disappearance of a particular injurious
species to some parasitic or predaceous species which has been let
loose upon it, and nothing but the most accurate observation will
determine the truth in such cases. The past year furnished a very
graphic illustration in point. Throughout Virginia and West Virginia,
where the spruce pines have for some years suffered so severely from
the destructive work of Dendroctonus frontalis, not a single living
specimen of the beetle has been found during the present year. This
has been observed by every one who has investigated the subject, and
particularly by several correspondents who have written to me; by Mr.
E. A. Schwarz, who was commissioned to investigate the facts, and by
Mr. Hopkins, who has made the study of the subject a specialty.

The clearest explanation of this sudden change is that the species
was practically killed out by the exceptionally severe cold of last
winter, since such was the case with several other insects. Now, fol-
lowing so closely on the introduction by Mr. Hopkins of Glerus formi-
cariusj how easy it would have been to attribute the sudden decrease
to the work of the introduced Olerus had not the decrease been so
general and extensive as absolutely to preclude any such possibility.
In like manner a certain Scale Insect (Aspidiotus tenelricosus) had
become exceedingly destructive to the Soft Maples in the city of Wash-
ington last year, whereas the present year it is almost entirely killed
off, evidently by the same exceptional cold. Many of the affected
trees were painted with whitewash, with a view of destroying the
Aspidiotus, and the death of this last might have been attributed to
the treatment (and naturally would be by those employing it) were it
not that the same result was equally noticeable on the trees not
treated. Reports from southern California would indicate that the Red
Scale (Aspidiotus aurantii) is, in many orchards, losing its destructive.
ness through agencies other than its insect enemies, and in this case
the facts are particularly interesting because of the ease with which

141

its* (iisabpeariiDce may be attributed to some of the recent introduc-
tions from Australia.'

The other law that is worth considering in this connection is that
experience has shown that, as a rule, the animals and plants of what
is known as the "Old" World — i. e., of Europe and Asia — when intro-
duced into North America have shown a greater power of multiplica-
tion than the indigenous species, and in a large number of instances
have taken the place of the native forms, which have not been able to
compete with them in the struggle for existence. The converse prop-
osition holds equally true, viz : that our species when taken to Europe
do not hold their own against the European indegenes. This is still more
true of the species introduced from the Old World, as well as from
America, into Australia, where the advantage of the introduced forms,
as compared with the indigenous, has been in many cases still more
marked. All other things being equal, therefore, we should expect the
species which are beneficial in Australia to be less so when brought to
this country, a deduction which brings out still more clearly the
exceptional nature of the case of Vedalia and Icerya, just as there are
some notable exceptions, as in the case of the Grape Phylloxera, in the
introductions between Europe and America.

There are some instances in which there can be no doubt whatever
as to the good which would flow from the introduction of beneficial
species, and an illustration is afforded in the Capri-fig insect, Blastophaga,
psenes. There can be no question as to the good which would result
from the introduction of this species from Smyrna into those sections
of California where the Smyrna fig is grown without its intervention
and there are other similar instances which promise well and involve
no risk. But I have said enough to show that the successful utiliza-
tion of beneficial insects is by no means a simple matter and that dis-
criminating knowledge is required to insure success or prevent dis-
aster, especially in the second category dealt with in this paper. The
danger attending introductions of beneficial species by unconsciously
accompanying them with injurious forms, or by failure to appreciate
the facts here set forth, is well illustrated by the introduction to
Europe of our Peronospora mticola, of the English Sparrow to America,
and of the Mongoose to Jamaica. Wherever the importance of the
matter leads to legislation, what are denominated " political" methods
are apt either to control or in some way influence the resulting efforts —
too often with unfortunate consequences. We should, as economic
entomologists, be on the alert for special cases where the introduction
or dissemination of beneficial species promises good results, and do
our best to encourage an intelligent public appreciation of such special
cases, while discouraging all that is of a sensational nature, as likely
to mislead and ultimately do our profession more harm than good.

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