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CIRCULAR No. 346 MARE H 4938, Depart
UNITED STATES DEPARTMENT OF AGRICULTURE |}tid!
WASHINGTON, D.C.

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INSECT PARASITES ile el OF INSECT

By Curtis P. CLAUSEN, senior entomologist, in charge, Division of Foreign
Parasite Introduction, Bureau of Entomology and Plant Quarantine

CONTENTS
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INTRODUCTION

The insects usually noticed by those engaged in the growing of
plants, whether farmers or gardeners, are the forms that feed upon
the plants or plant products and are consequently injurious. There
are, however, a very large number of insects that are entirely beneficial
in their relation to crop production. This circular deals only with
those species which, by preying upon or parasitizing other insects,
aid in preventing damage to agriculture. In general, it may be
stated that practically every insect in its native home has one or
more species which prey upon it and are dependent upon it for their
existence. Were it not for these parasites, many of our insect pests
would be able to increase to such an extent that the growing of crops
would be impossible. Insects have such an enormous capacity for
increase that some very definite checks are necessary to keep them
within bounds. When it is realized that some insects, such as the
aphids, are able to complete a generation in a week or less, it is clear
that they would very quickly become excessively abundant if no
restraining influences were present. While climatic conditions are
usually the most important factor in reducing the numbers of an
insect pest, yet under suitable conditions the parasites and predators
are of nearly as great importance. In most cases these factors pre-
vent the plant-feeding insects from becoming excessively injurious,
and only a very small proportion of these species of insects ever be-
come sufficiently abundant to cause injury to crops.

This circular is intended to present a general account of the vari-
ous forms of insects that prey upon or parasitize other insects. The

168635°——35— 1 1

2 CIRCULAR 346, U. S. DEPARTMENT OF AGRICULTURE

more common types encountered by plant growers are discussed,
and general information is presented regarding their habits, the
insects upon which they feed, and general descriptions by means of
which they may be identified. For purpose of ready reference,
these topics are dealt with under the primary headings of the insects
that are attacked.

CONTROL OF INSECT PESTS BY PARASITES AND PREDATORS

In most cases when insect pests have gained entry into the United
States they have not been accompanied by the parasites and preda-
tors which attack them in their native home. This being so, it is
quite understandable that the pests have been able to increase to
enormous numbers and to inflict great damage to crops. The im-
portation of the parasites and other insect enemies is an effort to
duplicate here the natural balance which exists in the former home
of the insect.

The first attempt at the control of an insect pest by the impor-
tation of its predators from abroad was the importation of the
vedalia beetle (Rodolia cardinalis Muls.) from Australia in 1888-89
to work against the cottony-cushion scale (Jeerya purchasi Mask.)
on citrus in California. Within a few years the scale was com-
pletely subjugated. This striking success led to further efforts
along the same line, but it was many years before so decisive a
result was again obtained. The most extensive program for para-
site importation was that against the gypsy moth (Porthetria dis-
par L.) and the brown-tail moth (Vygmia phaeorrhoea Don.). The
first shipments of parasites of these pests were received in 1905, and
the work was continued until 1912 and then resumed during the
period from 1922 to 1932. At the present time importations are
being made of the parasites of a number of insects, such as the
European corn borer (Pyrausta nubilalis Hbn.), the Japanese beetle
(Popillia japonica Newm.), the oriental fruit moth (Grapholitha
molesta Busck), and several forest insects. In general, it may be
said that the importation of parasites from abroad is one phase in
the attempted control of each of the most important foreign insect
pests that have become established in this country.

There are certain definite hmitations to the possibilities of con-
trol of insect pests by the use of parasites. Only in exceptional cases
can complete control be achieved by this means, In the great
majority of cases different degrees of partial control are secured.
For this reason the introduction of parasites should be considered as
supplementary to the usual methods of mechanical and chemical con-
trol rather than as a alternative method. The reduction in numbers
of the insect pest by the use of parasites renders outbreaks less fre-
quent, and control is then more readily accomplished by the use of
sprays or other mechanical or chemical methods.

There are two distinct phases in the.attempted control of an insect
pest by the importation of its parasites. The first phase comprises
the search for the parasites in foreign countries, the study of these to
determine their usefulness, and finally their shipment to the United
States; the second phase includes the rearing of the parasites and
their distribution throughout the entire area infested by the pest in
this country. It is obviously impossible to provide colonies of para-

INSECT PARASITES AND PREDATORS OF INSECT PESTS 3

sites for liberation on every farm or orchard, but the colonies are
placed at such intervals that natural spread will soon provide a
thorough distribution.

The foregoing statements apply entirely to the use of imported
parasites. Various attempts have also been made, however, to extend
the usefulness of the parasites native to this country. In some in-
stances this has been done with marked success, but these instances
have represented transfers of parasites from one part of the country
to another to which their natural spread has been prevented by var1-
ous physical barriers. In general, it may be stated that there is
little possibility of securing increased effectiveness by the hberation
of additional numbers of a parasite already present in a locality.

The natural enemies of various crop pests are often inconspicuous,
and their presence is not detected by persons unfamilar with them.
Many inquiries are received from growers regarding outbreaks of
field or orchard pests in which it is stated that the parasites are
absent and that. colonies are desired for liberation. To determine
definitely the presence or absence of these parasites, the assistance of
an expert from the State experiment station or from the Bureau of
Entomology and Plant Quarantine may be required. Usually it will
be found that the parasites are already present, though possibly only
in small numbers. Local or temporary conditions may be unfavor-
able to them and, if so, the same handicaps will restrict the increase
of any colonies that might be liberated. The Bureau of Entomology
and Plant Quarantine does not maintain stocks of either native or
imported parasites for general distribution to growers. The im-
ported ones are colonized directly and in accordance with a definite
plan of distribution.

ENEMIES OF APHIDS, SCALE INSECTS, AND MEALYBUGS

LADYBIRD BEETLES

The beetles of the family Coccinellidae, known variously as “ lady-
bugs”, “ ladybirds ”, “ladybird beetles”, or “lady beetles”, are
among the most common of all beneficial insects. Various species
of these useful insects are widely distributed and often occur in
enormous numbers. These beetles and their larvae feed upon a wide
variety of insects, though more particularly upon aphids, scale
insects, mealybugs, white flies, and red spiders. The various species
do not feed indiscriminately, however, but each is more or less
restricted to a particular insect or group of insects. Aphid-feeding
species, for instance, do not generally attack scale insects, nor will
feeders on mealybugs normally attack either scale insects or aphids.
Several species are known to feed exclusively upon fungi, but these
species are seldom encountered. ?

In this family there is one group, represented in this country by
the genus E’pilachna, which feeds exclusively on plant foliage and is
consequently harmful. The best known example is the Mexican
bean beetle ('pilachna corrupta Muls.), which was introduced into
the Eastern States from the Southwest about 1920, has spread north-
ward in recent years, and is now very injurious to the bean crop in
most of the States east of the Mississippi River. The adult beetlés
of this species may be recognized by the form of the body, which is

4 CIRCULAR 346, U. S. DEPARTMENT OF AGRICULTURE

more hemispherical than that of the common aphid-feeding beetles
of the family, and by the copper-colored back, which bears 16 black
spots.

ie majority of the common aphid-feeding species are red and
usually bear a variable number of black spots on the wing covers.
The convergent lady beetle (Hippodamia convergens Guer. ), ilus-
trated in fioure 1, 1s probably the one most frequently seen, particu-
larly in the W estern States. Nearly all species of aphids that do
not bear a waxy covering are attacked by this beetle, which often
plays an important part in checking aphid infestations.

The life histories of the beetles of this group are similar, and that
of Hippodamia convergens is quite typical. The eggs are lemon
yellow in color, spindle-shaped, and measure about one-twentieth of
an inch in length. They are deposited in compact clusters of from 10
to 30 upon the fohage, usually among or near the aphid colonies,
and each female may deposit as many as 1,000 eggs. Hatching
takes place in about 5 days under summer conditions. The larva
then feeds for about 16 days, and during this time it may eat from
200 to 500 aphids, as it is very active in its ssearch for food. When full

FiGuRB 1.—The convergent lady beetle (Hippodamia convergens), a feeder on aphids: A,
Adult beetle; B, pupa: C, mature larva; D, egg cluster. A, B, and (, about 4 times
natural size; D, 8 times natural size.

grown it has a length of one-half inch. At the end of the feeding
period the larva enters the resting or pupal stage and the compact
body remains attached by its tip to the leaf surface or to any other
object upon which it may rest. This resting stage covers from 6 to 7
days, after which the beetle appears and begins feeding immediately.
Each beetle may consume a maximum of about 100 aphids per day
during its active adult life. During early summer this may extend
over from 1 to 2 months, and the beetles that appear later may sur-
vive the winter and resume feeding and egg laying in the spring.

The overwintering habits of this and related species are of par-
ticular interest. At the end of the season the beetles leave the fields
and gardens where they have been feeding and migrate to mountain
canyons, where they assemble in vast numbers upon low shrubbery
and in rubbish ; here they pass the winter, usually deeply covered
with snow. <A single colony, covering only a few square yards, may
comprise a bushel or more ‘of the beetles. These over wintering col-
onies are most numerous in California, though they are encounter ed
in nearly all of the mountainous sections of the West.

The influences which bring about this assembling of beetles in
such large colonies are not well understood, but it is not induced
entirely by the lower temperatures of the fall months, Lar ge col-

INSECT PARASITES AND PREDATORS OF INSECT PESTS 5

onies have been seen early in July massed upon rocks near streams
and in bright sunlight, and in these instances the temperature of
the rocks was certainly above 100° F.

A considerable number of species of ladybird beetles feed upon
mealybugs, and the larvae of many of them bear a whitish waxy
coating that gives them a resemblance to the insects upon which they
feed. A few of the species that attack aphids, scale insects, and
white flies also bear a similar covering.

One of the most effective of these beetles is the so-called “Austra-
han ladybird beetle ” (Cryptolaemus montrouziert Muls.) which was
imported into California from Australia in 1891-92 for the control
of mealybugs attacking citrus in that State. Its life history differs
from that of Hippodamia convergens in that the eggs are laid singly
among the mealybugs, rather than in clusters, and the winter is
passed in the resting stage in curled leaves and rubbish beneath
the trees. This method of hibernation is a decided disadvantage
to the species under the conditions existing in this country, as the
fallen leaves decay, are blown away, or are plowed under during
the winter. Ag a result, relatively few of the insects survive until
the following spring. Because of this, the mealybugs are able to
get a good start and become very abundant and injurious before
the beetle is able to increase sufficiently to cope with them. This
difficulty was overcome by the development, by the California State
Department of Agriculture and the agricultural experiment station,
of rearing methods whereby millions of the beetles could be pro-
duced at relatively low cost and liberated in infested citrus groves
early each season. Effective control was thus obtained sufficiently
early so that little or no damage was done by the mealybugs.

Another imported ladybird beetle of great value is the far-famed
vedalia beetle (Rodolia cardinalis Muls.) (fig. 2), which, as previ-
ously mentioned, was imported into California from Australa in
1888-89 for the control of the destructive cottony-cushion scale
(Icerya purchasi Mask.) on citrus. So rapidly did this beetle in-
crease that within a few years this destructive scale ceased to be a
pest, and to the present day it is of little or no consequence in the
citrus groves. Occasionally a small infestation may appear, but this
may be quickly eliminated by the liberation of colonies of the beetle.
Usually, however, the beetles appear of their own accord. Follow-
ing this remarkable success, the beetle was introduced into many
other countries in which the cottony-cushion scale had become estab-
lished, and in nearly every instance similar striking results were
obtained.

Another importation from abroad is the Chinese ladybird beetle
(Chilocorus similis Rossi), which was brought from Asia for use
against the San Jose scale (Aspidiotus perniciosus Comst.). It was
found in the orchards for a number of years after liberation but
apparently did not become established. The adult beetles are shiny
black and bear one red spot on the center of each wing cover, thus
greatly resembling the twice-stabbed ladybird beetle (Chilocorus
bivulnerus Muls.), which is native to this country and also feeds upon
scale insects. The eggs are deposited singly among the scales or
beneath the scale covering. The spiny larvae chew holes through
the covers of large numbers of scales and feed upon the developing

6 CIRCULAR 346, U. S. DEPARTMENT OF AGRICULTURE

insects. At the time of pupation the larvae of this and some other
species of scale feeders have the habit of congregating in large
colonies on favored twigs or on the branches or trunk of a tree
(fig. 3). These colonies may contain several hundred individuals
and are often conspicuous.

CONTROL OF APHIDS, SCALE INSECTS, AND MEALYBUGS BY THE LIBERATION OF
LADYBIRD BEETLES

The fact that a number of serious insect pests have been fully
controlled by the liberation of ladybird beetles has led to the belief

FicurE 2.—The vedalia beetle (Rodolia cardinalis), an effective enemy of the cottony-
cushion seale on citrus trees: A, Larvae feeding upon an egg mass; B, pupa; C, adult
beetle; D, an infested twig showing eggs, larvae, and beetles among the scales. A, B,
Ema Ge S< Aoowiy 308 JD), S< De

among growers that many other farm, garden, and greenhouse pests
can be controlled in the same way. This belief does not take into
consideration the limitations of the different species as regards food
habits, the conditions necessary for maximum increase, and other
influences that control their effectiveness. The vedalia beetle, for
instance, is effective only against the cottony-cushion scale, and its
liberation in the hope of checking other pests cannot possibly be of
any value. Likewise no control can be hoped for by the lberation
of the convergent lady beetle upon trees infested with scale insects
or mealybugs.

INSECT PARASITES AND PREDATORS OF INSECT PESTS (

While the Australian ladybird beetle is very effective in controlling
mealybug infestations under orchard conditions, it is of little or no
value for use in greenhouses. The reason for this lies in the fact that
a fairly heavy infestation is necessary before the beetle is able to in-
crease rapidly. Orchard trees can stand this degree of infestation
with relatively lttle injury, whereas greenhouse plants are seriously
injured, or at least their market value is greatly reduced. The dam-
age is done before the infestation becomes sufficiently great to permit
of the i increase of the beetle, and for this reason it is necessary to rely
upon spraying or fumigation for control.

Many inquiries are received from residents in the mountainous
sections of the West who have noted colonies of aphid-feeding lady-

FIGURE 3.—Pupae of the Chinese ladybird beetle (Chilocorus similis) in typical clusters
on twigs. Those at left are natural size,

bird beetles and wish to be advised as to a possible market for them.
These beetles at present have no commercial value, although occa-
sionally quantities are required for experimental pur poses. This de-
mand, however, is so small as to be negligible, and returns are seldom
sufficient to defray the cost of collection and shipment. The presence
of these beetles in such quantities in winter quarters indicates. that
they occur in large numbers in the orchards and fields in those sections
during the spring and summer months. There is no advantage to
be gained by the liberation of additional numbers in orchards where
the beetles already occur. In general, these beetles appear in all
sections in which the aphid infestations give them an opportunity to
develop. The liberation of large colonies for the field control of
aphid infestations is not recommended,

8 CIRCULAR 346, U. S. DEPARTMENT OF AGRICULTURE
LACEWING FLIES

The lacewing flies are delicate, four-winged insects, so named
because of the delicate tracery of their comparatively large, fragile
wings. Their larvae are long-bodied, thickest in the middle section
of the abdomen, and bear very long, sickle-shaped mandibles by means
of which they seize and drain the body contents of their prey. Be-
cause of these formidable mandibles and the aggressiveness of the
larvae in attack, they are often termed “aphis lions.” There are
two groups of these insects, the green lacewing flies (family Chrysopi-
dae) and the brown lacewing flies (family Hemerobiidae).

The green lacewing flies (species of Chrysopa and related genera)
(fig. 4) have the body and wings of a light greenish color and the
eyes brillant gold. The larvae feed quite largely upon aphids, but
they may also attack thrips, jumping plant lice, mealybugs, scale

X ee Bian w Ze FGF
ge Pe z
Siena are eee Se

FIGURE 4.—Chrysopa califormmica Coq., a green lacewing fly; A, Adult lacewing; B, young
larva; C, a group of stalked eggs upon a leaf. A, X 214%; B, X 9Q.

insects, red spiders, and the eggs of various insects. The eggs are
green, about one-thirtieth of an inch in length, and are usually de-
posited singly upon the foliage. They are placed at the end of slender
silken stalks one-fourth to one-half inch in length, an arrangement
which is said to protect them from various enemies. Some species
place the eggs in groups upon a single stalk or upon a bundle of fused
stalks.

The larvae of many of the species of green lacewings have the
very interesting habit of covering their bodies with packets of trash
consisting of the shriveled bodies of aphids they have killed, molted
skins, and other material, this debris being loosely woven together
with silken strands. The body is often so completely covered by this
packet that it 1s not visible except while in motion, when what
appears to be a mere mass of trash proves to be the shelter borne
by the lacewing larva.

INSECT PARASITES AND PREDATORS OF INSECT PESTS 9

The resting stage, which immediately precedes the appearance of
the adult insect, is passed within a white, spherical, parchment-
like cocoon formed in a curled leaf or in some other protected

lace.

The brown lacewing flies (species of Hemerobius and related
genera) are similar in habit to the green lacewings mentioned above,
but the body and wings of the adult are brown and the eyes lack
the conspicuous golden color. The larvae do not carry the protective
packet of trash, and they feed largely on aphids and mealybugs.
The eggs are laid singly among the host insects and are not borne
upon stalks. Many species pass the winter in the mature larval form
in sheltered places rather than within the cocoon, as do the larvae of
the green lacewings. The cocoon of the brown species is delicate,

FiGuRE 5.—The adult of Sphaerophoria cylindrica Say, one of the hover flies. X T.

oval in form, and consists of a loose network of silken strands
through which the pupa can readily be seen.

HOVER FLIES

The hover flies, of the family Syrphidae (fig. 5), are known to
most growers as rather large, conspicuously marked flies with rela-
tively long body and wings, which have a characteristic habit of
hovering over the blossoms upon which they feed or over foliage
infested with aphids. The adult flies feed upon honeydew secreted
by aphids and scale insects and also upon the nectar of plants,
whereas the larvae feed directly upon aphids and to a lesser extent
upon other soft-bodied insects, such as mealybugs, immature leaf
hoppers, and red spiders. Most of the aphid-feeding species may
be found in greatest numbers in the field during the spring and early
summer months.

The eggs are usually about three times as long as wide, and those
of the larger species measure about one twenty-fifth of an inch in
length. They are chalky white and consequently conspicuous when
seen among the aphid colonies.

108635°—35 2

10 CIRCULAR 346, U. S. DEPARTMENT OF AGRICULTURE

The larva, or maggot, is sluglike and usually has a mottled brown
or green color. It moves slowly about the leaf in search of food,
seizes the aphid prey, and sucks out the body juices. During its
period of development each larva may consume up to 400 aphids,
' depending upon their size. The feeding period covers from 7 to 15
days.

The completion of feeding is followed by the resting, or pupal
stage, during which the transformation to the adult fly takes place.
The puparium, which encloses the insect while it changes to the
adult form, is tear-shaped, brown or green in color, and is usually
found among the aphid colonies where feeding took place or in
sheltered places upon plants or on the ground.

INTERNAL PARASITES

The various species of aphids, or plant lice, are attacked in large
numbers by minute wasps, which develop within the body. The

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FiGuRH 6.—An aphid parasite (Lysiphlebus testaceipes) in the act of stinging an aphid.
The egg is inserted in the body at this time. x 15.

common grain aphid known as the “ green bug ” (Toxoptera grami- .
num Rond.) is often heavily attacked by one of these (Lystphlebus
testaceipes (Cress.)) and under favorable conditions the pest is
greatly reduced, often to the point where no further damage is in-
flicted. In many instances, however, this control comes relatively
late in the season and after extensive damage has already been done.
The same is true of the parasites of other aphids occurring on the
different orchard, field, and garden crops.

The grain aphid parasite just referred to deposits its egg within
the body of the aphid (fig. 6), and the adult wasp emerges 1 week
later. The body contents of the parasitized aphids are entirely con-
sumed, and the bodies assume a characteristic mummified condition
(fig. 7,2) and adhere to the leaf surface. At times these mummified
remains may be seen in enormous numbers upon the foliage; in fact,
in far greater numbers than the healthy individuals. The mature
wasps emerge from the body of the host aphid by cutting a circular
lid in the body wall. The fact that the parasite completes a genera-
tion in from 7 to 10 days and that each adult may attack a total of 100

INSECT PARASITES AND PREDATORS-OF INSECT PESTS Lik

or more aphids makes possible an exceedingly rapid increase under
favorable conditions.

In many sections the destructive woolly aphid (Z7iosoma lanigerum
Hausm.) of the apple is quite effectively controlled by Aphelinus mali
Hald. Usually the parasites occur normally in the field where the
aphid host is found, and climatic conditions largely determine the »
extent to which they are able to increase. :

Practically all species of scale insects and mealybugs are attacked ~
by minute wasps which develop within the body. Individual scale

FIGURE 7.—Grain aphids parasitized by the wasp Lysiphlebus testaceipes: A, An aphid
showing the parasite larva within the body; B, a dead, mummified aphid; C, a parasite
en from an aphid, and two aphid bodies showing the typical emergence holes.

andepnS 12:

insects can normally be recognized as parasitized only after the adult
parasite has emerged, leaving its exit hole, for when the wasp reaches
maturity it chews a small circular hole through the upper side of the
scale sufficiently large to permit its escape. In heavy infestations of
the soft brown scale (Coccus hesperidwm I.) and the black scale
(Saissetia oleae Bern.) on citrus, the San Jose scale on apple, and
various others, a very large proportion of the scales may be found dead
because of parasite attack and showing these characteristic holes in
the body wall.

12 CIRCULAR 346, U. S. DEPARTMENT OF AGRICULTURE

Parasitized mealybugs are readily recognized by a swollen, mum-
mified condition. The parasite undergoes its transformations within
this hardened shell and finally gnaws its way out. Of the parasites
of mealybugs and scale insects, the majority of the species develop
singly, yet even among these some may develop to the number of
several dozen in a single host insect.

PARASITES OF CATERPILLARS

The caterpillars (larvae of butterflies and moths) and beetle and
sawfly larvae which feed upon the foliage of plants and those which
bore into the twigs and trunks of trees are attacked by a wide variety
of other insects. Among them are the parasitic flies, which develop
within the body of the host, and various wasps, which sting the
caterpillars and deposit their eggs either in or on the body.

Nearly every species of caterpillar is attacked by one or more
species of tachinid flies, most of which bear a considerable resemblance
to the house fly but may be much larger. The flies of this entire
group, and others as well, are beneficial rather than harmful. The
majority of these flies lay their eggs upon the body of the caterpillar,
where they may be recognized as white oval spots one twenty-fifth
of an inch or less in length. Caterpillars may often be seen bearing
many of these eggs, in exceptional cases as many as 50 to 100.
Whether only one or many eggs are laid on a caterpillar, generally
only a single parasite develops to maturity, though in one instance
80 were reared from a single individual.

The egg hatches within a few days after being laid, and the
minute maggot bores through the skin into the body. Here it feeds
upon the blood of the caterpillar, and after a variable period of
time completes its feeding upon the body contents and emerges.
It then enters the resting stage, usually in the soil, in a puparium
which is quite similar in appearance to that of the house fly and
the stable fly.

The small Apanteles wasps are frequently very effective in de-
stroying caterpillars. The cocoons of the parasites of this group
are often seen upon foliage and are conspicuous because of the
large number that may occur in each mass and by their white or
yellow color. In some species the cocoons are found singly, but
in others they occur in clusters of from 25 to 50 or more and are
often covered with a loose mass of silk. These cocoons may be
formed directly upon the body of the caterpillar (fig. 8) from
which the larvae emerged, or they may be scattered irregularly
about it upon a leaf, or in orderly tiers one above the other like
rows of bricks. An instance is recorded of more than 1,000 of these
parasites emerging from a single caterpillar. Many inquiries are
received regarding these cocoon masses, and they are often mistaken
for insect eggs and consequently destroyed.

One of the most common species of this group is A panteles glomer-
atus I.., which attacks the imported cabbage worm (Ascia rapae L.).
The female wasp stings the very young caterpillars and lays from
15 to 50 eggs within the body. The larvae feed upon the body fluids
for about 2 weeks and then emerge by cutting individual holes
through the skin of the still-living, nearly full grown caterpillar,
which may not die for several days. All of the larvae contained in

INSECT PARASITES AND PREDATORS OF INSECT PESTS 13

a single caterpillar emerge from it on the same day. The cocoons
are spun upon the foliage nearby. The cocoon stage covers about
5 days, and the adult wasp then emerges by cutting away a circular
cap from one end.

There are many other kinds of wasps that attack caterpillars.
These may attack the caterpillar directly during its feeding period or
they may attack the larva or pupa in the cocoon. Some of these
wasps are so small that several thousand may develop in each cater-
pillar, but as a rule only one matures. Often a collection of chrysa-
lids or cocoons will yield large numbers of these parasitic wasps and
flies instead of the butterflies and moths that were expected.

Figure 8.—Cocoons of the wasp Apanteles congregatus L. upon the tobacco hornworm.
Natural size.

Among those parasites that develop in considerable numbers in one
host is a group which has the remarkable habit of producing many
individuals from one egg. A single egg is laid in the host egg, but
development is delayed until the latter hatches and the larva begins
to feed and grow; then the parasite egg grows and divides repeat-
edly, and finally may give rise to hundreds of individuals. Instances
are known of several thousand minute wasps developing in this way
in a single caterpillar.

PARASITES OF WHITE GRUBS

The white grubs found so commonly in the soil and which feed
upon the roots of grasses and cultivated crops are the larvae of
beetles known as “June bugs”, “May beetles”, etc. When these

14 CIRCULAR 346, U. S. DEPARTMENT OF AGRICULTURE

grubs are exposed by plowing during the summer months they are
often found to bear larvae of some other insect attached to the body,
or the soil cells which they had occupied contain instead brownish-
colored, oval cocoons measuring from one-half to 1 inch in length.
Only the head and a portion of the skin remain to identify the origi-
nal occupant. The insect responsible for the death of the grubs is
one of the digger wasps, so called because of their habit of digging
burrows in the ground or wood to make nests for their young, or in
search of prey. |

As typical of this group Tiphia popilliavora Roh. (fig. 9), which
attacks the grubs of the Japanese beetle (Popillia japonica Newm.).

FIGURE 9.—The adult female of the black digger wasp Tiphia popilliavora. x 6.

may be mentioned. This wasp is jet black, with dusky wings, and
measures about two-thirds of an inch in length. It appears in the
field late in August and in September, and may be found feeding
upon the blossoms of wild carrot, smartweed, and other plants.
When the time for egg laying arrives, the female enters the soil in
search of grubs, and when one is found it is stung until completely
paralyzed and the egg is then laid on the underside of the body.
The grub recovers its powers of movement within about half an
hour and resumes feeding. The young wasp larva, immediately after
hatching, makes a feeding puncture through the skin of the grub
and sucks out the body juices. This feeding continues for 2 weeks or
more, and during this time the white parasite larva may be seen
lying across the abdomen of the grub (fig, 10,2). The beetle grub

INSECT PARASITES AND PREDATORS OF INSECT PESTS iS:

gradually becomes weakened by the feeding of the parasite and
finally dies.

Other species of this group may emerge during the spring months,
and the adults feed upon the honeydew secreted by aphids and
various other insects. Some species, such as the banded digger wasp
(Elis quinquecincta Fab.), paralyze their prey permanently, but
these seemingly lifeless grubs are seldom encountered, because the
parasite female usually buries the grub to a depth of 1 or 2 feet or
more before laying the egg upon it. Grubs parasitized by Tiphia,
and the cocoons which are formed later. are usually found near the
surface of the soil.

In addition to the wasps mentioned above, a number of parasitic
flies attack white grubs. The young maggots are deposited upon
the surface of the ground; they then penetrate the soil in search of
grubs upon which they may develop. When such a grub is found,

FicurE 10.—Two parasites of white grubs: A, A maggot of the fly Prosena sibirita com-
pleting feeding upon a grub; in its earlier stages it fed within the body of the living
grub. B, A half-grown larva of the black digger wasp, Tiphia popilliavora, feeding upon
a Japanese beetle grub. A, X 4; B, X 3.

the maggot enters the body and feeds upon the juices. The adult
flies are found in the field during midsummer. Typical of this
group are Microphthalma disjuncta Wied., which attacks the com-
mon white grubs infesting field and pasture lands in the Middle
West, and Prosena sibirita (Fab.) (fig. 10, 4), which attacks the
grubs of the Japanese beetle.

EGG PARASITES

Large numbers of insect eggs are destroyed by minute parasites
which develop in them, and some of these egg parasites are so small
that nearly 100 may reach maturity in each of the eggs of the larger
moths. The adult wasps of these species may measure only one
twenty-fifth of an inch or less in length.

The best known of the species which confine themselves entirely
to insect eggs is Trichogramma minutum Riley (fig. 11), which is
usually yellowish in the South, nearly black when found in the

16 CIRCULAR 346, U. S. DEPARTMENT OF AGRICULTURE

northern regions, and has large red eyes. This parasite is known
to attack the eggs of more than 150 species of insects, including
those of leaf hoppers, sawflies, butterflies, and moths.

The female 7richogramma wanders about upon the foliage in
search of eggs which she may attack. When these are found, she
climbs upon each one in turn, inserts the sting through the shell, and

‘\ \\

Www

\

NS

Sy

FIGURE 11.—Trichogramma minutum, a parasite of insect eggs: A, A female stinging
a moth egg and placing its own egg within it: B, a cluster of eggs, of which about
half have been parasitized and show the Trichogramma emergence holes. A, X 85.

deposits an egg within it. The development of the larva is very
rapid under summer conditions, and the entire life cycle may be
completed in 1 week. It is thus seen that an exceedingly rapid in-
crease in numbers is possible. During the summer and early fall
months more than 90 percent of the eggs of many species of insects
may be destroyed by this parasite, and consequently it plays an im-
portant part in holding various pests in check.

INSECT PARASITES AND PREDATORS OF INSECT PESTS 17

In recent years efforts have been made to extend the usefulness
of this parasite by rearing the species in enormous numbers upon
grain moth eggs and lberating them in the infested fields and
orchards early in the season. This has been tried on a number of
important pests of field crops and orchard trees, but the results thus
far have not been conclusive. This work is still in the experimental
stage, and at present it is not recommended to growers as a field
practice.

In addition to 7richogramma, many other species of minute wasps
parasitize the eggs of moths, butterflies, beetles, and plant bugs.
Two species, which attack the eggs of the gypsy moth, have been

Ficurn 12.—A, Several species of ground beetles of the genus Calosoma, about natural
= size; B, a typical ground beetle larva, enlarged about three times.

imported from Japan and one of them also from Europe, and are
now well established in this country. |

GENERAL INSECT FEEDERS

There is a wide variety of insects which, in either the larval or adult
stage, have the habit of feeding upon such soft-bodied insects as they
may encounter. Among these are the ground beetles, the tiger beetles,
the robber flies, and a number of common plant bugs.

The ground beetles of the family Carabidae (fig. 12) and their
larvae feed upon many kinds of insects. The adult beetles are found
mainly upon the surface of the ground, though some climb trees;
the larvae are generally found either in the soil or beneath rubbish,
but a few of these also climb trees in search of their prey.

18 CIRCULAR 346, U. S. DEPARTMENT OF AGRICULTURE

The green Calosoma (C. sycophanta L.), which attacks the gypsy
moth, the brown-tail moth, and others is of considerable importance
in checking these pests. This species was imported from Europe in
1905-10 and is now found in practically all sections infested by the
gypsy moth. The eggs are laid singly in the soil, and the larvae, im-
mediately after hatching , begin their search for food, which consists
largely of the caterpillars and pupae of butterflies and moths. These
may be found on the surface of the ground or in rubbish, or it may
be necessary for the Calosoma larvae to climb trees and bushes to
find them. WwW hen the prey is found it is seized between the mandibles,
a hole is cut in the skin, and the body juices and other materials are

eaten. A total of 40 or more full-grown gypsy moth larvae may be
consumed by a Calosoma larva during its period of development,
which covers from 2 to 4 weeks. The adult beetles feed largely upon
caterpillars and consequently spend considerable time in the trees.
The beetle spends the winter in a cell in the soil, and its life may
extend over more than 2 years.

Ficur® 13.—Orius insidiosus, a predacious flower bug: A, Nymph, X< 50; B, adult, X 15.

The tiger beetles (Cicindelidae) are usually found in dry and sandy
places. Their larvae build funnel-shaped pits in the soil and lurk
therein while awaiting their prey. They will eat almost any insect
that has the misfortune to come within reach of their formidable
mandibles.

While a majority of bugs, such as the harlequin bug (J/urgantia
histrionica Hahn), are plant feeders and consequently i injurious, some
species are of real value because of the number of plant- feeding i in-
sects which they destroy. There are a considerable number of com-
mon bugs, such as the assassin bugs (Reduviidae), the flower bugs
(Anthocoridae), the ambush bugs (Phymatidae), and some of the
stinkbugs (Pentatomidae), which feed extensively upon the eggs,
larvae, and adults of various insects, and they are often of consider-
able value in reducing infestations. The common flower bug (7 riph-
leps) Orius insidiosus (Say) (fig. 13) occurs throughout the United
States and feeds largely upon other insects. It has been recorded
as attacking the eggs and larvae of the corn ear worm (Heliothis
obsoleta Fab.) and is said to be one of the most important of the

INSECT PARASITES AND PREDATORS OF INSECT PESTS 19

natural enemies of that insect. This bug is also known as an impor-
tant enemy of the European red mite (Lar atetranychus pilosus C.
and F.) upon fruit trees, the common red spider (Tetranychus bi-
maculatus Harv.) on cotton, hops, and citrus, and of various species
of thrips. Aside from its insect- feeding habits it has been associated
with the transmission of certain diseases of corn.

Various bugs may at times be found with the beak imbedded in the
body of a caterpillar, from which they suck out the body juices. Some
of these species confine themselves to insect food while others may
subsist upon a mixed diet of insect and plant juices.

FiegurRn 14.—E#raz lateralis Macq., a robber fly: A, The adult fiy; B, the pupa; C, the
active larval form. xX 3.

The robber flies (fig. 14), which belong to the family Asilidae, feed
very extensively upon a wide variety of insects. Many of them are
large, powerful flies, capable of capturing beetles, flies, and other
insects while in flight. After seizing their prey they insert the beak
into the body and suck out the juices. The larvae of these flies live
in the soil and feed upon white grubs and other soft-bodied insects.
In appearance the larvae have a considerable resemblance to the wire-
worms that feed upon the roots of plants.

The praying mantids are large, conspicuous insects which attract
much attention because of the striking manner in which the front legs
are held while awaiting prey, The forelegs are long and armed w ith

20 CIRCULAR 346, U. S. DEPARTMENT OF AGRICULTURE

rows of teeth, by means of which the prey is grasped. In the waiting
position these legs are held raised and folded and give the appearance
of an attitude of prayer. The native species (Phasmomantis' caro-
lina Joh.) illustrated in figure 15, occurs commonly in the southeast-
ern part of the United States.

Two species are now becoming increasingly common in the North-.
eastern States, these being the Chinese mantis (Paratenodera sinensis
Sauss.), accidentally introduced from Japan about 1896, and the
European praying mantis (A/antis religiosa L.), likewise accidentally
introduced into this country about 1899.

FIGURE 15.—A partly grown praying mantid, Phasmomantis carolina, in the typical
waiting position upon a twig. About natural size.

The various species of mantids feed on a wide variety of insects, in-
cluding beetles, flies, aphids, and almost any others that come within
reach. They normally frequent flowers in search for food, and conse-
quently the flower-feeding insects comprise a large portion of their
prey. Studies have been made of the food habits of the Chinese
mantis, and these show that, while a great many injurious insects
are eaten, the insect most commonly captured is the honeybee. To
this extent, at least, the mantids may be considered as injurious rather
than beneficial.

The eggs are laid in large masses upon twigs of trees and upon
briers and grasses. They are covered with a mass of frothy material
which hardens to form a tough, protective covering. ‘These masses
are conspicuous and are often seen during the winter.

INSECT PARASITES AND PREDATORS OF INSECT PESTS 21

HY PERPARASITES

The term “ hyperparasite ” is applied to that group of insects which
attack the true parasites themselves rather than the insect species
which cause injury to crops. ‘They are thus injurious rather than
beneficial. As has already been stated, practically every injurious
insect has one or more primary par asites. Likewise these latter also
have their enemies which attack them. In nature this usually brings
about a balanced condition in which both the pest itself and the para-
sites which attack it are able to exist, but neither becomes over-
abundant.

Lf a cluster of cocoons of A panteles spun by larvae that have devel-
oped in the cabbage worm, the tobacco hornworm, the gypsy moth, or
any other of the numerous victims of this eroup of parasites, is set
aside for emergence it will often be found that a variety of minute
wasps rather than a single species will emerge from them. These are
the enemies of Apanteles, which have attacked the larvae in the co-
coons. From the puparia of the various fly parasites of caterpillars,
from those of hover flies, and from lacewing cocoons, wasps will often
emerge instead of the insects expected. There is thus revealed a
complicated relationship among the insects themselves which results
in a balance under natural conditions. This, however, is often upset
by the changes brought about by man. Instead of a varied vegeta-
tion, large tracts of land are brought into cultivation and devoted to
a single crop, frequently one which is new to the country. The result-
ing conditions have a marked effect upon the insect life of that section
and often result in disastrous outbreaks,

ORGANIZATION OF THE UNITED STATES DEPARTMENT OF AGRICULTURE
WHEN THIS PUBLICATION WAS LAST PRINTED

Secretary 07 AQriculinre—— = = Henry A. WALLACE.

Onder: SCOnetOl p= 2 Eee eee REx¥ForD G. TUGWELL.
ASSISLONT SCORER Meee as ae ee ees M. L. WILson.

Director of Hatension Work___ = C. W. WARBURTON.

Director of Personnel == a Se eee W. W. STOCKBERGER.

DiveClOrs Of LIN, ORMNCHOnN Se eee ee M. 8S. EISENHOWER.

DAT CCEOTZO[ BEAN ONE Ce a a eee ee W. A. JUMP.

SOM CULO ae NAL ENE Nel LE. aces i eee eae SETH THOMAS.

Agricultural Adjustment Administration_____ CHESTER C. Davis, Administrator.
Bureau of Agricultural Economics___--~___~ Nits A. OLSEN, Chief.

Bureau of Agricultural Engineering______-_~ S. H. McCrory, Chief.

Bureau of Animal Indusiry_____________-__- JOHN R. MOHLER, Chief.
Bureau of Biologicat Survey________________ J. N. DARwine, Chief.

Bureau of Chemistry and Soils____________- H. G. Knicut, Chief.

Office of Cooperative Extension Work______- C. B. SmirH, Chief.

Bureau of Dairy Indusiry_ ee O. E. Rep, Chief.

Bureau of Entomology and Plant Quarantine. LEE A. Strone, Chief.

Office of Haperiment Siations_______________ JAMES T. JARDINE, Chief.
Food and Drug Administration__________--_ WALTER G. CAMPBELL, Chief.

TH ORCSEISCIUCG SIS es Se et eee FERDINAND A. Sitcox, Chief.
Grain Futures Administration ______________ J. W. T. Duvet, Chief,

Bureau of Home EHconomics________--__--_- LovuIsE STANLEY, Chief.
ERGOT OT Y SEU oes BS Te ae a ee ee CLARIBEL R. BARNETT, Librarian.
bureau. of, Pleontindustry Se FREDERIOK D. RIcHEy, Chief.
Bureau of -Publie Roads - ss a eee THoMAS H. MacDonaxp, Chief.
WGeCihich ab uC Se eee ee ee ee WILLIS R, GREGG, Chief.

This circular is a contribution from

Bureau of Entomology and Plant Quarantine. Len A. Strone, Chief.
Division of Foreign PardsiteIntroduction_ C. P. CLAUSEN, Senior Entomolo-
gist, in Charge.
22

U.S. GOVERNMENT PRINTING OFFICE: 1935

For sale by the Superintendent cf Documents, Washington, D. C. - - - - - - Price 5 cents