INSECTS
If we look at a watch, we see that one wheel can not move until the one
next in order to it moves, and that, in turn, must be set in motion by
another wheel. In the same way nature adjusts itself in its various
parts. Before man enters a region, the balance is perfect. Plants crowd
each other out of the way, the weaker giving place to the stronger; then
insects come to destroy them. These insects are destroyed by birds,
small mammals or other insects. The birds are killed by animals and
other birds, which in turn are the food of larger animals. And so
through all nature runs this law of balance; nothing increases in too
great a proportion.
But when man comes, he thinks only of his own needs and wishes and
begins at once to upset the delicate balance. Year after year, he plants
large fields of a single crop, and, calling other plants weeds, because
they hinder the growth of his grain, he drives them out entirely. The
insects that feed on these plants, finding no food, soon disappear,
while the ones which feed on the farmers' crops, finding food so
plentiful, are able to increase in great numbers. They increase all the
more rapidly because man, not knowing or not caring to know who his real
helpers are, has killed and driven away the birds that would feed on
them.
In order to readjust matters, he must learn how to destroy the insects,
or he can not have crops. Both the plant enemies, the weeds, and the
insects are always trying to bring about nature's balance again by
driving out the over-abundant field crop, so he must constantly fight
them in order to secure his harvest.
In no country is more harm done by insects than in the United States.
The losses to live stock and to plants, both growing and stored,
resulting from insects are greater than all the expenses of the National
Government, including the pension roll and the yearly maintenance of the
army and navy.
Immense as is the value of our farm products, it would be much greater
if it were not for the work of these insects. Careful calculations
indicate that this loss will amount to not less than the enormous sum of
$1,100,000,000 annually and probably far more. The loss is usually
estimated at ten per cent. of the crop, but often is much heavier than
this, and many indirect losses are not taken into account in this table,
though we shall speak of them later.
Most insects pass through four stages: (1) the egg; (2) the worm or
larvæ; (3) the chrysalis, cocoon, or pupa; (4) the full-grown insect or
imago. Butterflies, moths and beetles are examples of insects in this
last stage.
As eggs, they are, of course, harmless, and during the chrysalis state
they lie perfectly inactive and are harmless, but many of them are very
destructive when they are worms or larvæ, others do most injury in the
full-grown state.
The insects that man has most reason to dread are: (1) Plant-lice, tiny
insects with soft bodies, usually green. They attach themselves to the
stems and leaves of plants and suck their juices, leaving them to wilt
and die. They are found on many kinds of plants--on corn, wheat and
other grains. They also flourish on garden vegetables and flowers.
(2) Scale insects. These are flat and appear to be only a scale on the
stem or fruit. They are usually covered with a hard crust-like covering
and are found on trees and bushes. They are usually the color of the
bark on which they are found.
(3) Worms and caterpillars are soft-bodied, the bodies being in
segments, and either smooth or covered with short bristly hair. They
spend nearly all their time in eating, and do immense damage to the
foliage of trees and vegetables and to fruit. The adult is a moth or
caterpillar. This class is among the farmer's worst insect enemies.
(4) Borers attack trees and tough-stemmed plants. The eggs are laid on
the stems, and after hatching, the larvæ bore into the stem or under the
bark, causing the foliage to wilt and die. We are all familiar with what
we call "worm-eaten" wood, with canals that have been eaten by these
borers running through it in all directions. This completely ruins some
of the best forest trees for lumber, and makes one of the greatest
losses of the forests.
(5) Beetles are insects in the adult state. They have hard, shiny
wing-covers. Many of the borers are beetles, and there are other
varieties which do great damage, though other kinds are useful to man in
destroying harmful insects.
(6) Bugs have their mouth parts prolonged into a sharp beak with which
they puncture the skin or bark, instead of chewing the leaves, as do
beetles. Flies, gnats, and other similar insects do not usually injure
vegetation so much as do some other classes of insects, the principal
damage being done to fruits; but they have been found to be the cause of
some of the most serious diseases in both man and the lower animals.
The Department of Agriculture divides the injuries done by insects into
classes according to the products injured, and in the list they place
first the injury done to cereal crops.
The insects which damage the corn crop most seriously are the corn-root
worm, which feeds on the roots of young corn, causing it to fall over
and die, and which sometimes takes the whole corn crop of a large
region. The next most important is the boll-worm or ear-worm. Most
persons have seen this worm in the ears of sweet corn; ninety ears out
of every hundred contain a worm which destroys from one-tenth to
one-half the corn. Some years every ear in large regions is infested. In
the South the field corn is attacked as badly as the sweet corn, but in
the great corn states the injury is much less. Even here, however, the
total loss is very great.
Almost equally important is the damage wrought by the chinch-bug, which
is also one of the greatest pests in wheat and oats.
Every year in different sections of the country, bill-bugs, wire-worms,
cutworms, cornstalk borers, locusts, grasshoppers, corn plant-lice and
other insects, destroy millions of bushels of corn.
Of the cereal crops, wheat suffers most from insects. Of the large
number of insects that attack wheat, the three important species are the
Hessian fly, the chinch-bug and the grain plant-louse or green-bug.
The Hessian fly has been known to destroy as much as sixty per cent. of
all the wheat acreage of a state. Fortunately, this damage is done early
in the year, so that when whole fields are destroyed they can be
replanted with other crops and only the cost of seed and labor is to be
counted as a loss. But more often the field is only partly destroyed by
the fly; it is not necessary to replant, but the yield is small, often
not more than one-third. Some years the loss from the Hessian fly is
very heavy, at other times comparatively light, yet there are few years
when the loss is less than ten per cent. of the total crop from this
insect alone,--which meant last year a loss of 72,500,000 bushels.
The chinch-bug is responsible for the loss of five per cent., or one
bushel out of every twenty. It attacks the straw, causing the heads of
wheat to fall over and wither away.
The injury done by the green-bug comes just as the wheat begins to
ripen, the tiny green creatures attaching themselves in great numbers to
the heads of the wheat. Other insects which prey on the wheat crop are
grasshoppers, the wheat midge, cutworms and army-worms.
If it were not for the attacks of these various pests the wheat crop
would be at least one-fifth larger than it is. Instead of 725,000,000
bushels, it would be 870,000,000; which, with wheat at a dollar a
bushel, amounts to a loss of nearly $150,000,000. Further, the world
loses all this valuable bread-stuff.
Oats, rye and barley suffer far less than wheat from insect ravages but
they are all attacked by the same insects, and on the whole, much damage
is done to them each year.
Hay, clover, and alfalfa have their enemies which destroy a considerable
part of the crops. The locusts and caterpillars, the army-worms and
cutworms are the best known, but the tiny leaf-hoppers, which spring up
at every step as we walk across the path or lawn, and the web-worms and
grass-worms and grubs which work about the roots of the plants all do
their part in lowering the production.
The principal insect enemies of cotton are the cotton boll-weevil, the
boll-worm, the cotton red spider, and the cotton-leaf worm. The control
of the boll-weevil is considered one of the most serious problems
confronting the agricultural men of the country. In the first years
after its introduction, it reduced the cotton crop fully fifty per
cent., and was the cause, not only of serious loss to the farmers, but
of the closing of the cotton mills in New England, of a scarcity of
cotton cloth and a decided rise in its price. The boll-weevil is a
beetle about a quarter of an inch in length. This little beetle eats
into the heart of each boll, which soon falls to the ground.
The cotton-leaf worm formerly caused heavy damage, as much as
$20,000,000 to $30,000,000 a year, but the loss has been greatly reduced
by the war which farmers have waged against it. It is still estimated at
from $5,000,000 to $10,000,000.
The boll-worm is chiefly destructive in the Southwest and does damage to
the extent of $12,000,000.
All in all no article of commerce is more seriously affected by insect
ravages than cotton, on account of its necessity, and the fact that it
can be raised only in certain regions.
Tobacco is one of the principal crops in several states and it suffers
heavily from insect damage. The large, showy tobacco-worm and the tiny
tobacco-thrips cause serious injury to the leaves.
Sugar-cane has its insect enemies which take on an average one stalk out
of every ten raised in this country, and reduce the crop in the same
proportion.
The cranberry is another valuable commercial plant that has been greatly
affected by an insect known as the cranberry fruit worm, but by
spraying, growers have been able to reduce the damage from sixty per
cent. down to fourteen per cent.
Garden vegetables suffer more than anything else from insects. Potatoes
are attacked by two species of insects, both destructive unless held in
check. One is the reddish brown blister-beetle. The eggs are laid on the
ground, and do not become adult insects until the second year. The other
is the striped Colorado beetle, the eggs of which are laid on the under
side of the leaves, and develop into adults in a short time. Two broods
of this beetle develop in a single season. Thus it may be seen that the
two are entirely different, though they are often supposed to be the
same. The Colorado beetle, by the immense damage it was doing to a
necessary food crop, first led to a regular method of fighting insects
in this country. This potato-bug is not feared as it was in the past,
since farmers have learned to control it in a great measure, but they
have only been able to lessen the evil, never to drive it out
completely.
Other insects that destroy garden vegetables are the well-known green
cabbage-worm, the harlequin cabbage-bug, the cabbage hairworm, the
asparagus-beetle, the squash-bug, the squash-vine borer, the striped
cucumber or melon beetle, the melon aphis, the corn boll-worm, the
cornstalk borer and many others.
In addition to these insects that attack special plants, all vegetables
are preyed on by the grub-worm, the cutworm, the aphis and various tiny
hoppers.
The grub-worms which work about the roots of plants are, in the adult
state, the June-bugs or cock-chafers which fly about our lights in the
spring and early summer, and which themselves do considerable damage by
eating leaves of trees and bushes.
Orchards and small fruits suffer heavily from insect pests, both on
account of the direct loss and on account of the expensive treatment.
There are several hundred insects which ravage fruit trees, attacking
the roots, trunk, foliage and fruit.
Among these are the scales, of which there are many species, but of
which the most widely known and dreaded is the San Jose scale, so called
because San Jose, California, was its starting place in America. It is
the only one of the scales which, if not checked, will, in two or three
years, completely destroy the tree on which it feeds. It attacks the
citrus fruits, orange, lemon, grape-fruit, and the apple, pear, and
peach as well as small fruits, particularly currants.
Among the many varieties that do serious damage are the black olive
scale, plum scale, hickory scale, locust scale, frosted black scale, red
oak scale, the cottony maple scale, greedy scale and oyster shell
scale.
The woolly aphis injures the roots of our fruit trees; the trunk and
limb borers, the peach tree borer, the apple borer, all stand ready to
assail the life of the entire tree. The various leaf worms attack the
life of the tree also. The grape-leaf skeletonizer eats every particle
of green from the leaves, leaving only the veins. The canker-worms and
the destructive tent-caterpillars also cause the death of many fruit
trees.
Of insects which attack the fruit, the list is long. The codling-moth of
the apple causes a greater money loss than any other enemy of fruits.
Various estimates of the loss have been made, and in general it is
believed that it causes the loss of one-fourth to one-half of the apple
crop of the United States each year.
The plum-curculio attacks nearly all stone fruits. Its natural food
plant is probably the native wild plum, and the plum continues to be its
favorite food, consequently this fruit suffers most from the attacks of
the insect. In years of short crops very little fruit remains on the
tree to ripen. But peaches, apricots and cherries also suffer heavily,
and apples and pears in a less degree.
The insects which injure the hardwood forest trees are principally the
leaf-eaters, such as the gypsy and brown tail moths, which have almost
stripped the New England shade trees, and done great damage to the
forests; the elm leaf beetles and the numerous borers, both beetles and
grubs, which from eggs laid in or just beneath the bark, hatch into
larvæ which burrow into the wood, destroying its usefulness for lumber.
Among the borers which do most injury in destroying valuable timber are
the hickory-bark beetle, the bark-boring grubs which kill oak, chestnut,
birch and poplar trees, the locust borer, the chestnut timber-worm and
the Columbian timber beetle.
All these represent the loss from insects to the growing product; but
when it is stored, there is seemingly no less danger of attack by a
different class of insects. These include grain weevils and beetles,
flour-moths, the small fruit and vinegar flies, buffalo-moths and dozens
of others.
After these comes the loss to man and animals from insects. The cattle
tick alone, through the dreaded Texas fever, causes a loss of from
$10,000,000 to $35,000,000 in various years. The ox warble also preys on
cattle and causes a loss of probably $3,000,000 more. The buffalo-gnats,
gadflies, and other flies do on the whole a large amount of damage each
year.
Man has only discovered in recent years how serious a factor in his own
health as well as comfort, is the insect life about him. This subject is
more fully treated under the subject of health, so for the present we
need only say that flies, mosquitos and other insects are supposed to
cause some of our most serious diseases, and to be the indirect cause of
the loss of hundreds of millions of dollars and many human lives each
year.
Having thus summed up the damage done by insects, let us see what may be
done to prevent their spread and if possible drive out the most harmful
species entirely. Unfortunately, that seems almost impossible; so far
all man's efforts have only resulted in saving a larger or smaller
proportion of the various crops each year.
In insect control we turn first to the natural means of destruction.
Chief among these means are birds,--of which we will speak in another
chapter,--snakes and toads.
Toads live entirely on insects and catch large quantities of them. It is
estimated that a single toad is worth almost twenty dollars a year in a
field or garden. English gardeners are said to pay high prices for them
and to keep as many as possible in their gardens. Toads will eat almost
any kind of insect, are absolutely harmless, and should be carefully
protected.
There is one class of insects which, so far from being an enemy to man,
combines with him to kill the harmful insects. Among these are the black
beetles which feed on cutworms and other larvæ which injure the roots
of plants. Lady-bird beetles destroy large numbers of plant-lice, and
the Asiatic lady-bird has been found to be the natural destroyer of the
San Jose scale. These little insects are now being hatched in this
country, and it is hoped through them to stamp out the pest. A number of
larger insects prey on the smaller ones.
Other insects, such as the Hessian fly, the green-bug or spring grain
aphis, the army-worm and various species of grasshoppers are killed by
tiny parasitic insects whose eggs are laid in the bodies of the larger
insects, but which, after being hatched, feed on them.
To these natural methods of control man has added others. Cultivation is
one of these methods. As insects flourish when given an unusually large
amount of food of a particular kind, and starve when that food is taken
away from them, so rotation of crops proves to be one of the best means
of getting rid of those insects which can not travel far for their food.
Farmers who practise rotation of crops are much less troubled with
insects that injure the roots of plants than those who do not.
One of the best means of preventing damage from the Hessian fly is to
sow a narrow strip of wheat all around the edges of the field several
weeks before the main crop is to be sowed. The flies will gather in
this strip and lay all their eggs in the early wheat. Just before the
main crop is sowed, the narrow strip is plowed up and thoroughly
harrowed and the larvæ perish for want of food.
The best known means of getting rid of grasshoppers is to destroy the
eggs. This should be done by plowing and harrowing all roadsides, ditch
banks, uncultivated fields and grassy margins around fields in the fall
or winter.
Fall harrowing and deep spring plowing will prevent many of the bugs and
beetles which spend the larval state in the ground from hatching. This
method will also destroy the plum-curculio in orchards.
In attempting to control the boll-weevil of the cotton fields, it has
been found that the best method to pursue is the simple one of planting
the crop very early, so that the cotton passes the danger stage before
the insects emerge, and removing all the plants in the fall.
Worms that infest fruit can be checked for the following year by fall
plowing in the orchard and by destroying the decayed fruit as it falls.
The farmer who lets his decayed fruit lie on the ground is preparing for
a heavy crop of insects to eat his fruit the following summer.
Fruit and forest trees are both protected by a burlap band or a band of
"sticky" fly-paper placed around the tree, to prevent insects from
crawling up.
The use of poison in destroying insects is now the one most generally
and successfully employed by farmers and fruit growers.
Poisons may be liquid or dry. The liquid is made by mixing with water,
and for large plants and trees is put on with a spray or force-pump that
carries the poison to every part of the plant.
Some insects, such as beetles, caterpillars and grasshoppers, chew the
leaves or stems of plants, and the poison may be applied to their food;
but others, such as plant-lice, scale insects and all bugs suck the
juice, usually from the stem or bark. Poisons must be applied to the
insect itself to be effectual in this case.
These are some of the insect poisons most in use:
Paris green, which will kill all insects that chew the leaves, may be
used in small quantities in gardens by mixing one-half teaspoonful to a
gallon of water, or in large quantities with one pound to one hundred
and fifty or two hundred gallons of water.
White hellebore is used to destroy currant worms and is usually dusted
on dry.
Pyrethrum is used as a spray, mixing one ounce to two gallons of water,
to destroy cabbage-worms and many other garden insects. If the dry
pyrethrum powder is blown from a bellows into a tightly closed room, it
is said to destroy all the flies.
Bordeaux mixture is made by dissolving four pounds of copper sulphate in
hot water and mixing with an equal quantity of a solution made by mixing
four pounds of lime with water. This is then mixed with fifty gallons of
water. Paris green is sometimes added. This mixture is largely used in
orchards and for destroying insects on a large scale. It is also useful
for curing diseases of plants.
An excellent spray for orchards both for removing fungous diseases and
scale insects is a home-made lime-and-sulphur solution. Enough for
spraying a large orchard is prepared as follows:
Add three gallons of boiling water to fifteen pounds of lime. Then add
ten pounds of sulphur and three gallons more of hot water. Allow this to
boil about twenty minutes in its own heat, then add enough water to make
fifty gallons of the mixture. Dilute with water in the proportion of one
part of the solution to seventy-five of water.
Small quantities are made by using a fractional part of this recipe.
Whale-oil soap dissolved in water and used as a spray is an effective
remedy for the San Jose scale.
Kerosene emulsion is used to kill the insects which suck the juices of
plants and trees. It is made by mixing a half-pound of hard soap with
one gallon of hot water and stirring into it, so as to mix thoroughly,
two gallons of kerosene oil. This may be kept on hand for use, and is
mixed with ten parts of water to one of the emulsion.
For use in large orchards force-pumps operated by compressed air and
drawn by two horses are used. The spraying should be done as soon as the
blossoms drop, and many orchards are sprayed three times in a season,
but the work should never be done while the trees are in blossom.
Vegetables should be sprayed many times through the season.
A careful study of these methods of control, adapted to the various
plants and the insects which prey on them, with the natural enemies of
insects encouraged and protected, would go far to prevent the
wide-spread and serious damage now affecting our crops, our vegetables,
our orchards, and our forests.
REFERENCES
Circulars of the Bureau of Entomology. Dept. of Agriculture. List
furnished on application.
Annual Loss Occasioned by Destructive Insects. Yearbook 1904.[C]
[Footnote C: Some of the Yearbooks of the Dept. of Agriculture contain
very instructive reports on Insects and on Birds. Reprints on various
subjects have been made from them which are available in pamphlet form,
or the entire Yearbook may be had in many cases.]
Value of Insect Parasitism to the American Farmer. Yearbook 1907.
House Flies. Dept. of Agriculture. Bulletin 71.
The Grasshopper Problem. Bulletin 84.
The Boll-Weevil Problem. Bulletin 344.
The Most Important Step in the Control of the Boll-Weevil. Bulletin 95.
The San Jose Scale. Yearbook 1902.
The Plum-Curculio. Bulletin 73.
The Apple Codling-Moth. Bulletin 41. Price 20c.
The Gipsy Moth and How to Control It. Bulletin 275.
The Brown-tail Moth and How to Control It. Bulletin 264.
The Spring Grain Aphis or Green-Bug. Bulletin 93.
The Army-Worm. Bulletin 4.
The Hessian Fly. Bulletin 70.
The Chinch-Bug. Bulletin 17.
The Principal Household Insects of the U. S. Bulletin 4.
Insects Affecting Domestic Animals. Bulletin 5.