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]

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.