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 cuc.u.mber 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 c.o.c.k-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 sh.e.l.l 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 a.s.sail 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 princ.i.p.ally 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 larvae 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 cla.s.s 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 quant.i.ties 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 cla.s.s 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 larvae 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 gra.s.shoppers 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 larvae perish for want of food.
The best known means of getting rid of gra.s.shoppers is to destroy the eggs. This should be done by plowing and harrowing all roadsides, ditch banks, uncultivated fields and gra.s.sy 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 pa.s.ses 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 gra.s.shoppers, 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 quant.i.ties in gardens by mixing one-half teaspoonful to a gallon of water, or in large quant.i.ties with one pound to one hundred and fifty or two hundred gallons of water.
White h.e.l.lebore 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 quant.i.ty 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 quant.i.ties 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.