Agriculture for Beginners by Daniel Harvey Hill (top ten ebook reader TXT) 📖
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Fig. 139. The House Fly
a, egg;
b, larva, or maggot;
c, pupa;
(All enlarged)
Fig. 139a. The House Fly
adult male. (Enlarged)
The chief classes of insects are as follows: the flies, with two wings only; the bees, wasps, and ants, with four delicate wings; the beetles, with four wings—two hard, horny ones covering the two more delicate ones. When the beetle is at rest its two hard wings meet in a straight line down the back. This peculiarity distinguishes it from the true bug, which has four wings. The two outer wings are partly horny, and in folding lap over each other. Butterflies and moths are much alike in appearance but differ in habit. The butterfly works by day and the moth by night. Note the knob on the end of the butterfly's feeler (Fig. 143). The moth has no such knob.
Fig. 140. A Typical Bug
a, adult;
b, side view of sucking
mouth-part Both a and b
are much enlarged
It is important to know how insects take their food, for by knowing this we are often able to destroy insect pests. Some are provided with mouth parts for chewing their food; others have a long tube with which they pierce plants or animals and, like the mosquito, suck their food from the inside. Insects of this latter class cannot of course be harmed by poison on the surface of the leaves on which they feed.
Fig. 141. Beetle
a, larva;
b, pupa;
c, adult;
d, burrow
Many insects change their form from youth to old age so much that you can scarcely recognize them as the same creatures. First comes the egg. The egg hatches into a worm-like animal known as a grub, maggot, or caterpillar, or, as scientists call it, a larva. This creature feeds and grows until finally it settles down and spins a home of silk, called a cocoon (Fig. 145). If we open the cocoon we shall find that the animal is now covered with a hard outside skeleton, that it cannot move freely, and that it cannot eat at all. The animal in this state is known as the pupa (Figs. 145 and 146). Sometimes, however, the pupa is not covered by a cocoon, sometimes it is soft, and sometimes it has some power of motion (Fig. 141). After a rest in the pupa stage the animal comes out a mature insect (Figs. 142 and 143).
From this you can see that it is especially important to know all you can about the life of injurious insects, since it is often easier to kill these pests at one stage of their life than at another. Often it is better to aim at destroying the seemingly harmless beetle or butterfly than to try to destroy the larvæ that hatch from its eggs, although, as you must remember, it is generally the larvæ that do the most harm. Larvæ grow very rapidly; therefore the food supply must be great to meet the needs of the insect.
Fig. 142. Moth and Cocoon
Some insects, the grasshopper for example, do not completely change their form. Fig. 147 represents some young grasshoppers, which very closely resemble their parents.
Fig. 143. Butterfly
Fig. 144. Structure of the Caterpillar
Fig. 145. Moth Pupa in Cocoon
Fig. 146. A Butterfly Pupa
Note outline of the butterfly
Fig. 147. The Growth of a Grasshopper
Insects lay many eggs and reproduce with remarkable rapidity. Their number therefore makes them a foe to be much dreaded. The queen honeybee often lays as many as 4000 eggs in twenty-four hours. A single house fly lays between 100 and 150 eggs in one day. The mosquito lays eggs in quantities of from 200 to 400. The white ant often lays 80,000 in a day, and so continues for two years, probably laying no less than 40,000,000 eggs. In one summer the bluebottle fly could have 500,000,000 descendants if they all lived. The plant louse, at the end of the fifth brood, has laid in a single year enough eggs to produce 300,000,000 young. Of course every one knows that, owing to enemies and diseases (for the insects have enemies which prey on them just as they prey on plants) comparatively few of the insects hatched from these eggs live till they are grown.
The number of insects which are hurtful to crops, gardens, flowers, and forests seems to be increasing each season. Therefore farm boys and girls should learn to recognize these harmful insects and to know how they live and how they may be destroyed. Those who know the forms and habits of these enemies of plants and trees are far better prepared to fight them than are those who strike in the dark. Moreover such knowledge is always a source of interest and pleasure. If you begin to study insects, you will soon find your love for the study growing.
EXERCISE
Collect cocoons and pupæ of insects and hatch them in a breeding-cage similar to the one illustrated in Fig. 149. Make several cages of this kind. Collect larvæ of several kinds; supply them with food from plants upon which you found them. Find out the time it takes them to change into another stage. Write a description of this process.
The plant louse could produce in its twelfth brood 10,000,000,000,000,000,000,000 offspring. Each louse is about one tenth of an inch long. If all should live and be arranged in single file, how many miles long would such a procession be?
Fig. 148. Plant Lice Fig. 149.
Fig. 149. Cage in which to breed
Insects Flower-pot, lamp-chimney, and cloth SECTION XXXII. ORCHARD INSECTS
The San Jose Scale. The San Jose scale is one of the most dreaded enemies of fruit trees. It is in fact an outlaw in many states. It is an unlawful act to sell fruit trees affected by it. Fig. 150 shows a view of a branch nearly covered with this pest. Although this scale is a very minute animal, yet so rapidly does it multiply that it is very dangerous to the tree. Never allow new trees to be brought into your orchard until you feel certain that they are free from the San Jose scale. If, however, it should in any way gain access to your orchard, you can prevent its spreading by thorough spraying with what is known as the lime-sulphur mixture. This mixture has long been used on the Pacific coast as a remedy for various scale insects. When it was first tried in other parts of the United States the results were not satisfactory and its use was abandoned. However, later experiments with it have proved that the mixture is thoroughly effective in killing this scale and that it is perfectly harmless to the trees. Until the lime-sulphur mixture proved to be successful the San Jose scale was a most dreaded nursery and orchard foe. It was even thought necessary to destroy infected trees. The lime-sulphur mixture and some other sulphur washes not only kill the San Jose scale but are also useful in reducing fungous injury.
Fig. 150. San Jose Scale Fig. 151.
Fig. 151. Single San Jose Scale
Magnified
Fig. 152. The Codling Moth
a, burrow of worm in apple; b, place where worm enters;
c, place where worm leaves; e, the larva;
d, the pupa; i, the cocoon; f and g, moths;
h, magnified head of larva
There are several ways of making the lime-sulphur mixture. It is generally best to buy a prepared mixture from some trustworthy dealer. If you find the scale on your trees, write to your state experiment station for directions for combating it.
The Codling Moth. The codling moth attacks the apple and often causes a loss of from twenty-five to seventy-five per cent of the crop. In the state of New York this insect is causing an annual loss of about three million dollars. The effect it has on the fruit is most clearly seen in Fig. 152. The moth lays its egg upon the young leaves just after the falling of the blossom. She flies on from apple to apple, depositing an egg each time until from fifty to seventy-five eggs are deposited. The larva, or "worm," soon hatches and eats its way into the apple. Many affected apples ripen too soon and drop as "windfalls." Others remain on the tree and become the common wormy apples so familiar to growers. The larva that emerges from the windfalls moves generally to a tree, crawls up the trunk, and spins its cocoon under a ridge in the bark. From the cocoon the moth comes ready to start a new generation. The last generation of the larvæ spends the winter in the cocoon.
Fig. 153. Spraying the Orchard brings Luscious Fruit
The picture in the corner at the top shows the right time to spray for codling moth
Treatment. Destroy orchard trash which may serve as a winter home. Scrape all loose bark from the tree. Spray the tree with arsenate of lead as soon as the flowers fall. A former method of fighting this pest was as follows: bands of burlap four inches wide tied around the tree furnished a hiding-place for larvæ that came from windfalls or crawled from wormy apples on the tree. The larvæ caught under the bands were killed every five or six days. We know now, however, that a thorough spraying just after the blossoms fall kills the worms and renders the bands unnecessary. Furthermore, spraying prevents wormy apples, while banding does not. Follow the first spraying by a second two weeks later.
It is best to use lime-sulphur mixture or the Bordeaux mixture with arsenate of lead for a spray. Thus one spraying serves against both fungi and insects.
Fig. 154. Plum Curculio
Larva, pupa, adult, and mark on the fruit.
(Enlarged)
Fig. 155. Leaf Galls of
Phylloxera On Clinton
Grape Leaf
The Plum Curculio. The plum curculio, sometimes called the plum weevil, is a little creature about one fifth of an inch long. In spite of its small size the curculio does, if neglected, great damage to our fruit crop. It injures peaches, plums, and cherries by stinging the fruit as soon as it is formed. The word "stinging" when applied to insects—- and this case is no exception—means piercing the object with the egg-layer (ovipositor) and depositing the egg. Some insects occasionally use the ovipositor merely for defense. The curculio has an especially interesting method of laying her egg. First she digs a hole, in which she places the egg and pushes it well down. Then with her snout she makes a crescent-shaped cut in the skin of the plum, around the egg. This mark is shown in Fig. 154. As this peculiar cut is followed by a flow of gum, you will always be able to recognize the work of the curculio. Having finished with one plum, this industrious worker makes her way to other plums until her eggs are all laid. The maggotlike larva soon hatches, burrows through the fruit, and causes it to drop before ripening. The larva then enters the ground to a depth of several inches. There it becomes a pupa, and later, as a mature beetle, emerges and winters in cracks and crevices.
Treatment. Burn orchard trash which may serve as winter quarters. Spraying with arsenate of lead, using two pounds of the mixture to fifty gallons of water, is the only successful treatment for the curculio. For plums and peaches, spray first when the fruit is free from the
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