Page:Popular Science Monthly Volume 42.djvu/661

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641
AN AGRICULTURAL REVOLUTION.

ing a dwarfing and malformation that are very vexatious to the horticulturist. An apple thus damaged is shown in Fig. 3.

The eggs of the curculio are deposited beneath the skin of the fruit, and the larvæ remain concealed until full-grown. Consequently the early stages of the insect can not be reached by spraying. Fortunately, however, the parent beetles can be killed before many eggs are deposited, by sparsely coating the foliage and fruit with poison from the spraying machine, and thus the plums will be saved. The practicability of this has been proved repeatedly by commercial orchardists.

PSM V42 D661 Canker worm.jpg
Fig. 4.—Canker Worm: e, eggs;, f, larva; g, pupa; a, male moth; b, female moth. (After Riley.)

In addition to the insects affecting orchard fruits, there are hosts of enemies to the foliage. Nearly all of the latter, fortunately, are also open to destruction by means of the spraying machine. The canker worm is one of the most destructive of these foliage pests; at occasional intervals during the last century it has denuded thousands of orchard and shade trees in many parts of Canada and the United States. Its different stages are shown in Fig. 4. The damage is done by the worms or larvæ which hatch from masses of small cylindrical eggs (e), usually deposited upon the bark of the trees. These larvæ feed upon the parenchyma of the leaves, and sometimes cause a badly infested orchard to appear brown and seared, as if scorched by fire. They continue feeding for several weeks before becoming full-grown. Then they descend to the ground, burrow into the soil a short distance, and spin silken cocoons within which they change to the pupa or chrysalis state, remaining in this condition a few weeks, when the moths come forth. The two sexes of these moths differ greatly: the male (a) has large, well-developed wings, while the female (b) is wingless. The latter is of an ash-gray color. On emerging from the chrysalis she crawls to the base of the tree and ascends the trunk some distance; here the male finds her, and, after mating, she deposits her eggs on the twigs or branches of the tree.

The canker worm, like nearly all similar leaf-eating caterpillars, is so easily destroyed by spraying that, while in years past it was greatly dreaded by orchardists, it now inspires little fear.

The three insects above mentioned are all examples of those species having biting mouth-parts, and which in consequence attack the plant by biting piece by piece the tissues of leaf, stem, or fruit. It is on this account that they are open to destruction