are then hung in the air to harden, then dampened and split. The sides are flattened and leveled by the currier. In finishing they are scoured and stuffed, set out, whitened and finished by machines, and blacked with soap blacking or other compounds. Two pieces on the rump of the horsehide are known as the shell. After the hide is through the lime this shell is cut out and tanned separately, as it requires different treatment and makes finer leather than the other portion. It is finished on the flesh side, while the rest of the hide is finished on the grain.

ALLIGATOR LEATHER.

Only the belly and sides of the alligator skin are tanned. The back is scaly and not fit to be turned into leather. The skins are soaked two to four days in clear, cold water. They are then limed from eight to fourteen days, according to size of skins, after which they are bated with hen manure made weak, and in this way they are handled ten to fifteen hours, and then cleansed and thrown into a vat of weak hemlock liquor, which is gradually strengthened to 20° in twenty days time, when they are taken out and hung in the open air. They are softened on the flesh side with a tool made for the purpose, then handled in tan liquor of 10° for six or eight days, taken out, scoured and slickered on both flesh and grain side, and stuffed with tallow and oil, set out, blacked with logwood and copperas on the grain side, glassed, "pasted over the black," glassed again, and finished on the grain side with gum tragacanth. When these skins are intended for satchels and pocketbooks they are not blacked, but finished natural color or by the application of aniline dyes.

Imitation alligator leather is made from split steer hides prepared in the ordinary process by tanning in a drum with gambier or oak tanning liquors, dried and treated with a composition of linseed oil boiled with litharge or sugar of lead, mixed with naphtha, benzine, or camphene, with sufficient lampblack to give it coloring. Four or five layers of this composition are applied, the hide being dried and pumicestoned between each operation. The last coat is not smoothed off, but the side is then dampened and passed between rollers or dies, when it is embossed with the desired impression to represent an alligator hide. Any desired impression for furniture leather, wall leathers, or hangings can be given by rolls made to produce any figure required.

CHAPTER XVII.

INJURIOUS AND BENEFICIAL INSECTS IN THE UNITED STATES; INSECTICIDES AND INSECTICIDE APPLIANCES.

By C. V. RILEY.

INSECTS INJURIOUS TO AGRICULTURE IN THE UNITED STATES.

The injury to agriculture occasioned by insects is more marked in the United States than in any other country of the world. This excessive depredation may be in part explained by the exceptionally large number of native injurious species. Of about 25,000 described species in the United States, Prof. Lintner (4th Rep't, Ins. N. Y., p. 188) estimates that at least one-half prey upon materials useful to man, and that from 7,000 to 8,000 of these are sufficiently injurious to be justly ranked as pests. He records no less than 210 as affecting the apple, and concludes that we have at least 1,000 fruit insects alone. A list nearly equal in number to that of the apple insects could be made for many other of our principal fruits, or for each of the cereals, grasses, and forest trees. The condensed catalogue of the exhibit (See Appendix IV.) gives a general view of the insects affecting particular trees, fruits, or crops, and especially of those species which from their excessive depredations are of most concern to American agriculture.

In addition to our native species we have to contend with many of the most injurious insects of foreign countries; for many species have been and are constantly being introduced, especially along the chief lines of travel. Prominent among these are the Wheat Midge (Cecidomyia tritici), Hessian Fly (Cecidomyia destructor), Hop Louse (Phorodon humuli), Imported Cabbage Worm (Pieris rapa), and Codling Moth (Carpocapsa pomonella), the Fluted Scale (Icerya purchasi), in California, and hosts of others, many of which are perhaps not particularly injurious in their native countries, but which, brought to America, without their accustomed bird and insect enemies, or the infectious diseases which attack them in their native home, multiply excessively and become most serious pests.

"But there are other just as potent facts which tend to bring about the greater destructiveness of introduced species, and one that has not been fully realized has always struck me with much force. It is this, that most of such species are introduced from Europe or older civilizations, where, on evolutional grounds, it is natural to suppose that they are the very species which have become accustomed to the civilized conditions. In other words, the species which most abound, and have most successfully accustomed themselves to such artificial conditions, have, in the geologically brief period of man's preeminence, acquired advantages over species which have not been submitted to such environment. The former, when brought

into competition with the latter, under such conditions, rapidly outnumber them and get the upper hand."

The peculiar methods of American husbandry are also chargeable, to a considerable extent, with the prominence assumed by noxious insects. Our wide extent of territory, and the consequent cheapness of land, have induced slack methods of cultivation not seen in older and more thickly settled countries. This, with the growth of the same plant, year after year, and over large areas, has enabled many insects to multiply to an extent that would have been impossible with careful and clean husbandry following a rational system of rotation of crops.

The losses occasioned by insects injurious to agriculture are, in the aggregate, enormous, and have been variously estimated at from $300,000,000 to $400,000,000 annually. Crops are often reduced one-fourth or one-half, and sometimes are destroyed over large areas.

The damage done to the wheat crop of New York in the year 1854 by the Wheat Midge was estimated by Dr. Fitch to exceed the value of $15,000,000, The cash value of the corn and wheat destroyed by the Chinch Bug (Blissus leucopterus) in the State of Illinois in 1867 was over $73,000,000.

The loss occasioned by the Rocky Mountain Locust (Caloptenus spretus) to corn, potato, and other crops in 1874 in the States of Kansas, Nebraska, Iowa, and Missouri was estimated at $56,000,000, and considering the effect of the very general failure of these crops upon business men and mechanics, the actual loss to these four States in a single year by this one insect amounted to at least $100,000,000. (First Report United States Entomological Commission, 1877, p. 21.)

The loss to the principal cotton-growing States by the Cotton Worm (Aletia xylina, Say), I have shown by careful estimates (Fourth Report United States Entomological Commission, p. 3) to amount, in years of great prevalence of this pest, to about $30,000,000, and the average annual loss, prior to the investigations I made and the mode of prevention now generally adopted, was $15,000,000.

LITERATURE OF ECONOMIC ENTOMOLOGY IN THE UNITED STATES.

In view of these yearly losses from noxious insects, the very creditable work done in applied entomology in the United States, as compared with that of older countries, is not more than should be expected.

While, in the systematic study of insects, the description and proper grouping of species, various European countries have taken the lead and have accomplished the bulk of the work, the United States may justly claim to have excelled in the study of the life histories of injurious insects, and more especially in the discovery of methods of checking or controlling their ravages, as also in fostering beneficial species.

The credit for our superior literature of applied entomology and for the discovery by us of the more important insecticides and appliances now in use the world over, and, in fact, the establishment of practical entomology on a scientific basis is due, in a large measure, to the more liberal aid given to the work, especially of late years, by both our National and State governments than has been afforded by other countries.

METHODS AND DIFFICULTIES OF INVESTIGATION.

In order that the work done in the study of noxious insects in the United States may be more fully appreciated it may be well here to indicate the knowledge of the facts regarding any particular species which is essential to the intelligent control, and of the difficulty frequently experienced in obtaining such knowledge. In doing so I quote more or less directly from my previous writings on the subject.

* From a paper by the author read before the Philosophical Society of Washington, March 31, 1858, upon Some Recent Entomological Matters of International Concern."

In the first place the full life-history and habits of the species to be dealt with must be known, and this implies a great deal of close and accurate work in field and laboratory, frequently necessitating the joint efforts of a large number of observers continued through a series of years. The relation of the species to wild plants, as well as to the particular cultivated crops which it affects must be studied, as also its relations to other animals. "Indeed, its whole environment must be considered, especially in connection with the farmer's wants, the natural checks which surround it, and the methods of culture that most affect it. The habits of birds, the nature and development of minute parasitic organisms, such as fungi, the bearing of meteorology must all be considered, and yet with the knowledge that a study of all that these things implies, one will frequently fail of practical results without experiment and mechanical ingenuity. Mere study of this kind, however essential, is not often productive of those important practical results which follow when it is combined with field-work and experiment by competent persons and upon scientific principles. * It took me five years, with a number of observers at command, to definitely settle some points in the life history of the Cotton Worm, and with all the resources of the French Government, its liberal premiums, its superior and subcommissions appointed for the purpose and at work for the past fifteen years, there is much that is yet mooted in reference to the Grape Phyllox

*

*

*

Studies of such widespread and national species as the Rocky Mountain Locust, Chinch Bug, Hessian Fly, Army Worm (Leucania unipuncta), Codling Moth, Imported Cabbage Worm, Cotton Worm, Plum Curculio (Conotrachelus nenuphar), and a host of other insects have been carried on continuously through a great number of years; yet previously unknown facts or new methods of preventing their deprodations are discovered almost every year.

The recent successful use of arsenical poisons against the Codling Moth, and in a less satisfactory degree against the Plum Curculio, the use of kerosene, resin and soap emulsions more particularly against plant-lice (Aphididœ) and scale insects, (Coccida), the study of contagious diseases of the Cabbage Worm and Chinch Bug with relation to their use in controlling these pests, may also be mentioned to illustrate the advance that is constantly being made in our knowledge of methods of preventing the attacks of species long known and well studied.

My recent studies of the Hop Plant-louse, a species which concerns both the American and European hop grower, will serve to illustrate the complicated problems with which the economic entomologist has to deal. For a summary of the facts the reader is referred to the Report of the United States Entomologist for 1888, from which the following concluding passages are taken : "The exact knowledge thus gained simplifies the protection of the hop plant from Phorodon attack. Preventive measures should consist in destroying the insect on plum in early spring where the cultivation of this fruit is desired, and the extermination of the wild trees in the woods wherever the hop interest is paramount; also in avoiding the introduction of the pest into new hop countries in the egg state upon plum cuttings or scions. Direct treatment is simplified by the fact that the careful grower is independent of slovenly neighbors, infection from one hop-yard to another not taking place.

The bearing of these facts will probably best be brought home by the statement that hitherto hop growers have been groping in the dark and working to prevent injury by applications to the soil. In fact the English hop growers have been led by their very best authorities to waste their energies in this direction. The importance of the matter will appear when I state that the hop crop, which is quite an important one in some parts of this country, and especially important in some parts of Europe, annually suffers from the ravages of this, its worst insect enemy, and in some years is rendered a total failure by it. Further, that some parts of this

* General Truths in Applied Entomology, 1884.