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This species cannot be identical with the willow-louse, Aphis Salicis of Linnæus, which has a spotted body; and therefore I propose to call it Aphis Salicti, the plant-louse of willow groves. When crushed, it communicates a stain of a reddish or deep orange color. .
Some plant-lice live in the ground, and derive their nourishment from the roots of plants. We annually lose many of our herbaceous plants, if cultivated in a light soil, from the exhausting attacks of these subterranean lice. Upon pulling up China Asters, which seemed to be perishing from no visible cause, I have found hundreds of little lice, of a white color, closely clustered together on the roots. I could never discover any of them that were winged, and therefore conclude from this circumstance as well as from their peculiar situation, that they never acquire wings. Whether these are of the same species as the Aphis radicum of Europe, I cannot ascertain, as no sufficient description of the latter has ever come to my notice. These little lice are attended by ants, which generally make their nests near the roots of the plants, so as to have their milch kine, as the plant-lice have been called, within their own habitations; and, in consequence of the combined operations of the lice and the ants, the plants wither and prematurely perish. When these subterranean lice are disturbed, the attendant ants are thrown into the greatest confusion and alarm; they carefully take up the lice which have fallen from the roots, and convey them in their jaws into the deep recesses of their nests; and here the lice still contrive to live upon the fragments of the roots left in the soil. It is stated that the ants bestow the same care and attention upon the root-lice as upon their own offspring, that they defend them from the attacks of other insects, and carry them about in their mouths to change their pasture; and that they pay particular attention to the eggs of the lice, frequently moistening them with their tongues, and in fine weather bringing them to the surface of the nest to give them the advantage of the sun. On the other hand, the sweet fluid supplied in abundance by these lice forms the
• See Kirby and Spence's Introduction to Entomology, Vol. II. pp. 91, 92.
chief nutriment both of the ants and their young, which is sufficient to account for their solicitude and care for their valuable herds.
The peach-tree suffers very much from the attacks of plantlice, which live under the leaves, causing them by their punctures to become thickened, to curl or form hollows beneath, and corresponding crispy and reddish swellings above, and finally to perish and drop off prematurely. Whether our insect is the same as the European Aphis of the peach-tree (Aphis Persicæ of Sulzer) I cannot determine, for the want of a proper description of the latter.
The injuries occasioned by plant-lice are much greater than would at first be expected from the small size and extreme weakness of the insects; but these make up by their numbers what they want in strength individually, and thus become formidable enemies to vegetation. By their punctures, and the quantity of sap which they draw from the leaves, the functions of these important organs are deranged or interrupted, the food of the plant, which is there elaborated to nourish the stem and mature the fruit, is withdrawn, before it can reach its proper destination, or is contaminated and left in a state unfitted to supply the wants of vegetation. Plants are differently affected by these insects.. Some wither and cease to grow, their leaves and stems put on a sickly appearance, and soon die from exhaustion. Others, though not killed, are greatly impeded in their growth, and their tender parts, which are attacked, become stunted, curled, or warped. The punctures of these lice seem to poison some plants, and affect others in a most singular manner, producing warts or swellings, which are sometimes solid and sometimes hollow, and contain in their interior a swarm of lice, the descendants of a single individual, whose punctures were the original cause of the tumor. I have seen reddish tumors of this kind, as big as a pigeon's egg, growing upon leaves, to which they were attached by a slender neck, and containing thousands of small lice in their interior. Naturalists call these tumors galls, because they seem to be formed in the same way as the oak-galls which are used in the making of ink. The lice which inhabit or produce them generally differ from the others, in having shorter antennæ, being without honey-tubes, and in frequently being clothed with a kind of white down, which, however, disappears when the insects become winged.
These downy plant-lice are now placed in the genus Eriosoma, which means woolly body, and the most destructive species belonging to it was first described, under the name of Aphis lanigera, by Mr. Hausmann," in the year 1801, as infesting the apple-trees in Germany. It seems that it had been noticed in England as early as the year 1787, and has since acquired there the name of American blight, from the erroneous supposition that it had been imported from this country. It was known, however, to the French gardeners † for a long time previous to both of the above dates, and, according to Mr. Rennie, is found in the orchards about Harfleur, in Normandy, and is very destructive to the apple-trees in the department of Calvados. There is now good reason to believe that the miscalled American blight is not indigenous to this country, and that it has been introduced here with fruit-trees from Europe. Some persons, indeed, have supposed that it was not to be found here at all, but the late Mr. Buel has stated that it existed on his apple-trees, and I have once or twice seen it on apple-trees in Massachusetts, where, however, it still appears to be rare, and consequently I have not been able to examine the insects sufficiently myself. The best account that I have seen of them is contained in Knapp's “Journal of a Naturalist," from which, and from Hausmann's description, the following observations are chiefly extracted.
The eggs of the woolly apple-tree louse are so small as not to be distinguished without a microscope, and are enveloped in a cotton-like substance furnished by the body of the insect. They are deposited in the crotches of the branches and in the chinks of the bark at or near the surface of the ground, especially if there are suckers springing from the same place. The young, when first hatched, are covered with a very short and fine down, and appear in the spring of the year like little specks of mould on the trees. As the season advances, and the insect increases in size, its downy coat becomes more distinct, and grows in length daily. This down is very easily removed, adheres to the fingers when it is touched, and seems to issue from all the pores of the skin of the abdomen. When fully grown, the insects of the first brood are one tenth of an inch in length, and, when the down is rubbed off, the head, antennæ, sucker, and shins are found to be of a blackish color, and the abdomen honey-yellow. The young are produced alive during the summer, are buried in masses of the down, and derive their nourishment from the sap of the bark and of the alburnum or young wood immediately under the bark. The adult insects never acquire wings, at least such is the testimony both of Hausmann and Knapp, and are destitute of honey-tubes, but from time to time emit drops of a sticky fluid from the extremity of the body. These insects, though destitute of wings, are conveyed from tree to tree by means of their long down, which is so plentiful and so light, as easily to be wafted by the winds of autumn, and thus the evil will gradually spread throughout an extensive orchard. The numerous punctures of these lice produce on the tender shoots a cellular appearance, and wherever a colony of them is established, warts or excrescences arise on the bark; the limbs thus attacked become sickly, the leaves turn yellow and drop off; and, as the infection spreads from limb to limb, the whole tree becomes diseased, and eventually perishes. In Gloucestershire, England, so many apple-trees were destroyed by these lice in the year 1810, that it was feared the making of cider must be abandoned. In the north of England the apple-trees are greatly injured, and some annually destroyed by them, and in the year 1826 they abounded there in such incredible luxuriance, that many trees seemed, at a short distance, as if they had been whitewashed.
* Illiger's Magazin, Vol. I. p. 440. † Salisbury's Hints on Orchards, p. 39. Insect Miscellanies, p. 180. $ New England Farmer, Vol. VII. p. 169; Vol. IX. p. 178.
Mr. Knapp thinks that remedies can prove efficacious in removing this evil only upon a small scale, and that when the injury has existed for some time, and extended its influence over the parts of a large tree, it will take its course, and the tree will die. He says that he has removed this blight from young trees, and from recently attacked places in those more advanced, by painting over every node or infected part of the tree with a composition consisting of three ounces of melted resin mixed with the same quantity of fish oil, which is to be put on while warm, with a painter's brush. Sir Joseph Banks succeeded in extirpating the insects from his own trees by removing all the old and rugged bark, and scrubbing the trunk and branches with a hard brush. The application of the spirits of tar, of spirits of turpentine, of oil, urine, and of soft soap, has been recommended. Mr. Buel found that oil sufficed to drive the insects from the trunks and branches, but that it could not be applied to the roots, where he stated numbers of the insects harbored. The following treatment I am inclined to think will. prove as successful as any which has heretofore been recommended. Scrape off all the rough bark of the infected trees, and make them perfectly clean and smooth early in the spring; then rub the trunk and limbs with a stiff brush wet with a solution of potash as hereafter recommended for the destruction of bark lice; after which remove the sods and earth around the bottom of the trunk, and with the scraper, brush, and alkaline liquor, cleanse that part as far as the roots can conveniently be uncovered. The earth and sods should immediately be carried away, fresh loam should be placed around the roots, and all cracks and wounds should be filled with grafting cement or clay mortar. Small limbs and extremities of branches, if infected, and beyond reach of the applications, should be cut off and burned.
There are several other species of Eriosoma or downy lice in this State, inhabiting various forest and ornamental trees, some of which may also have been introduced from abroad. The descriptions of foreign plant-lice are mostly so brief and imperfect, that it is impossible to ascertain from them which of our species are identical with those of Europe; I shall therefore omit any further account of these insects, and close this part of the subject with a few remarks on the remedies to be employed for their destruction generally, and some notice of the natural enemies of plant-lice.