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Solutions of soap, or a mixture of soapsuds and tobaccowater, used warm and applied with a watering-pot or with a garden engine, may be employed for the destruction of these insects. It is said that hot water may also be employed for the same purpose with safety and success. The water, tobaccotea, or suds should be thrown upon the plants with considerable force, and if they are of the cabbage or lettuce kind, or other plants whose leaves are to be used as food, they should subsequently be drenched thoroughly with pure water. Professor Lindley recommends syringing plants, as often as necessary to remove the lice, with a solution of half an ounce of strong carbonate of ammonia in one quart of water, which has the merit of being clean as well as effectual. Lice on the extremities of branches may be killed by bending over the branches and holding them for several minutes in warm and strong soapsuds, or in a solution of whale-oil soap. Against the depredations of the plant-lice that sometimes infest potatofields, dusting the plants with lime has been found a good remedy. Lice multiply much faster, and are more injurious to plants, in a dry than in a wet atmosphere; hence in greenhouses, attention should be paid to keep the air sufficiently moist; and the lice are readily killed by fumigations with tobacco or with sulphur. To destroy subterranean lice on the roots of plants, I have found that watering with salt water was useful, if the plants were hardy; but tender herbaceous plants cannot be treated in this way, but may sometimes be revived, when suffering from these hidden foes, by free and frequent watering with soapsuds.
Plant-lice would undoubtedly be much more abundant and destructive, if they were not kept in check by certain redoubtable enemies of the insect kind, which seem expressly created to diminish their numbers. These lice-destroyers are of three sorts. The first are the young or larvæ of the hemispherical beetles familiarly known by the name of lady-birds, and scientifically by that of Coccinella. These little beetles are generally yellow or red, with black spots, or black, with white, red, or yellow spots; there are many kinds of them, and they are very common and plentiful insects, and are generally diffused among plants. They live, both in the perfect and young state, upon plant-lice, and hence their services are very considerable. Their young are small flattened grubs of a bluish or blue-black color, spotted usually with red or yellow, and furnished with six legs near the fore part of the body. They are hatched from little yellow eggs, laid in clusters among the plant-lice, so that they find themselves at once within reach of their prey, which, from their superior strength, they are enabled to seize and slaughter in great numbers. In July, 1848, a friend sent to me a whole brood of lady-bird grubs, which, being found upon potato-vines, were thought by some of his neighbors to be the cause of the rot. In a few weeks, the grubs were transformed to beetles, about as big as half a pea, and having nine black dots on their dull orange-colored wing-shells. Hence they derive their name of Coccinella novemnotata, the ninedotted Coccinella. It need hardly be added that these little insects were wholly innocent of all offence to the plants, upon which, when infested with the common potato plant-lice, they may always be found. It is amusing, however, that both of these kinds of insects should have been charged with the same fault, one having no more to do with producing the disease than the other.
There are some lady-birds, of a very small size, and blackish color, sparingly clothed with short hairs, and sometimes with a yellow spot at the end of the wing-covers, whose young are clothed with short tufts or flakes of the most delicate white down. These insects belong to the genus Scymnus, which means a lion's whelp, and they well merit such a name, for their young, in proportion to their size, are as sanguinary and ferocious as the most savage beasts of prey. I have often seen one of these little tufted animals preying upon plant-lice, catching and devouring, with the greatest ease, lice nearly as large as its own body, one after another, in rapid succession, without apparently satiating its hunger or diminishing its activity.
The second kind of plant-lice destroyers are the young of the golden-eyed lace-winged fly, Chrysopa perla. This îly is of a pale green color, and has four wings resembling delicate lace, and eyes of the brilliancy of polished gold, as its generi. cal name implies; but, notwithstanding its delicacy and beauty, it is extremely disgusting from the offensive odor that it exhales. It suspends its eggs, by threads, in clusters beneath the leaves where plant-lice abound. The young, or larva, is a rather long and slender grub, provided with a pair of large curved and sharp teeth (jaws), moving laterally, and each perforated with a hole through which it sucks the juices of its victims. The havoc it makes is astonishing; for one minute is all the time it requires to kill the largest plant-louse, and suck out the fluid contents of its body.
The last of the enemies of plant-lice are the maggots or young of various two-winged flies belonging to the genus Syrphus. Many of these flies are black with yellow bands on their bodies. I have often seen them hovering over small trees and other plants, depositing their eggs, which they do on the wing, like the bot-fly, curving their tails beneath the leaves, and fixing here and there an egg, wherever plant-lice are discovered. Others lay their eggs near the buds of trees, where the young may find their appropriate nourishment as soon as they are hatched. The young are maggots, which are thick and blunt behind, tapering and pointed before; their mouths are armed with a triple-pointed dart, with which they pierce their prey, elevate it above their heads, and feast upon its juices at leisure. Though these maggots are totally blind, they are enabled to discover their victims without much groping about, in consequence of the provident care of the parent flies, which leave their eggs in the very midst of the sluggish lice. Mr. Kirby says, that, on examining his currant-bushes, which but a week before were infested by myriads of aphides, not one was to be found; but beneath each leaf were three or four full-fed maggots, surrounded by heaps of the slain, the trophies of their successful warfare. He also says that he has found it very easy to clear a plant or small tree of lice, by placing upon it several larvæ of Coccinella or Syrphi.
3. BARK-LICE. Coccidæ. The celebrated scarlet in grain, which has been employed in Asia and the South of Europe, from the earliest ages, as a coloring material, was known to the Romans by the name of Coccus, derived from a similar Greek word, and was, for a long time, supposed to be a vegetable production, or grain, as indeed its name implies. At length it was ascertained that this valuable dye was an insect, and others agreeing with it in habits, and some also in properties, having been discovered, Linnæus retained them all under the same name. Hence in the genus Coccus are included not only the Thola of the Phænicians and Jews, the Kermes of the Arabians, or the Coccus of the Greeks and Romans, but the scarlet grain of Poland, and the still more valuable Cochenille of Mexico, together with various kinds of bark-lice, agreeing with the former in habits and structure. These insects vary very much in form; some of them are oval and slightly convex scales, and others have the shape of a muscle; some are quite convex, and either formed like a boat turned bottom upwards, or are kidney-shaped, or globular. They live mostly on the bark of the stems of plants, some, however, are habitually found upon leaves, and some on roots. In the early state, the head is completely withdrawn beneath the shell of the body and concealed, the beak or sucker seems to issue from the breast, and the legs are very short and not visible from above. The females undergo only a partial transformation, or rather scarcely any other change than that of an increase in size, which, in some species indeed, is enormous, compared with the previous condition of the insect; but the males pass through a complete transformation before arriving at the perfect or winged state. In both sexes we find threadlike or tapering antennæ, longer than the head, but much shorter than those of plant-lice, and feet consisting of only one joint, terminated by a single claw. The mature female retains the beak or sucker, but does not acquire wings; the male on the contrary has two wings, but the beak disappears. In both there are two slender threads at the ex tremity of the body, very short in some females, usually quite long in the males, which moreover are provided with a stylet at the tip of the abdomen, which is recurved beneath the body.
The following account* contains a summary of nearly all that is known respecting the history and habits of these insects. Early in the spring the bark-lice are found apparently torpid, situated longitudinally in regard to the branch, the head upwards, and sticking by their flattened inferior surface closely to the bark. On attempting to remove them they are generally crushed, and there issues from the body a dark colored fluid. By pricking them with a pin, they can be made to quit their hold, as I have often seen in the common species, Coccus Hesperidum, infesting the myrtle. A little later the body is more swelled, and, on carefully raising it with a knife, numerous oblong eggs will be discovered beneath it, and the insect appears dried up and dead, and only its outer skin remains, which forms. a convex cover to its future progeny. Under this protecting shield the young are hatched, and, on the approach of warm weather, make their escape at the lower end of the shield, which is either slightly elevated or notched at this part. They then move with considerable activity, and disperse themselves over the young shoots or leaves. The shape of the young Coccus is much like that of its parent, but the body is of a paler color and more thin and flattened. Its six short legs and its slender beak are visible under a magnifier. Some are covered with a mealy powder, as the Coccus Cacti, or cochenille of commerce, and the Coccus Adonidum, or mealy bug of our greenhouses. Others are hairy or woolly; but most of them are naked and dark colored. These young lice insert their beaks into the bark or leaves, and draw from the cellular substance the sap that nourishes them. Réaumur observed the ground quite moist under peach-trees infested with bark-lice, which was caused by the dripping of the sap from the numerous punctures made by these insects. While they continue their exhausting suction of sap, they increase in size, and during this time are in what is called the larva state. When this is completed, the insects will be found to be of
It was drawn up by me in the year 1828, and published in the seventh volume of the “New England Farmer,” pp. 186, 187.