M. de Geer found the aphis of the pine viviparous, and propagating without copulation in summer, and ovi parous often have copulated in the later season of the year.
Another species of aphis lives on the pine, which, the same author affirms, is always oviparous, and never viviparous. There is only one generation of them throughout the year, in which respect, they also differ from the common aphides; they lay eggs in July, pro ducing apterous young, which never acquire wings; and survive the winter with hardly any sensible incre ment. In spring they prepare a gall among the shoots of the tree, which is a nest for the young. This gall is first occasioned by the punctures of a single aphis ; on opening it, a number of young ones are found within, whose repeated punctures contribute to increase its size. The mother having prepared this habitation, for the re ception of her young, dies and dries up ; for, after the 8th or 12th of June, her body is uniformly found dead and emaciated. The gall afterwards bursts of itself, and allows an exit to the young, which acquire wings, though the mother is apterous. These animals are very dull and sluggish; they can with difficulty reco,er themselves when reversed. Indeed they have little need of motion, being constantly shut up in galls. The posi tion of the trunk is remarkable, it being in the middle of the body, between the first pair of legs.
Ti. is a remarkable fact, that the excretions of aphides, and the exudations of the cornicula, are real liquid ho ney, on their native plants. They are surrounded by numbers of other insects to collect it, but especially ants. The proceedings of this industrious little animal, to gain the object of its pursuit, are amply detailed by Mr P. Huber. But, not content with resorting to the place of their abode, the ants actually convey aphides below ground, to their subterraneous galleries. In doing so, they practise the utmost care and gentleness ; the aphis is transported without injury in the teeth of the ant. Mr Huber saw a single ant, successively, carry thrcc aphi des, each larger than itself. In the ant-hills of the yel low ant, they are always found in considerable numbers. During the height of summer, when the weather is hot and dry, and aphides most abundant, the foliage of plants is often covered by a sweet clammy substance, called honey dew. Some naturalists are induced to consider
the origin of this as belonging to these animals alone. It is supposed never to exist, except when they are pre sent; for they are invariably discovered in its vicinity. We do not presume to determine this question ; but we must remark, that it seems possible to us, if aphides have the power of extracting a saccharine substance from plants, that certain relative conditions, between the at mosphere and plants, may promote its secretion, and bring it into view.
The aphis, sometimes little larger than a grain of sand, is, nevertheless, a formidable enemy to vegeta tion. The loftiest tree, and the humblest weed, are equally exposed to its pernicious attacks ; the trunk, branches, leaves, and krk, all c 'ford it harbour. But, unlike the ravages of larger animt.ls, such as caterpil lars, locusts, and others, in devouring the solid sub stance of the plant. destruction is more insidiously and impel ceptibly accomplished. The aphis, provided with a long, sharp proboscis, punctures the plant ; these punctures, often repeated, and made by thousands of animals, closely crowded around it, and excluding the external air, independent of exhausting its fluids, in jure its texture ; whence it blackens, fades, and dies. Even when the attacks are less fatal, the vegetable be comes disfigured and distorted ; the leaves curl up, nourishing an host of enemies within ; vesicles and galls are formed, and the whole exterior evidently be trays the progress of disease. The aphides have been considered the chief cause of blights of plants ; and hence its more recent name, the blighter. Whether or not it may actually produce what is generally called a blight, it is certain, that it has been the principal cause of the failure of entire crops of different vegetables, in different seasons. Nor ought this to be so much the subject of surprise, if we reflect on the great fecundity of these animals ; that ten successive generations fol low in a single season, and that some of them never quit the branch, where they are once established, until its destruction causes their own. Thus their multitudes are innumerable ; millions will spring from one in the course of a few generations.