APHIS, in entomology, a genus of the Hemiptera order, which has engaged the attention of naturalists for various rea sons: their generation exhibits a singular and surprising phenomenon, and their in stinctive economy differs, in some res pects, from that of most other animals. Linnmus defines the generic character of the aphis thus; beak inflected, sheath of five articulations, with a single bristle a antenna setaceous, and longer than the thorax ; either four erect wings or none ; feet formed for walking; posterior part of the abdomen usually furnished with two little horns. Geoffroy says, the aphides have two beaks, one of which is seated in the breast, the other in the head ; this last extends to and is laid upon the base of the pectoral one, and serves, as that writer imagines, to convey to the head a part of that nourishment which the insect takes, or sucks in, by means of the pecto ral beak. Gmelin enumerates about 70 species, all of which, and doubtless many others, are found in different parts of Eu rope and America. They infest an end less variety of plants ; and it is believed each species is particularly attached to one kind of vegetable only; hence each sort has been hitherto uniformly named after the individual species or .genus of plants on which it feeds ; or if that could not be ascertained, that on which it had been found ; for some species are rather uncommon and little known,though others are infinitely too numerous. The aphi des are sufficiently known by the indiscri minate term of plant-lice ; they abound with a sweet and grateful moisture, and arc therefore eagerly sought after by ants, and are devoured by the larva of coccinel la, and many other creatures, or they would become, very probably, more de structive to the whole vegetable creation than any other race of insects known. if Bonnet was not the first naturalist (as is generally acknowledged) who discovered the mysterious course ofgeneration in the aphides, or, as he calls them, pucerons, his experiments, together with those of his countryman Trembly, tended at least to confirm, in a most satisfactory manner, the almost incredible circumstances re specting it, that an aphis or puceron, brought up in the most perfect solitude from the moment of its birth, in a few days will be found in the midst of a nu merous family ; and that if the experi ment be again repeated on one of the individuals of this family, a second gene ration will multiply like its parent; and the like experiment may be many times re peated with the same effect, until at last the progeny becomes barren, unless again impregnated by the male; after which se veral generations may be again produced without further aid of the male, as before.
The history of aphides has also been very copiously treated upon by Dr. Rich ardson, in a paper printed in the 41st vol. of the Philosophical Transactions ; and by the late ingenious Mr. Curtis, in the sixth volume of the Transactions of the Linnman Society. The tenor of Dr. Rich ardson's remarks is briefly this : the great variety of species which occur in the in sects now under consideration may make an inquiry into their particular natures seem not a little perplexing, but by redm cing them under their proper genus, the elifficulty is considerably diminished. We may reasonably suppose all the insects, comprehended under any distinct genus, to partake of one general nature ; and by diligently examining any particular spe. cics, may thence gain some insight into the nature of all the rest. With this view, Dr. Richardson chose out of the various sorts of aphides the largest of those found on the rose-tree ; not onlyas its size makes it more conspicuous, but there are few of so long duration. This sort appears ear ly in the spring, and continues late in au tumn, while several are limited to a much shorter term, in conformity to the diffe rent trees and plants whence they draw their nourishment. If, at the beginning of February, the weather happens to be so warm as to make the buds of the rose tree swell and appear green, small aphides are frequently to be found on them,though not larger than the yolmgones in summer when first produced. it will be found, that those aphides which appear only in spring proceed from small black oval eggs, which were deposited on the last year's shoot; though when it happens that the insects make too early an appearance, the greater part suffer from the sharp wea ther that usually succeeds, by which means the rose-trees are some years in a manner freed from them. The same kind of animal is then at one time of the year viviparous, and at another oviparous. These aphides, which withstand the se. verity of the weather, seldom come to their full growth before the month of April, at which time they usually begin to breed, after twice casting off their ex uvia, or outward covering. It appears that they arc all females, which produce each of diem a numerous progeny, and that without having intercourse with any male insect : they are viviparous, and, what is equally singular, they all come into the world backwards. When they first come from the parent, they are enveloped in a thin membrane, having in this situation the appearance of an oval egg ; these egg like appearances adhere by one extremity to the mother, while the young ones con tained in them extend to the other, and by that means gradually drag the ruptured membrane over the head and body to the hind feet. During this operation, and for some time after, the fore part of the head adheres, by means of something that is Mutinous, to the vent of the parent. Be mg thus suspended in the air, it soon frees itself from the membrane in which it was confined ; and after its limbs are a little strengthened, is set down on sonic tender shoots, and is left to provide for itself. In the spring months, there appear on the rose-trees but two generations of aphides, including those which proceed immediately from the last year's eggs ; the warmth of the summer adds so much to their fertility, that no less than five generations succeed one another in the in terval. One is produced in May, which casts off its covering ; while the months ofJune and July each supply two more, which cast off their covosings three or four times, according to the different warmth of the season. This frequent change of their outward coat is the more extraordinary, because it is repeated more often when the insects come the soonest to their growth, which sometimes hap pens in ten days, when they have had plenty of warmth and nourishment Early in the month of J one, some of the third generation, whith v6 ere produced about the middle ofMay,after casting off the last covering, discover four erect wings,much longer than their bodies; and the same is observable in all the succeeding genera tions which are produced duringthe sum mer months, but still without any diversi ty of sex : for some time, before the aphides come to their full growth, it is easy to distinguish which will have wings, by a remarkable fulness of the breast, which in,the otheis is homily to be dis tinguished from the body. When the last covering is rejected, the wings which were before folded op in a very narrow compass, are gradually extended in a sur prising manner, till their dimensions are at last very considerable. The increase of these insects in the summer-time is so very great, that by wounding. and exl must ing the tender shoots, they would fre quently suppress all vegetation, had they not manv enemies to restrain them. Not withstanding these insects have a numer ous tribe of enemies, they are not without their friends, if those may be considered as such, who are officious in their atten dance for the good things they expect to reap thereby. The ant and bee are of
this kind, collecting the honey in which the aphides abound, but with this differ ence that the ants are constatnt visitors, tbe bee only when flowers are scarce ; the ants will suck in the honey, while the aphides are in the act of discharging it; the bees onlv collect it from the leaves on which it has tallen. The aphides are often carried home by the ant, carefully attend ed, and regularly supplied with food. See Formica. In the autumn three more ge nerations of aphides are produced, two of which generally make their appearance in the month of August, and the third be fort the middle of September. The two first differ in no respect from those which are found in slimmer, but the third differs greatly from all the rest. Though all the aphides which have hitherto appeared were female, in this generation several male insects are found, but not by any means so numerous as the females. The females have at first, the same appearance as those of the former generations, but in a few days their colour changes from a green to a yellow, which is gradually con verted into an orange before they. come to their full growth ; they differ, also, in another respect, from those which occur in summer, for all these yellow females are without wings. The male insects are, however,still more remarkable, their out ward appearance readily- distinguishing them from this and all other generations. When first produced they are not of a green colour like the rest, but of a red dish brown, and have afterwards a dark line along the back : they come to their full growth in about three weeks, and then cast off their last cover' ng,-the whole insect being, after this, of a bright yellow colour, the wings only excepted ; but af ter this change they become of a deeper yellow, and in a very- few hours of a dark brown, if we except the body, which is something lighter coloured and has a red dish cast. The males no sooner come to maturity than they copulate with the fe males, who, in a day or two after their in tercourse with the males, lay their eggs, generally near the buds. Where there are a number crowded together, they, of course, interfere with each other, in which case they will frequently deposit their eggs on other parts of the branches.— It is highly probable that the aphides de rive considerable advantages by living in society ; the reiterated punctures of a great numberiff them may attract a larger quantity of nutricious juices to that part of the tree or plant where they have taken up their abode. The observations of 3Ir. Curtis on the aphides are chiefly intended to shew that they are the principal cause of blights in plants, and the sole came of the honey-dew. He therefore calls them the aphis, or blighter ; and after ob servipg, that, in point of numbers, the in dividuals of the several species composing kt surpass those ofany other ge»us in the country; speaks thus, in general terms, of the whole tribe. These insects live en tirely on vegetablis. The loftiest tree-is »oleos liable to theirattacks than the most humble plant. They prefer,,the young shoots pn account of their tenderness, and on this principle often insinuate them selves into the very heart of the plant, and do irreparable mischief before they are discovered. But, for the mast part, they beset the foliage, and are mostly found on the undertiide of the leaf, which they prefer, not only on accountof its be ing the most tender, but as it affords them protection from tbe weather, and various injuries to which they would otherwise be exposed. Sometimes the root is the object of theirchoice, which, from the na ture of these insects, one would not, a priori, expect ; vet I have seen the roots of lettuces thickly beset with them, and the whole crop rendered sickly and of lit tle value ; but m105 instances are rare. They seldom attach themselves to the bark of trees, like the aphis salicis, which, being one of our largest species, and hence possessing superior strength,is enabled to penetrate a substance harder than the leaves themselves. In the quality of the excrement voided by these insects, there is something wonderfully extraordinary. Were a person accidentally to take up a hook, in which it was gravely asserted, that in some countries there were certain animals which voidedr liquid sugar, he would lay it down, regarding it as a fabu lous tale, calculated to impose on the cre dulity of the ignorant ; and yet such is literally the truth. Mr. Curtis collected some on a piece of writing-paper, from a brood of the aphis salicis, and found it to he sweet as sugar ; and observes, that, were it not for the wasps, ants, Hies, and other insects, that devour it as quickly as it is produced, it might, no doubt, be col lected in considerable quantities, and by the processes used with other saccharine juices, might be converted into the choic est sugar or sugar-candy. The sweetness of this excrementitious substance, the glossy appearance it gave the leaves it fell upon, and the swarm of insects This matter attracts, led him to imagine that the ho ney-dew of plants was no other than this secretion, which further observation has since fully confirmed; and not, a§ its name implies, a sweet substance fallingfrom the atmosphere. On this opinion it is further remarked, that it neither Nis from the atmosphere, nor issues from the plant it self, as is easily demonstrated. If it fell front the atmosphere, it would cover every thing it fell upon indiscriminately, where as we never find it but on certain living plants and trees. We find it also on plants in stoves and green-houses, covered with glass. If it exuded from the plod, it would appear on all the leaves generally and u ask on] y ; whereas its appearance is ex tremely irregular,mot alikt on any two leaves of the sametree or plant, some having none of it, and others being covert ed with it but partially. It is probable that there neverexists any honey-dew but where there are aphides ; though such often pass unnoticed;being hidden on the underside of the leaf: and wherever ho ney-dew is observable upon a leaf, aphides will be found on the under side of the leaf or leaves immediately above it, and under no other circumstance whatever. If by ac cident anything should intervene between the aphides and the leaf next beneath them, there well be no honey-dew on that leaf: and thus he conceives it is incontro vertibly proved, that is are the true and only source of -honey-dew. Of the British species of aphides, one ofthe larg est and most remarkable is the aphis sali cis, which is found on the difterent kinds of willows. W hen bruised,these insects stain the fingers with red. Towards the end of September multitudes of the full-grown insects of this species, both with and with out wings, desert the 'willows on which they feed, and ramble over every neigh bOuring object in such numbers, that we can handle nothing in their vicinity with out crushing some of them, while those in a younger or less.advanced state still re main in large masses upon the trees. Aphis rosa: is very frequent, during the summer months, on the voutg shoots and buds of roses : it is of a bright green colour : the males are furnished with large transpa rent wings. A. yids is most destrucUve to vines; as A. admi is to the elm-tree. Plate I. fig. 3.