Aphis

“ Everybody knows the aphides well by sight, in one of their forms at least, the familiar rose aphis; but probably few people ever look at them closely and critically enough to observe how very beautiful and wonderful is the organisation of their tiny limbs in all its exquisite detail. ”

“ Aphis, a genus of insects (called plant-lice) of the ord. Hemiptera, the type of the family Aphĭdēs. The species are very numerous and destructive. The A. rosæ lives on the rose; the A. fabæ on the bean; the A. humŭli is injurious to the hop, the A. granaria to cereals, and A. lanigĕra or woolly aphis equally so to apple trees. The aphides are furnished with an inflected beak, and feelers longer than the thorax. In the same species some individuals have four erect wings and others are entirely without wings. ”

“ It is not surprising that the grower absolutely refuses to believe that the whole of this infinite number of creatures were floating in the air waiting to pounce upon his plants at the very instant when, weakened by the frost, they are the less able to resist its attacks.
What renders the problem still more difficult is that the aphis army is not homogeneous. Each plant has its own tribe that prey upon its juices. The bean aphis differs from that of the rose, and this again from the hop fly; and, indeed, the number of varieties of aphis is exceedingly large. ”

“ A week after a sharp frost on a May morning the whole of the rose growers in the district affected by the frost will find their plants attacked by the aphis, while the wail of the hop growers at the appearance of the fly will rise simultaneously over a whole district. The scientific explanation is that the appearance of the aphis in such vast numbers simultaneously is due to its prolific nature, but the practical man refuses to credit the suggestion. The aphis is prolific, but not prolific in the same way as is the white ant. ”

“ As a further proof that the bitter principle of the hop is distasteful to the aphis, it is noticeable that when the fly first arrives it always attacks the topmost shoots of the bine where the leaves have not developed, and where the active principle is likely to be weakest. The same position is selected by the aphis of the rose, the bean, and every plant or tree subject to aphis attack—it is the undeveloped and therefore unprotected part which is chosen. ”

“ The ants do not hurt the aphides, but follow them for what they can get out of them. They are continually seen in company; and the ants sometimes drive off the lady-birds and other foes.
The aphis, when attacked by its mortal foe the lady-bird, submits with a good grace. Never did Turk bend his neck to the bow-string, or rush upon the cimeter with greater courage, than the aphis submits itself to the murderous jaws of its devouring foes. It seems quite at ease, and enjoys life to the last bite or sup, while its companions are being killed, and their carcasses heaped up around it. ”

“ Its life is spent in the pursuit and destruction of the aphis, which, were it not for its vigilance, would so increase that it would become, in temperate climates, as great a scourge as is the locust in the localities it inhabits. Not only does the ladybird as a perfect insect live upon the aphis, but in its earlier, though less known, stage it is equally destructive to them, and from the time when it issues from the egg to its death its whole life is passed in the destruction of these pests of the farmer and gardener. ”

“ A "white" aphis can be seen in the photograph at the base of the upper leaf stem. With a small pocket lens the details of this creature's structure can be easily made out. There are several of these aphides on the vine, but the one mentioned is the largest and the most conspicuous. They, are much larger than the nectar-producers, are oval in shape, and distinctly flattened. ”

“ In a work of this character it seems needful to treat more fully of those pests which prove so destructive to plant life, than we have in our brief references.
The Aphis or green louse is the one that most frequently infests our plants, and the rapidity with which it multiplies, is astonishing. Reaumer has proved that in five generations one aphis may be the progenitor of six thousand millions, and there may be ten generations in a year! ”

“ True, the Aphis may at first struggle, the maggot, pierced by the ovipositor, may flinch for a moment, but after that there is complete passivity, without which there can be no complete acquiescence. Self-absorption, that is the moral of it all; for the true self of the Aphis, which is not represented by the outer husk, is absorbed into the Ichneumon, and so in regard to the latter. Thus, throughout the animal kingdom we must look to the inner, and not to the outer, significance. ”

“ Like all insects the aphis has its special insect enemies, among which the lady-bird ("lady-cow" in Worcestershire) is the most important. It lays its eggs in clusters on the hop-leaf, and in a few days the larvæ (called "niggers") are hatched, aggressive-looking creatures with insatiable appetites. It is amusing to watch them hunting over the lower side of the leaf like a sporting dog in a turnip field, and devouring the lice in quantities. ”

“ The aphis will produce twenty-five offspring daily, but this will not account in any way for the fact that within a day or two of the pest making its appearance hundreds of thousands are to be found on every rose bush. Could the female aphis, like the termite, produce eighty thousand per day, the argument that the whole of the rose trees in a garden have been covered by the offspring of comparatively few females who found their way there might be accepted readily enough; but the rate of increase is incredible when we know that each female can produce but twenty-five young in twenty-four hours. ”

“ Aphis in some form or other is the most persistent and perplexing of plant pests. The Green Fly is the enemy of the softer kinds of vegetation, and the Blue and the Black Fly are common plagues of the Peach-house and the orchard. The tender body of the Aphis is instantly affected by conditions unfavourable to its life, and it is therefore easily killed ”

“ But some such aids to faith seem to be necessary when those who are not tolerably familiar with these insects are told of their amazing fertility. Linnæus long since estimated, in regard to one species, that in the course of one year a single Aphis will give rise to a quintillion of descendants—all produced without the aid of a male. ”

“ Do not wait for the aphis to appear before beginning warfare against him. You can count on his coming, therefore it is well to act on the offensive, instead of the defensive, for it is an easier matter to keep him away altogether than it is to get rid of him after he has taken possession of your bushes. If he finds the tang of Nicoticide clinging to the foliage on his arrival, he will speedily conclude that it will be made extremely uncomfortable for him, if he decides to locate, and he will look for more congenial quarters elsewhere. ”

“ While the caterpillar devours the substance of plants, the aphis only sucks their juices, and kills by so enfeebling the shoots that they are unable to put forth their leaves. It is an awkward, slow-moving creature, with its heavy green body swelled almost to bursting with vegetable juice, supported by legs so thin and fragile that they can scarce hold up its weight ”

“ Here, for instance, a wee babe just out of the egg slides down the stalk, and falls plump among a whole family of the aphides. In a twinkling a young aphis larger than himself is impaled on his sharp teeth and its body sucked dry. But this is merely an appetizer; he has only to extend his jaws on right or left to secure another similar [126] morsel, which is emptied in the same manner, and his first meal would only seem to be limited by the number of victims available, so insatiate is his craving. ”

“ The stem mothers of the rosy aphis give birtb parthenogenetically to a second generation of females which are mostly wingless like their mothers; but in the next generation many individuals have wings. Several more generations now rapidly follow, all females; in fact, as with the green aphis, no males are produced till late in the season. ”

“ Besides the Wheat Aphis, which but for such arrangements as have here been glanced at, would almost deprive us of bread, we have the Hop Aphis, a species the dread of which is still more strongly disseminated amongst the masses of this country, inasmuch as its interference would be with the supply of beer. ”

“ Nothing could be less scientific than these arguments, but as somehow there is common sense in them, they commend themselves to the minds of the foolish multitude, who, in spite of the teaching of their instructors, still believe the evidence of their own eyes that the aphis is the product of a certain unhealthy state of the juice of plants. ”

“ A female Blight, as one creature is termed—a very destructive aphis—which was shut up for observation by another naturalist, brought forth ninety-five little ones in less than three weeks, and she can repeat this as often as twenty times during one summer if the weather be favourable to her. ”

“ These may be observed in summer running pretty briskly over all kinds of plants; and, if narrowly watched, they will be found to devour the aphides wherever they find them. The same may be observed of the lady-bird, in its perfect state. Another most formidable enemy to the aphis, is a very minute, black, and slender ichneumon fly, which eats its way out of the aphis, leaving the dry inflated skin of the insect adhering to the leaf like a small pearl: such may always be found where aphides are in plenty. Different species of aphides are infested with different ichneumons. ”

“ But up to this time nearly all the aphides have been females; in the last generation the winged males appear, and are seen assembled among the swarm—the last mother brood laying the eggs which are to start anew the cycle of life the following season.
So far as I have observed, however, the woolly species of aphis never acquires wings, nature having in a measure compensated for their absence in the growth of plumy down, which, according to [237] Harris, is so buoyant as to enable the insect to be borne upon the breeze from tree to tree. ”

“ So long as the hop plant maintains its health the aphis is comparatively harmless, for the plant is then able to elaborate to the full the bitter principle which is its natural protection. On a really hot day in July it is sometimes possible to detect the distinctive scent of the hop quite plainly in walking through the plantation, long before any hops appear, and when this is noticeable very little of the aphis blight can be found. ”

“ It is obvious that as the chief attack is made by aphis on the wing, dressings put on the ground with a view to kill the aphides in the soil are of little avail, for from a neighbouring or even a distant garden where the hills have been not so treated, may come a flight of aphides causing desolation in their track. ”

“ The female produces two kinds of young, as do all the genus Aphis, one normal the other abnormal; the first are alone capable of reproducing their species, while the latter retain their original form, which is not changed throughout their existence. They increase so slowly in size that it may appear doubtful whether they eat, the mouth being rudimentary; they undergo no change; do not acquire wings, and their antennæ always retain the five joints peculiar to all young Aphides before the first moult. ”

“ Kirby informs us what particular species formed these immense flights, but it is most probable they belonged to the Hop-fly, Aphis humuli.
Reaumur tells us that in the Levant, Persia, and China, they use the galls of a particular species of Aphis for dyeing silk crimson.897
In England, the mischief caused by the Hop-fly, Aphis humuli, in some seasons, as in 1802, has brought the duty of hops down from £100,000 to £14,000.
A quite common, though erroneous, belief in England is, that Aphides are produced, or brought by, a northern or eastern wind. Thomson has fallen into the error ”

“ Owen, who adopts the calculations of Tougard to the effect that by agamic multiplication "a single impregnated ovum of Aphis may give rise, without fecundation, to a quintillion of Aphides," Prof. Huxley says:
"I will assume that an Aphis weighs 1/1000 of a grain, which is certainly vastly under the mark. A quintillion of Aphides will, on this estimate, weigh a quatrillion of grains. He is a very stout man who weighs two million grains ”

“ The mountain-ash (Pyrus aucuparia) has its leaves and young shoots frequently affected in this way, and sometimes exhibits galls larger than a walnut or even than a man’s fist; at other times they do not grow larger than a filbert. Upon opening one of these, they are found to be filled with the aphides sorbi. If taken at an early stage of their growth, they are found open on the under side of the leaf, and inhabited only by a single female aphis, pregnant with a numerous family of young. ”

“ Generation after generation is then rapidly produced, numbering sometimes eight or ten before autumn. These are produced alive, and without the intervention of the male. Reaumur estimated that a single Aphis might produce six thousand millions in one summer. The first hatching can be prevented by washing the plant with soft soap and water, or with whale-oil soap, before the buds commence swelling. When the plant is infested with them, it can be washed with tobacco-water and then rinsed in clean water. If in a house, fumigation with tobacco is better. ”