The Aphids, or Plant-Lice
KNOW of no more diverting occupation than watching a colony of aphids through a lens; these insects are the most helpless and amiable little ninnies in the whole insect world; and they look the part, probably because their eyes, so large and wide apart, seem so innocent and wondering. The usual color of aphids is green. As they feed upon leaves, this color protects them from sight; but there are many species which are otherwise colored, and some have most bizarre and striking ornamentations. In looking along an infested leaf stalk, we see them in all stages and positions. One may have thrust its beak to the hilt in a plant stem, and is so satisfied and absorbed in sucking the juice that its hind feet are lifted high in the air and its antennæ curved backward, making altogether a gesture which seems an adequate expression of bliss; another may conclude to seek a new well, and pulls up its sucking tube, folding it back underneath the body so it will be out of the way, and walks off slowly on its six rather stiff legs; when thus moving, it thrusts the antennæ forward, patting its pathway to insure safety. Perhaps this pathway may lead over other aphids which are feeding, but this does not deter the traveler nor turn it aside; over the backs of the obstructionists it crawls, at which the disturbed ones kick the intruder with both hind legs; it is not a vicious kick but a push rather, which says, "This seat reserved, please!"
It is comical to see a row of them sucking a plant stem for "dear life," the heads all in the same direction, and they packed in and around each other as if there were no other plants in the world to give them room, the little ones wedged in between the big ones, until sometimes some of them are obliged to rest their hind legs on the antennæ of the neighbors next behind.
Aphids are born for food for other creatures—they are simply little machines for making sap into honey-dew, which they produce from the alimentary canal for the delectation of ants; they are, in fact, merely little animated drops of sap on legs. How helpless they are when attacked by any one of their many enemies! All they do, when they are seized, is to claw the air with their six impotent legs and two antennæ, keeping up this performance as long as there is left a leg, and apparently to the very last, never realizing "what is doing." But they are not without means of defence; those two little tubes at the end of the body are not for ornament nor for producing honey-dew for the ants, but for secreting at their tips a globule of waxy substance meant to smear the eyes of the attacking insect. I once saw an aphid perform this act, when confronted by a baby spider; a drop of yellow liquid oozed out of one tube, and the aphid almost stood on its head in order to thrust this offensive globule directly into the face of the spider—the whole performance reminding me of a boy who shakes his clenched fist in his opponent's face and says, "Smell of that !" The spider beat a hasty retreat.
A German scientist, Mr. Busgen, discovered that a plant-louse smeared the eyes and jaws of its enemy, the aphis-lion, with this wax which dried as soon as applied. In action it was something like throwing a basin of paste at the head of the attacking party; the aphis-lion thus treated, was obliged to stop and clean itself before it could go on with its hunt, and the aphid walked off in safety. The aphids surely need this protection because they have two fierce enemies, the larvæ of the aphis-lions and of the ladybirds. They are also the victims of parasitic insects; a tiny four-winged "fly" lays an egg within an aphid; the larva hatching from it feeds upon the inner portions of the aphid, causing it to swell as if afflicted with dropsy. Later the aphid dies, and the interloper with malicious impertinence cuts a neat circular door in the poor aphid's skeleton skin and issues from it a full fledged insect.
The aphids are not without their resources to meet the exigencies of their lives in colonies. There are several distinct forms in each species, and they seem to be needed for the general good. During the summer, we find most of the aphids on plants are without wings; these are females which give birth to living young and do not lay eggs. They do this until the plant is overstocked and the food supply seems to be giving out, then another form is produced which has four wings. These fly away to some other plant and start a colony there; but at the approach of cold weather, or if the food plants give out, there are male and female individuals developed, the females being always wingless, and it is their office to lay the eggs which shall last during the long winter months, when the living aphids must die for lack of food plants. The next spring each winter-egg hatches into a female which we call the "stem mother" since she with her descendants will populate the entire plant.
Plant-lice vary in their habits. Some live in the ground on the roots of plants and are very destructive; but the greater number of species live on the foliage of plants and are very fond of the young, tender leaves and thus do great damage. Some aphids have their bodies covered with white powder or with tiny fringes, which give them the appearance of being covered with cotton.
The aphids injuring our flowers and plants may be killed by spraying them with soapsuds made in the proportion of one-quarter pound of ivory soap to one gallon of water. The spraying must be done very thoroughly so as to reach all the aphids hidden on the stems and beneath the leaves. It should be repeated every three days until the aphids are destroyed.
The Aphids, or Plant-Lice
Leading thought—Aphids have the mouth in the form of a sucking tube which is thrust into the stems and leaves of plants; through it the plant juices are drawn for nourishment. Aphids are the source of honey-dew of which ants are fond.
Method—Bring into the schoolroom a plant infested with aphids, place the stem in water and let the pupils examine the insects through the lens.
1. How are the aphids settled on the leaf? Are their heads in the same direction? What are they doing?
2. Touch one and make it move along. What does it do in order to leave its place? What does it do with its sucking tube as it walks off? On what part of the plant was it feeding? Why does not Paris green when applied to the leaves of plants kill aphids?
3. Describe an aphid, including its eyes, antennæ, legs and tubes upon the back. Does its color protect it from observation?
4. Can you see cast skins of aphids on the plant? Why does an aphid have to shed its skin?
5. Are all the aphids on a plant wingless? When a plant becomes dry are there, after several days, more winged aphids? Why do the aphids need wings?
6. Do you know what honey-dew is? Have you ever seen it upon the leaf? How is honey-dew made by the aphids? Does it come from the tubes on their back? What insects feed upon this honey-dew?
7. What enemies have the aphids?
8. What damage do aphids do to plants? How can you clean plants of plant-lice?
I saw it (an ant), at first, pass, without stopping, some aphids which it did not however disturb. It shortly after stationed itself near one of the smallest, and appeared to caress it, by touching the extremity of its body, alternately with its antennæ, with an extremely rapid movement. I saw, with much surprise, the fluid proceed from the body of the aphid, and the ant take it in its mouth. Its antennæ were afterwards directed to a much larger aphid than the first, which, on being caressed after the same manner, discharged the nourishing fluid in greater quantity, which the ant immediately swallowed: it then passed to a third which it caressed, like the preceding, by giving it several gentle blows, with the antennæ, on the posterior extremity of the body; and the liquid was ejected at the same moment, and the ant lapped it up.
Pierre Huber, 1810.