THE MOTHER OF MILLIONS

Otago Witness, Issue 2927, 20 April 1910, Page 88

THE MOTHER OF MILLIONS

By Panax.

"Nature never makes mistakes." How often have we heard it? Accepted as a truth by some, rejected indignantly by others. I elect to stand with the latter party, and hereby nominate the aphis family as just grounds for my belief. Go to the turnip fields of the Taieri—but taKe your smelling salts; enter the kitchen garden of any suburbanite, note the cabbages, the savoy, and the emaciated curly-green —and vote with me. But do not dismiss them as uninteresting, for in this muchscattered family we find much that is instructive.

The most pleasant to handle is undoubtedly the "green .fly" of the rose bush. Take the- tip of almost any young shoot, and there, by 'the help of an ordinary lens, examine at your leisure one of the marvels of the insect world. How motionless they seem. Let us single out this green one and observe. The six legs —one pair forward and the other two pair aft—seem placed to secure the insect securely to the succlent shoot. The two antennae wave aimlessly about, otherwise the creature seems asleep. But, unfortunately for the plant, the aphis is pursuing its mission in life, sucking from the plant the rightful nourishment of the shoots and leaves. The proboscis is forced into the sappy growth, and then a bountiful Providence (for the parasite) steps in, for as the creature sucks, a supply is sent up to counteract the deficiency, which merely provides for the material comfort of our friend the plant-louse. Getting their living so easily, it is not to be marvelled at that their bodies are very tender, being practically the sap of their unwilling host. They are easily destroyed—an energetic finger and thumb can squash hundreds in a few minutes. But what does that matter to the family? Comparatively nothing. Birds and insects, not to mention irate gardeners with mysterious concoctions, slaughter them by thousands, but still they increase, stili"they flourish and thrive. And what is the explanation? It is their wonderful reproductory powers. A single aphis will produce 90 young ones ; the second generation will give 8100; these give .a third generation, which amounts to 729,000 ; the fourth, 65,610,000; the next, 590,490,000, will produce the sixth generation of 53,142,100,000; the seventh, 4.782,789,000.000. In some years 11 generations make their appearance. It is not a matter of surprise that when the weatheir conditions are favourable the pest becomes almost unendurable. Out on the Taieri Plain just now huge swarms, resemblinig clouds of dust, may be seen. The turnips are practically ruined. The nurserymen around Dunedin are throwing away their cabbage plants by the thousand. The housewives will have to pay for the attentions of these little visitors, as the crisp savoy and curly borecole will be dear throughout the coming winter and early spring. But almost every plant has its own particular variety. The cabbage are infested by a small greenish gray one. The. apple tree has its particular species—on any neglected apple tree, swellings, on which a white fluff is noticeable, may be seen. This woolly aphis, or American blight, like its relation installed on the rose bush, pursues its vocation, drawing the sap from the wound, and Jie accelerated flow to the particular point causes a swelling to appear. Down in the Jubilee Park the other day I was attracted by the autumn glory of the silver birches. . Sitting there on the dry bank, I became aware of the presence of hundreds of wax-eyes plantively "cheeping," but apparently intent on business. Hanging on by their claws, the little acrobats twisted to the underside of the leaves, and there seemed to gather some delicacy. Knowing that they were not after fruit, and suspecting their object. I closely examined some birch leaves, and there, under each leaf, was a little family of half a dozen aphides. The "twinkie" is sometimes called the blight bird, and so he is. Many a time I have admired him cleaning my rose bushes, but never before have I noticed the pest on the birches. It has been such a dry summer that while the slugs (thank (goodness!) have suffered, these other pests have improved the shininor hour. Bird preys on bird, and insect on insect! The following cablegram, dated April 3, from Washington, is suggestive : " Fifty-two million ladybirds, weighing a ton, reared at the State insect institution at Sacramento, have been sent to the melon fields of the State of California to kill aphides and other pests." Only when we remember the importance of the fruit and seed industry in California can we

realise that it pays to rear the ladybird such quantities. The much-abused sparrow sometimes lends a hand in the work; he amuses himself by. chasing the flying insects •as they hover over the garden plots. Two very interesting points may now be mentioned. The first is that of the mode of reproduction. Charles Bonnet, the great naturalist of Geneva, made the astounding discovery that aphides can increase in numbers without the intercourse of the sexes. He procured a young aphis and isolated it, meanwhile studying it intently. Let us hear the story as he tells it. "... My plant-louse

changed its skin four times : on the 23rd, in the evening-; on the 26th, at 2 in the afternoon ; on the 29th, at 7 in the morning ; and on the 31st, at about 7 in the evening. . . . Happily delivered from

these four illnesses through which it was obliged to pass, it at last reached that point to which, by my care, I had been trying to bring it. It had become a perfect, plant-louse. On June 1, at about 7 in the evening, I saw, with great satisfaction, that it had given birth to another ; from that time I thought I ought to look upon it as a female. From that day up to the 20th inclusive, she produced ninety-five little ones, all alive and doing well, the greatest number of which were born under my own eyes." Encouraged by these results, the gifted naturalist pursued his investigations. " On July 12, about 3 o'clock in the afternoon, I shut U'p a plant-louse that had been borne under my eyes. On the 20th of the same month, at 6 o'clock in the morning, it had already produced three little ones. But I waited till the 22nd, towards noon, before I shut up a plantlouse of the second generation, because I could not manage earlier to be present at the birth of those produced by the mother I had condemned to live in solitude. I always continued to observe the same precautions. I shut up only those plant-lice which were born under my very eyes. A third generation began on August 1; it was on this day that the plant-louse I had shut up on July 22 gave birth to this generation. On August 4, about 1 o'clock in the afternoon, • I put into solitary confinement a plant-louse of the third generation. On the 9th of the same month, at 6 in the evening-, a fourth generation, due to this last one, had already seen the light—it had given birth to four little ones. On the same day, towards midnight, all intercourse with its own species was forbidden to the plant-louse of the fourth generation born at that hour. On the 18th, between 6 and 7 o'clock in the morning, I found this last in the company, of four little ones to which it had given birth." Neglect to supply the insects with food, brought this, experiment to a close with the fifth generation; but many subsequent experiments prove that the foregoing are true and correct in every particular. If a cabbage leaf be examined carefully with the glass, two distinct types will be noticed —one with wings and the other without. . The wingless insects produce the young alive during the warm months. But with the cold of winter the aphides are ail killed. How then do they reappear each season? The winged individuals are male and female, and as the autumn advances the latter lays eggs which survive the regours of the winter, and in spring hatch out. The larvae grow and commence reproducing their kind as recorded in the first quotation. Nature has blessed them, so that they may be a curse to us ! It must have cost hundreds of dollars to rear those ladybirds ! And turnips will be dear this winter!

The other point of interest about these little creatures is their relations with the ants. The latter are often held up for inspection and approbation. We have all heard about the ants' "cows." Now these " cows " are aphides. Take a specimen from the rose-bush again, and observe that, sticking upwards and backwards from the hinder part of the abdomen, are two " horns." If you are careful and patient enough you may discover at the extremity of these movable "horns" a little drop o\ a surgary secretion, made by the aphis. It has been noticed that the young ones partake of this fluid before they are old enough to absorb plant juices. The wise ants have discovered this interesting fact. M. Morren, a celebrated French observer, has the following : —" It has been already noticed that the ants waitedl for the moment at which the plant-lice caused this precious manna to come out of their abdomen, which they immediately seized. But I discovered that this was the least of their talents, and that they also knew how to manage to be served with this liquid at will. This is their secret. A branch of a thistle was covered with brown ants and plant-lice. I observed the latter for some time, so as to discover, if possible, the moment when they caused this secretion to issue from their bodies; but I remarked that it very rarely came out of its own accord, and that the plant-lice, Avhich were at some distance from the ants, squirted it out with a, movement resembling a kick. How did . it happen, then, that thet ants wandering about on the thistle were nearly all remarkable for the size of their abdomens, and were evidently full of some liquid? This I discovered by narrowly watching one ant. whose proceedings I am going to describe minutely. I saw it at first passing, without stopping, over some plant-lice, which did not seem in the least disturbed by its walking over them; but it soon stopped close to one of the smallest, which it seemed to coax with- its antennae touching the extremity of its abdomen very rapidly, first with one of its antennte and then with the other. I saw with surprise the liquid come out of the body of the plant-louse, and the ant forthwith seize upon the droplet and convey it to its mouth. It then brought ite antennae to bear upon another plant-louse, much larger than the first; this one, caressed in the same manner, yielded the nourishing fluid from its body i» ftjjxiuch larger dose. The ant ad-

vanced and took possession of it. It then passed to a third, which, it cajoled as it had the preceding ones, giving it many little strokes with its antennse near the hinder part of it® body; the liquid came out immediately and the ant picked it up. . .«* • A small number of these repasts are sufficient to satisfy the ant's appetite." To ensure a supply of aphides, the ants tend the eggs themselves, andl care for the young until the latter are fit to take their places in the milking herd.

And so we see that this little parasite, repulsive in some ways, is attractive in others. Little aphis—a curse to the gardener, a cow to the ant, a meal to the ladybird,—what is your part in the great scheme of things?