Part 5 (1/2)

EOCENE.

OROHIPPUS.

FOOTNOTES:

[5] I use the word ”type” because it is highly probable that many of the forms of _Anchitherium_-like and _Hipparion_-like animals existed in the Miocene and Pliocene epochs, just as many species of the horse tribe exist now; and it is highly improbable that the particular species of _Anchitherium_ or _Hipparion_, which happen to have been discovered, should be precisely those which have formed part of the direct line of the horse's pedigree.

[6] Since this lecture was delivered, Professor Marsh has discovered a new genus of equine mammals (_Eohippus_) from the lowest Eocene deposits of the West, which corresponds very nearly to this description.--_American Journal of Science_, November, 1876.

FIGHTING PESTS WITH INSECT ALLIES

LELAND O. HOWARD

[Dr. Howard is Chief of the Division of Entomology in the United States Department of Agriculture at Was.h.i.+ngton. He is a lecturer at Swarthmore College and at Georgetown University. He has written ”The Insect Book,” published by Doubleday, Page & Co., New York; and a work on Mosquitoes, issued by McClure, Phillips & Co., New York. Both are books of interest from the hand of a master: they are fully ill.u.s.trated. The narrative which follows appeared in _Everybody's Magazine_, June, 1901.]

Some twenty-five years ago there appeared suddenly upon certain acacia trees at Menlo Park, California, a very destructive scale bug. It rapidly increased and spread from tree to tree, attacking apples, figs, pomegranates, quinces, and roses, and many other trees and plants, but seeming to prefer to all other food the beautiful orange and lemon trees which grow so luxuriantly on the Pacific Coast, and from which a large share of the income of so many fruit-growers is gained. This insect, which came to be known as the _white scale_ or _fluted scale_ or the _Icerya_ (from its scientific name), was an insignificant creature in itself, resembling a small bit of fluted wax a little more than a quarter of an inch long. But when the scales had once taken possession of a tree, they swarmed over it until the bark was hidden; they sucked its sap through their minute beaks until the plant became so feeble that the leaves and young fruit dropped off, a hideous black s.m.u.t-fungus crept over the young twigs, and the weakened tree gradually died.

In this way orchard after orchard of oranges, worth a thousand dollars or more an acre, was utterly destroyed; the best fruit-growing sections of the State were invaded, and ruin stared many a fruit-grower in the face. This spread of the pest was gradual, extending through a series of years, and not until 1886 did it become so serious a matter as to attract national attention.

In this year an investigation was begun by the late Professor C. V.

Riley, the Government entomologist then connected with the Department of Agriculture at Was.h.i.+ngton. He sent two agents to California, both of whom immediately began to study the problem of remedies. In 1887 he visited California himself, and during that year published an elaborate report giving the results of the work up to that point. The complete life-history of the insect had been worked out, and a number of washes had been discovered which could be applied to the trees in the form of a spray, and which would kill a large proportion of the pests at a comparatively small expense. But it was soon found that the average fruit-grower would not take the trouble to spray his trees, largely from the fact that he had experimented for some years with inferior washes and quack nostrums, and from lack of success had become disgusted with the whole idea of using liquid compounds. Something easier, something more radical was necessary in his disheartened condition.

Meantime, after much sifting of evidence and much correspondence with naturalists in many parts of the world, Professor Riley had decided that the white scale was a native of Australia, and had been first brought over to California accidentally upon Australian plants. In the same way it was found to have reached South Africa and New Zealand, in both of which colonies it had greatly increased, and had become just such a pest as it is in California. In Australia, however, its native home, it did not seem to be abundant, and was not known as a pest--a somewhat surprising state of affairs, which put the entomologist on the track of the results which proved of such great value to California. He reasoned that, in his native home, with the same food plants upon which it flourished abroad in such great abundance, it would undoubtedly do the same damage that it does in South Africa, New Zealand, and California, if there were not in Australia some natural enemy, probable some insect parasite or predatory beetle, which killed it off. It became therefore important to send a trained man to Australia to investigate this promising line.

After many difficulties in arranging preliminaries relating to the payment of expenses (in which finally the Department of State kindly a.s.sisted), one of Professor Riley's a.s.sistants, a young German named Albert Koebele, who had been with him for a number of years, sailed for Australia in August, 1888. Koebele was a skilled collector and an admirable man for the purpose. He at once found that Professor Riley's supposition was correct: there existed in Australia small flies which laid their eggs in the white scales, and these eggs hatched into grubs which devoured the pests. He also found a remarkable little ladybird, a small, reddish-brown convex beetle, which breeds with marvellous rapidity and which, with voracious appet.i.te, and at the same time with discriminating taste, devours scale after scale, but eats fluted scales only--does not attack other insects. This beneficial creature, now known as the Australian ladybird, or the Vedalia, Mr. Koebele at once began to collect in large numbers, together with several other insects found doing the same work. He packed many hundreds of living specimens of the ladybird, with plenty of food, in tin boxes, and had them placed on ice in the ice-box of the steamer at Sydney; they were carried carefully to California, where they were liberated upon orange trees at Los Angeles.

[Ill.u.s.tration: Vedalia, or Australian Ladybird]

These sendings were repeated for several months, and Mr. Koebele, on his return in April, 1889, brought with him many more living specimens which he had collected on his way home in New Zealand, where the same Vedalia had been accidentally introduced a year or so before.

[Ill.u.s.tration: Larvae of Vedalia eating White Scale]

The result more than justified the most sanguine expectations. The ladybirds reached Los Angeles alive, and, with appet.i.tes sharpened by their long ocean voyage, immediately fell upon the devoted scales and devoured them one after another almost without rest. Their hunger temporarily satisfied, they began to lay eggs. These eggs hatched in a few days into active grub-like creatures--the larvae of the beetles--and these grubs proved as voracious as their parents. They devoured the scales right and left, and in less than a month transformed once more to beetles.

And so the work of extermination went on. Each female beetle laid on an average 300 eggs, and each of these eggs hatched into a hungry larva.

Supposing that one-half of these larvae produced female beetles, a simple calculation will show that in six months a single ladybird became the ancestor of 75,000,000,000 of other ladybirds, each capable of destroying very many scale insects.

[Ill.u.s.tration: Twig of olive infected with Black Scale]

Is it any wonder, then, that the fluted scales soon began to disappear?

Is it any wonder that orchard after orchard was entirely freed from the pest, until now over a large section of the State hardly an Icerya is to be found? And could a more striking ill.u.s.tration of the value of the study of insects possibly be instanced? In less than a year from the time when the first of these hungry Australians was liberated from his box in Los Angeles the orange trees were once more in bloom and were resuming their old-time verdure--the Icerya had become practically a thing of the past.

[Ill.u.s.tration: Rhizobius, the imported enemy of the Black Scale of the Olive.]

This wonderful success encouraged other efforts in the same direction.

The State of California some years later sent the same entomologist, Koebele, to Australia to search for some insect enemy of the black scale, an insect which threatened the destruction of the extensive olive orchards of California. He found and successfully introduced another ladybird beetle, known as _Rhizobius ventralis_, a little dark-coloured creature which has thrived in the California climate, especially near the seacoast, and in the damp air of those regions has successfully held the black scale in check. It was found, however, that back from the seacoast this insect did not seem to thrive with the same vigor, and the black scale held its own. Then a spirited controversy sprung up among the olive-growers, those near the seacoast contending that the _Rhizobius_ was a perfect remedy for the scale, while those inland insisted that it was worthless. A few years later it was discovered that this olive enemy in South Europe is killed by a little caterpillar, which burrows through scale after scale eating out their contents, and an effort was made to introduce the caterpillar into California, but these efforts failed. Within the past two years it has been found that a small parasitic fly exists in South Africa which lays its eggs in the same black scale, and its grub-like larvae eat out the bodies of the scales and destroy them. The climate of the region in which this parasite exists is dry through a large part of the year, and therefore this little parasitic fly, known as _Scutellista_, was thought to be the needed insect for the dry California regions. With the help of Mr.

C. P. Lounsbury, the Government entomologist of Cape Colony, living specimens of this fly were brought to this country, and were colonized in the Santa Clara Valley, near San Jose, California, where they have perpetuated themselves and destroyed many of the black scales, and promise to be most successful in their warfare against the injurious insect.