At the recent Yale College Lectures, Dr. Fitch made the following interesting remarks on Insects Injurious to Fruit-Trees. He is certainly mistaken, however, in saying that but one slit is made on a fruit; we have often seen two, and no doubt others have. So, too, the statement that plum-trees the branches of which hang over water are exempt from the curculio, has no foundation in fact. We have examined a number of such trees, and found them invariably just as badly stung as others, except in some cases where other means of protection had been resorted to. It is a matter of every-day observation, that trees which overhang water are no more exempt from insects than others, and it may be safely assumed that the curculio has no such instinct as is here imputed to it - Ed.

There are at present known to us, in the United States, 60 different insects which prey upon the apple, 12 on the pear, 16 on the peach, 17 on the plum, 85 on the cherry, and 30 on the grape. Prominent among these is the plum weevil, or curculio, which Dr. Fitch stigmatized as the worst insect of our country; for though the midge is at present causing a greater amount of pecuniary loss, he thought its career would be like that of its predecessor, the Hessian fly, and that it would eventually be mastered and subdued by its parasite destroyers. Unlike the wheat midge, the curculio is a native insect of this country, which has now been known upwards of a century, during all of which time it appears to have gradually multiplied and increased its forces, without any important cessations or intervals in its ravages, no parasite destroyer of it having ever been discovered till within a few months past. It was first noticed by the botanists Collinson and Bartram, in 1746, as totally destroying the nectarines in and about Philadelphia, while the plums were but slightly molested. Their turn came next, however, and each subsequent investigator found it ravaging a different section of country.

Notwithstanding the volumes written upon it, we do not to this day know where the curculio lives, and what it is doing for three-quarters of the year. All that is currently known of it is, that it is a small brown and white beetle, which makes its appearance on plum-trees when the young fruit is half grown; that it cuts a crescent-shaped slit upon the side of the fruit and drops an egg into the wound, from which egg a small white worm hatches, which burrows in the fruit, causing it to wilt and fall from the tree, whereupon the worm crawls into the ground to repose for two or three weeks during its pupa state; and that it comes out in the latter part of July a beetle, like the parent which six weeks before stung the fruit. This, which is currently supposed to be the main and essential part of its history, Dr. Fitch judges to be quite the reverse; and he is convinced that if there were no fruit for the curculio to eat, it would still thrive to its entire satisfaction.

In New England and New York, the beetle may be found abroad the last of March, if the weather is fine, though usually it is not till about the middle of May; and in a week or two after it becomes quite common. It is found standing or slowly walking upon the trunk and limbs of the plum, cherry, apple, the wild thorn-apple, the butternut, and other trees. Those on the butternut are plumper than the others. From this time onward, till cold weather returns, we continue to meet with it, and late in autumn it is to be seen on the flowers of the golden-rod as plentifully as at any time through the season. When the young fruit appears in June, it attacks it with the skill of an epicure, selecting the choicest varieties first. Its crescent-sbsped incision is the signal of destruction, as was the crescent banner of the Moslem of old. The slit made, one egg is deposited; and but one slit is made on a fruit. The peach, plum, and apple, when stung, wilt and fall; but the cherry and thorn-apple do not. This is because the larger fruit contains a sufficient amount of nourishment to mature the worm; while the smaller ones must grow on to elaborate the quantity of food which the worm needs.

It is a fact not generally known, that apples are attacked by the plum curculio, yet so great are the losses of this particular fruit, that the lecturer gave it as his opinion that the poorer yield of our orchards now, as compared with heretofore, is due to this insect The wilted fruit literally covers the ground, under many trees, the fore part of July. Cut into this fruit, and you will find the same curculio worm therein as in the fallen plums.

From the fact that this insect comes forth three weeks before there is any fruit ready for it to eat, and remains after the fruit is gone, Dr. Fitch thinks that it has other places of refuge to cradle its young besides the young fruit. In fact, it is well ascertained that it breeds in the black knot excrescences on plum and cherry-trees, as eagerly as in young fruit. Hence it has been thought to cause the excrescences. But having examined the black knots fully in every stage of their growth, Dr. Fitch says decidedly they are not produced by this or any other insect, nor are they a vegetable fungus, but are purely a local disease of the limbs, in which the bark and wood are swollen and changed to a spongy substance, but without any of the juiciness which belongs to young fruit. This disease has some analogy to the cancer in the human body, and its cure is the same, namely, the knife, removing the diseased part totally, as soon as discovered.

With Melsheimer, Dr. Fitch believes that the curculio breeds in the bark as well as the fruit of trees, for on a specimen of pear-wood sent him some years ago, his microscope revealed crescent cuts in the bark, like those on young fruit, in which little maggots were lying side by side, ready to eat their way onward when the warmth of spring revived them.

Within six months D. W. Beadle, of St. Catharine's, C. W., has sent the Doctor a curculio parasite, which is furnished with a bristle-like sting, with which it pierces the black knot to where the curculio larva lies, and deposits an egg in the body of the latter, to hatch and gradually kill it. The late David Thomas, of Union Springs, New York, first recommended knocking the plum-tree to remove weevils. The remedy is partial, but not infallible. Mr. A. P. Cum-ings, of New York, recommends to syringe the trees with a mixture of four gallons lime-water, four gallons tobacco-water, one pound whale-oil soap, and four ounces sulphur. The tobacco and soap in solution Dr. Fitch thinks good, but doubts whether the other ingredients add anything to the value of the mixture. There is much testimony to substantiate the fact that trees, whose limbs project over water, always bear fine crops of plums, the curculio being aware that its young will drown if the fruit drops into the water.

Another important insect is the apple-tree borer, a long grub which resides under the bark and bores into the solid wood, sometimes below, but usually slightly above the ground, and is two or three years in getting its growth. A few years since, an agent of one of our large nurseries canvassed Washington county, N. Y.f disposing of trees to the amount of three thousand dollars. More than half of these trees have since been destroyed by this borer; a direct loss of $5,000 from this insect in that single county, in addition to the labor lost in planting and nursing these perished trees. This must not be confounded with the borer in the roots of peach-trees, which is the progeny of a moth, while this is the young of a brown, long-horned beetle, having two white stripes the whole length of its back. Specimens of this, as of the other insects spoken of by the lecturer, and of the wood as perforated by it, were passed from hand to hand through the audience. The common soft soap rubbed on the bark of the trees the latter part of May, prevents the attack of this insect.

If this be neglected, and the borers have made a lodgement in the bark, their presence is usually shown by particles like sawdust, which they thrust out of their burrows, and when discovered they should be cut out with a knife or chisel without delay.