PARASITE AND ITS DESTROYER. THEIR DIFFERENT YOTIONS. dinal vein is perceptible, which, near its middle, gives off a branch running almost to the inner hind end of the wing. The hind wings are much smaller and without veins, except a brown subcostal one, which extends. into the outer margin and abruptly ends a little beyond the middle.

All the examples of this species which I have obtained from cocoons upon the Tobacco-worm have been females. The last of August 1862, I received from Dr. Allen of Saratoga Springs, a larva of the Sphinx Kalmiæ to which thirty-six cocoons were adhering. And the middle of July, the following year, H. Markham, Esq., of Stony Brook, Long Island, sent me the same larva, similarly infested. It may here be incidentally observed that both these gentlemen met with these larvæ upon the leaves of the grape vine. As I have repeatedly observed it, in different years, upon the lilac, the leaves of which are certainly its usual food, the interesting query arises, whether, when it is infested internally with parasites, they do not cause a morbid appetite in the worm, whereby it ceases to relish its natural food and comes to crave the leaves of the grape in place of those of the lilac ? Flies were obtained from more than half the cocoons upon the first mentioned worm, and these being all of one species I supposed they were probably the true parasites of the Lilac-worm But I now find on comparing them, that they are identical with this species which is now under consideration. It thrus appears that the cococns adhering to the Lilac-worm had been formed by a species of Microgaster, probably this same species which infests the tobacco-worm, and that the flies I obtained were its parasites and consequently were protectors instead of destroyers of the Lilac-worm. The cocoons from Mr. Markham, might perhaps have given more light upon this subject, and I now regret that, when they came to hand, supposing they would only produce the same flies which I had examined the preceding summer, I felt that it would be a waste of time to attend to the rearing of their inmates.

Of the flies obtained from the Lilac-worm, four were males, whereby it appears that this sex differs from the females above described, in the following particulars: Ist, their color is lighter and more bright, being brilliant metallic green, when dried becoming blue green; 2d, their antennæ are tarnished yellow, longer, and not at all thickened toward the tips, their joints being cylindric and a third longer than thick, with the last joint egg-shaped and but little longer than its predecessor; 3d, the abdomen is flattened oval and rounding at its tip, with a large translucent pale yel. low spot near the base; 4th, the legs are paler and pure yellow without any mixture of orange tawny.

One who is acquainted with this insect and the Microgaster fly, will readily distinguish them by their motions, nothwithstanding their smallness and similarity in size. The Microgaster is very brisk and active in its movements, running about with agility and flying away if any danger menaces it. This insect, on the other hand, appears tame and sedate, walking around slowly, and as if with deliberation as to what it is doing; and if any annoyance approaches it, to escape therefrom it gives a slight skip, throwing itself about an inch, and repeating this leap again and again if pursued, it being not at all inclined to take wing.

[ocr errors]



TOBACCO-WORY. And after these flies have left their cocoons, it is readily told by the appearance of each cocoon whether it is a Microgaster or a Pteromalus fly which has come out from it. The Microgaster, by which all the cocoons are constructed, makes an opening for its escape, in a more neat and artistic manner than does its destroyer. When it passes from its pupa state and awakes to life in its perfect form, it finds itself closely pent up within its narrow cell -80 closely that about the only motion it is able to make is to turn its head from side to side. And it discovers that by grasping with its jaws the wall of its cell, it is hereby able to gradually roll itself over in its bed. And now, with the minute sharp teeth at the ends of its jaws, it cuts a slit transversely through the wall of its cell, lengthening this slit more and more as it gradually turns itself around. Thus it cuts the end of its cocoon smoothly off in the form of a little lid, a few unsevered fibres being left on one side, which serve as a hinge to hold this lid in its place. The inclosed fly then pressing its head against this lid raises it up and crawls forth from its prison. Thus the evacuated cocoon has its end smoothly cut off, with the severed portion usually adhering to it. The Pteromalus fly, on the other hand, being a size smaller, is able to move about and can probably turn itself around inside of the Cocoon. And to make its escape, it gnaws a hole through the side near one end, of sufficient size for its body to pass through, this hole in different instances being round, oval, or irregular, and its edges ragged and uneven.

In addition to the eggs of the Microgaster, which are inserted under the skin of the Tobacco-worm and thus are not visible externally, I have occasionally met with a worm having one or more eggs glued upon its surface, usually placed in a crease of the skin to render the attachment to it more secure. These eggs are about three-hundredths of an inch long and a third as thick, oval, white, smooth and glossy like enamel. Within them a minute soft white worm or maggot becomes formed, which is hatched by gnawing through the shell of the egg at one end, and as it is coming out, it sinks itself downward through the skin of the worm and into its body, a blackish dot upon the skin near the end of the empty egg marking the point where it has entered. Its history I have not been able to trace further than this. The facts show it to be another parasite destroying the Tobacco-worm, and that it is probably a two-winged fly belonging to the order DIPTERA.

The remedies for this insect are remaining to be spoken of. But as we have had no personal experience in combatting it, it will not be expected that we dwell upon this branch of the subject at any length.

The leaves of the potato and tomato being of no value, the presence of this worm upon them' is wholly disregarded, as its limited numbers never consume the foliage to such an extent as to perceptibly diminish the growth of the tubers in the one or of the fruit in the other of these plants. But with the tobacco it is very different. The whole value of this plant depends upon its leaves; consequently every morsel which this worm consumes from them is a loss, and if the leaves are much eaten the loss is great. The utmost vigilance is therefore required to save the tobacco from injury from POTATO-BETTLE. ITS LOCALITIES. ITS KAXE. this enemy. At the South, where they have had long and sore experience with the twin sister of our insect, the only remedy found to be effectual is searching out and destroying the worms. This "worming” of the tobacco fields, as it is termed, is an indispensable measure, forming a regular part of the tobacco culture. After the leaves are grown to a sufficient size for the worm to begin to feed upon them, not a day is suffered to pass without examining them. The leaves are so large and so very tender and brittle, except for a short period at mid-day, when they become pliant from being somewhat wilted by the heat of the sun, that the utmost care is requisite in passing among them to avoid breaking and tearing them. Notwithstanding the closest scrutiny some of the worms will be overlocked, at each search which is made. Moreover, new moths are coming out and depositing their eggs day after day, whereby a succession of worms are appearing. Thus it becomes necessary to repeat this examination daily, searching out and destroying every worm while it is yet young and small.

When these ugly looking worms first began to be noticed upon the tomatoes in our gardens, some sensitive persons were much alarmed with fears that they were poisonous and would render the fruit deleterious if they happened to touch or crawl over it. But such fears are wholly groundless. The sharp, thorn-like tail of this worm, however, if it chances to penetrate the skin, inflicts a painful wound. This is the only thing to be guarded against.

[ocr errors]

10. TEN-LINED POTATO-BEETLE, Doryphora 10-lineata, Say. (Coleoptera. Chry:

somelidæ.) Plate 4, figure 6. Eating the leaves of the potato in immense numbers through the whole summer; a thick, oval beetle nearly half an inch long, and of a pale yellow color with five black stripes on each wing cover, accompanied by its thick-bodied, worm-like larva of a pale yellow color with rows of black dots, and six legs upon its breast and a pro-leg at the pointed end of its body.

In connection with the foregoing potato-worm, some account may here be given of a new enemy which, within the past two or three years, has fallen upon the potato-vines in numerous places all over the Northwestern States, stripping them of every vestige of their foliage and eating the stalks also, and hereby arresting the formation and growth of the tubers. Specimens of this insect are being frequently sent me for information respecting it, whereby I am able to present a description of it in its different stages of life and several important facts respecting it. Fortunately for us, it is not an inhabitant of our State, being found only in the valley of the Mississippi at a distance from our borders.

This insect was first discovered as being common on the Upper Missouri, by Mr. Say, when accompanying Long's Exploring Expedition to the Rocky Mountains. He met with it upon the Arkansas river also. In 1823, he published a description of it (Journal of the Academy of Natural Sciences, vol. iii, p. 453), naming it from the number of the stripes upon its wingcovers Doryphora 10-lineata or the Ten-lined Doryphora—this genus having been separated from the old genus Chrysomela, by Illiger, to include a number of South American species which have the middle portion of the


POTATO-BEETLE. breast prolonged into a horn-like point, wherefore the name; Doryphorus being a Greek word meaning a spear-bearer, and particularly memorable as the name of one of the most celebrated statues of the sculptor Polycletus. But our insect and a few other species of this genus are destitute of the sharp, thorny point alluded to. Chevrolat, in Dejean's Catalogue, proposed to form these into a distinct genus, named Polygramma—i. e., many. lined. But this step has not been approved of by subsequent authors.

The year after Say described this insect, the distinguished German entomologist Germar also published it, under the name Doryphora juncta, which, of course, will be merely a synonym of the anterior name.

The first notice of this as being an injurious insect, appears in the Prairie Farmer of August 29th, 1861 (vol. viii, p. 116), in a letter from J. Edgerton, of Gravity, Iowa, saying that "they made their appearance upon the vines as soon as the potatoes were out of the ground, and there being a cold, wet spell of weather about that time, they devoured them as fast as they were up.” They appeared most fond of the Prince Albert variety, doing but little injury to several other kinds. Several generations appeared to grow up in the course of the summer. The specimens were sent to C. Thomas, Esq., of Marion, Williamson county, Ill., who in reply announces them to be the species above named, and says that this same insect "is found in abundance in Southern Illinois; but so far I have only discovered it on worthless weeds and low shrubs; and here it has not proved injurious to useful vegetation," wherefore he thinks it is only accidental that it has fallen upon the patotoes in Mr. Edgerton's vicinity, and that some peculiarity of the plants, state of the atinosphere, or other influence may next year cause it to forsake the potato and take up its residence upon some other plant.

The next year, Thomas Murphy, of Atchison, Kansas, sent a number of the beetles to the Valley Farmer, with an accompanying letter, published in that periodical July, 1862 (vol. xiv, p. 209), saying that in August, 1881, “soon after a heavy shower of rain, these bugs suddenly made their appear. ance in large numbers on the potato vines. They were so numerous that in many instances they would almost cover the whole vine. It is no exaggeration when I tell you that we have often, in a very short time, gathered as many as two bushels of them. When the cold weather set in they disappeared. Early this spring I was setting out some apple trees, and away down in the hard yellow clay, I found these bugs apparently dead, but put them in the sun and they immediately came to life. They have again (May 220) made their appearance in large numbers in my garden. Last year they first ate up everything green on the potato vines, then commenced on the tomatoes, and so on, on everything green. Strange to say, they trouble no one else.” Some of the beetles had been forwarded to Benj. D. Walsh, Esq., of Rock Island, Illinois, who communicates their name and a good figure, but is singularly unfortunate, not to say erroneous, in several of his statements made in connection with this subject; for instance, that the New York weevil is “an exclusively western species," " Mr. Murphy's account is the first on record of this beetle occurring in gardens in such


ITS EGGS AND LARVA DESCRIBED. numbers as to be injurious," &c. He regards the fact of Mr. Murphy's finding the beetles under ground in the spring, as full proof that this insect always goes under ground to pass its pupa state; overlooking the additional fact that Mr. M. found these beetles lying dormant and apparently dead, which indicates that no warmth had at that time penetrated the earth sufficient to change them from their pupa to their perfect state. Mr. M's. recital of his observations would seem to make it plain that it is in their perfect, not in their pupa state that they hibernate. He says the beetles were immensely numerous; but when the cold weather set in they disap peared. Early the next spring he again found them away down in the hard yellow clay, apparently dead but immediately reviving when exposed to the sun. And finally, May 22d, they had again made their appearance abroad in large numbers. Everything thus appears to show that these beetles remain abroad in full force until a frosty night cuts off their food and chills them, whereupon they hasten into any crack they can find in the hard clay soil, or under any log or stone lying on the surface. They there become dormant and thus repose through the winter, and with the warmth of returning spring revive and issue from their retreats.

Specimens of this beetle, its eggs and larvæ, we received first from John 8. Bowen, Elkhorn city, Nebraska, in May 1863. Similar remittances have since come to hand from different parts of Iowa. A correspondent at Webster City writes that these insects are "very voracious feeders, not only denuding the vines of every vestige of a leaf, but also devouring the stalks. Killing them seems to do no good, they breed so rapidly; and as they fly through the air, they would soon be re-established were they all exterminated from a field. It is now August 1st, and few if any tubers are yet set upon my potatoes, though the planting was very early." And from New Sharon we are told that soine have been discouraged from planting potatoes, the ravages of this potato-bug have been so great.

The beetles though sent from such a great distance have in every instance reached me alive, whilst the larvæ accompanying them have been nearly or quite dead, except in two or three instances. The eggs also uniformly batch and the young from them perish before they come to hand. Kept in confinement, the beetles usually live so long as they are supplied with food. I have thus kept an individual captured in May, until the frosts of autumn destroyed my supply of potato and tomato leaves. And beetles newly born, if gradually exposed to the cold, will undoubtedly become torpid and dormant, and lying in this state through the winter will revive and return to activity with the return of warm weather.

The female in confinement drops her eggs in little clusters upon the leaves on which she has been feeding. The eggs are bright yellow, smooth and glossy, 0.06 long and 0.035 broad, of an oval form with rounded ends.

The Larva when full grown is over a half inch in length and half as thick, being thickest back of the middle and tapering to a point at its tip. It is a thick plump grub, strongly arched above, and when viewed on one

[ocr errors]
« ElőzőTovább »