Page images
PDF
EPUB

states,* that the worms are about one tenth of an inch in length, and of a yellow or straw color; and that, in the month of November, they appeared to have passed to the chrysalis state. They live through the winter unchanged in the straw, many of them in the stubble in the field, while others are carried away when the grain is harvested.

When the barley is threshed, numerous small pieces of diseased straw, too hard to be broken by the flail, will be found among the grain. Some of these may be separated by the winnowing machine, but many others are too large and heavy to be winnowed out, and remain with the grain, from which they can only be removed by the slow process of picking them out by hand.

In the winter of 1829, Cheever Newhall, Esq., furnished me with a few pieces of diseased barley-straw, each of which contained several small whitish maggots. Since that time this affection of the barley has only once fallen under my notice, though I have reason to think that it continues to prevail in many parts of Massachusetts. Each maggot was imbedded in the thickened and solid substance of the stem, in a little longitudinal hollow, of the shape of its own body; and its presence was known by an oblong swelling upon the surface. In some pieces of straw the swellings were so numerous as greatly to disfigure the stem, the circulation in which must have been very much checked if not destroyed. Early in the following spring these maggots entered the pupa or chrysalis state, and on the fifteenth of June the perfected insects began to make their escape through minute perforations in the straw, which they gnawed for this purpose. Seven of these little holes were counted in a piece of straw only half an inch in length. The insects continued to release themselves from their confinement till the fifth of July, after which no more were

Much to my surprise they proved to be minute, fourwinged fies, belonging to the genus Eurytoma. Supposing these insects to be parasites, in accordance with the known habits of others of the same family, I described them as such, under the name of Eurytoma Hordei (so called from Hordeum, the Latin for barley), in the “New England Farmer," for July 23, 1830,* and in the first edition of this work. It was then my belief that the true culprits, or original cause of the disease, would prove to be some species of Cecidomyia, allied to but distinct from the Hessian fly; and that they, while in the larva or pupa state, had been preyed upon and destroyed by the Eurytoma. The larvæ of the Hessian fly are often destroyed by a somewhat similar Chalcidian parasite, great numbers of which have been observed, in their winged form, in wheatfields, and have then been mistaken for Hessian flies. The body of the Eurytoma Hordei is jet black, and slightly hairy. The head and thorax are opaque, and rough with dilated punctures. The hind body is smooth and polished. The thighs, shanks, and claw-joints are blackish; the knees, and the other joints of the feet are pale honey-yellow. The females are twelve or thirteen hundreths of an inch long. The males are rather smaller, and are distinguished from the females by the following characters. They have no piercer. The joints of their antennæ are longer, and are surrounded with whorls of little hairs. The hind body is shorter, less pointed behind, and is connected with the thorax by a longer stem or peduncle. These insects are very active, and move by little leaps; but the hindmost thighs are not thickened. About eight years ago, some of these insects, that had come from a straw bed in Cambridge, were shewn to me. They had proved very troublesome to children sleeping on the bed; their bites or stings being followed by considerable inflammation and irritation, which lasted several days. So numerous were the insects that it was found necessary to empty the bed-tick and burn the straw. Since that time, I have heard nothing more either of the insects or of the disease of barley-straw in this part of the country

seen.

• "New England Farmer," Vol. VIII., p. 138.

My attention was again called to the history of the barleystraw insect by an article on the joint-worm, published at Albany in " The Cultivator,” for October, 1851. The account given in this magazine, by Mr. Rives, of the ravages of the

* Vol. IX., p. 2.

joint-worm in the wheat-fields of Virginia, and the remarks by Dr. Fitch on the peculiar affection of the wheat-straw produced by this worm, led me to suspect that the disease was identical with that which had been observed in barley-straw, and that it originated from the same cause. In the article above named, Dr. Fitch appears to have come to the conclusion that the disease was produced by some species of Cecidomyia. He found the disease of the wheat-straw to be situated immediately above the lower joint, in the sheathing base of the leaf, the substance of which, for a distance exceeding half an inch, was much swollen, and was changed to a more solid and wood-like texture, while the surface exhibited several long pale spots, slightly elevated like a blister. The hollow of the stem was entirely obliterated, at some parts, by the pressure of the enlarged portion of the sheath, and was hardly visible at others. Each of the blistered spots covered an elongated cavity, containing a footless worm or maggot, about ten hundredths of an inch long, of an oval form, rather more tapering posteriorly than towards the head, and divided by slight constrictions into thirteen segments. The worm was soft, shining, of a uniform milk-white color, with a small V shaped brown line marking the situation of the mouth. “So exactly," remarks Dr. Fitch, "does this worm in its form and appearance resemble the larvæ of the Hessian fly and other species of Cecidomyia which have fallen under my examination, that I entertain no doubt it pertains to the same genus of insects."

On the 16th of March, 1852, F. G. Ruffin, Esq., of Shadwell, Virginia, the editor of “ The Southern Planter," sent to me that paper for July, 1851, containing some account of the joint-worm, and with it a few samples of diseased wheat-straw. A much larger quantity of the straw, soon afterwards received from him, was divided into two unequal portions, the larger of which was sent to Dr. Fitch, in the hope that between us something definite concerning the origin of the disease might be obtained. Upon examining my samples, I found that the disease was not invariably confined to the sheathing base of the leaf, but that, in many cases, it was seated in the joint itself, the whole substance of which became enlarged and distorted. In a smaller number of cases, it was found to occupy the culm or stem, above the joint, which was swollen so as to form an irregular gall-like tumor, while the leaf-sheath remained unaffected. These woody tumors had several little cells in them, varying in number from six to ten or more; and every cell contained an insect, in the pupa or chrysalis state. The samples of straw reserved for myself were put into a small glass jar to secure the insects when they had completed their transformations. Early in May, winged insects began to perforate the tumors and come forth, and they continued to issue during ten days or more. Their appearance was probably hastened by the jar being kept in the house instead of being exposed to the air abroad. These insects so nearly resemble in form, size, and color, the Eurytoma formerly obtained from the barley-straw, that I am persuaded they are, at least, mere varieties of the same species, if not absolutely identical. The only apparent difference between them consists in the color of the fore shanks; these, in the wheat-insects, being pale yellow, and faintly tinged with black only on the outer edges, in a few individuals. Among fifteen specimens only one male was found, and this did not appear till the month of June. Dr. Fitch obtained from his samples of straw above one hundred specimens of the same kind of Eurytoma, and all of them females. Among them he found another Chalcidian insect, a species of Pleromalus, probably a parasite of the Eurytoma, and has favored me with a description of it. The head and thorax are of a dark metallic green color; the abdomen is slightly depressed, polished, purplish black above, bright copper-colored beneath. The antennæ are black, except the basal joint, which is of a brilliant copper-color. The thighs are pale yellow; the shanks and feet blackish, the hind pair with a broad pale ring around the bottom of the shank and the contiguous part of the foot. The length of the body is ten hundredths of an inch, being somewhat less than that of the Enrytoma. From my samples of the straw I have obtained another and a different parasite, belonging to the same family, but to the genus Torymus. The specimen is a female, and,

like others of the same genus, it is provided with an exserted slender piercer, nearly as long as its own body. The latter is about as long as that of the Pteromalus above described, and is of a deep black color, slightly tinged with green on the face and thorax, both of which are rough and opaque, while the hind body is smooth and polished. The fore wings have an elongated cloudy spot near the middle, and the oblique branch is very short. The thighs, claws, and the antennæ except the basal joint, are blackish, the other parts of the legs and the base of the antennæ are pale yellow. The hindmost thighs are much thicker than the others, and are notched beneath the end. The eyes have a dull reddish tinge, perhaps not their true color in life. Professor Cabell has sent to me some specimens of this Torymus, including a male, which differs from the female in having all the joints of the antennæ black. · The ravages of the joint-worm in the wheat-fields of Virginia are said to have been first observed in Albemarle county, about four or five years ago. They have alarmingly increased from year to year, and have extended over many parts of the adjacent counties, becoming more aggravated each time that they are renewed in the same place. The loss occasioned thereby often amounts to one third of the average crop, and is sometimes much greater; and during the present season, "some farmers did not reap as much as they sowed.” These statements are made chiefly on the authority of Professor J. L. Cabell, of the University of Virginia, who has given some attention to the natural history of the joint-worm, and has recently communicated to me the result of his interesting observations. He has come to the conclusion that the jointworm is the larva of a Hymenopterous and not of a Dipterous insect. He finds that the parts of its mouth are very different from those of the dormant larva of the Hessian fly (the latter extracted from its flax-seed case before it had undergone any change of form), and that the mouth of the former agrees essentially with that of the larvæ obtained from galls of the oak. In the mouth of the joint-worm he observed that "the mandibular hooks cross each other on the middle line," while in the Hessian fly larva the "two hooks are directed down

« PreviousContinue »