694 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



and brittle, so that the straw above the disease is impoverished, and 

 seldom produces any grain. Suckers, however, shoot out below, and 

 afterward yield a partial crop, seldom exceeding one-half the usual 

 quantity of grain" (Gonrgas as quoted by Harris). The worms 

 have been found living in swellings, sometimes from six to ten in a 

 tumor situated between the second and third joints, or immediately 

 above the lower joint in the sheathing-base of the leaf, or in the joint 

 itself. In November, in the New England States, the fully-fed larviB as 

 a rule (many do not until the spring) change to a chrysalis or pupa 

 within the tumor, and in this state spend the winter in the straw or 

 stubble or even in some cases in the harvested grain. In Virginia, the 

 larva passes into the pupa state in February and March. From early in 

 May until early in July, but mostly in New York in June, the four- 

 winged flies issue from the galls, the males first appearing, and about 

 the 10th of June, in Canada, the females deposit their eggs in the stalks 

 of the young, healthy wheat. The larvae hatch in a few days, and by 

 the first week of July the young are nearly one-half grown. By the 

 first of September the galls become hard and the worms fully grown. 



I have endeavored to represent on the accompanying map the area 

 of distribution of the joint-worm, but the area is probably too restricted. 

 No facts are, however, at hand showing that it has occurred west of 

 longitude 82° or south of latitude 3fP, with the exception that a "joint- 

 worm " is reported in the Monthly Reports of the Agricultural Depart- 

 ment as having injured wheat in Kansas, but the species referred to has 

 not, so far as I am aware, been referred to a competent botanist. I should 

 be greatly obliged for specimens of this or any "joint-worm" from any 

 l^art of the country. 



The joint-worm of late years has been, so far as reports go, much less 

 abundant than between the years 1825 and 1800, and it is to be hoped 

 that it will not again be so prevalent. In former years the losses in 

 Virginia amounted to over a third of the entire wheat-crop, while some 

 crops in that State were not thought to be worth cutting. It was par- 

 ticularly abundant on rye, barley, and oats in the New England States 

 and Canada, while in New York it was known to destroy one-half the 

 barley-(;rop. Dr. Fitch has described several so-called species, allied to 

 Isosoma hordei, and he supposed that they were restricted to different 

 species of cereals. Mr. Walsh, however, has endeavored to show, with 

 good reason, we think, that they were simply varieties of I. hordei, and 

 that this well known species feeds upon all the small grains as well as 

 wheat. 



Either two or three specimens of ichneumon or chalcis flies, belonging 

 to the same family {Chalcidid(v) of hymenopterous insects as the joint- 

 worm itself, prey upon the larva, and probably tend to reduce its num- 

 bers. Harris states that the larvae of a species of Torylfius^ one of these 

 chalcid flies, destroy the joint-worm. A species of Torymits (T. harrisii 

 Fitch), perhaps the adult of the larval Torynms described by Harris, and 

 a species of Pteronialus, also prey upon it. 



Larva : The joiut-worm is described by Harris, from sijecimens received from Vir- 

 ginia, as a round, cylindrical, footless, maggot-like worm, varying from one-tentb to 

 three-twentieths of an inch in length. It is pale yellowish and without hairs. The 

 head is round and partly retraotiie, with a distinct pair of jaws, and can be distin- 

 guished from the larva; of the dipteuous gall-llies by not having the usual V-shaped 

 organs on the segment succeeding the head. 



Adult : The imago or adult lly is a four-winged, hymenopterous insect, a'member of 

 the family Chalcidida; most ot which are insect-parasites. It is jet black, and the 

 thighs, shanks (tibiie), and claw-joints of the feet are blackish, while the knees and 

 other joints of the feet (tarsi) are pale yellow; sometimes the legs are entirely yellow. 

 The females are 0.13 inch in lengtb, while the males are smaller, have a club-shaped 

 abdomen, and the joints of the anteuuoe are surrounded by a verticil of hairs. 



