jointworm

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A larva of any of various chalcid wasps of the family Eurytomidae, especially of Tetramesa tritici, that infests grains, causing swelling and subsequent breakage near the first joint of the stem.

from The Century Dictionary.

• noun A jointed worm; an intestinal worm of the genus Tænia; a tapeworm. See cut under Tænia.
• noun The larva of a chalcid hymenopterous parasite of the genus Isosoma, as I. hordei, which is very destructive to crops of barley, wheat, and rye in the United States.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) The larva of a small, hymenopterous fly (Eurytoma hordei), which is found in gall-like swellings on the stalks of wheat, usually at or just above the first joint. In some parts of America it does great damage to the crop.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The larva of a hymenopterous fly, found in gall-like swellings on wheatstalks, usually around the first joint.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun larva of chalcid flies injurious to the straw of wheat and other grains