☆ the larva of a genus (Harmolita, family Eurytomidae) of small wasps which attack grain stems and cause galls to form in the joints
See jointworm in American Heritage Dictionary 4
(jointˈwûrmˌ)
noun
The larva of certain wasps of the family Eurytomidae, especially of Harmolita tritici, that infest grains and cause hard swellings near the first joint of the stems.