1. The maggot bores into the growing point of the tiller and causes abnormal growth of the leaf sheath, which becomes whitish tubular and ends bluntly.
2. It may be pale green, pink or purplish. Further growth of tiller is arrested. This is called onion shoot or silver shoot.
3. The feeding by the maggot and the larval secretion, which contains an active substance called cecidogen, is responsible for cell proliferation of the meristematic cells and gall formation.
4. It is a pest in irrigated and wet season crop. Tillers in 35 to 53 days old crops are preferred.