Grape tumid galls, also called grape tomato galls, are caused by larvae of a small fly known as the grape tumid gallmaker (GTG). This pest is native to the northeastern United States and southeastern Canada. It infests only wild and cultivated grapes (Vitis spp.). Infestations are generally spotty both within vineyards and within infested vines. In the past, tumid galls were attributed to as many as five species of flies, but it is now thought that the single species Janetiefla brevicauda accounts for almost all of the damage seen in northeastern vineyards.