TerelliaTerellia is a genus of tephritid or fruit flies in the family Tephritidae.SpeciesSubgenus Cerajocera Rondani, 1856Subgenus Terellia Robineau-Desvoidy, 1830Terellia ruficauda feeds on Canada thistle has been reported to be the most effective biological control agent for that plant. Its larvae parasitize the seed heads of the plant feeding solely upon fertile seed heads.