Dichotomous table for gallers on Onopordum
by Hans Roskam
1a Receptacle thickened and hardened, with several oblong oval chambers vertical to surface, each containing a single maggot. O. acanthium, cynarocephalum: Tephritis postica
1b Similar malformations. O. acanthium: Urophora mauritanica
1c Larger parts of rosette leaves strongly curved downwards and curled; discoloured dark green close to the froth-covered nymph O. acanthium: Philaenus spumarius