1a larva with thoracic feet and a chitinised head => 2

1b larva a maggot => 4

1c galls, etc => Tables for all parasites per species

2a mine a large corridor; larva mines all its life: Digitivalva arnicella

2b mine tiny, irregular; older larvae live free among spun leaves => 3

3a larva with black pinacula: Cnephasia stephensiana

3b pinacula colourless: Cnephasia incertana

4a corridor, widening into a large blotch: Phytomyza arnicae

4b corridor from begin to end => 5

5a pupation within the mine, in a, usually lowr-surface, pupal chamber: Chromatomyia cf. syngenesiae

5b pupation outside the mine => 6

6a frass in small grains, close together, or in pearl chains: Phytomyza conyzae

6b frass in large, widely separated grains: Phytomyza arnicicola