Arnica
Dichotomous table for leafminers
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
Not included in the key: Coleophora paripennella.