1a mine full depth; larva with feet and chitinised head: Digitivalva granitella

1b mine upper- or lower-surface; larva a maggot without feet or apparent head => 2

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

2a primary blotch, may be preceded by a corridor => 3

2b corridor, rarely a secondary blotch => 4

3a blotch preceded by a long corridor: Phytomyza kyffhusana

3b no trace of an initial corridor: Nemorimyza posticata

4a corridor pinnately branched, main branch on top of the midrib: Liriomyza strigata

4b corridor not or little branched, independent of the venation of the leaf: Phytomyza conyzae