1a short gallery, that ends or begins on a thick vein; the larva essentially lives as a borer in the veins, petiole, or stem: Ceutorhynchus pallidactylus

1b the larva does not mine in (though sometimes upon!) the veins => 2

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

2a pinnately branched gallery, main and side branches on top of the midrib and side veins: Liriomyza strigata

2b blotch, or little, not pinnately, branched gallery; mine not determined by the leaf venation => 3

3a larva a maggot; mine partly or entirely upper- or lower-surface => 4

3b larva with chitinised head; mine full depth => 8

4a gallery from start to end => 5

4b blotch, may begin with a gallery => 7

5a pupation within the mine, in a, generally lower-surface, pupal chamber; frass in well-spaced grains: Chromatomyia horticola

5b pupation external; frass in strings => 6

6a larva: rear spiraculum with 3 papillae: Liriomyza brassicae

6b rear spiraculum with 7-12 papillae: Liriomyza bryoniae

7a frass powdery, in dark green “clouds” in corners of the mine, often visibly only after the mine has been opened: Scaptomyza flava

7b frass in black strings: Liriomyza xanthocera

8a larva with prolegs; older larvae live free at the underside of the leaf: Plutella xylostella

8b no prolegs; larvae mine all their life => 9

9a larva with thoracic legs: Phyllotreta nemorum

9b larva without legs: Ceutorhynchus minutus