1a mine either ends, or begins, in the stem, petiole or midrib => 2

1b mine at most on the midrib, or free in the leaf blade => 4

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

2a corridor that vanishes in a thick vein: Phytomyza rufipes

2b narrow corridor (sometimes overrun later), widening into an irregular blotch on, partly also within, the midrib => 3

3a frass in thread fragments; mines in May-June: Liriomyza xanthocera

3b frass powdery, in blackish-green clouds; mines in May-October: Scaptomyza flava

4a mine, at least largely, full depth; larva with chitinised head => 5

4b mine upper- and/or lower-surface (patches sometimes full depth); larva a maggot => 10

5a small blotch, < 1 cm; larva later lives free => 6

5b mine > 1 cm, blotch or corridor => 8

6a older larvae live free at the underside of the leaves: Plutella xylostella

6b older larvae live among spun leaves => 7

7a larva with reddish brown length lines: Hellula undalis

7b no length lines: Cnephasia asseclana

8a larva without feet; mine an irregular gallery: Ceutorhynchus minutus

8b larva with thoracic feet; last part of the mine more or less a blotch => 9

9a bloth roundish with a green centre; species of Maideira and the Selvagens: Xenostrongylus histrio

9b blotch elongate without a green centre; common species all over Europe: Phyllotreta nemorum

10a corridor from start to end => 11

10b irregular blotch, preceded by a fine corridor (may have been overrun) => 3

11a broad, pinnately branched corridor, main branch overlying the midrib; pupation after the mine has been vacated; frass in strings: Liriomyza strigata

11b corridor little branched, not pinnate => 12

12a puparium in the mine, in a, generally lower-surface, pupal chamber; frass in discrete grain: Chromatomyia horticola

12b pupation external; frass in strings: Liriomyza brassicae