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

1b mine at most overlying the midrib, otherwise free in the leaf disc => 5

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

2a larva a maggot => 3

2b larva with chitinised head => 4

3a mine more or less a corridor, until it disappears into a thick vein: Phytomyza rufipes

3b corridor, turning into an irregular blotch on, and partly in, a thick vein: Scaptomyza flava

4a larva with thoracic feet; in autumn: Psylliodes napi

4b larva without thoracic feet; in spring: Ceutorhynchus pallidactylus

5a mine full depth; larva with chitinised head => 6

5b mine upper- or lower-surface (little patches may be full depth); larva a maggot => 8

6a small blotch, < 1 cm; larva, with abdominal feet, later lives free: Plutella xylostella

6b mine > 1 cm, a corridor or blotch; larva, without abdominal feet, remains in the mine until close to pupation => 7

7a larva without thoracic feet; mine an untidy corridor: Ceutorhynchus minutus

7b larva with thoracic feet; final part of the mine widening blotch-like: Phyllotreta nemorum

8a corridor from start to end => 9

8b irregular blotch, preceded by a narrow corridor (may be overrun): Scaptomyza flava

9a broad, pinnately branched corridor; main branch overlying the midrib; frass in strings; pupation outside the mine: Liriomyza strigata

9b corridor little branched, not pinnate, not associated with the midrib; frass in discrete grains; puparium in the mine, in a, usually lower-surface, pupal chamber: Chromatomyia horticola