1a most frass is expelled, part of it is trapped in spinning below the leaf; larva with chitinised head => 2

1b mine contains much frass; larva a maggot => 3

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

2a species of the Canary Islands: Cosmopterix turbidella

2b species of southern and western Europe: Cosmopterix pulchrimella

3a mine begins (usually in the centre of the leaf) with a number of close, intestine-like, loops; frass partly in a long thread; larva solitary: Agromyza anthracina

3b mine, usually at the leaf margin, without an intestine-like start; frass not in a thread; larvae generally communal => 4

4a larva: the anteriorly-pointing arm of the cephalic skeleton two-coloured: frontal half dark brown, proximal part red brown: Agromyza reptans

4b this arm uniformly dark brown: Agromyza pseudoreptans