1a fleck mine: Coleophora pennella

1b blotch, at least locally full depth; larva with feet and chitinised head: Dialectica imperialella

1c mine upper- or lower-surface; larva a maggot => 2

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

2a corridor from start to end; puparium in the mine; frass in discrete grains: Chromatomyia horticola

2b eventually an upper-surface blotch; pupation usually after the mine has been vacated; frass partly in thread fragments => 3

3a larva: mandible with 2 alternating teeth (seen from aside seemingly 4!); mine communal, 5-10 mm wide at its very beginning: Agromyza ferruginosa

3b larve: mandible with 2 not alternating teeth; mine initially individual, starting with a 1-maggot corridor (that will be overrun later); usually several young mines coalesce, forming one large communal mine: Agromyza abiens