1a fleck mine: Coleophora pennella

1b eventually a blotch => 2

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

2a larva solitary (always?): Agromyza myosotidis

2b larva communal => 3

3a larva a white maggot, without feet: Agromyza abiens

3b larva white or full grown, red, with feet and a sclerotised head: Dialectica imperialella