1a frass powdery, in blackish-green clouds, often only visible in the opened mine; larva a maggot: Scaptomyza flava

1b frass coarser; larva with distinct head => 2

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

2a frass in grains; the larva, with thoracic feet, mines only briefly; older larvae live free under a leaf: Plutella xylostella

2b frass partly in strings; larva, without feet, mines all its life: Ceutorhynchus minutus