1a larva a maggot; frass powdery, in green clouds; when held against the light the blotch is irregular in transparancy: Scaptomyza flava

1b larva with sclerotised head; frass black, coarser; mine transparant all over => 2

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

2a corridor, starting in the leaf base or at a thick vein: Orthochaetes insignis

2b mine begins free in the leaf, corridor-like, but may locally be considerably widened: Ceutorrhynchus minutus