1a primary blotch => 2

1b more or less broad corridor => 3

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

2a larva solitary; rear spiraculum with 3 papillae: Liriomyza puella

2b larvae often communal; rear spiraculum with 8 papillae: Liriomyza sonchi

3a long corridor, party lower-, partly upper-surface, almost independent of the leaf venation: Phytomyza marginella

3b corridor not remarkably long, following the leaf venation, of originating from a vein => 4

4a several short corridors, originating independently from the midrib: Ophiomyia pulicaria

4b corridor overlying the midrib and lateral veins => 5

5a corridor broad; primary and secondary feeding lines conspicuous; frass in angular grains: Trypeta immaculata

5b corridor narrow; only secondary feeding lines visible; frass in strings: Liriomyza strigata