1a small, full depth mine of indefinite shape; larva with a recognisable head and thoracic feet: Cnephasia incertana

1b evident, upper- or lower-surface corridor, not unusually small; larva a maggot => 2

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

2a pupation within the mine in a, generally lower-surface, pupal chamber; frass in well-separated grains: Chromatomyia horticola

2b pupation outside the mine; frass in strings => 3

3a pinnately branched corridor, main branch overlying the midrib; larva: rear spiraculum with 9-13 papillae: Liriomyza strigata

3b corridor not pinnate, windding freely through the leaf; larva: rear spiraculum with 7-9 papillae: Liriomyza bryoniae