Dichotomous table for leafminers
1a frass, at least in some parts of the mine, in a thread thin line; mine a very narrow corridor: Ochrosis ventralis
1b frass irregularly scattered everywhere; mine very variable, at timmes strongly resembling that of the previous species: Orthochaetes insignis
1c galls, etc => Tables for all parasites per species
Not included in the key: Chromatomyia horticola.