Dichotomous table for leafminers
1a initially a hair-thin corridor along the leaf margin; older larvae make blotch mines from the leaf margin: Bucculatrix cristatella
1b gallery from begin to end, not unusually narrow; pupation within the mine: Chromatomyia ciliata
1c galls, etc => Tables for all parasites per species
Not included in the key: Phytomyza pullula.