Descurainia flixweed, tansymustard
Dichotomous table for leafminers
1a larva a head- and feetless maggot: Chromatomyia horticola
1b larva with chitinised head => 2
1c galls, etc => Tables for all parasites per species
2a larva without feet: Ceutorhynchus minutus
2b larva with thoracic feet: Phyllotreta nemorum