The identification of these larvae has not be confirmed by breeding; they therefore can just as well be A. nigrella!
Elytrigia repens, Nieuwendam
‘head’ and rear end
front and rear spiraclum, dorsal
mandible and rear spiraculum, lateral
? Dactylis glomerata, Diemen
As the pictures show, the larva has behind the mandibles a finely spinulose field. This places the species in the Agromyza ambigua species group, which includes among others A. ambigua, mobilis, nigrella, nigrociliata and rondensis, and which is placed by Griffiths (1963a) opposite to the nigripes group, with A. albipennis, hendeli, nigripes and phragmitidis.
Venturi (1936a) presents a beautifully illustrated description of the larva, but Spencer (1973b) expresses doubt about the identification.