Overproduction of eggs?
Sometimes an excessive number of eggs is deposited on a small number of leaves. By far most of the resulting larvae perish.
Quercus robur, Hoog Soeren
Of the four larvae on this picture only the lowest, largest, is still alive.
The number of these failed mines in a leaf can be considerable.
In the dead larve the the ventral plates are quite conspicuous, as a series of grey disks.
Some larvae die already in a very early stage