I suspect this solitary endoparasitoid to be one of the Lissonotinae (Banchinae) which usually attack young lepidopterous larvae but don't kill the host until it is fully grown.
It may well belong to the genus Glypta (Glyptini) which attack partially concealed larvae of various small lepidoptera, especially tortricids. I wonder if it is Glypta gracilis which has been described previously from this host.
Unfortunately the parasitoid died before it reached the adult stage.
