There are many variations on the theme: sometimes the host larva is kept alive and it can move away after the wasp larva has emerged. This is thought to be a distraction strategy where the host larva acts as a decoy, attracting secondary parasitoids that would normally target the primary parasitoids using the host as a vector.
I recently found specimens of the aphid Eucallipterus tiliae on lime and spotted this odd structure under one specimen.
So in addition to using the aphid as a food source, it's also using it as shelter for pupation.
To give some sense of scale, the 'podium' is about 2 mm. diameter at the base.
Here's a shot of some of the earlier instar aphids on a leaf:
Eucallipterus tiliae aphids on Tilia
No matter how much I find out about these wasps, I am constantly surprised by their range of habits and techniques.
Both species are new to my Species list, and Praon flavinode is a first Irish record.