Miniscule mummification

Following yesterday's post about aphid-feeding hoverfly larvae, I went out into the garden and found evidence of another aphid-bothering insect - the empty skin or 'mummy' of an aphid stuck to the underside of a sycamore leaf by a domed silken cocoon on which it lies. The whole arrangement is only about 2mm long so it was tricky to get good photos even under the microscope due to the white structures tending to overexpose, but this is what I managed...

Aphid 'mummy' attached to a silken cocoon

There are numerous parasites of aphids (technically 'parasitoids' as they develop inside them) and one key group is the aphidiiine wasps (subfamily Aphidiinae within the Braconidae), tiny wasps that lay eggs directly into living aphids. Some, such as the genus Aphidius, produce larvae that cut their way out of the abdomen leaving an empty aphid with a neat lid. However this arrangement - an aphid 'mummy' atop a domed silken cocoon containing pupa/e (the larvae will have fed on the aphid internally) - is typical of the genus Praon.

Aphid mummy attached to the top of a Praon cocoon - the developing Praon have left the aphid and have pupated beneath it.

When a Praon adult leaves the cocoon it cuts a small hole through which to exit, but the photo above shows the cocoon to be intact and skirt-like with the developing wasp/s inside. It is impossible to identify further at this stage, although P. volucre is a common species - however, I have retained the leaf and cocoon and hope to raise at least one adult for identification - I'll be looking out for a tiny black wasp with orange-yellow legs: another often-overlooked gardeners' friend!