A new garden species: the ichneumonid wasp Pimpla turionellae [1,2] (determination confirmation by Fons Verheyde).
At the end of the afternoon this female prowler stalked what turned out to be a nest with two caterpillar larvae. She continuiously walked around and over it until she finally lower her ovipositor into the nest once.
The nest was occupied by two moth larvae of the Apple ermine (Yponomeuta malinellus). The situation was a bit odd since the nest was almost dried up and in the direct vicinity there were no green leaves. These larvae usually feed on neighbouring leaves from the protection of the nest.
Another odd thing was the difference in size between the two larvae. Again normally they all hatch at the same time and more or less develop in the same rate.
As the wasp seemed to have laid an egg in the nest I thought to put the whole nest in a rearing box. Unfortunately the larvae didn’t seem to eat from fresh leaves and the small one quickly died. Closer investigation did not reveal any eggs so I ended up returning the remaining larve back to the apple tree from where it came.
In the nest also hung an unidentified empty cocoon.
References1 Nederlands Soortenregister
2 FITTON, Michael Geoffrey, et al. Pimpline ichneumon-flies. Hymenoptera, Ichneumonidae (Pimplinae). Pimpline ichneumon-flies. Hymenoptera, Ichneumonidae (Pimplinae)., 1988, 7.1.