The bark lice Nitela digger wasps use for their brood are caught on Lilac (Syringa vulgaris). This female hunted for them on the stem. The female louse in the photo evaded the wasp by running exceptionally fast to a safer distance.
The identity of this bark louse is probably Mesopsocus fuscifrons. The specimen is a female. They are wingless, which made me erroneously think it was a nymph. See more here.
References1 Nederlands Soortenregister