Thanks a lot Paolo.
I note that in Chrysis database there is no know host for H.
longicolle (only: ?Halictus (Abeille, 1877)).
I can tell you that I observe this Chrysididae surveying and coming inside Cerceris's burrow (gpe rybiensis: most probably C.sabulosa).
This picture shows H.
longicolle checking burrow, and same burrow with Cerceris head inside.
You can see a little video there:
Cerceris coming back with prey.