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As far as I know OCGW are solitary and at 2-3mm pretty small, scarcely even a snack for a hornet. The only proven killer of OCGW is the Torymus sinensis Kamija mentioned above, which has been deployed in Italy, Spain & France, (within Europe).
mespilus-
Ah.
Yes might be a slight size mismatch there. :o)
I have seen a European Hornet in the middle of my Uni halls on parquet flooring. Long time ago now.
I remember it well because it actually looked round at me.
Articulated it's head not body.
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I'd say the size of OCGW probably wouldn't be an issue for hornets (even though hornets are several centimetres long, they still benefit from eating many of them), but as smaller insects are for the most part incredibly fast, it would probably be difficult for the rather large, lumbering hornet (by insect standards) to catch any (if they were even suitable for hornets to eat). You'd need smaller, faster predators for that. I'm sure they exist, but I don't know much about insect-insect predation.
Ordinata
Oliver Schick
Like Council bouncers.
I wonder if they prey on OCGW?
Maybe the bees are too easy.