Unripe grapes being eaten

x

 

Looks like you've caught the culprit on cam! Is it a wasp though? I had a similar problem with wasps a few years ago, they love victoria plums! So much that I couldn,t get past the tree so I took it out.
John

 

I think thats a hoverfly.

I cant tell from the thumnails but in you main picture I cant see any small grapes, the bunch is only just starting to flower and the hoverfly is probably helping pollination.

just run your hand through the bunches at mid day when the flowers are open and move from bunch to bunch moving pollen from one to the other.