Well... the isolation distance in the greenhouse is pretty much zero. I guess I should consider bagging some blossoms.
I was thinking perhaps the earliest fruit would be okay, but I don't know exactly when these critters emerged, either. And they do seem to have a secretive lifestyle..
This is a great video of a sweat bee on a tomato flower!
https://www.youtube.com/watch?v=iXHksIkAqLA