I know this doesn't help you but there is a good portion of the southeast US that would appreciate a pest that can kill an Empress tree.

Would you care to post a photo...it might help narrow down the cause.

please stop spraying ANYTHING .. until you ID the problem ...

odds are.. whoever made the holes is long gone.. hence the reason you cant find them ... and why anything sprayed now.. is just pollution ...

you claim all the leaves getting eaten almost killed the tree.. but then say no such thing happened .. as it came back with gang busters like most weed trees do ... bugs rarely kill their host ... as it would be a form of suicide on some level ... and also.. plagues of bugs come year in and year out ... and rarely is it required that we do anything but complain ....

find out if this tree is invasive you your county by calling your county extension office... and if it is.. get rid of it.. it solves all your bug problems...

there are so many good trees out there...

and never forget.. if you planted it because it was fast to grow.. the rest of the equation is fast to problems.. fast to decline.. and fast to death.. all contemplated in tree years ...

i highly doubt the wasps have anything to do with this.. if in fact.. they are wasps ...

a pic might get you some relevant info ...

ken

wasps?.....wasps are predators that eat caterpillars so that might be the reason they are there.....Japanese beetles might also be the culprit

Ray, what part of the country are you in? That tree is frequently reported as invasive and as a DO NOT PLANT by many tree hugging Department of Natural Resources and the like. Up further north it doesn't seem to be a problem.