I have what looks like caterpillar damage on some of my apple trees and my rhubarb plants have been decimated.

I have found the occasional caterpillar on my trees. They're not the green stripe eastern tent caterpillars I've had issues with before as I've learned to kill them in their nests.

I also sprayed BT twice so far this year on the apple trees but I still see leaf damage which looks like caterpillars despite the fact that with very few exceptions I've seen no caterpillars.

So ...

if caterpillars where do I look for them?

if not, then what.

any reason not to keep spraying with BT? some other pesticide recommended?

thx in advance for help.