Lepitect (from Rainbow)? I haven't used it for caterpillar control, but acephate has a long history of being effective against lepidoptera and Lepitect does move into the tree well. It has a short (30 day) residual, so you need to time it well.
Not many other options for soil-injected cat control. Dinotefuran seems promising, but doesn't have as much history. I've read this article about it being effective against bagworm, which is promising.
It stinks to high heaven and back again. I have a partially used package in 3 ziplock bags and an ammo box and my pesticide cabinet still stinks from Lepitect.