BT is bacillus thurengensis (sp). It's a bacteria that gives larva, tomato horn worms, etc, a bad stomach ache, and they croak.
BTW, Bacillus israeliensis (sp) is the stuff in those mosquito dunks that gives mosquito larvae/wigglers a stomach ache so they die.
Thanks, I remember that now. My memory was the first thing to go, I forget what the second was.
I guess I was just too sorry to look it up again.