Do you just spray the BT on the frames and let them set? I have used BT in my garden. It is death to caterpillars.
There are several varieties of BT. Be sure and get the right one.
Has Sundance made it to this forum yet?
He has not, and all his threads on Bee Source have been deleted for some reason.
Xentari is the form we can get in USA, it is organic as Minniemo said, and will cause no harm even if sprayed directly on bees and frames with larvae. But the better method is to spray drawn comb properly out of the hive. Anecdotal evidence in USA says it will last multiple seasons , I am moving into year three with some frames but have not yet checked my stored frames
Xentari was being sold on Amazon for awhile , but sadly no longer.
It is NOT approved for beekeeping in USA , but used to be , and is used in Canada , UK and other places so if buying it you will have to buy for your Cabbages

I grow a lot of cabbage .......