oh yah, BTI, that's one more the folks, thanks DB! Bacillus thuringiensis (subspecies) Israelensis, thats completely natural. There's a product called Microbe Lift, thats what it is.
its good for the larvae, and kills mosquito larvae too which might be good in summer especially if collecting rain water.
But yeah NEMs do need multiple apps hey, I kinda found that too, we just used a spoonful every second day, in conjunction with potato traps and DE Rock Pebbles, and pretty much everything else on the list, at the same, time, and they were gone! aha.
I think people can get larvae with just leaving their worm farm out to collect in the open, thats why I always chuck good scraps in the freezer right away now.