Not sure how cold my freezer was. And I only did it for 24 hours. I suppose there is a temp and time period that will kill them. Maybe two days at below 0 will, where my one day at somewhere below 32 did not.
I know the larvae were solid frozen, but perhaps another day would of worked better.
Just remember about not putting too much comb on in the brood chamber that the bees can not defend. They are mainly after the brood comb with pollen.
SHB like sandy soil and shade locations. Put the hives in full sun and look into putting down a big rubber tarp under your hives. You can sprinkle something Borax around the edges. It will kill the larvae if they get that far.