The purpose of salting the earth, (I assume you mean to place a layer of salt under the entrance) would be for the larva to fall onto it and become dehydrated by it? Or do you mean for the salt to have a different effect on the larva?
Lime may be another thing that could be placed to have a dehydrating effect but I would think that you would need to make a box or something large enough to cover the full width of the landing board and then some to ensure the larva drop into the salt or what ever. The other thing is that it would need to be replaced after rain I would expect.
a couple of other things. If you get to the point where you are killing larva your hive is most likely in trouble. If there is beetle in it it is much easier to trap if the hive is strong and has aggressive tendencies towards the beetle. I think that what you dont want are beetle laying eggs which turn into larva and then do the damage throughout the hive. If the colony is covering the frames and is proactive towards the beetle they do not have a lot of time to lay eggs unless they can hide in cells or elsewhere where they can take a rest and lay without harrassment.[...]
I do mean as a dehydrating agent -if that's how it works - I don't live far from the gulf of Mexico - and as plants go - there are only a few which can tolerate the salty soil (within about 1000M of shore). I suppose the salt tolerant plants have filters of a sort.
(and there is a different kind of itchy biting insect from the mosquito near shore).
I was told to use lime in the trap, but I wasn't sure it was safe to treat the ground with it (as a back up)
If I understand correctly; trapping and treating the ground should help prevent you from reaching infestation levels - of course with new beetles arriving from elsewhere somewhat(?) regularly.
I like your idea of preemptive trapping, but the attractant would have to be more powerful than the hive itself.
(I would think breeding a varroa mite that prefers the hive beetle to the honeybee might promote mutual extinction in the two pests leaving the bee in peace, but you can't grow cotton candy either [candy floss?])
Bear in mind I'm a newbie, and I hope a more experienced beek can address my guesses.