Outside, it’s dark, and there

Outside, it’s dark, and there is an inch of frozen ice mixed with snow on the ground, and the sleet is pounding fiercely at the windows. Inside, a warm, bright, and humid tropical paradise. There is trouble in paradise, though, at least as far as my Begonia Rex "Escargot" is concerned. This is an amazing variety that was bred in Holland and introduced in the UK in the fall of 1998; I brought a specimen back from Vancouver’s magical Southlands Nursery a couple of months ago.

Now, I suspect a mite of some kind is attacking the plant. The leaves are curling under and drying up along the edges. I’ve sprayed it several times with a neem/insecticidal soap solution, and moved it out from under the light stand and into a corner of my grow room, in the hope that the higher humidity will help.
If you have any suggestions, write me. I’d hate to lose this spectacular plant.