Is teflon tape adequate for sealing threads for a box rated for wet locations? Its for PVC adapters (male pipe thread to socket), one connecting to a nonmetallic weatherproof box and another connecting to a metallic outlet box.

Really no need to worry about sealing the threads. They are OK as is. I have not had any leaks around the threads on a box. But since this is PVC conduit there are no worries about disrupting a ground connection since the PVC pipe does not ground the box like a metal conduit would. Use the tape if you want.

I'll use it since it won't hurt and i have lots of teflon tape. The box itself says to use thread sealant.

Thanks 3phase

Teflon tape is really only a thread lubricant and even though it can attribute to sealing, you don't want to have to depend on it to seal in a wet location. If this connection is for an outdoor electrical box then I would suggest you either use a connector that's approved for wet locations or apply a caulking to the threads before screwing them in.