If it is spider mites, you can tell by using a magnifying lense and you will see those little mites crawling around. Or you can wet a white paper towel and wipe the under leaves and you will see the mites as black little dots on the paper towel.
My Dwarf Pink Singapore plumerias were heavily infested with spider mites couple winters ago. ( I tried to keep them inside since they didn't loose their nice green leaves. Plus they still had blooms that I didn't want to lose.) I had to cut off Some leaves to improve air circulation, mist them everyday and wipe the underleaves with paper towel to disrupt their egg production. Then when week-ends were warmer. I would bring them outside and spray the leaves so they stay wet for some time. Spider mites didn't like the wet leaves...and that seemed to do the trick. I haven't seen those mites lately.
