That would be my first thought too, spider mites. Have y'all been dry for a while? You could also have a severe Mg deficiency, but mites are what you want to rule out first. I dose all my plumeria (and orchids) with Mg every 3-4 months. With the plumeria, they get a dose in the spring and then get a second dose in mid-summer. To keep spider mites in check (I simply don't ever see them), I spray all the leaves of my plumeria every day, either in the AM or late afternoon. Mites don't like the wet.
