At first, I thought/assumed it may be starting to drop leaves in prep for dormacy (normal yellowing from the bottom leaves). After seeing your pictures, I suspect it's a bug. Spider mites or whiteflies (probably the latter). Are they in an area that gets a lot of air circulation? That will help. I had a few seedlings in my greenhouse that got whiteflies and looked similar. I put them outside, after cutting off the leaves and spraying and they're fine. I'm also in S. FL.

They are on our screened in back porch.. circulation. Well, not the best I would say. How best to eradicate these pests? If I were to remove the affected leaves, we are talking a stump on some of them. I just need them to hold on a few more weeks!! Aarrgh!!!

Look at Home Depot for something that kills Whiteflies. I think I used something by Ortho. As for taking off the leaves, that is going to happen anyway soon when they go dormant. Then in the spring, they should leaf out again. You need to kill the whiteflies and keep them off.

If you can find a source of good grade worm castings, these spread and watered into the ground quarterly will discourage whitefly and other leaf chewing insects. This is also excellent for hibiscus. Also your plants seem to really like this.

That's interesting. I've heard great things about worm castings (not sure how to tell good quality though). If it takes care of whiteflies, it's even more beneficial!

I'm sorry that your plumeria have whiteflies, but I'm so happy that you posted your concern with a photo. I've been trying to find out what is going on with one of my plumeria and your picture is exactly what my plant looks like. I'm unhappy that the darn whiteflies have come to visit, but now I know what they are, they will soon be eliminated.

If you have white flies, you can usually see them flying around when you rustle the leaves a bit. I used a spray from Home Depot and it worked well, but you must follow up with another application.