Mealy or scale, it doesn't matter (my vote is for some sort of scale, Bois-duval maybe?), since mealy is a kind of scale and you treat them the same way. First line of defense is to wipe off all the visible pests. Next, spray with an insecticidal soap or horticultural oil. Keep at this for a while and that should take care of it. Be persistant, this kind of scale is insidious!

It's called whitefly... a nasty parasite that loves hibiscus. The only thing to do is spray constantly, a systemic pesticide is best. Oil based sprays are probably effective too but don't last long. Spray often. If you don't spray your entire plant will have wisps of whlte cottony stuff all over it. I hate whitefly .... but it can be beaten. Is it what is in this link to pictures with whitefly? https://www.google.com/search?q=whitefly+on+hibiscus+image&client=palemoon&rls=Palemoon:en-US&tbm=isch&tbo=u&source=univ&sa=X&ei=4ObdU6CbKMz1oASgmoDYAQ&ved=0CB4QsAQ&biw=1536&bih=665 good luck. Mike

Folks elsewhere are dealing with jumping white critters that sound similar. If your critters are the same, they're leafhoppers by the name of Metcalfa pruinosa.

You may be on to something. I haven't seen an actual insect that looks like the picture, but the foam looks like what is described here: https://www.insectidentification.org/insect-description.asp?identification=Two-Lined-Spittlebug