im guessing theyre "white flies"
do they fly?..white flies look like a small white moth about 0.04 inch long...adults have wings...they first appear near the top of the weakest plant...
white flies are attracted to the color yellow so to get rid of them you cancover a bright yellow object with a sticky substance like "tanglefoot". place the traps next to the plants and discard when full
or cut all leaves with over 50% damage...and spray pyrethrum (aerolsol) applied every 5-10 days should do the trick too...
hope that helped a tad