Problem with fruit flies is they die in one day anyway, and the new ones the next morning are all newly hatched!  Frustrating!

sounds like whiteflies!  They are hiding on the UNDERSIDE of the leaves, so if you are spraying with soap solution, be sure to spray under the leaves.  They LOVE yellow.  Garden centers will have yellow sticky tapes, tabs or flags that you can put around the plants and they will be covered with the little pests in no time. They don't often kill plants, but they can sort of wear them down because they suck the moisture out of the leaves and such, and they can spread to other plants very easily. 

It takes time to get rid of them because most of the ones you get rid of are the adults, not the eggs and nymphs.  Garden centers should have a light oil based not terribly nasty insecticide spray that will smother the eggs and nymphs and keep them from hatching or developing which is good.  That's what I'd go for myself, as well as some of the yellow sticky tapes to trap any on the fly.  I'm all in favor of staying away from poisons, but this is a very safe product, don't know any names off the top of my head just now though.  Hopefully others will toss out some brands.

THAT's it!  Thanks Heather!