The only way to really kill them off is freezing or heating the soil in an oven.

The best way to deal with this is just to put a bag over the pot and tie it off at the trunk or stem.

Of course, that won't work with some bushes. Maybe some DE (Diatomateous Earth) sprinkled over the top and a bit in the drain holes would kill them. That wouldn't do anything about the eggs though.

For the past 3 years I have submerged all my plants in a container of soapy water before bringing inside. This has worked very well. It possibly might not kill some white fly eggs but has been a great help.
rose