Natural enemies of aphids are not normally effective on whiteflies. The predators might take a few whitefly larvae but the parasitoids definitely won't. You'll have to use specific parasitoids for whitefly and Encarsia formosa and Eretmocerus eremicus are both commercially available. 'Just Green' actually do a dual pack containing both wasps.

If your whitefly problems are only just beginning (ie. you are only seeing a sporadic appearance of the adults with no juveniles on the lower leaves), then a weekly application of a sufactant product would be the best strategy to control things. SB Plant Invigorator is currently having some very good reviews at the moment.