Ladybugs do eat whiteflies. 
More Info: There are plenty of beneficial insects that will feed upon whiteflies and ladybugs are one of them. Also know as lady beetles, coccinellids, and lady birds, ladybugs can purchased commercially, or more effectively, you can attract them to your home garden naturally.
The Problem with Commercial Ladybugs
Commercially sold ladybugs are not always an effective solution to your whitefly problems. The act of collecting, packaging, storing, and shipping ladybugs can stress or injure the beetles interfering with their natural habits. Females especially are at risk of flying off if not heavily fed. A more economical solution is to attract them to your garden naturally.
How to Attract Laydbugs Naturally
Attracting ladybugs to your garden is as simple as planting vegetation that will provide ladybugs with adequate food and shelter. Ladybugs love pollen and vector plants. They also like grains. Many weeds are attractive to ladybugs as well.
A combination of whey and yeast, called wheast, sprayed on the plants will artificially attract ladybugs.
Keep insecticidal sprays to a minimum. These poisons not only kill pests, they kill beneficial insects as well and will deter future populations of beneficial insects from your garden.
What Else Eats Whiteflies
Encarsia Formosa: is a parasite that is widely used as a biological control agent especially in commercial greenhouses. This little parasite lays its eggs inside of the whitefly pupa and then consumes it from the inside out.  Successfully tested in greenhouses, it is unclear whether these parasites are as effective in an open air situation.
Lacewing: Because the lacewing larvae feed ravenously on soft-bodied insects, they are possibly the best all-purpose beneficial insect to invite into the garden. The adults will lay their eggs right next to a population of bugs that are invading a plant to ensure that the larvae will have a good food supply.
 “G7275 Managing Whiteflies on Indoor and Outdoor Plants | University of Missouri Extension.” University of Missouri Extension Home. N.p., n.d. Web. 25 May 2011. <http://extension.missouri.edu/publications/DisplayPub.aspx?P=G7275>.
 Hoddle, Mark, Department of Entomology, University of California, and Riverside. “Encarsia formosa.” Biological Control : A Guide to Natural Enemies in North America. N.p., n.d. Web. 25 May 2011. <http://www.biocontrol.entomology.cornell.edu/parasitoids/encarsia.html>
“Lady Beetle, HYG-2002-98.” Ohioline. N.p., n.d. Web. 25 May 2011. <http://ohioline.osu.edu/hyg-fact/2000/2002.html>.