Made from a flower (Chrysanthemum cinerariaefolium), pyrethrum is one of the safest ways to kill whiteflies. While bieng very safe for humans it is highly toxic to bee's and fish so do not spray your fish with it.
http://en.wikipedia.org/wiki/Pyrethrin
It also helps biocontrol by providing them a non-moving target...hint hint.
but alas it is probably made by some giant evil corporation who's CEO believes in world domination or something like that.