I am sure this question has been posed quite a few times( if so I apologise) but I couldn't find a response specific to tomatoes.

I'm surprised you didn't find the many threads about whiteflies, b'c heaven's knows they are a huge problem for some folks in some areas and there are many threads here about them re tomatoes.

But I confess I'm whitefly negative so haven't researched the best thing to do so can't answer.

See if you can't find the whitefly thread started by Torquill ( Alison), b'c it was excellent.

if not, then I'm sure some whitefly positive persons will be able to help.

Carolyn, who suggests using the search feature and entering Torquill first, then checking and then trying whitefly in the search box at the bottom of this page.

I had a problem with them a couple of weeks ago, and I remembered a thread a couple of years ago that suggested Pantene clarifying shampoo and water sprayed topically. I had also read awhile back that seaweed spray was effective, so being the curious sort, and willing to try unconventional methods, I made up a spray with one gallon of water, a "squirt" of the shampoo, and a couple of tablespoons of seaweed liquid, and applied with a pressure sprayer. I had my doubts that it would work since whiteflies can be such a stickler of a problem, but I haven't seen but three or four since. I'll apply again at the first sign of a reinfestation, and maybe even as a preventative, but it has worked in this one-time experience (so far).
Mrs H

Commercial growers in Florida at one time bought Dawn soap in 55 gal. drums for spraying tomatoes to control whitefly. I dont know the dilution rate but you can probably find out. Soap will kill adults but a new batch will come along soon so you have to stay on top of it and keep spraying.