Some info about tomato hornworms,some of which was posted much earlier in this thread,but it looks like those who posted later didn't see those comments.
First,the life cycle of the tomato hornworm
https://www.google.com/search?hl=en&....0.ZIKSL9OpRIA
What I would normally do is to go down through the rows of my tomatoes and when I'd spot one I'd pick it off and stomp on it and step back as the green liquid innards sprayed all over the place.
But if I saw any with white eggs on it's back I'd leave it alone
https://www.google.com/search?q=Horn...&bih=815&dpr=1
I'd leave it alone b/c when those eggs hatch they go inside the worm and kill it, as in dead.
I know of no effective products/sprays that are effective in preventing/killing hornworms. And the frequency of their occurence can change from year to year.
So I just let nature take its course and would greatly prefer to deal with hornworms rather than Colorado Potato beetles on my tomato plants.
Carolyn