Cross-striped cabbage worm. The leaves supply nutrients to the plant, so if they are decimated, it stands to reason that you will get less production out of it.

Bt is an friendly bacteria culture that when sprayed o leaves of all plants will make the insects, in this case, worms/caterpillers, die for starvation in just a couple of days. About the only caterpiller that feeds on toxic tomato leaves are the green hornworms. It may be yours are very yound and not fully grown yet. They can get to 3 inches long and as big around as an index finger. Bt is not harmful to people.B sure to get the right type (strain). The plants need only a couple of applications to get rid of most of the buggers. Flicking them off isn't very effective as they can easily return. Picking them off is time consuming and is definately something you would do only when you see them (at night). Just looking for a well disguised green worm is a task. Last year, my fruit tees were attached by leaf eaters. Most were caterpillers dropping down from an over hanging oak tree, but I still can't figure out how my peach/plum got attacked as it was well away from any trees. I need to spray Bt on my fruit trees very soon as they are just starting to leaf out

Very common pests of petunias are the Petunia or Tobacco (Geranium) Budworms and one means of control for these is Bacillus thuringiensis - Kurstaki. I have used several brands of BtK and have not had any that had an odor so you may want to look around for another brand. There are several. Neem Oil products, possibly Spinosad, maybe a pyrethrin may also help. Systemics are not a good choice since they are linked to the death of pollinators.

Looks like a western yellow striped armyworm to me, but the picture isnt quite clear enough to tell. If there is one, there are hundreds closeby. The adults lay a mass of hundreds of eggs, two generations per year. And in my experience they are opportunistic feeders with few preferences, meaning they eat just about anything (at least in my veggie garden with flowers).