I don't believe it to be a caterpillar at all. They look more like the larvae/pupae of a beetle...maybe a Colorado potato beetle? I wouldn't wait around for an ID, though. Yikes! Rather than experiment with a home made brew, I'd strongly suggest a spray of insecticidal soap directly on these little pests. Jean...what do you think these might be?

I use a BT spray once a week as soon as I start getting green tomatoes and that seems to prevent the caterpillars from eating them. The first year I grew tomatoes they ate holes in most of them but I've used the BT every year since with no problems. It is an organic pesticide that only works on caterpillars. The kind I buy is a concentrate that you mix with water. There is also a powder but I find it messy-looking and harder to apply than the spray.

Looks a lot like the fruit I just tossed that had been sampled by a hornworm. Those big caterpillars do a lot of damage, fast. Before I spotted the hornworm, I had been thinking voles and meadow mice after the water in the fruit, but is was strangely flat damage, not like I remembered the mouse damage last year. Then I caught the hornworm in the act, aha!

I don't think you'll need a fungicide if you stop the critter that's eating your tomatoes from damaging them and giving the mold somewhere to grow. But it won't hurt anything. Squirrel and bird damage look very different. Bird damage looks like someone has stabbed your tomatoes. Squirrel damage looks like something has chewed your tomatoes. Bird damage also tends to be on tomatoes that have turned color, whereas squirrels and other rodents will go for green fruit as well. Some birds can often be stopped by putting out some water, as many of them eat tomatoes when they can't find water. There aren't that many birds that prefer tomatoes, although mockingbirds are notorious tomato eaters. Netting will work for many birds. It's less effective on determined rodents.