The pinworms I had in my tomatoes made a smaller hole than that. I did not do anything to them and it got to where they were getting about into about 90% of my crop. They were most often in the stem area. If I ever have them again I will start treating the plants at first sight.

I had them a few yrs ago and they would make lots of holes about the size of a safety pin around the stem. I don't think that is a pin worm hole. But lots of other worms attack tomatoes also.

That likely is the hole from a tomato fruitworm, aka corn earworm. They do not attack only tomatoes or only corn, but also will attack many other fruiting vegetables. It also could be a tomato hornworm. This year, for the first time ever (which is hard to believe, because I routinely grow over 100 tomato plants per year and very rarely spray them with anything ever), when I cut into a tomato that had a hole about that size, I found some sort of hornworm or fruitworm inside, already with its little brown cocoon forming. It may have been a fruitworm because normally the hornworm (either the tomato hornworm or tobacco hormworm, and I usually see the tobacco ones not the tomato ones) makes its cocoons in the ground. I know this because I find them when amending the soil and destroy them.

You could cut into it to see if the worm is still inside. Sometimes it is, but sometimes it does a certain level of damage and then leaves. I don't know why.

The solution is to spray your plants with a pesticide containing Bt 'kurstaki' on a regular basis. I think the one I have out in my shed was purchased at Tractor Supply Company and is just labeled Worm Killer or Caterpillar Killer or something generic, but it does list Bt as the active ingredient. You can get Bt in both liquid and powder formulations. Bt works pretty well, but washes away in heavy rainfall, so you may need to reapply regularly. The label directions usually state how often to reapply, if needed.

Tomato pinworms are very tiny and the holes they make usually are near the stem end of the plant and literally do look like you stuck a pin or large sewing needle into your fruit. The size of the hole you see depends on how big the pinworm was before it tunneled in to your fruit. The few times that I've seen them, the hole was about the size you'd expect if you pierced the tomato with a corsage pin. In some places (like Florida), they seen pinworm damage from worms that have gotten pretty big before getting into the fruit, and might see holes as big as the one in your photo, so I cannot say that there is a 100% chance your hole is not a pinworm hole, just that it more likely than not is a fruitworm hole.

You often can see signs of the pinworms before you see their holes. The moths lay the eggs on a leaf and fold over the leaf, using webbing to keep it closed. When I see a leaf like that, I pick it and bag it up inside the house in the household garbage to ensure it doesn't hatch out someplace else....like on my compost pile for example. I found three or four pinworm leaves on plants this year and removed them, but haven't seen any more and haven't found any pinworms inside any fruit. To keep pinworms out of your fruit, you have to be spraying not only the foliage of the plants, but any green fruit as well, with Bt or with the synthetic pesticide of your choice that is labeled for use on tomato plants for tomato pinworms.

This is the worst caterpillar year I've seen in a long time. I normally don't have hornworms or fruitworms on my fruit, and this year I've seen both. I grow so many tomato plants that I can afford to lose a little bit of fruit to the caterpillars, so I haven't even gotten wound up enough to spray my plants with anything. However, if I had only 8 or 10 or even 20 plants and I wanted lots of fruit for canning, I'd be frustrated by the high level of caterpillar damage this year. I'm guessing the cooler (until recently) and wetter weather must be perfect for their population to grow and explode.

Tomato Pinworm