Ok, please do not try this without checking it out first. Here is my story. I had this problem more then once. The first time I got these crawly threadlike things in my soil (ie. Last summer), I ended up throwing out my Thanksgiving Cactus. So last November, I purchased a few more Thanksgiving Cactus from the supermarket. I noticed those pesky tiny fruit flies/knats flying around my plants. ( they usually lay their eggs in the soil ) Well that was it! I mixed a combo of rubbing alcohol and water and sprayed the surface of the dirt on my newly purchased plants really well. I have knat/fruit fly traps all over...ie.. Near each plant. For the first time since the Fall, I recently saw the first little bugger and put out my traps. I may do my alcohol/ water spray again. But this is risky. It did not kill my plants, but it can kill them if you overdo this. Proceed at your own risk. Best to try to control this problem. I do not think you can completely avoid it if you have live plants in the home. They LOVE organic soil and there may be unhatched eggs in the organic soil you buy at the garden center to transplant your thanksgiving cactus into a new pot in the Spring. So far I have NOT transplanted anything. Nor have I fertilized anything. These tiny fruit flies/knats come in through screens or with your groceries/fruit that you buy at your local supermarket. They can even come up out of the drain in your sink! I have added photos of these traps. They work well so far for me. You can purchase them at Home Depot or True Value Hardware.

Thanks for your replies and suggestions. I will take a sample and visit my local extension service office. That was really great advice. :) However, I wish those "3 tiny holes" were the extent of the damage This leaf is actually in very good shape. There are no aphids that I can see and I have not been able to find any other bugs on the plant. I will visit my local extension office where I can find some help and not criticism.. Perhaps I am wrong about these bugs causing the damage, but there is no doubt lots of damage to my tomato plant. I had holes inside some of my small fruit, even after this posting.. I opened one of the fruit and found nothing living inside.

I live in the UK. And thanks! I've posted into that forum. Sorry about that, didn't know there was a separate insect forum.

Leafminers. They pierce the leaf-surface and eat the goodies in between the top & bottom surface in patches as you show. As for control, I don't know. https://en.wikipedia.org/wiki/Leaf_miner