What are the bugs in your tomato plants?

Aphids are soft-bodied insect pests

Specifically, aphids have piercing mouthparts known as stylets. They inject the stylets into tomato (and other) plants to access phloem and xylem sap. They leave behind sheaths which -- along with the insect's toxic saliva -- facilitate the entry of viruses into the plant. They secrete honeydew which encourages ant infestations as well as sooty mold. The costs will be high in terms of a tomato plant's decline and disfigurement.