What kind of insect has wings with 3 black stripes and is very small?

The insect you're describing sounds like a type of small fly, possibly a species of the family Tephritidae, commonly known as fruit flies or braconid flies. Many species within this family exhibit distinct wing patterns, including black stripes. Another possibility could be a species of wasp, such as a small parasitic wasp, which can also have striped wings. For accurate identification, consulting a local entomologist or a field guide specific to your region would be helpful.