This one's easy.

Those are leaf miners.
Don't panic, they are no big deal.

Those trails are caused by the larval stage of a small fly.
It lays eggs in/on the leaf and the larvae burrow and eat until they are ready to pupate.

No chemical controls needed here.
And the damage that you can see is the whole deal with these guys.

Just pinch both ends of the trail with your thumb nail.
('cause one end has the worm, and you don't want them "hatching" and laying more eggs)
Or, if there's only a few, you can resection the affected areas and discard.

Aloha,
Weezard.