This is a picture of leek moth damage to onions. On onions, leek moth larvae move into the hollow portion of onion leaves and feed from the inside out, creating 'window panes' in the leaf tissue. They usually cause large areas of damage. Leafminers, on the other hand, also feed from the inside out but they create long, sometimes windy paths as they consume tissue. The best way to differentiate the damage is to open up damaged leaves and look for the larva. Also, you can install leek moth pheromone traps to confirm leek moth are in the area.