larvae of the sawfly is eating your leaves. The wasp-like adults lay eggs between the leaf layers, and the larvae emerge to feed, leaving translucent "windows" on the leaves. As they grow, the larvae consume entire leaves. Then they drop to the soil to pupate. In some places there may be multiple generations during a summer. Natural enemies usually keep them in check. Unless there is a large infestation, they can cause cosmetic damage but not harm the plant.
You can hose off the larvae with a blast of water or handpick them. If the infestation continues, spray neem or insecticidal soap. Be sure to spray the entire plant, including the undersides of leaves.