Many herbs are natural insect repellants and most often if an insect is eating any plant you will find either the insect or evidence of that insects presence. How far off the ground is this balconey? About the only problem I see with Marjoran, Sage, and Parsley is that rabbits like them. I have not seen, in some 45 years, any evidence of insects munching on mine.

Many (most) herbs can fall prey to a wide variety of insect pests, including aphids, caterpillars, beetles, and spider mites (which are not insects).

I'd even consider squirrels or chipmunks nibbling on those particular herbs.

If you aren't seeing any insects then it might be squirrels. Check in the early mornings and throughout the day, if possible.

A $*(#! squirrel eat my Italian parsley, dill, stevia, green onions and cilantro (in addition to my cucumber, tomato, beans, radish, eggplant and zucchini plants). He can strip all leaves off a plant and leave just the main stem or sometimes he eats that too!

I tried hot sauce spray, it seemed to work for a day or so but some of the plants reeeally didn't like it and withered. I tried it again today but I later saw him eating my squash leaves. Bird netting kept him away for a couple of days but now he's finding a way under it. Fox urine and commercial repellent w/blood didn't work at all.

Good luck.