It's not a set number and will vary quite a bit depending on his mood and where he is in his growth cycle. I suggest offering them in small batches so they are easy to track, maybe 3-5 at a time. Dust them with calcium supplement using a small cup and shake them so they have a light even coat then offer them up a few at a time. Repeat this for about 10 min (ish) or until he loses interest. For a young dragon I would do this twice per day until he is through his major growth spurts at around 8-12 months old. Then offer one meal per day. After about 12-18 months when he is fully grown, slowly offer bugs every other day, then every third day, then once or twice per week while still getting a nice big salad every day.