its normal for beardies under 1 year to neglect their salad, mine is several months old and rarely eats her salad. when they get older they will need to eat mainly salad. you can try to intice your beardie by spraying water on the salad and moving it because they like things that move. if your set on feeding him more salad you can cut back on his insects, but this is not advised because your beardie is so young. I would just keep the salad in there everyday but still feed him his insects and wait for him to get older before weening him of insects. also you can get a product called jurassifriut, strawberry or banana, it has a powerful fruit smell that atracts your beardies nose to the salad.
never heard of the fruit stuff before I might have to check that out. From what I always heard is to put the insects in the salad so when they go to eat them they get some greens also. depending on what you feed him sometimes they insects will eat the greens and will stay in the bowl for a bit.