I'm having the exact same problem and have a thread on it in the general discussion section. You're cham seems to be on a hunger strike, meaning in your case he will eat mostly mealworms, and not much of anything else (which is bad considering mealworms are unhealthy). What you need to do is completely cut off the mealworms until he realizes that he's not getting anymore, and he gets really hungry. He will then start eating the locusts. After that, it will be okay to give him a mealworm possibly once a week as a treat.