have you checked that the water is in good condition?
If you got yabbies that are nicking the food before the convict can get to it, can you not remove them? even if it's just until you can get convict used to eating food. It could well be that because he hasn't really been any other food, he's not used to it. Other than him not eating does he seem okay? is his breathing labored at all? we want to try and determine whether he is not eating because he isn't used to food, or may be there is something wrong with him. You said he tried to eat a worm, that is a good sign however, he does sound rather shy,if he didn't have anything to compete aagainst when it came to feeding, he might start eating okay.