Well without knowing more...my first question is why do you want to increase appetite? We as obese Americans think our animals need to be as fat as we are. In the wild chams do not eat everyday, and the insects they are eating are definitely not the gut-loaded super bugs we feed.
Take a look at some pics of WILD chams, notice the difference, they are lean hunting machines!
All that aside variety is always the key. The more wild caught insects the better, the more types of insects you can raise the better. Flying insects always incite feeding IMO.
In addition DO NOT leave insects in the cage ever. You desensitize the cham to the insects and cause it stress. Only put in what they will eat in a few minutes, feed every other day or so. Then every time you put food in the natural prey drive kicks in, moving bug = food not distraction. Imagine living in a room with crickets crawling all over your walls you'd get sick of them to!