I bought some dubias once... and not a single one of my panthers would eat a single roach (not even my wild-caughts would eat them). I actually gave up and released something like 200 dubias into my jerk neighbor's yard (lol, but true).
All of my chameleons seem to like crickets though...
Here are some possible explanations for the picky cricket eater:
1) All of the panthers I've raised slowed their eating habits as they grew older. When they were 3 - 6 months old, they would go crazy and devour crickets almost instantly when they were offered. As they matured, they began to eat less often and I began to see crickets walking around in the cage the following day (which never happened when they were young little cricket destroying machines). I started to offer fewer crickets and after some trial and observation, I found a nice balance again. All of my adult panthers are fed less frequently than my juveniles and they are quite happy and healthy, so it could just be a matter of growing up...
He'll happily accept locusts, just down right refusing crickets even I did try and lower the amount I offered
2) Stress can cause a chameleon to alter its eating habits. If you have other chameleons, make sure there is a visual barrier between the cages so that they absolutely cannot see each other. If you have a cat who hangs out in your chameleon room or something like that, try putting a stop to it for a week and see if that helps...
I have dogs that wonder around but they don't bother him even when I have the cage open hand feeding locusts. My veiled chameleon died this wee but when it was alive, both chameleons were in the same room but one was at one end of the room and my panther the other but I had their tanks on a tilt so they didn't see each other.
3) Does your chameleon open its mouth to breathe from time to time? When your chameleon does open its mouth, does it have any mucus inside the mouth? It is winter, and sometimes the cold dry air can lead to an increase in respiratory infections (I'm sure there's a thread somewhere on here about respiratory infections if you want more info, but let's hope this isn't the case). Chameleons with respiratory infections will usually slow their eating habits until they stop eating altogether. The good news is that most respiratory infections can be treated and the chameleon stands a good chance at making a full recovery (but again, let's hope this isn't the case with your chameleon).
No, my chameleon is breathing fine, never seen him with his mouth open
4) Your chameleon doesn't like you... alright, I kid... but sometimes I wonder whether they do stuff just to spite their owners...
I had no luck with dubias, but my chameleons readily accept almost any form of worm (with a special affinity for superworms and hornworms). I can understand your hesitation to start them on worms for fear that they won't ever go back to crickets, but I would still recommend trying superworms from time to time as the good outweighs the bad in my opinion.
looks like he'll only eat locusts at the moment 
