Hello Ann,
Wow, that does not look good.
Do you have them housed together? I suggest trying to separate them just in case she did bite him & it is getting infected. Also, like I said, don't leave any crickets in with them as the crickets are extremely carnivorous & will bite causing infection.
What is your humidity in the tank?
Has he been on any medications?
That kind of looks like Yellow Fungus though. Is that the only area on his body but you said it was spreading?
I would honestly take him to the vet to determine if it is an infection or a fungus. It kind of looks like it could also be a bite, but do you see any bite or puncture marks on the underneath side of that area? A cricket bite could do that too, because they would nibble on a small sore making it worse. So there are several things that it could be. At the moment, I would keep it clean & use neosporin or polysporin on it to try to keep more infection away.
If you need help finding a vet, try
http://www.herpvetconnection.com
If it is an infection, it will continue to spread until it is treated. If it is fungal, it will spread if it is not treated.
Keep us posted on him.
Tracie