You checked and made sure he doesn't have fleas? Where is he biting? Is it all over or confined to one spot? My guess would be if the food you are feeding him is the same flavor and brand he has been eating for awhile with no problems then just because it is puppy food and not adult shouldn't be causing this biting problem. You could compare the two ingredient lists to see if they are the same but my guess is there probably isn't much if any difference between chicken and rice puppy food and chicken and rice adult food if they are both made by the same company. You could give him a Benadryl to see if it helps. It could either help or not and is a very safe thing to try. The dose is 1mg per pound of body weight so if he is 25 lbs then he gets one adult Benadryl. Childrens Benadryl is 12.5 mg per pill and adult is 25mg per pill.
Is he doing anything else besides biting himself?
How did you make out after the hurricane? We just got our power back today. It's been a long 3 days without it and everything in our fridge and freezer has to be thrown out. Hope you and Jimmy survived ok =]