seasonal skin issue?

[Pans Daddy]

My 11 month old Panzer developed what looked like some scattered shallow scabs around his neck last Fall. He didn't scratch them and really didn't appear bothered at all. The scabs would come off easily and didn't even go deep enough to bleed. I checked the rest of his body and found nothing. I considered bugs or mange but our other Rot Maggie doesn't have any. I tried treating with peroxide and bag balm twice a day and that seemed to help. They went away in a couple of months.
Now that the weather has gotten hot again they have come back. Dogs eat the oatmeal and rice Nutro, and are on Frontline monthly. I'm in Tucson. Does anyone have a clue?