Hen missing feathers on her lower back...NOT a rooster!

Hens will be laying more frequently when days get longer as summer is approaching. I'll bet roosters increase breeding frequency when hens' fertility rate rises.
My rooster doesn't seem to breed a hen that isn't laying. My hens have individually or both not been laying at times, and he seems to limit his breeding to only a hen that is currently laying.

We have been having this problem with our chickens since the summer! (So 9+ months). In the summer a chick was born in the coop, and when we brought it inside it was not thriving. I was looking at it and thought I saw something by its eye, but it disappeared. Later in the day it happened again, and as I sat there and watched I saw little black mites crawling over it! I picked it up and was determined to get the bugs off, but it was impossible to find them - they are tiny and quick! The chick ended up dying.

All of that is to say it is VERY hard to tell when your chickens have mites! The chick was the only proof that we had them - no signs anywhere else, except the missing feathers. They are missing just above the tail on the back, and now on the shoulders/wing area. I am pretty sure this is a result of the chickens pecking their own feathers due to the irritation from the bugs. I have seen them reach their heads around and scratch at the exposed area, and it's exactly where they can reach. We dusted them with Sevin and thought that should do the trick, but there was no improvement. One time is apparently not enough - the Sevin kills the live bugs, but I believe the insect eggs laid on the bird hatch and need another application. I would imagine it'll take 4-6 treatments to break that life cycle, but I need to research that more. We also cleaned out and dusted the coop with Sevin, but no help.

Also, we have several varieties. Our Buff Orpington and Delawares don't have any feather loss. Our red sexlinks and Barred Rocks are the ones with the missing feathers. Interesting ...

I read the wild birds can often introduce bugs and parasites to your flock, and we have these little tiny birds that can fit in through the chicken wire holes of our coop, so I think they have introduced this problem. If anyone has more suggestions I would be very happy to hear them! This problem and the ugly birds are making me re-think my backyard chickens ...

This sounds like my problem too. My girls all take dust baths but I will definitely try wood ash. I guess I assumed since I didn't see any bugs on any of the hens that wasn't the problem. They have dirt in the bare spots, but I watched it for signs of movement and didn't see anything. Here's a pic of my two of my hens with the spots, the worst is on the black ameracauna. If anyone can give me advice I'd appreciate it!

I have a WLHORN hen that is near 2 yrs, but she is not growing feathers back, and top of both wings are red raw, and her back, but I put DT on them daily for weeks, the other two WLHORNS are growing feathers back. But I have 25 egg layers and none of my brown layers have this problem. I've noticed she does separate herself at night, and sleeps alone, but she still lays eggs daily, I've wormed them, and just don't know what to do? If you find the answer text me 731-659-123zero. Thanks