Feather loss, can this be a sign of mites?

[Certified Chicken Lover]

A little while ago I started noticing that one of my Ameraucanas was losing feathers around her neck, but not because she was molting and at first I thought maybe she was just getting picked on but from my observations this was not the case. A few days later I noticed that a few more of my girls and my rooster had the same thing, and assuming it was mites I bought garden star poultry dust (a website said it would kill the mites) and dusted all over my chickens, but it's been a few weeks now and even after repeated dustings nothing has changed if anything it may have gotten worse. As you can see from the picture below my poor babys are losing lots of neck feathers, I have no idea what this is or what to do. Please help!

 

[Certified Chicken Lover]

has anyone else had a similar experience?

 

[nuthatched]

Nipped off feathers are a sign of mites or picking, usually. It could be molting. What is their diet?

 

[Certified Chicken Lover]

I feed them Purina layer crumble. If its mites how do I treat them?

 

[nuthatched]

I feed them Purina layer crumble. If its mites how do I treat them?

Roosters shouldn't eat layer continuously but that's not the problem here. low protein might lead to picking problems.
It could be broken from grooming for molting, old feathers coming out.
The poultry dust will treat all but shaft mites, it doesn't quite look like those.