15 to 17 month old hens stopped laying in May and haven't started again

I have searched and searched and haven't found a good reason for all my hens to stop laying. Starting in late May early June the production went from 4 or 5 eggs a day from 6 hens (3 stars, 2 aracauna, cochin and silky) to 1 maybe 2 eggs a day. I don't see any bugs, but dusted twice anyway with no change. I hear about molt and that it looks like a pillow fight gone wrong inside the coop, and I don't see that either. A few are missing some feathers and it doesn't look like there are replacements growing in. I understand when the cochin or silky go broody, but the stars were good for one a day each even in winter. Could it be they are just molting? Should I try worming, or dusting again? I probably wouldn't think twice about this, and just assume they are molting, but this spring when we went to a chicken chat at the local feed store they said this would be our most productive year.