Symptoms of lice are damaged feathers, not loss of feathers. Also, decreased laying, but if they're only 8 months old, that wouldn't be an issue. Lay them upside down on your lap and look closely at the skin around the vent and surrounding areas. Also, look at the base of the feathers around...
I'm having the same issue, plus a little. Now that we don't have a rooster, my hens' back feathers are growing back, but there have been lots of fresh feathers all over the floor below their roost every morning - the smaller, downy ones - is this just a molt? Their laying has gone way down!