Getting hit hard on survival of hives - less than 20%. This years hives all died. Hives had good stores of honey and pollen. hives were normally active through the early fall. Queens OK. Treated with Ox acid the three times and screen boards were not showing a parasite infestation. With in two weeks, hives were all dead: bees piled on bottom and stuffed in the entrance. A few hundred bees were pushed out on the grass in front of the hive. No signs of bee poop on the hive exterior. This is the third year in a row I have had die offs like this ( although this year was the worst). I have used new wood and bought my starts from different suppliers. I really am at a loss as to what is knocking off my bees. Thank-you.