Fig 1. Normal and diseased bees associated with the winter bee cluster.

Active bees (white arrow) as well as immobilized living and dead bees (red arrow) were seen when the outdoor temperature was -7°C. These bees were located on the inner cover of a representative Langstroth hive in Wisconsin. The active bees were contiguous with the winter cluster that extended through the 27.2 cm² rectangular opening in the inner cover. The immobilized living and dead bees were marginalized from the cluster on top of the inner hive cover as shown. The immobilized bees included living SIW that revealed high densities of Ss1 when cultured on LB agar as described in the Methods.