What is it?
"Chalk Brood is caused by the fungus Ascophaera apis, widespread and found in seemingly unaffected colonies – often appears in the Spring in expanding colonies. The trigger is not completely understood. High carbon dioxide levels in the brood nest, as may occur if there are insufficient bees to ventilate the colony, and deficiencies of pollen are possible factors. It may also be genetic, in which case re-queening may be the cure. The fungal spores are ingested by the larvae and germinate in the gut. Strands of fungus invade the larval tissue and the larva dies, frequently after the cell has been capped. The dead larva is chalky white at first, often with a yellow centre, and becomes very hard and loose in the cell (mummies). Additional black/grey spores may develop on the surface. Mummies are removed by house bees and can be seen outside the hive or on the floor. Chalk Brood mummies should not be confused with discarded mouldy pollen, which has coloured layers. Combs can be sterilized using acetic acid."
Mostly genetic and 6 cells are nothing to worry about. I have moved badly affected hives and the mummies make an unmistakable sound of rattling across the mesh in the floor. I re-queened as soon as.
Relax.
PH