What accumulates in old cells, causing the need for comb replacement?

The accumulation of cocoons in old cells is the primary reason for the need for comb replacement. As bees raise brood, they create these wax cells and the developing larvae eventually spin cocoons as they mature. Over time, these cocoons can accumulate and contribute to a buildup of debris and waste materials within the cells. This accumulation makes the cells less suitable for future brood rearing, leading beekeepers to replace old comb to maintain a healthy environment for the colony.

While wax is essential for building new comb, it does not accumulate in the same way and does not necessitate comb replacement. Pollen and honey, although key components in a hive, do not cause similar issues regarding cell cleanliness or brood rearing efficiency. Thus, the presence of accumulated cocoons directly impacts the hygienic conditions of the hive and is the primary factor prompting beekeepers to replace old comb.