The cell builder feeds the accepted queen cells until they are sealed. It largely determines the eventual quality of the queen.

The difference from a starter

• Starter: Secures acceptance. Queenless, very crowded, rich in young bees
• Finisher: Continues feeding. May be queenright, with the queen behind an excluder

Combining both functions in one colony is possible, but separating them gives better and more uniform cells.

What a good cell builder has

• Many young bees: Only they have functioning brood food glands
• Abundant pollen in the brood nest
• Sufficient stores, or continuous feeding
• Warmth: A dense covering of bees around the cell bar

Where quality is lost

• A colony that is too weak — the cells receive too little brood food
• No pollen — the glands do not function
• Not feeding during a forage interruption
• Too many cells at once for the colony's strength
• Chilling during transfer

The result is a queen that looks normal and starts laying normally, but with fewer ovarioles and a shorter life. That only becomes apparent a season later.

Building it up

A cell builder is not made on the day. It is strengthened days in advance with sealed brood frames and pollen, so the young bees are present at the right moment.

Rotating

In continuous rearing, cell builders are used in rotation. A colony that feeds series after series becomes exhausted and quality declines.

After sealing

Cells must go to the mating nuclei before emergence. This is why the grafting date must be written down.

If a queen emerges in the cell builder, she destroys the remaining cells.