The Pratt-Doolittle Method: Practical Queen Rearing

The secrets of the world’s most widespread method of queen bee rearing, which allows for obtaining fully developed and high-performance queens through precise control over larval age and development conditions.

Why the Pratt-Doolittle Method?

Artificial queen rearing is based on a biological phenomenon where bees, upon losing their queen, are capable of raising a young worker larva into a fully developed queen, provided it is given an adequate amount and quality of food (royal jelly). The method developed in the late 19th century by E. Pratt (introduction of artificial queen cups) and refined by G. Doolittle (production of wax cups by dipping a template) became the foundation of modern commercial beekeeping.

The main advantage of this technology is the ability to obtain tens of thousands of queens from selected genetic material at strictly defined times. The key to success is the rigorous adherence to technical parameters: from larval age to the strength of the starter/finisher colony.

Step 1: Preparing the Equipment

The basis of the method is transferring a larva from a brood cell to an artificially made queen cup, mimicking the natural start of a swarm queen cell.

1. Making the cups: Use a wooden template (a round stick 100–200 mm long with a tip diameter of 8–9 mm, finely polished). Dip the template in water, then 2–3 times in liquid, light-colored wax (temp. approx. 80°C) to a depth of 5–6 mm.
2. Grafting frame: Glue the cups onto the bars of the grafting frame. A standard frame has 2–3 bars, on which 10–16 cups are placed.
3. Polishing: Good practice is to place the frame with empty cups into the starter/finisher colony 24 hours before grafting, so the bees can “polish” them and give them the hive scent, which increases the acceptance rate.

Step 2: Preparing the Starter/Finisher Colony

Rearing must take place in a colony with maximum biological potential, in a state similar to swarming but controlled.

• Colony strength: It must be a very strong colony, with a bee mass of at least 2.5–3.0 kg, densely covering 8–9 frames.
• Resources: The brood nest must contain at least 6–8 kg of honey and 2–3 frames of bee bread.
• Stimulative feeding: Begin feeding the colony syrup or honey syrup (200–500 g daily) 5–10 days before introducing larvae to stimulate the bees to intensive royal jelly production.
• Queenlessness: The best larval acceptance is achieved in queenless colonies (starters). The queen should be removed 5–6 hours (or up to 24h) before introducing the grafting frame.

Step 3: Selecting Breeding Material

The quality of the future queen critically depends on larval age.

• Optimal age: The best queens are obtained from larvae under 12 hours old (maximum up to 24h).
• Visual parameters: A 12-hour-old larva is about 1.5–3.0 mm long, and a 24-hour-old one is about 2.5–4.0 mm. A larva for grafting should be smaller than 2.5 mm and slightly curved in a comma shape.
• Impact on anatomy: Using larvae older than 1.5–2 days results in a lower queen weight and a drastic reduction in the number of ovarioles – a fully developed queen should have over 400.

Step 4: Larval Grafting Technique

Work should be conducted in a clean, bright room at a temperature of 20–25°C (or up to 35°C in an incubator) and humidity of 70–75% (not less than 50%) to prevent larvae and royal jelly from drying out.

1. Moistening the cups: Before transferring the larva, place a droplet of fresh royal jelly (diluted with warm water in a 1:1 ratio) in the cup.
2. Picking up the larva: Use a special grafting tool (grafting needle) with a tip diameter of 1.5–2.0 mm. Slide the tool under the larva from the side of its convex back, taking care not to interrupt its breathing (the larva must “float” on the tool in royal jelly).
3. Placing: Gently place the larva on the droplet of royal jelly in the cup, maintaining the same position it had in the brood cell.
4. Double grafting (optional): To obtain super-queens, after 8–10 hours, remove the previously grafted larvae and place new, fresh larvae in their place (on an abundant supply of royal jelly).

Step 5: Series Care and Isolation

• Acceptance check: Check progress 24 hours after introducing the frame. Accepted larvae are abundantly covered in royal jelly, and the edges of the cups are built up with wax.
• Colony load: One starter/finisher colony should receive no more than 20–30 larvae at once (maximum 40 during abundant nectar flow).
• Queen cell isolation: No later than the 10th day after grafting, mature, capped queen cells must be placed in protective cages (queen cell protectors). This is necessary because the first emerged queen would destroy the remaining queen cells in the series.

Summary of Technical Parameters:

• Template tip diameter: 8–9 mm
• Incubation temperature: 35°C
• Maximum larval age: 12–24h
• Time from queenlessness to introducing larvae: 5–6h
• Number of queen cells per colony: 20–30 pcs.

A correctly conducted process guarantees rearing queens with a weight above 200–220 mg, which translates into their high fertility and longevity in the bee colony.