Biotechnical Methods: Drone Brood Removal & Brood Breaks

Biotechnical methods are procedures for Varroa control that work without chemical active substances. They use knowledge of the mite's biology to specifically deprive it of reproduction opportunities. The principle: if Varroa reproduces almost exclusively in capped brood, then we remove precisely that brood.

These methods are an indispensable building block in integrated Varroa management. They do not replace acid treatments, but they significantly reduce the infestation pressure during the season -- and thereby reduce the amount of chemical treatment needed.

Overview: Which Methods Exist?

Drone Brood Removal: The Standard Method

Drone brood removal is the simplest and most widely used biotechnical method. The principle is elegant: since the Varroa mite infests drone brood 8-12 times more than worker brood, we deliberately offer drone comb -- and remove it along with the mites once it is capped.

Why It Works

Drone cells offer the mite optimal conditions:

• Longer capping period (14-15 days versus 12 for workers) = more offspring
• Stronger attractant chemicals from drone larvae
• Larger cell = more space for the mite family

By providing an empty drone frame (a frame without foundation), we provoke the bees' natural building instinct -- they preferentially construct drone cells here. The mites concentrate in these brood cells -- and are removed with the capped drone comb.

Step-by-Step Instructions

1. Insert the Drone Frame (April)

   Hang an empty frame (only top bar and side bars, no foundation) at position 2 or 3 in the brood box -- near the brood nest. The bees will build drone comb here within 1-2 weeks. Tip: A small starter strip (2 cm) helps the bees build straight comb.

2. Check the Comb (after 10-14 days)

   Check whether the drone comb is capped. Drone brood is easy to recognise by the distinctly domed, larger cell cappings. Wait until at least 3/4 of the surface is capped -- then most mites are trapped in the cells.

3. Cut Out the Capped Comb

   Cut out the capped drone comb with a sharp knife. Work over a tray so no comb material falls into the colony. The cut-out brood pieces are disposed of (organic waste) or melted down (wax recovery).

4. Rehang the Drone Frame

   Hang the empty drone frame back in immediately. The bees will start building again within a few days, creating a continuous cycle.

5. Maintain the Rhythm

   Repeat the procedure every 24 days (one drone brood cycle). From April to the end of June, this typically yields 3-4 cutting rounds per season.

Total Brood Removal (TBR)

Total Brood Removal is the most effective biotechnical method with an efficiency of 90-95 %. However, it is labour-intensive and represents a major intervention in the colony. It is primarily used for high infestation during the season when regular formic acid treatment is not yet possible (e.g. during the honey flow).

When Is a TBR Appropriate?

• Infestation value in June/July above the threshold (>5 mites/day or >3 % infestation)
• Varroa collapse the previous year and uncertain winter treatment
• Colonies with brood diseases (foulbrood remediation)
• When regular summer treatment cannot be delayed

Principle

The colony has all brood frames removed. The bees are placed on foundation or empty drawn comb. Since approximately 80 % of the mites are in the capped brood, removing the brood frames eliminates the bulk of the mite population in one stroke.

1. Preparation

   Prepare a second brood box with foundation sheets or drawn empty combs. You also need a spare hive for the removed brood (brood bank) and feed frames or liquid feed.

2. Secure the Queen

   Find the queen and place her in a cage or on an empty comb in the prepared brood box. The queen must NOT be removed with the brood frames!

3. Remove All Brood Frames

   Remove all frames with capped and open brood from the colony. Brush the bees back into the colony -- the mites on the bees will be dealt with later by an oxalic acid treatment.

4. Create an Artificial Swarm

   Place the queen with the bees on the foundation together. The colony now sits brood-free on new combs. This is an artificial swarm -- it behaves like a natural swarm and immediately begins building comb.

5. Immediate OA Treatment

   Since the colony is now brood-free, you can immediately treat with oxalic acid (trickle method). All remaining mites are on the bees and reachable. Efficacy: >95 %.

6. Manage the Brood Bank

   The removed brood frames go into a separate hive (brood bank). The emerging bees can later be added back to the colony or used as a nucleus. The mites in the brood bank are also treated after emergence.

Trapping Comb Method

The trapping comb method is a gentler alternative to TBR. Instead of removing all brood frames at once, the queen is confined (trapped) on a single comb and the remaining brood runs out over 3 weeks.

Procedure

1. Find the Queen and Place on a Brood Frame

   Find the queen and place her on a comb with predominantly open brood. Confine her to this single comb using a queen excluder (trapping comb).

2. Wait 9 Days

   The queen only lays on the trapping comb. In the rest of the hive, existing brood runs out. At the same time, mites preferentially move into the last available brood -- the trapping comb.

3. Remove Trapping Comb, Set a New One

   After 9 days: Remove the trapping comb (with capped brood and concentrated mites). Give the queen a new empty comb as a second trapping comb. The first trapping comb is melted down or placed in a brood bank.

4. Wait Another 9 Days

   The remaining old brood in the colony continues to emerge. The queen lays on the new trapping comb.

5. Remove Second Trapping Comb + OA Treatment

   After a total of 18-21 days, the colony is largely brood-free. Remove the second trapping comb. Now is the ideal time for an oxalic acid treatment.

Queen Caging

Queen caging is the technically simplest method to enforce a brood break. The queen is confined in a cage attached to a comb for 21-25 days. Workers can feed and tend to her, but she cannot lay eggs.

Principle

Without eggs, there is no new brood. After 21 days (the development period of a worker bee), all existing brood has emerged. All mites are now on the bees -- and can be dealt with highly effectively by a single oxalic acid treatment.

Advantages

• Simple: Only one intervention (caging) + one intervention (release + treatment)
• Highly effective: In combination with OA treatment, up to 95 % reduction
• Gentle: No brood removal, colony remains intact
• Flexible: Can be carried out in July/August

Disadvantages

• Colony development: 3 weeks without brood reduces the bee population
• Finding the queen: The queen must be found (challenging in large colonies)
• Swarming risk: During the swarming phase, caging can cause problems
• Timing: Must be precisely planned (brood-free state + OA treatment)

Advantages and Disadvantages of Biotechnical Methods

Biotechnical measures are not a substitute for acid treatment, but they are an indispensable building block. Anyone who consistently practises drone brood removal has a significantly easier time with the formic acid treatment in late summer.

Decision Aid: Which Method When?

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Knowledge Check

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In the next lesson, things get chemical: You will learn everything about formic acid treatment -- the centrepiece of summer Varroa treatment.