Brood Interruption Techniques

Varroa reproduces only in capped brood cells. If you leave a colony without brood for a few weeks, the mites can neither reproduce nor hide, and are left exposed on the bees; a single organic acid treatment at this time clears out most of the mites. Caging the queen, the trap comb, the artificial swarm and the split are four ways of creating this opportunity; the price of all of them is a temporary pause in colony development.

Why is it so effective?

The female mite enters the cell next to the larva just before the cell is capped; after capping she lays eggs, and her offspring mature inside the cell, feeding on the pupa. When the bee emerges, the mother mite and her mature offspring come out too. In a normal colony, therefore, a large proportion of the mites are inside the capped brood, where contact-acting medicines cannot reach them.

In the broodless period, on the other hand, almost all the mites are on the adult bees. A substance such as oxalic acid, which does not penetrate capped brood but is very effective against mites on the bees, gives its best result when applied at exactly this moment. The method also carries no risk of resistance.

The basis of timing: brood development times

A worker larva is capped about 8–9 days after the egg is laid. So in a colony that has just started laying again, the first capped cells do not appear before this time; the treatment of the broodless colony must also be carried out within this window.

1. Caging the queen

The queen is put in a cage that workers can enter to feed her but that does not allow her to lay, and the cage is hung in the middle of the brood area.

1. Find the queen and put her in the cage; place the cage between two brood frames.
2. Check after about a week; if the colony has drawn queen cells, destroy them.
3. After about 24–25 days, all the worker and drone brood will have emerged. Check a few frames to confirm that no capped brood remains.
4. At this point treat with an authorised oxalic acid product according to the label instructions, and release the queen.
5. A few weeks later, measure the mite level again with a wash method.

Advantage: The queen is not lost and the colony is not divided.
Price: No new brood is produced for about a month; the colony shrinks noticeably. Some queens are slow to start laying again after caging.

2. Trap comb method

The queen is confined to a single comb with a frame cage made of queen excluder. As the other brood in the colony emerges, the only open brood that mites can enter remains on that comb; the mites gather there.

1. Shut the queen in on an empty, drawn comb. The comb fills with eggs.
2. After about nine days move the queen onto a second empty comb; the first comb is left to be capped.
3. Remove the capped trap comb from the hive before the bees emerge and destroy it or set it aside for melting.
4. Continue the process until all the old brood in the colony has emerged (usually two or three combs).

Advantage: Most of the mites are removed without medicine; an organic acid treatment can also be applied together with the last trap comb.
Price: The schedule must be followed strictly. If a trap comb is removed late, the mites emerge having multiplied and the method backfires. Note every step with its date.

3. Artificial swarm (shook swarm)

The bees, together with the queen, are shaken into a clean hive containing only foundation (or empty, drawn comb). The brood combs are left behind; the mites in the capped brood go with them.

• The colony in the new hive has no capped brood at all. Within the first few days, before the new eggs are capped, apply an organic acid treatment.
• Feed the colony with syrup; it needs to draw comb.
• The brood combs left behind are either destroyed or used as a new colony in a separate hive. In the second case this colony must also be treated separately as soon as it becomes broodless; otherwise you will have spread the mites again.

Advantage: It gives a very high mite drop and provides an opportunity to replace old combs.
Price: The colony has to build comb from scratch; this takes food and time. If done late in the season, the colony cannot go into winter strong.

4. Brood break by splitting

When a colony is split, the queenless part raises a new queen. After the old brood has emerged, a natural broodless period follows until the new queen starts laying and the first cells are capped.

• Check the queenless part about three weeks after splitting. If no capped brood remains, it is time to treat.
• Because the queenright part has brood, it needs a separate plan (for example caging the queen later, or a suitable medicine).
• This is a practical way of combining swarm prevention and mite control in a single operation.

Treatment: what is done to the broodless colony?

The real value of the broodless period lies in an organic acid treatment carried out at that time. Use an oxalic acid product authorised in your country; for dose and method, go only by the label instructions.

• Treat only after you have seen that there really is no capped brood left. Even a few capped cells leave the mites a place to hide.
• The trickling method also puts a strain on the bees; it is recommended not to repeat it within the same broodless period.
• If you use the vaporisation method, a suitable mask, goggles and gloves against the acid vapour are essential.

When should it be done?

The brood break is usually carried out in midsummer, after the main flow is over. That way the harvest is not affected and the mite level is brought down before the bees that will overwinter are raised. If it is left too late, the colony cannot go into winter with enough young bees; if it is done too early, the mites multiply again before the end of the season.

Beekeepers who go to late flows such as pine honeydew or who work migratory should plan their calendar around the flows; a brood break reduces the colony strength needed for the next flow.

What to watch out for

• Measure the mite level before and after the brood break using the same method.
• Do not apply it to weak colonies; they may not recover.
• A broodless, shrinking colony is vulnerable to robbing. Reduce the entrance, and do not leave syrup or comb in the open.
• Confine the queen only in cages made for this purpose, in which workers can move about; a shipping cage is not suitable for long-term confinement.
• With the trap comb and split methods, write down the dates; a delay of a few days can reverse the result.