Bald brood is a relatively common problem that impacts the developing honey bee pupae. Beekeepers will observe linear rows of uncapped brood with the exposed larvae still developing in their cells.
The uncapped cells result from Greater Wax Moths tunneling through the comb. Worker bees uncap cells to locate the moth larva and remove it from the hive. Once the job is done, they don’t replace the cappings.
Bald brood is often confused with hygienic behavior, where bees chew off the cappings to keep the colony healthy. Infestations of varroa mites are a common cause of this activity.
Causes of bald brood
Bald brood is a symptom of wax moth infestation. The Greater wax moth (Galleria mellonella) is the biggest offender, while Lesser wax moths (Achroia grisella) have less impact on hives.
Wax moth larvae tunnel underneath the comb, causing massive destruction to the hive. To counter the invasion, honey bees remove the cell cappings, remove the silky tunnels, and evict the unwanted pests.
The wax moth larvae burrow through comb in straight lines. This is why bald brood patterns are typically linear, making it easy for beekeepers to identify the problem during inspections.
Learn more about the lifecycle of wax moths here.
What if the bald brood pattern is irregular?
Comb with randomly scattered bald brood often results from other hive issues. These include:
- Genetic disposition: Random uncapped cells may result from an underperforming colony with a sub-par genetic disposition. In this case, requeening is an option.
- Hive faults: Bee hives with frames positioned too closely together may cause bees to make room by uncapping cells.
- Other pests: Varroa mites are a common pest that will result in some uncapped developing brood. Heavy Tropilaelaps mite infection is also a cause. Source.
Is bald brood harmful to bees?
Bald brood is considered a minor problem for honey bees. However, it isn’t ideal for bees to develop in exposed conditions. While the bee usually reaches adulthood, it may be smaller, malformed, or have larvae feces stuck to it.
As with many honey bee issues, thriving hives commonly deal with the underlying problem. Weak hives struggling with other diseases or threats will find removing the wax moth infestation more challenging.
Bald brood vs. hygienic behavior
Bald brood occurs when worker bees remove the cappings of brood cells due to the presence of wax moth larvae. Hygienic behavior in honey bees involves detecting, uncapping, and removing diseased or parasitized brood before the issue spreads.
While bald brood has a straight-line pattern, hygienic behavior will appear random. Bald brood usually has raised sidewalls that extend slightly above the other sealed brood. This differs from uncapped cells resulting from the presence of Varroa and Tropilaelaps mites.
Recommended reading: A guide to testing for Varroa mites>
Commonly asked questions
Why don’t bees recap bald brood?
There is limited research on why honey bees don’t recap bald brood. An interesting hypothesis is that bees don’t reseal the cells due to the lack of pheromones prompting them to do so. Source.
How can I tell the difference between bald brood and sacbrood?
At a glance, sacbrood and bald brood look similar with their uncapped cells. But unlike sacbrood, bald brood will have normal-looking larvae in each exposed cell, with regular features and eyes forming.
Watch the video
Here’s a short video showing bald brood resulting from wax moth larvae. Notice how the wax moth larvae are still in the hive, causing mass destruction beneath the comb.
No treatments exist for bald brood. Beekeepers should look at the cause of the problem, wax moths, and decide whether action is required.
Healthy hives with a thriving population can usually remove threats like wax moths and their larvae.
Weak colonies may need beekeeper assistance. We suggest reading our guide on how to treat wax moths if there appears to be a severe infestation. Other helpful articles include:
- A guide to wax moth detection>
- The best ways to prevent wax moth infestations>
- How to treat Varroa mites>
If the condition results from the queen bee’s genetic traits, re-queening should fix the problem.
Further reading: https://beehealth.uada.edu/assets/pages/beebroodconditions.html