Introduction
Chalkbrood is a fungal disease in honey bee colonies, caused by the pathogen Ascosphaera apis. This disease primarily affects bee larvae, leading to “mummified” chalky-white larvae, and is most commonly observed in the UK and Ireland. While chalkbrood is generally not fatal to a colony, it can significantly hinder bee population growth and honey production. In this guide, we’ll explore the nature of chalkbrood, identify its signs, and cover practical management techniques to minimise its impact.
Understanding Chalkbrood
The fungal spores of Ascosphaera apis are ingested by bee larvae via contaminated food, where they germinate in the larval gut. Once established, the fungus spreads through the larva’s body, killing it and giving the larvae a chalky appearance. Over time, these infected larvae turn hard and “mummified,” eventually turning grey or black as the fungal spores mature. Spores can persist in the hive for years, spreading through equipment, drifting bees, and stored pollen, which poses an ongoing risk to new generations.
Signs of Chalkbrood
Beekeepers can identify chalkbrood by the following signs:
- White “mummified” larvae: Larvae may be covered in a white, chalky layer.
- Hard, chalk-like texture: Infected larvae often dry out and harden, filling the hexagonal cell.
- Mummified larvae on the hive floor: Bees remove affected larvae, leaving “mummies” on the hive floor or entrance board.
- Shrunken brood cappings: Capped cells may appear sunken or perforated, resembling the symptoms of other brood diseases like AFB.
Risk Factors for Chalkbrood
Chalkbrood thrives under cool, damp conditions, often surfacing in spring or early summer when colonies are growing but may be more prone to chilling. Several factors increase the likelihood of chalkbrood infection:
- Poor ventilation: Insufficient airflow can create a damp environment ideal for fungal growth.
- Chilling of brood: Colder temperatures, especially when brood is left on the periphery, can lead to chilling and increase susceptibility.
- Weak colonies: Colonies with fewer bees may struggle to maintain optimal brood nest temperatures, enabling chalkbrood to take hold.
Preventing and Managing Chalkbrood
While no chemical treatments are approved for chalkbrood in the UK, good hive management practices can help reduce its occurrence:
- Improve Hive Ventilation: Keep hives well-ventilated with open mesh floors (OMFs) and elevated off the ground. This reduces moisture and helps maintain optimal temperatures.
- Maintain Strong Colonies: Avoid manipulations that leave colonies with a low ratio of adult bees to brood, as these colonies are less able to regulate temperature and remove infected larvae.
- Ensure Adequate Nutrition: Provide consistent food sources, especially pollen, as nutritional stress can make larvae more vulnerable.
- Requeen with Hygienic Stock: Requeening from hygienic lines of bees can help, as some strains naturally clear infected larvae more effectively.
- Avoid Transferring Contaminated Material: Spores can persist in pollen, honey, and wax, so avoid moving equipment or combs from infected colonies to healthy ones.
A popular folk remedy involves placing a banana on top of brood frames, as some beekeepers claim this encourages bees to clean out mummies more diligently. Though unproven, it may be worth trying if chalkbrood persists.
Chalkbrood vs. Other Diseases
For beginners, chalkbrood can resemble other diseases like European foulbrood (EFB) or mouldy pollen. However, mummified larvae are distinctive for their hard texture and chalky look. Experienced beekeepers and inspectors can differentiate them, but beginners may find it helpful to seek confirmation if uncertain.
Final Thoughts on Chalkbrood Management
Chalkbrood may be minor compared to other bee diseases, yet it can weaken a colony’s productivity if left unmanaged. By focusing on ventilation, colony strength, and good nutrition, beekeepers can help their hives stay resilient against this fungal infection. Proper observation and a patient approach are essential to managing chalkbrood without the use of chemicals or intensive interventions.
More info on the NBU website.