Chalkbrood

Fungal Mummies

Chalkbrood is caused by the fungus Ascosphaera apis, which infects bee larvae when they ingest fungal spores in contaminated food. The fungus grows inside the larva, eventually killing it and consuming the body tissue. The dead larva dries into a hard, shrunken, chalk-white pellet, sometimes called a "mummy," that house bees eventually remove from the cell and discard at the hive entrance or on the bottom board. If spores of the opposite mating type are present, the mummy turns dark grey or black, which indicates sporulation and increased contamination potential.

Stress-Related

Chalkbrood is considered a stress disease. Healthy, strong colonies with good ventilation and adequate nutrition rarely develop significant infections. The disease tends to appear when conditions are suboptimal: in early spring when colonies are small and nighttime temperatures chill the brood, in poorly ventilated hives where humidity is high, or in colonies weakened by other stressors like varroa mites or poor nutrition.

Management

There is no approved chemical treatment for chalkbrood. Management focuses on improving conditions: ensuring adequate ventilation (screened bottom board, upper entrance), replacing old contaminated comb, requeening with hygienic stock (queens whose workers are genetically disposed to detect and remove diseased larvae quickly), and maintaining strong colony populations that can fully cover and warm all brood frames. Most chalkbrood outbreaks resolve on their own as weather warms and colony populations grow in spring.