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Stonebrood Disease—Histomorphological Changes in Honey Bee Larvae (Apis mellifera) Experimentally Infected with Aspergillus flavus

Summary

Researchers studied how a rare fungal disease called stonebrood affects honey bee larvae by infecting them with the fungus Aspergillus flavus. They found that the fungus establishes in the bee’s gut within 24 hours and kills the larvae within two days, likely through production of toxic compounds. The study reveals three stages of infection progression and highlights why beekeepers need protection when handling infected colonies.

Background

Stonebrood is a rare fungal disease of Western honey bees caused by Aspergillus species. Despite being the only zoonotic disease of honey bees, the pathogenesis remains poorly understood, with most information dating from a 1930 study. Understanding the disease progression is important for beekeeper safety and colony health.

Objective

To describe the pathogenesis of stonebrood by analyzing histomorphological changes in artificially reared, pathogen-free Apis mellifera larvae experimentally infected with Aspergillus flavus. The study aimed to clarify the progression of infection and mechanisms of larval death under standardized conditions.

Results

Of 43 infected larvae collected, 19 (44%) showed histological signs of infection with germinating spores or fungal mycelium. Infected larvae were significantly smaller than controls on days 2, 4, and 5 post-infection. Three distinct infection phases were identified: establishment (fungus germination in midgut), spreading (mycelium throughout larval body), and distribution (cuticle penetration and conidiophore formation). First dead infected larvae appeared by day 2 post-infection.

Conclusion

A. flavus establishes rapidly in bee larvae within 24 hours and causes death within 48 hours. The aggressive pathogenesis is characterized by a short incubation period and rapid disease progression, with death likely caused by mycotoxin exposure rather than mechanical tissue damage. The formation of characteristic mummified larvae occurs in the late stages after larval death.
  • Published in:Veterinary Sciences,
  • Study Type:Experimental Study,
  • Source: 10.3390/vetsci12020124, PMID: 40005884
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