Honey bees (Apis mellifera) are essential pollinators in natural and agricultural ecosystems. However, their populations are vulnerable to a variety of pathogens and parasites that can lead to colony collapse, reduced productivity, and increased management costs. Understanding the pathology, symptoms, transmission, and control methods of major bee diseases is crucial for maintaining healthy colonies and sustainable beekeeping practices.
1. American Foulbrood (AFB)
Causative Agent: Paenibacillus larvae (a spore-forming Gram-positive bacterium)
Transmission:
- Spread by contaminated equipment, robbing bees, drifting bees, or beekeepers’ hands.
- Spores are highly resistant and can survive in old comb for decades.
Symptoms:
- Capped brood cells appear sunken and perforated.
- Larvae decompose into a sticky, brown, foul-smelling mass.
- Use of the “rope test” – when a toothpick is inserted into the cell and withdrawn, the larval remains form a mucus-like thread >10 mm.
- Scales (dried larvae) stick firmly to the cell base.
Diagnosis:
- Field diagnosis through visual inspection and rope test.
- Laboratory confirmation via microscopy or PCR analysis.
Control & Management:
- Burning infected colonies and equipment (required in most jurisdictions).
- Antibiotic treatment (e.g., oxytetracycline), under veterinary supervision and only where legally permitted.
- Regular hive inspections and isolation of new colonies.
- Use of resistant or hygienic bee strains.
2. European Foulbrood (EFB)
Causative Agent: Melissococcus plutonius (non-spore-forming Gram-positive bacterium)
Transmission:
- Spread by contaminated food, water, and tools.
- Often appears in stressed or weakened colonies.
Symptoms:
- Irregular brood pattern.
- Larvae die before being capped, often twisted or displaced in the cell.
- Yellow to brown discoloration, sour odor (less intense than AFB).
Diagnosis:
- Field signs and lab confirmation via bacterial culture or PCR.
Control & Management:
- Shook swarm method: transferring adult bees to clean equipment with fresh foundation.
- Requeening with a resistant queen line.
- Improve nutritional resources and reduce colony stress.
- Antibiotics (where permitted), though not always effective due to reinfection risk.
3. Varroa Mite Infestation (Varroosis)
Causative Agent: Varroa destructor (external parasitic mite)
Transmission:
- Direct contact between bees, robbing, drifting, or hive manipulation.
- Mites prefer drone brood due to its longer development period.
Symptoms:
- Visible mites on adult bees or brood.
- Deformed Wing Virus (DWV) symptoms: bees with shrunken or missing wings.
- Spotty brood pattern, colony decline.
Diagnosis:
- Alcohol wash or sugar roll method to estimate mite infestation.
- Drone brood uncapping to observe mites.
Control & Management:
- Chemical treatments: amitraz, formic acid, oxalic acid, thymol (rotate to avoid resistance).
- Mechanical methods: drone brood trapping, screened bottom boards.
- Biotechnical methods: queen caging, brood interruption.
- Breeding and use of Varroa-resistant bee strains (e.g., VSH bees).
4. Nosema Disease (Nosemosis)
Causative Agents:
- Nosema apis (traditional European species)
- Nosema ceranae (more virulent, now dominant globally)
Transmission:
- Ingestion of spores via contaminated water, food, or feces.
- Spores germinate in the midgut and damage digestive tissue.
Symptoms:
- Dysentery (more common with N. apis).
- Reduced foraging, sluggish behavior, shortened lifespan.
- Queen supersedure, poor brood pattern.
Diagnosis:
- Microscopy to detect spores in gut contents.
- PCR for species identification.
Control & Management:
- Regular replacement of old combs.
- Adequate nutrition and fresh water.
- Fumagillin-B (only in countries where approved).
- Keep hives dry and well-ventilated.
5. Chalkbrood
Causative Agent: Ascosphaera apis (fungus)
Transmission:
- Inhalation or ingestion of fungal spores by larvae.
- Spread favored by cool, damp hive conditions.
Symptoms:
- Mummified larvae, white or black in color, resembling “chalk.”
- Brood die after capping, found at hive entrance or bottom board.
Diagnosis:
- Visual inspection of brood and comb.
- Microscopy to identify fungal structures.
Control & Management:
- Requeen with resistant queens.
- Improve hive ventilation and reduce moisture.
- Regular comb rotation and sanitation.
6. Sacbrood Virus (SBV)
Causative Agent: Sacbrood virus
Transmission:
- Oral route via nurse bees.
- Spread facilitated by stress and poor nutrition.
Symptoms:
- Larvae die upright inside cells with translucent sacs of fluid.
- Dead larvae form banana-shaped scales.
Diagnosis:
- Visual signs; laboratory confirmation via ELISA or RT-PCR.
Control & Management:
- Requeening and strengthening colonies.
- Remove and destroy infected brood combs.
- Improve colony hygiene and food availability.
7. Wax Moth Infestation
Causative Agents:
- Greater wax moth (Galleria mellonella)
- Lesser wax moth (Achroia grisella)
Transmission:
- Opportunistic infestation of weak or dead colonies.
- Moths lay eggs in crevices; larvae tunnel through wax.
Symptoms:
- Webbing and frass (larval waste) in comb.
- Tunnels in frames and damage to comb structure.
Control & Management:
- Maintain strong, populous colonies.
- Freeze or fumigate stored combs (e.g., with acetic acid or sulfur).
- Use moth traps in storage areas.
General Preventive Practices
- Apiary Management:
- Maintain strong colonies through proper nutrition and requeening.
- Isolate new or suspect colonies before integration.
- Hygiene & Equipment Sanitation:
- Regularly clean hive tools and gloves.
- Replace old, dark comb every 2–3 years.
- Monitoring & Record-Keeping:
- Conduct seasonal disease inspections.
- Keep detailed records of colony health, treatments, and productivity.
- Education & Legal Compliance:
- Stay informed on local laws regarding bee diseases.
- Report notifiable diseases like AFB to authorities promptly.
Conclusion
Managing bee diseases is a critical component of sustainable apiculture. With the rising global concern over bee population declines, proactive health management through early diagnosis, integrated control strategies, and continuous education is more important than ever. By adopting sound practices, beekeepers can ensure the long-term viability and productivity of their colonies.