Like viruses, bacterial infections pose a serious threat to honey bees. While bees have defenses against bacteria, large infections can overwhelm their immune systems. Learning about the most common bacteria, their transmission, symptoms, and prevention methods is key for beekeepers in supporting hive health.
What are bacterial infections?
Bacteria are single-celled microorganisms that are essential for ecosystems. Some bacteria are beneficial, like those used in the production of cheese. Some are harmful, like E. coli found in the intestines of cattle, which can cause serious illness in humans if consumed. Like most living things, honey bees can be infected by different bacterial species that can interfere with their growth and development.
Where do honey bee bacteria come from?
Bees can pick up infections through contaminated food, tools, drifting bees, robbing honey from other hives, and the environment. Stressors like varroa, pesticides, and malnutrition also play a role by suppressing immunity, increasing susceptibility to infection.
Common bacterial infections in honey bees
American Foulbrood (AFB)
American Foulbrood is caused by the spore-forming Paenibacillus larvae bacterium. When bee larvae ingest these spores along with their food, the spores germinate in their gut and multiply rapidly, killing them after their cells are capped with wax. The dead larvae turn brown and ropey as their tissue breaks down, eventually drying into a dark scale stuck on the cell bottom. The decaying larvae give off an extremely foul odor similar to dead fish.
While most larvae die before becoming infectious, some survive to the “melting stage” where their bodies decompose into a sticky, glue-like substance containing millions of infectious AFB spores. Adult bees cleaning out these cells spread the spores throughout the hive. The spores can survive for over 50 years, making AFB extremely contagious and difficult to eliminate entirely.
AFB spores contaminate honey stores, allowing the oral transmission to larvae. Robbing bees, drifting bees, and tainted beekeeping equipment spread it between colonies. Even wind and water can even transport spores from faraway hives. AFB thrives in crowded, stressed colonies and hot weather.
Curbing hive robbing and bee drifting limits the spread, but the highly contagious AFB easily jumps apiaries and can spontaneously reappear years later. There is no cure, only vigilant control efforts.
Beekeepers must monitor diligently for the earliest signs of infection. Isolating suspect hives and sterilizing equipment helps limit transmission. Promptly killing infected colonies is essential. The honey should never be harvested or fed to bees. Hives must be burned or irradiated.
While devastating, AFB can be survived through responsible management. Maintaining good bee nutrition, limiting stressors, regularly sanitizing the hive, and replacing old comb helps resist infection. Advancements in bacteriophage therapy and resistant bee stocks show promise for future control efforts against this bacterial scourge.
European Foulbrood (EFB)
European Foulbrood is caused by the bacterium Melissococcus plutonius. EFB infects larvae early like AFB, but kills them before their cells are capped over with wax. The dead larvae initially turn yellowish, then brown as they break down. Eventually they decompose into a contagious slimy mass with a distinctive sour ammonia-like odor.
While an infected larva contains up to 100,000 bacteria, EFB does not spread as aggressively between hives. However, the bacteria remain alive in the dead brood, allowing for transmission via nurse bees, contaminated nectar stores, and hive pests.
Adult bees are driven to remove the decaying EFB larvae, but are often unable to keep pace with the infection.
EFB thrives in crowded, poorly ventilated hives and when colonies are under stress. Lack of pollen diversity, presence of other diseases, overuse of antibiotics, and pesticide exposure can all increase susceptibility. The bacteria can persist in abandoned hives or wild nests, representing an ongoing reservoir of infection. EFB can reappear unpredictably, even years after an outbreak.
Symptoms tend to show up in Spring as colonies are building up. Spotty and uneven brood patterns are an early warning sign of contamination. Sunken, discolored cell cappings may be punctured or chewed through by bees trying to remove dead larvae. The younger the larva is when infected, the darker it becomes post-death.
Without treatment, EFB will continue to grow within a colony, progressively weakening it over several seasons. However, heavy rainy periods, nectar dearth, or other stressors can trigger epidemics that rapidly consume bee brood.
Preventing Bacterial Infection in Bees
While treatment can help, prevention is still better to avoid bacterial issues. Beekeepers remain vigilant in identifying early symptoms, properly sterilizing all equipment, replacing old brood combs, reducing stressors like varroa mites, and ensuring bees have adequate nutrition keeps their immune systems strong. With proactive management, beekeepers limit the impacts of bacterial infections on their hives’ health and honey production.
